COLD STARTING OF METHANOL-FUELED ENGINES USING DIRECT FUEL INJECTION SYSTEM by PURVARAG SUMANCHANDRA SHAH, B.E. A THESIS IN MECHANICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING
Approved
Accepted
May, 1992 ACKNOWLEDGEMENTS
I am greatly indebted to Dr. Timothy T. Maxwell for his excellent technical
guidance, continuous support and patience during the course of this research. I extend
my sincere appreciation to Mr. Jesse C. Jones for helping me with his engineering
expertise and suggestions during the experimentation and the documentation of this
research project. I am grateful to Dr. Jerry R. Dunn for his involvement in this research
and for serving on my thesis committee. I thank Dr. Harry W. Parker for contributing
his ideas and timely assistance in the course of this research.
I would like to point out the superb work done by Mr. Christopher Boyce in
implementing the instrumentation and data acquisition system for the test set up. His
engineering knowledge, experience and innovative suggestions helped me in solving some
major technical complications I had to face during the experiments.
I thank Mr. Lloyd Lacy for his assistance in the engine modifications carried out
on the test engine used for cold-start experiments. I also thank the staff of Mechanical
Engineering Machine Shop for their help during the experimental work.
I am indebted to the Vice-President of Research and Development for Kawasaki
Motor Corporation for their generous donation of Tengai 650 cc motorcycle and a spare engine. These engines were a major part of the experimental equipment for this research.
I have no words to express my feelings for Mrs. Hernandez Carmen whose loving nature and a cheerful smile always made me feel a little less away from home. I express my appreciation to Mr. Lloyd Lacy and Mr. Patrie Nixon for answering my curious
11 questions on American culture, slang and for explaining the jokes that puzzled me!
Finally, I express my love to my friends, fellow students and professors who made my stay at Texas Tech University enjoyable, rewarding and memorable.
lll TABLE OF CONTENTS
ACKNOWLEDGEMENTS 11
ABSTRACT Vll
LIST OF TABLES Vlll
LIST OF FIGURES IX
CHAPTER
I. INTRODUCTION 1
The Need for Alternate Fuels 1
Available Alternate Fuels 2
Methanol As a Fuel a 5
Advantages of Methanol 5
Disadvantages of Methanol ~ 7
Summary 9
II. RESEARCH OBJECTIVES 10
Project Objectives 10
The Cold-start Problem' 10
Techniques Employed for Cold-starting Using Methanol. 11
Techniques for Cold-start with MIOO • 11
lV m. LITERATURE SURVEY 13
Overview of Methanol Cold-start Research , 13
Fuel Blending~ 13
Engine Modifications 16
Reconfigured Engines 16
Engines Modified to Improve In-Cylinder Mixture Formation and Ignition 17
Engines Modified to Improve Mixture Formation External to the Cylinder 23
IV. DESCRIPTION OF THE EXPERIMENT 29
Direct Injection Concept 29
Plan of the Experiment 29
Modified Test Engine 32
Fuel Injection System 37
The Injector 39
Injector Control Mechanism 41
Refrigeration System 44
Data Acquisition System 47 v. TEST PROCEDURE 48
Tests Without Methanol Injection 48
Tests With Methanol Injection 48
Cold-start Tests With Wide-Open Throttle 49
Cold-start Tests With Closed Throttle 50
v VI. OBSERVATIONS 51
Compression Tests Without Methanol Injection 51
Compression Tests With Methanol Injection 54
Cold-start Tests With Wide-Open Throttle 54
Cold-start Tests With Closed Throttle 61
The Phenomenon of Cold-Starting Methanol Engines 73
Calculation of the Percent Methanol Vapor in the Air 73
Investigation of Cold-starts at Temperatures Below -10 °C 75
The Mechanism for a Successful Cold-start 83
Vll. CONCLUSIONS 93
Conclusions 93
Suggestions for Future Research 94
REFERENCES 96
Vl ABSTRACT
In the late 1970s, attention to alternate fuels was prompted by fuel shortages, high oil prices, and foreign oil dependency concerns. Today there is also wide-spread concern for "clean air," which calls for more strict standards for engines and fuels that produce objectionable emissions. Methanol is identified as one of the most desirable alternatives to petroleum-based automotive fuels. One of the major problems remaining to be solved in the development of vehicles that run on methanol is cold-starting. When the outside temperature is less than 50 °F (10 °C), the engine has difficulty in starting.
The objective of this research was to develop an economical and a reliable technique to start the engine on pure methanol (MlOO) at ambient temperatures down to-
20 °F ( -28 °C). To solve this problem, direct injection was employed. Direct injection involves injecting methanol directly into the combustion chamber. A Kawasaki 650 cc, four-stroke, single-cylinder, spark-ignition motorcycle engine was modified to perform these cold-start tests. By employing an innovative technique of "Direct In-Cylinder
Injection of Methanol at Sub-atmospheric Cylinder Pressures," successful cold-starts were achieved at temperatures as low as -38 °C ( -36 °F) without using any external heat source. The formation of a 6% methanol vapor concentration at the instant of spark was determined to be the criterion for a successful cold-start.
Vll LIST OF TABLES
Table
1.1 Fuels for the Future 3
1.2 Fuel Properties of Methanol and Gasoline ' 8
4.1 Test Engine Specifications 33
6.1 Results of Wide-open Throttle Cold-start Tests 56
6.2 Results of Closed Throttle Cold-start Test 62
vm LIST OF FIGURES
Figure
3.1 Categories for Methanol Cold-start Research 14
4.1 Overall Experimental Set up 31
4.2 Modified Test Engine 34
4.3 Modified Test Engine Views 35
4.4 Modified Test Engine Details 36
4.5 Fuel Injection System 38
4.6 Injector Spray Pattern 40
4.7 Injector Control Mechanism 42
4.8 Piston Position Sensor Mechanism 43
4.9 Refrigeration System 45
6.1 Plot of Cylinder Temperature Rise in Compression for Starting Temperature 23 oc 52
6.2 Plot of Cylinder Temperature Rise in Compression for Starting Temperatures 23, 9, 0, -10, -20, and -33 °C 53
6.3 Effect of Sudden Injection of Methanol on Cylinder Temperature 55
6.4 Cylinder Temperature Plot for Cold-st;:ut at 5 °C Starting Temperature With the Throttle in a Wide-open Position 57
6.5 Cylinder Temperature Plot for Cold-start at 0 °C Starting Temperature With the Throttle in a Wide-open Position 58
6.6 Cylinder Temperature Plot for Cold-start at -5 °C Starting Temperature With the Throttle in a Wide-open Position 59
IX 6.7 Cylinder Temperature Plot for Cold-start at -11 °C Starting Temperature With the Throttle in a Wide-open Position 60
6.8 Cylinder Temperature Plot for Cold-start at -38 °C Starting Temperature With the Throttle in a Closed Position 63
6.9 Intake Manifold Pressure Plot for Cold-start at -38 °C Starting Temperature \Vith the Throttle in a Closed Position 64
6.10 Cylinder Temperature Plot for Cold-start at -30 °C Starting Temperature With the Throttle in a Closed Position 65
6.11 Intake Manifold Pressure Plot for Cold-start at -30 °C Starting Temperature With the Throttle in a Closed Position 66
6.12 Cylinder Temperature Plot for Cold-start at -25 °C Starting Temperature With the Throttle in a Closed Position 67
6.13 Intake Manifold Pressure Plot for Cold-start at -25 °C Starting Temperature With the Throttle in a Closed Position 68
6.14 Cylinder Temperature Plot for Cold-start at -20 °C Starting Temperature With the Throttle in a Closed Position 69
6.15 Intake Manifold Pressure Plot for Cold-start at -20 °C Starting Temperature With the Throttle in a Closed Position 70
6.16 Cylinder Temperature Plot for Cold-start at -10 °C Starting Temperature With the Throttle in a Closed Position 71
6.17 Intake Manifold Pressure Plot for Cold-start at -10 °C Starting Temperature With the Throttle in a Closed Position 72
6.18 Plot of Percent Methanol Vapor for Various Temperatures and Pressures 74
6.19 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at -38 °C Starting Temperature With the Throttle in a Closed position 78
6.20 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at -20 °C Starting Temperature With the Throttle in a Closed position 79
X 6.21 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at -0 °C Starting Temperature With the Throttle in a Closed position 80
6.22 Plot of Percent Methanol Vapor and Cylinder Temperature for an Unsuccessful Cold-start at -8 °C Starting Temperature With the Throttle in a Wide-open position 81
6.23 Plot of Percent Methanol Vapor and Cylinder Temperature for an Unsuccessful Cold-start at -11 °C Starting Temperature With the Throttle in a Wide-open position 82
6.24 Phases of a Successful Cold-start at -38 °C With the Throttle in a Closed Position 85
6.25 Plot of Percent Methanol Vapor Versus Cylinder Temperature Showing Different Phases of a Successful Cold-start at -38 °C With the Throttle in a Closed Position 86
6.26 A Start for a Closed Throttle Cold-start Test at -25 °C 87
Xl CHAPTER I
INTRODUCTION
The Need for Alternate Fuels
Fuels that can be derived from non-crude oil resources are generally called alternate fuels. It is a fact that, with continuous use over the years, the world's resources of petroleum are not going to last forever. In the late 1970s, attention to alternate fuels was prompted by fuel shortages, high oil prices, and foreign oil dependency concerns.
Over 63% of total U.S. oil consumption is used for transportation, which is more than all the oil produced in the U.S.[l]. It should be noted that auto emissions have decreased by approximately 95% since 1970, but total vehicle emissions have increased because of the increase in the number of vehicles. Since the dawn of the Industrial Age in the mid-
19th century, massive quantities of carbon dioxide have been added to the atmosphere.
Carbon dioxide is one of the major heat trapping greenhouse gases in the atmosphere.
Other greenhouse contributory gases include methane, oxides of nitrogen, and chloroflurocarbons. Apart from pollution from industry, there is a growing problem of pollution from automobile exhaust emissions resulting from combustion of gasoline and diesel fuels, especially in metropolitan areas. The principal exhaust gas pollutants are hydrocarbons, carbon monoxide and oxides of nitrogen which contribute to the formation of "smog," as well as to acid rain. It is widely felt that the contribution of vehicle exhaust emissions to atmospheric pollution should be reduced. There are two ways of doing this: (1) by reducing gasoline consumption and (2) by eliminating the use of
1 2
gasoline altogether. The prospect of increasingly strict particulate, NOx, CO,
hydrocarbons and smoke standard emissions controls for passenger cars and heavy duty
diesel engines has further increased the motivation to develop engines that run on
alternate fuels.
An alternate transportation fuel that will minimize or eliminate dependency on
petroleum and reduce air pollution from exhaust emissions is a highly sought goal for the
future. With more than 100 U.S. cities in violation of clean-air requirements, gasoline
replacement is a top priority.
Available Alternate Fuels
There are several alternate fuels available, but not all will meet the requirements
for a satisfactory replacement for gasoline. A satisfactory replacement must be cost
competitive, environmentally benign, and come from a feedstock that is available in the
U.S. and worldwide. Table l.llists some of the alternate transportation fuels considered to be prime candidates for use in the future.
Gaseous fuels perform better than liquid fuels in spark-ignition engines. This better performance is due to the fact that, under normal conditions, gaseous fuels mix readily with air in any proportion. Unlike liquid fuels, gaseous fuels do not need to vaporize before they will burn. Thus, starting the engine (at low ambient temperatures) is not a problem and cold-starting enrichment is not generally required. Cold-start enrichment is a major source of emission-related problems in gasoline fueled vehicles.
Gaseous fuels have characteristics very different from those of gasoline or diesel. These 3
characteristics, in tum, require changes to both existing vehicle technology and fuel
distribution systems. Methane (Natural Gas), propane (LPG) and hydrogen are major
gaseous fuels.
Table 1.1 Fuels for the Future
Gaseous Fuels Liquid Fuels
Methane (Natural Gas) Alcohols (Methanol, ethanol, and blends)
Propane (LPG) Diesel fuel extenders (Alcohol, water)
Hydrogen Hydrocarbons derived from coal
Hydrogen can be extracted from most hydrocarbons, but the extraction requires significant energy and is expensive. Since hydrogen does not have carbon-carbon bonds in its structure, it does not produce any carbon-based emissions when it is burned. The use of liquid hydrogen as a transportation fuel is limited by the fact that it is highly volatile at ambient temperatures, thus it must be stored at very low temperatures. This requires a very complex storage system.
Compressed natural gas (CH4) has considerable potential as a "clean" fuel.
Compared to gasoline it has a much smaller and simpler molecule, so it burns cleaner and produces less reactive hydrocarbon emissions. The combustion of CNG involves less complex reactions, which reduces the probability of incomplete combustion. 4
CNG also has a few drawbacks. It has low energy density, so large vehicle tanks are required. CNG requires six times the storage volume required for gasoline on an equivalent energy basis. To overcome these deficiencies, CNG is stored on the vehicle at up to 3600 psi pressure, which requires fuel tanks heavier than conventional gasoline fuel tanks. Also, compressors are required at refueling facilities to compress the gas. To satisfy these requirements, a totally new infrastructure is required.
Methanol and ethanol, which are liquid fuels, can be used in the existing fuel distribution systems more easily than CNG. However, it must be noted that some of the materials used for gasoline distribution systems are not compatible with methanol and will have to be changed. Currently, ethanol is produced from com as a feedstock. Present production facilities of ethanol can supply only 1% of the projected demand if it were used as a transportation fuel. Because of the price of the com, ethanol is 3 to 4 times more expensive than methanol or petroleum fuels.
The search for a practical electric car is continuing in the U.S. In 1988, Congress appropriated $14.1 million for R & Don electrically powered vehicles. In Europe, BMW and Mercedes-Benz have electric car development programs. Electric vehicles are limited by battery technology. The batteries are heavy, expensive and need to be recharged frequently, which is a very time-consuming process. When using off-peak electrical power to charge batteries, the cost of operation is still high, about $1.50/gallon of gasoline equivalent. 5
Methanol as a Fuel
Methanol has been identified as one of the most desirable alternatives to petroleum-based automotive fuels. Methanol can be made from feedstocks such as natural gas and coal, or from renewable energy sources such as biomass, and urban refuse. When methanol is made from biomass or urban waste, significant net energy is produced and little or no fossil energy is consumed. Methanol can be produced from the distillation of wood, but it is commonly synthesized from coal or natural gas. At present, most of the methanol produced in the U.S. is produced from natural gas. The known reserves of coal in the U.S. and worldwide are significant and the coal has great potential as a feedstock for methanol.
Advantages of Methanol
( 1) Methanol bums more cleanly than gasoline. Some of the emiSSions from
methanol are the same as for gasoline, viz. carbon monoxide (CO), carbon
dioxide (C02) and the oxides of nitrogen (NOx). However, the amount of
carbon dioxide (C02), a significant contributor to the greenhouse effect, is 7% to
16% less for methanol. Compared to the gasoline molecule, the methanol
molecule is simple in structure and has fewer carbon-carbon bonds. Methanol
bums cleanly forming mostly C02 and H20 and a smaller amount of uncombusted
and photochemically active hydrocarbon compounds. 6
(2) As can be seen from Table 1.2, methanol has a very high octane rating, which
allows for its use in engines with higher compression ratios, which in turn will
produce greater power output and improved efficiencies over lower compression
engines that run on gasoline. In addition, methanol is ideal for supercharging or
turbocharging to further increase the specific output of an engine and thus
allow the use of small engines with the rated power of a larger gasoline engine.
(3) There are no carbon-carbon bonds in methanol, thus essentially no soot is
produced when it is burned. Methanol also absorbs about 3 times more energy
while vaporizing than does gasoline. Thus, temperatures in the cylinder during
Combustion temperatures are lower. This in tum reduces the heat loss from the
engine during combustion.
(4) The lower combustion temperature also means less NOx production. Methanol
produces a larger ratio of combustion products to reactants which increases the
overall mean effective pressure during the expansion stroke.
(5) Due to its higher heat of vaporization, at a given air temperature less methanol
will vaporize in the inlet manifold than with gasoline.
( 6) Existing processes for producing methanol from coal are expensive and inefficient.
However, considerable research is underway on the development of more efficient
and economical methods. According to a study funded by the Department of
Energy and conducted by Air Products & Chemicals, Inc., at La Porte, Texas, 7
produced methanol was produced at rates up to three times faster than
commercially available processes. This program showed the potential for
producing methanol for 40¢/gal, which is 20% less than current commercial
processes.
Disadvantages of Methanol
(1) The major problem with methanol is cold-starting. During starting, when the
engine is cold (below approximately lOOC or 50°F ambient temperature), methanol
remains as a liquid and does not ignite. This poor cold-starting behavior of
methanol can be attributed to its low volatility, high low flammability limit,
and high heat of vaporization.
(2) Another disadvantage of methanol 1s its low energy density as shown by
Table 1.2. To provide a g1ven amount of energy, the amount of methanol
required is approximately twice that of gasoline. Thus, either larger fuel tanks or
more frequent refueling stops are necessary. To handle this deficiency, smaller,
more powerful and efficient engines are required. 8
Table 1.2 Fuel Properties of Methanol and Gasoline
Properties Methanol Gasoline
Volatility (RVP-psi) 4.6 to 5.3 9 to 15 (11.5)
Vapor Density (relative to air) 1.11 3.4
Flammability limits:
Volume Percent in Air 6.0 to 36.5 1.5 to 7.6
Latent Heat of Vaporization(Btu/lb) 506 150
Heat of Combustion
1. Btu/lb 8570 18,500
2. Btu/gallon 56,900 114,700
Boiling Point CF) 148 77- 419
Electrical Conductivity (CU) 3*107 3 - 10
Octane Number 101.5 90.5
Cetane Number 0 to 5 40
Flame Spread Rate (m/s) 2-4 4-6 9 (3) Methanol 1s highly corrosive, and it selectively attacks certain materials.
Methanol also acts as a solvent for many elastomers, which will requrre
replacement of many materials presently used in vehicles.
(4) Methanol can also form flammable mixtures in the fuel tank at normal
temperatures, and it burns with a nearly invisible flame.
(5) Vehicles fueled with methanol generate less objectionable hydrocarbon emissions,
however, the level of aldehydes in the exhaust is a point of concern.
Summary
Although methanol is energy deficient compared to gasoline, methanol production costs (by certain processes) are comparable. Methanol's most desirable features include its low hydrocarbon, carbon monoxide and particulate emissions. To overcome the problem of cold-starting, research is being conducted with promising results. Before methanol (or any other alternate fuel) can be introduced as a replacement for gasoline, a production and supply/distribution infrastructure must be established. In view of the advantages of methanol, it is clearly one of the most satisfactory replacements for gasoline. CHAPTER II
RESEARCH OBJECTIVES
Project Objectives
,f" ~!llain objective of this research project was to develop an economical and ~t~~hniqu~ f~~-starting spar~_~g_nition engines fueled \\lith neat ~ethanol·- (MlOO) at ambient temperatures down to -20 °F ( -28 °C). -- ---
The Cold-Start Problem
In order to start a spark _ignition engine, a coll1bustible fuel-vapor-air -~~ture rich enough to ignite easily at starting temperatures must be located near the spark plug._At ------· ... ------. low am}?ien!.._temperatures, only a small portion of the fuel fed into the combustion ~ - . ------chamber vaporizes, so the fuel-air vapor mixture is very lean. The problem is worse in ------__ .. _ ---..
~Qf_~ngines with carburetors, since the cold air prevents fuel atomization and a portion of the fuel remains in liquid form inside the manifold. The problem of cold-starting is --- - l~gel y one of getting sufficient fuel vaporization, which means a more, volatile fuel is required. M~_!!lan.ol _!las a poor cold-staning behaviorat ambient tempenltpres belo_w 1_9·c or so·F. When the engine is col~! methanol does not vaporize and r~ains liquid, making it impossible to ignite. This particular behavior of methanol can be attributed to its ------
~atively low volatility, high low flammability limit- and high heat of vaporization.
10 11
Techniques Employed for Cold-Starting Using Methanol
Several methods for solving the cold-start problem have been proposed. Methods that have been attempted include:
( 1) blending small amounts of hydrocarbon fuel with methanol to raise the volatility
level,
(2) use of duel fuel systems, I.e., using methanol as a primary fuel and a more
volatile fuel for starting,
(3) electric heating of methanol to promote vaporization,
(4) plug-in heating systems to heat up the engine and the fuel system before starting.
All these methods have met with some degree of success but no satisfactory and reliable technique has been developed so far.
Techniques for Cold-Start with MlOO
Two techniques for development of an effective cold-start capability for spark ignition automotive engines fueled with neat methanol were evaluated. An effective concept was considered to be the one that provided easy ignition and engine startup at low temperatures without unduly increasing the load on the vehicle's battery.
(1) Improvement of fuel vaporization to produce an ignitable fuel-air mixture by
injecting methanol directly into the cylinder at low cylinder pressures and
increasing the in-cylinder methanol vapor/air concentration during cold
temperature starts. This technique was evaluated in this research work. 12
(2) Decomposition of methanol into hydrogen and carbon monoxide and injection into
the carbureted engine to enhance ignition during cold temperature starts. This
technique was a topic of another thesis associated with the research. CHAPTER ill
LITERATURE SURVEY
Overview of Methanol Cold-Start Research
Over the past ten to fifteen years, studies have been conducted by a number of agencies on the cold-starting of spark-ignition (SI) engines using methanol and other alcohol fuels. The research for cold-starting of methanol fueled engines has followed two approaches: (1) to use fuel blending and (2) to modify the engine and the cylinder configuration to increase the vaporization of methanol. Figure 3.1 shows categories for methanol cold-start research.
Some of these studies used entire vehicles cold-soaked in refrigeration chambers, whereas others used engines only under laboratory conditions. Some studies gathered data on cold-startability as part of a larger fleet or in-service trial of the vehicles, under primarily ambient conditions.
Fuel Blending
The simplest method of improving cold-startability with methanol is "blending" - • mixing more volatile fuels with methanol to increase vapor pressure. Some of the major methanol blends used are the following:
(1) methanol-gasoline (M90, M85),
(2) methanol-dimethyl ether,
13 Increasing Cranking Speed and Engine Compression Ratio
Combined Effects of Cranking Speed,Cranking Time, and Fuel Quantity
Fuel Atomization
Direct Injection Stratified Charge Engines
Categories for Methanol Cold start Research Electric Vaporizers
Flame Vaporizers
Methanol-gasoline (M90,M85)
Methanol-iso-pentane
Methanol-butane
Figure 3.1 Categories for Methanol Cold-start Research
-+;l. 15
(3) methanol-iso-pentane, and
(4) methanol-butane.
M95 (95% methanol+5% gasoline by volume) has been shown to give lower cold starting limits [2] than even the best reported vaporizer or catalytically aided pure methanol results. With good fuel metering strategies, M85 (85% methanol+ 15% gasoline) can match or exceed the cold-starting limits normally expected of winter grade gasoline
[3,4].
Although blending has shown favorable results, it has certain drawbacks. Use of blends necessitates more hardware at manufacturing or distribution sites in case of premixed blends, and more vehicle hardware and consumer effort if methanol and volatiles are sold separately. Pure methanol and M85 represent two competing strategies for transportation vehicle fuelling safety issues such as flammability, toxicity, and flame luminosity are being addressed.
The addition of volatile components to methanol produces a fuel with inherently better cold-starting characteristics, but the possibility of the volatiles dissociating from the methanol in the storage or vehicle tanks is a problem, depending on how much and what kind of volatile additive is used. The question with regard to pure methanol is whether or not improvements to engine hardware and calibration can overcome the poor cold starting behavior, thereby eliminating cold-startability as an issue in the pure methanol versus blended fuel debate [5]. 16 Engine Modifications
In the category of engine modifications, cold-startability has been addressed as follows:
(1) Reconfigured engines (gasoline engines converted to methanol using "unaided"
starting);
(2) Engines modified to improve in-cylinder mixture formation and ignition; and
(3) Engines modified to improve mixture formation external to the cylinder.
Reconfigured Engines
At the present, there are no passenger car engines made specifically for methanol fuel. All methanol-fueled passenger car engines are converted gasoline engines. The reconfiguration includes mixture enrichment, modifications to the spark timing, colder spark plugs and the use of methanol tolerant materials and lubricants.
With basic reconfigured engines, the starting problems begin to occur at a temperature of 10°C [6,7,8]. In some studies the air/fuel ratio during cold cranking was enriched by the same amount as that during normal operation with gasoline. With pure methanol, a very rich mixture will not increase the total quantity of volatile components as it will with gasoline. Thus, employing a richer F/A mixture ratio with methanol cannot be expected to benefit cold-starting as much as with gasoline. Despite this reasoning however, several studies have shown that very rich mixtures significantly lower the minimum starting temperature of reconfigured engines using neat methanol. Freeman and
Goetz [1 0] achieved starts at 0°C on methanol with carburetted versions of both the Ford 17 Escort and Volkswagen Golf 1.6 liter engines. Gardiner, Caird and Bardon [11] also
reported cold-starts at subzero temperatures using equivalence ratio ( ct>) as high as 13 to
16. They tested a range of starting temperatures with the carburetted Escort engine and
found that using values of ct> between 1 and 2, the minimum starting temperature limit
is only +10°C. With mixtures enriched to value of ct> of 13 to 16 the Escort engine
started easily at 0°C, and with relatively long cranking periods (up to 120 seconds), down
' Engines Modified to Improve In-Cylinder Mixture Formation and Ignition
The criteria for a successful cold-start found most often in the literature is the
formation of an ignitable gas-phase mixture around the spark-plug at the time the spark
occurs. To satisfy this requirement, cold-start improvements should be aimed at:
( 1) increasing fuel vaporization and,
(2) providing a source for igniting mixture with lean A/F ratios.
It is obvious that because of its inherent low volatility at low temperatures, very
little methanol can vaporize in the intake system. Thus, the vapor required for cold-
starting must be produced by charge heating. For neat methanol, the equilibrium
volatility limit is determined by the amount of charge heating occurring during
compression. The following methods have been employed to optimize in-cylinder vaporization by maximizing the temperature and fuel vaporization during compression:
( 1) increasing cranking speed and engine compression ratio,
(2) increasing cranking speed, cranking time and fuel quantity, 18 (3) fuel atomization to improve fuel vaporization rate,
(4) direct injection stratified charge engines (DISC),
(5) use of high energy ignition systems.
Increasing Cranking Speed and Engine Compression Ratio
Generally, in-cylinder compression temperatures are increased by increasing the
engine cranking speeds. The effect of cranking speeds on the cold-starting of
homogeneous charge engines fueled with pure methanol has been studied by Gardiner and
Bardon [12] and Blair [8]. Some work also has been done by Siewart and Groff [13] and
Jorgenson [14], and Nakajima et al.[15].
Gardiner and Bardon [12] used an air-cooled 2-cylinder engme which was
basically an engine used in military generator applications. With high cranking speeds
and very high +6°C to -4°C, while a cranking speed of 600 rpm gave further improvement to only -S°C. The reason for good cold-startability despite the low compression ratio (6:1) with this engine was the high compression temperatures (peak temperatures of 120°C at ambient temperatures near to -30°C) achieved. A tentative explanation for the high compression temperature was that large quantities of liquid fuel in the cylinder might have improved piston ring sealing by filling up the leakage paths between the rings, pistons and cylinder walls. Gardiner and Bardon ascribed the increase in compression temperature to increase in compression ratio from "residual fuel in the cylinder." With a higher compression 19 ratio, engine even better results could be expected. By studying the effects of different cranking speeds over a range of ambient temperatures, Gardiner and Bardon [14] and Nakajima [15] found that the effect of cranking speed is not as significant at higher ambient temperatures (+10°C to +20°C) as at ambient temperatures below 0°C. At subzero temperatures, faster cranking gave higher peak gas temperature increases. Blair [8] found that increasing the cranking speed of a 1.6 liter 4 cylinder engine up to 480 rpm did not reduce the minimum starting temperature below the limit of +10°C achieved with cranking speed of 240 rpm. The Nakajima data also show that for an ambient temperature of + 1ooc to OOC, cranking speeds above 200 rpm gave little or no increase in the peak compression temperature. Since the time for fuel vaporization decreases as cranking speed increases, a deterioration in the startability would be expected if the speed giving highest compression temperatures was exceeded. Combined Effects Of Cranking Speed, Cranking Time, and Fuel Quantity According to a study by Gardiner and Bardon [12], a combination of cranking speed and fuel quantity used greatly affects cold-startability. For example, minimum starting temperatures with a 400 rpm cranking speed matched or exceeded those achieved with 600 rpm when a richer mixture was supplied at a lower speed. The explanation given for this behavior was that large quantities of liquid fuel improved piston ring sealing by filling the leakage paths between the rings, the piston, and cylinder walls. Nakajima et al [15] also observed that excess liquid fuel in the cylinder increased the gas temperature by increasing the cylinder pressure during cranking. However, Gardiner and 20 Bardon ascribed this behavior to an increase in "compression ratio" from "residual fuel in the cylinder." Increase in cylinder pressure from cycle to cycle was due to the fact that more fuel entered the cylinder than was exhausted during each cycle. The best minimum starting temperatures with methanol-fueled reconfigured engines [10,2,16] required long cranking times, which is unacceptable in practice. According to Nakajima et al.[15], if spark plug wetting can be avoided, very rich mixtures can reduce cranking times until first fire. The Escort tests of Gardiner, Caird and Bardon [16] pointed out that the time taken from the first fire until running was sustained was excessive and needed to be reduced. Fuel Atomization to the Improve Fuel Vaporization Rate Fuel atomization is one of the principal methods proposed to improve the fuel vaporization rate. Improved fuel atomization is probably the most frequently discussed method in the literature regarding improvements to pure methanol cold-starting. As the research shows, this method is yet to show much success in practice. In fact, several studies have shown no benefits at all [6,8]. Most studies have shown that tests with "totally atomized fuel" did not improve the cold-starting to a great degree. Menrad et al. [6] found that totally atomized fuel with a carburetted, methanol-fueled Volkswagen 4-cylinder engine did not improve cold starting. Nichols [17] used timed, high pressure (250 psi) mechanical fuel injection at inlet ports for a 14:1 compression ratio, Ford 2.3 liter, 4-cylinder methanol engine. This fuel injection system was designed to give fme atomization, but starting was reported only 21 to +4 oc. Similarly, Blair [8] achieved no significant improvements with devices for very fme micron size atomization in carburetted engines. A theoretical model proposed by Browning and Raghuraman [18] predicts that if a delivered equivalence ratio of 1.0 was composed of 10 micron droplets, vaporization would be fast enough to produce a flammable vapor-air equivalence ratio down to -15°C. Because of the lack of experimental hardware to produce 10 micron droplets, no experimental attempts to achieve this have been reported. However, a study by Pefley and Browning [7] shows that with 38 micron size droplets, starting temperature was reduced by only 2°C (from +TC to +5°C), but there was substantial reduction in cranking time (from 80s toSs). Similar results were reported by Armand and Gudder [19] with 30 micron droplets and starts down to + 3 oc in a 10: 1 compression ratio engine cranked at 200 rpm. The minimum temperatures achieved by Armand and Gudder do not necessarily mean that droplets produced survived into the compression stroke to produce vapor. Engine Starts may have been achieved with most of the fuel reaching the inlet valve as an unatomized wall film [10,2,16]. From all the fuel atomization attempts and their relative successes and failures, one criterion for effective compression vaporization can be introduced. To be effective in increasing fuel vaporization and enabling fuel mist combustion to take place, the droplets must survive until the latter part of the compression stroke. In addition, atomized fuel must avoid coming in contact with inlet port walls and the inlet valve, as well as piston combustion chamber and cylinder wall surfaces. Also, as observed by Peters [20] atomization seems to be largely controlled by the flow conditions past the inlet valve 22 rather than the degree of atomization at the injector. For proper cold-start by fuel atomization, providing atomized fuel is not sufficient. Special conditions for droplet vaporization in the cylinder also need to exist. The apparent failure of improved atomization in cold-starting is not due to an inherent flaw in the principle but due to an inability to implement the technique with existing fuel system hardware. Direct Injection Stratified Charge (DISC) Engines A DISC engine is more like a spark-ignition diesel engine than a homogeneous charge automobile engine. Several diesel engines have been converted to run on pure methanol. Siewert and Groff [13] used a UPS-292-SC engine which was a converted GM 292 cu.in., 6-cylinder SI engine. The UPS-292-SC was started on pure methanol at -29°C in about 4 seconds. Jorgensen [14] later measured the compression temperatures in the same engine and proposed an explanation for the excellent cold-start results. He suggested that ignition proceeded independent of the compression heating, as all or part of the liquid droplets could be vaporized by one pulse of the 4000 Hz AC ignition system. By the time, a second spark occurred there was enough vapor around the spark plug for vapor phase ignition to occur. For this mechanism to work, it is necessary that the spark plug be flring when the fuel arrives to avoid shorting or fouling. The UPS-292- SC engine employs an alternating current spark system and timed, high pressure fuel injection into the cylinder aimed at the spark plug. After ignition, there is a static flame front near the spark plug and the fresh densely packed droplets continue to be sprayed into this flame front with swirling incoming air to support the combustion. 23 High-Energy Ignition Systems Devices such as high-energy plasma igniters that can distribute ignition energy throughout the combustion chamber volume have also been evaluated [21]. This approach does not depend on having the right size fuel droplets in the right place at the right time, since the plasma can fmd random groups of droplets with enough regularity to maintain combustion. Blair [8] tested various ignition systems with enhanced fuel atomization and high cranking speeds. Various ignition systems ranging from 10 KV A.C. arc to 40 KV were used. None of these systems showed any improvement over conventional ignition systems. Theoretically, plasma jet ignition systems can produce better results since they produce a higher energy and the plasma jet can penetrate through a larger portion of combustion chamber exposing a larger amount of charge to the ignition energy. Engines Modified to Improve Mixture Formation External to the Cylinder Many types of out-of-cylinder heated starting devices have been used for pure methanol cold-starting. Basically two types can be identified: ( 1) those which produce vaporized methanol (electric vaporizers and flame vaporizers), (2) those which use methanol to produce a gaseous starting fuel (catalytic devices). Both can be considered as auxiliary devices or starting aids rather than engine modifications. While these devices have not matched the startability of gasoline, or the best primed methanol fuels, the results are roughly 15°- 25°C better than those using recalibrated engines and in-cylinder mixture formation approaches. 24 Vaporizers Methanol vaporizers may be heated electrically or by a diffusion flame burner fueled by methanol. Thus, two classes of vaporizers have been developed and used in experiments, namely, electric vaporizers and flame vaporizers. Electric vaporizers are commonly used because they are simple in design, more compact, and easier to install. Typically, heating elements are ceramic positive temperature coefficient honeycomb units, common resistance heaters, or diesel glow plugs. Because of the limited power of the battery, the electric heating elements are required to be as efficient as possible. For efficient use of electric heaters, only heating of fuel and not the fuel-air mixture is recommended [6]. Vaporizer power levels are generally about 1 KW. Different researchers have tried a variety of heating devices and vaporizers. Generally, their experiments require larger vehicle batteries or longer preheat periods. By using multi-point vapor injection systems with resistive heating Nebolon, Chan, Pefley, and Browning [22] achieved minimum starting temperatures of +SOC to as low as -15°C. The system was designed to provide vaporized methanol at 0.75 g/s (1.5 times idle fuel condition) using 880 KW heating and a system pressure of 302 KPa. Starting at -15°C required 3 min. cranking. Vapor was injected continuously into each port, and the vapor may have condensed prior to entering the cylinder if it arrived while the inlet valve was closed. According to Nebolon et al.[22], the ability to supply small droplets for compression vaporization is a very important factor controlling the cold starting. At low ambient temperatures, the vapor may condense into a fme mist, producing very small droplets which may remain suspended during the induction and 25 compression process. As reported by Weber and Huttebraucker, a reliable cold-start at- 1o·c to -15·c is possible (two minute preheating) with heated fuel injectors. They used multi-point mechanical fuel injection (KE-Jetronic) with injector nozzles preheated to 2oo·c by means of conventional cylindrical glow plugs. The preheating of methanol as it passes through the injector nozzle allowed boiling fuel injection (flash boiling atomization). The boiling fuel condensed into a fme mist before entering the combustion chamber. From the above studies, it appears that the heating of the pressurized fuel prior to injection (flash boiling atomization) assures substantial improvements in compression vaporization-based SI engine cold-starting. Flame Vaporizers The energy limit placed on electric heating can be avoided by using flame heating systems. Various researchers have tried different approaches such as heating the inlet air, heating the air and fuel, and heating the combustion chamber walls. Compared to electric heating, flame heating has proven to be an inferior method for cold-starting. Flame vaporizers require long heating periods up to 15-17 minutes. The minimum starting temperature achieved was only o·c. Hochsmann [23] used a flame-heated cold-starting aid for heating the inlet air of a methanol-fueled 2.5 liter, 4-cylinder, Porsche engine. He used a "flame glow plug" to heat the methanol, and supplied the combustion air with a small 12-V fan. To prevent the heater from consuming the oxygen from the engine air, a heat exchanger was placed in the inlet manifold. With this apparatus, it took 10 minutes to preheat the air to +45·c 26 from OOC ambient temperature, but starts could not be achieved. The system was modified by adding a electric fuel heater. Still, it took 8 minutes to raise the fuel temperature from OOC to +50°C. After heating the inlet air for 17 minutes to a temperature of 130°C, the engine was started at OOC ambient in 14 seconds. Hochsmann concluded that intake air and fuel preheating had relatively little influence on cold-starting improvement. Despite the very high output of the entire system (4.6 KW), it failed to achieve results as good as those using electric heating of 1 KW or less [23]. The factors responsible for failure of flame heating system can be listed as following: ( 1) heating the air instead of the fuel, and (2) considerable heat loss from the air to the passage through the inlet valve and metal surfaces of the cylinder. In conclusion it can be said that flame heating has the inherent disadvantages of longer heating time and greater energy consumption relative to electric heaters. Catalytic Devices Producing Gaseous Fuels By passing the methanol over heated catalytic materials, it is possible to produce starting fuels which are gaseous at low ambient temperatures. Dissociation/decomposition of methanol to hydrogen and carbon monoxide is one such method. Experimental studies 27 using this concept have included cold-starting tests using bottled CO+H2 gas to simulate the decomposed methanol [7], using only reactor devices [24], and using a methanol reactor to actually start an engine. In an another catalytic approach [9], methanol is is dehydrated to produce dimethyl ether which is used as a primer for methanol fuel blends [10,2]. Weber and Hiitterbraucker achieved starts at -15°C to -20°C ambient temperature by using a device called a "catalytic cracking carburetor." This device produced hydrogen and carbon monoxide as a starting fuel. Since this reaction is highly endothermic, heat was supplied by burning methanol in a flaming glow plug to bring the catalyst to the reaction temperature. The pure methanol for the catalytic reaction was sprayed onto the catalyst using a conventional cold-start injector and air was supplied with an electric pump. Following this, the engine was started at temperatures down to -15°C to -20°C. Considering the minimum starting temperatures achieved and relatively brief preheating period required, this represents the best homogeneous charge SI engine cold-starting on pure methanol reported to date. Kazole and Wallace [9] have pointed out that the dehydration of methanol to dimethyl ether is exothermic over a certain temperature range. This reaction "requires some heat addition to warm the catalytic reactor and vaporize the methanol." However, the net heat input is much lower than that required by the devices producing Hz and CO, which makes it possible to use electric heating rather than flame heating in vehicle applications [9]. 28 Kazole and Wall ace [9] performed experiments to evaluate the effects of partial substitution of methanol with DME (dimethyl ether) during cold-starting. The DME was supplied from gas cylinders rather than an actual catalytic device. Kazole and Wallace used a single cylinder 12:1 compression ratio, port fuel-injected engine. The quantities of liquid methanol and gaseous DME injected were such that the overall mixture was stoichiometric. Even the lowest mass fraction of DME tested (30%) provided cold starting at -15·c with 10 seconds of cranking. With pure methanol, starts below +1o·c could not be achieved. Karpuk and Cowley [25] tested a variety of dehydration catalysts and obtained good results using fluorinated y-alumina material. This catalyst was said to be very active and selective for methanol dehydration between 25o·c and 35o·c. The researchers designed a reactor that heated from -2o·c to operating temperature in 15 seconds using 500 W power. This reactor provided DME at 1 kg/hr with a steady state power consumption of 440 watts. CHAPTER IV DESCRIPTION OF THE EXPERIMENT Direct Injection Concept As stated earlier, methanol exhibits poor cold-starting behavior because of its low vapor pressure and very high latent heat of vaporization (506 Btu/lb), which is more than three times that of gasoline (150 Btu/lb). Both these factors contribute to the problem of cold-starting. An important prerequisite to cold-starting is the adequate supply of a combustible mixture rich enough to ignite easily, near the spark plug. If the methanol vapor/air mole fraction can be raised to a satisfactory level, it should be possible to initiate combustion and start the engine at extremely low temperatures. The concept of direct injection of methanol involves injecting methanol directly into the combustion chamber (as in a diesel engine). By using direct injection at low cylinder pressures the methanol vapor/air mole fraction required to start the engine at very low ambient temperatures can be achieved. Plan of the Experiment In the early phase of the project, the following equipment was identified as being required to set up the experiment: (1) A test engine representative of today's automotive engineering technology which could be modified to employ direct injection. (2) A refrigeration system capable of cooling the test engine to -20°C. 29 30 (3) An injector capable of being used for methanol injection at pressures up to 200 psi. (4) An electronic control mechanism to control the timing and duration of fuel injection. (5) A fuel system to store and transfer pressurized liquid methanol (180-200 psi.) to the injector. ( 6) An efficient data acquisition system to record all important experimental parameters. In addition, a piston position sensor mechanism was developed to time the methanol injection with respect to the piston position. Also the test engine had to be modified to permit the placement of the direct injector, piston position sensor mechanism, thermocouples (K-type) and other measurement devices at critical locations. The complete experimental setup used (as shown in Figure 4.1 and Figure 4.2) in this research work consisted of the following systems and mechanisms: ( 1) Modified test engine, (2) fuel injection system, (3) the Injector, (4) injector control mechanism, (5) refrigeration system for engine, fuel and intake air cooling and (6) data acquisition system. S~tinless steel 1. Intake air temp. sensor / tubing 2. Intake pressure probe ~ 3. Piston position sensor Pressure Control 4. Combustion chamber temp. senso 6 Regulator Valve 5. Fuel temp. sensor 1--' 6. Exhaust gas temp. sensor ' Nitrogen M~:n~~~Biced Valve L-..J Cylinder Exhaust....,.,...~ ----.. Fan Data Acquisition .- Board .-- \ ~ t lrl ~ .... ::I 0 Cooling • ~ ~ ~~R Cabmet --- Figure 4.1 Overall Experimental Set up \.;.)- 32 Modified Test Engine A single cylinder, 4-stroke, direct overhead 4-valve, liquid cooled, spark-ignition, KL650-B1 Kawasaki motorcycle engine was used for the experiment. A list of general specifications for this engine is given in Table 4.1. This particular engine was used for cold start experiments for following reasons: (1) This engine has a high compression ratio, 9.5:1, which ensured higher compression temperatures in the engine cylinder. (2) Because of liquid cooling system employed by this engine, it was possible to chill the engine to low temperatures by circulating chilled antifreeze coolant through engine water jacket. (3) A single cylinder engine helped reduce experimental hardware cost and simplify engine modifications required to employ direct injection in the engine combustion chamber. This engine was modified to directly inject the methanol into the cylinder. Originally, this engine used a carburetor. The carburetor was removed and the engine head was modified to accommodate the methanol fuel injector. The injector was placed in the spark plug location and the spark plug was moved to the side wall of the combustion chamber. The injector was fitted in the engine head by enlarging the spark plug hole. A detail of the injector and the spark plug assembly in the engine head is shown in the Figure 4.3. The spark plug was secured in a sleeve that sealed against the coolant circulating in the water jacket. 33 Table 4.1 Test Engine Specifications Type 4-stroke, DOHC, 4-valve, !-cylinder Cooling System Liquid-cooled Bore and stroke 100.0 * 83.0 mm Displacement volume 651 mL Compression ratio 9.5:1 Fuel System Modified for direct fuel injection of methanol (originally carburetted) Lubrication Forced feed, SAE lOW-40 Valve timing Inlet Open 19° (BTDC) Close 69° (ABD) Duration 268 ° Exhaust Open 57° (BBDC) Close 31 ° (ATDC) Duration 268 ° 34 4 1. Combustion chamber temperature sensor 2. Exhaust pon temperature sensor 3. Split fire spark plug 4. Injector 5. Sleeve for the injector Figure 4.2 Modified Test Engine 35 (a) Top view of the engine head (b) Inside view of the combustion chamber Figure 4. 3 Modified Test Engine 36 (a) Spark plug location (b) Injector location Figure 4.4 Modified Test Engine Details 37 Thermocouples were placed at all strategic locations on the engine. To determine the temperature in the engine combustion chamber a hole was drilled through the engine head a thermocouple was installed in the engine combustion chamber. Figures 4.3 and 4.4 show different views of the modified engine head showing the locations of the injector, spark plug and the thermocouple. The engine was equipped with a decompression mechanism (in the exhaust valve mechanism) to reduce load on the starter motor by reducing the relative compression pressure during starting. This mechanism was deactivated so that full compression would be available during the cold-start tests. The thermostat was removed from the coolant circuit to permit circulation of coolant at all temperature. A cradle was fabricated to mount the test engine and bolt it to the engine stand. For the cold-start tests with constant cranking speed, the starter motor provided on the engine was used for cranking with power supplied by a battery. For the cold-start tests with variable cranking speeds, the electric motor on the engine stand was used for cranking. The wiring circuits were completed to make the ignition and starting systems fully functional. Fuel Injection System The fuel injection system for this experiment is shown in the Figure 4.5. In order to for the injector to inject methanol against the compression pressure inside the combustion chamber, it was necessary to have the fuel line pressure upstream the injector more than the maximum compression pressure so that the fuel will not be forced back Pressure Regulator On-Off Control Valve On-Off Control Valve \ T-Join 1/4" Stainless Steel Tubing / Methanol Fuel Tank / (al 190 psi) Fuel Cooli .. o '--V" f:::] :::;;1 ~[1 1" Foam Rubber /L...-..--.1 Insulation Pressurized Nitrogen Tank On-Off Control Valve / Foam Rubber Insulation Engine block" Figure 4.5 Fuel Injection System VJ 00 39 in the fuel tank. A pressure regulator controlled the supply pressure to the fuel tank, which ensured the fuel line pressure upstream of the injector to 190 psi (the maximum compression pressure inside the combustion chamber was measured 170 psi). The plumbing and the fuel tank were of stainless steel to prevent corrosion from methanol. To simulate the cold-starting conditions (ambient temperatures to -35°C), it was necessary to cool the methanol to the cold-start test temperature. A 1/2" diameter copper coil which carried chilled antifreeze coolant, was wrapped around the fuel tank to form a cooling coil. The copper cooling coil and all plumbing was insulated with a 1" thick foam rubber insulation. To measure the temperature of methanol at time of injection, a thermocouple was placed on the fuel line, just upstream of the injector. The Injector A Lucas gasoline port electronic injector was used for direct injection of methanol into the cylinder. The injector was located centrally in the cylinder head as shown in figure 4.2 and 4.4. This injector was modified so that it could function in close proximity to the engine combustion chamber. Originally, this injector had a spray guide made of delrin material for inlet port injection. To prevent this spray guide from melting under the very high combustion temperatures, it was removed from the injector. A spray pattern test was conducted on the modified injector to check for any significant change in the spray pattern. The test revealed that the spray pattern of the modified injector did not change significantly. Figure 4.6 shows a view of spray pattern with the modified injector. 40 .. Figure 4.6 Injector Spray Pattern 41 Injector Control Mechanism In order to control the timing and the duration of injection, an injector control mechanism was developed. Figure 4. 7 shows the schematic of the injector control mechanism. An injector controller supplied by Moog Controls, Inc. was used to switch the injector on and off and to control the duration of injection. This Moog controller provided adjustments for "injection delay" and "injection width." The "injection delay" is the time period between receiving a pulse by the controller and the moment when the controller triggers the injector open. "Injection width" is the time the injector remains open (pulse width). A piston position sensor mechanism (as shown in Figure 4.7) was developed to accurately locate the position of piston during the working cycle of the engine. This mechanism was coupled with the injector control mechanism so that it would be possible to time the methanol injection with respect to piston position during the working cycle of the engine. Figure 4.8 shows a photograph of the piston position sensor mechanism mounted on the test engine. The piston position sensor mechanism consisted of a cam degree wheel and a magnetic pickup device. The cam degree wheel was a graduated disc which was bolted on the intake valve shaft. To fmd the bottom dead center (BDC) position of the piston, the crankshaft was turned manually until the top dead center (TDC) mark on the magneto flywheel was located. The corresponding position of the cam degree wheel was identified as TDC and the BDC position was marked exactly 180°C from the TDC position mark. 42 c e f a. Cam degree wheel b. Magnet piece c. Magnetic sensor d. Injector controller e. Fuel line f. Injector g. Magnetic sensor position adjustment h. Intake manifold Figure 4.7 Injector Control Mechanism 43 Figure 4.8 Piston Position Sensor Mechanism 44 To take maximum advantage of the compression heating, methanol was injectedin the engine combustion chamber at the BDC position of the piston. To ensure correct injection timing, a small flexible magnet was placed at the BDC position mark on the cam degree wheel. A magnetic sensor was positioned close to the rim of the cam degree wheel so that the sensor picked up a magnetic pulse every time the magnet passed by. This sensor was connected to the Moog controller, which in tum was connected to the injector. For every rotation of the cam degree wheel, the magnetic sensor picked up the BDC position of the piston and sent out a signal to the Moog controller. Upon receiving a signal from the magnetic sensor, the Moog controller triggered the injector open. By adjusting the "injector delay" knob, the time of injection from the BDC position of the piston can be controlled. In order to inject right at the BDC position of the piston, the "injection delay" knob was turned to the zero injection delay mark. The duration of injection was controlled by adjusting the "injection width" knob provided on the Moog controller. Thus, timed injection of methanol at the BDC position (when the piston is on the compression stroke) was accomplished. Refrigeration System Figure 4.9 shows the refrigeration system for the experiment. A conventional refrigeration system was used to cool a large quantity of antifreeze down to below OOC. Dry ice was then added to the antifreeze to achieve temperatures down to -40 OF in the reservorr. ~ 1(1." Copper Tubing ' ·.· ·· :·.·. : .·. · .·.·.: .·.·.·.·.: .·.·.·.·. [ . ~ Methanol Fuel Tank Fuel Cooling Coil Foam Rubbe_.!__ _ Coolant Circulating Pump Insulation - I ~J&mr: :::••U¥@~~ /~ ~t Submersible 1(2" Copper Tubing Pump Methanol ~ Injector Vortex lube Compressed Air In ~Glass Wool Insulation Air Cooling Coil \ t Cooler Box ~ Figure 4.9 Refrigration system +:>. (..fl 46 A pump with a flow rate of 4 gallons per minute was used to circulate the chilled antifreeze through the engine. The temperature of the engine was controlled using a bypass to regulate the amount of coolant flowing through the engine. To cool the air supplied to the engine during the cold-start tests, two techniques were used. First, air at high pressure (100 psi) was passed through a coil immersed in the chilled antifreeze. The air from the cooling coil was then passed through a vortex tube to achieve further cooling of the air. The vortex tube, manufactured by Vortec Engineering, Inc., is usually used in place of conventional liquid coolant for rapid cooling of cutting tools and other equipment during various machining operations. The vortex tube has a small nozzle which accelerates and directs the compressed air supplied to it into two opposing streams of air. The result is very low temperature air emerging from one end of the vortex tube and high temperature air emerging from the other end at a much greater flow rate. The vortex tube provided adjustments for various combinations of temperatures and flow rates for hot or cold air flows. During the cold-start tests, the vortex tube provided cold air at temperatures as low as -35°C at atmospheric pressure. A temperature sensor in the intake manifold measured the intake air temperature. A pressure sensor was located on the downstream side of the throttle valve to measure the pressure of the air supplied to the engine. 47 To achieve fuel cooling, a 0.5" diameter copper tubing coil was wrapped around the methanol tank to form a cooling coil. A submersible pump circulated chilled antifreeze through this copper coil. To prevent heat transfer to the surrounding atmosphere, the methanol tank and the copper tubing were insulated with foam rubber insulation. All fuel lines were insulated with foam insulation as well. Data Acquisition System Rapid and accurate data acquisition was necessary to record starts and firings. The data acquisition system consisted of an ffiM XT computer with two Metrabyte data acquisition boards. All the thermocouples and the pressure sensors were connected to the data acquisition boards. All the transducers were sampled at rates up to 25 samples per second. CHAPTER V TEST PROCEDURE The experiments conducted to study the cold-starting behavior of the test engine by injecting methanol directly into the engine's combustion chamber are described below. To ensure correct functioning of all the systems and normal performance of the modified engine, it was initially operated for a few hours on methanol. During this initial run the performance of all systems was carefully observed. Malfunctioning of the systems or modified engine, was corrected before cold-start tests were initiated. Tests Without Methanol Injection A series of tests were conducted to determine the maximum temperature achieved in the cylinder by compression heating without fuel injection. A typical compression test run involved cranking the engine for 90 seconds. The starter motor provided on the engine was used for cranking with power supplied by a battery. A thermocouple in the engine combustion chamber continuously measured the cylinder temperature throughout the complete run. A K-type thermocouple was used to measure the cylinder temperature. Tests were conducted at different engine temperatures. To determine the actual cylinder temperature increase due to compression, methanol was not injected during these tests. 48 49 Tests With Methanol Injection A series of tests were conducted to determine the possible cooling effect of methanol injection on the maximum cylinder temperature achieved during compression. A typical test involved cranking the engine for 90 seconds. The temperature of the methanol and the combustion chamber were continuously measured over the complete test run. During this test series, the methanol was maintained at the same temperature as that of the engine. Tests were run at varying starting temperatures. Cold-Start Tests With Wide-Open Throttle A series of tests was carried out to determine the minimum starting temperature at which the engine failed to start. For these tests, the throttle valve in the intake manifold was maintained at the wide-open position. A pressure sensor located on the downstream side of the throttle valve sensed the intake air pressure for each cycle of the engine throughout the complete run. The cylinder pressure at the BDC position of the piston was determined by this pressure sensor to be approximately 5 psia. The pressure in the fuel line upstream of the injector was maintained at 190 psi. The injector control mechanism was set to start injecting the methanol at the BDC position of the piston when it was on the compression stroke. During these cold-start tests, the engine, methanol and the intake air were all maintained at the same temperature. The engine was cranked for 90 seconds using the electric motor provided on the engine stand. If the engine started during this period of 90 seconds, the next test was conducted at a lower starting temperature. This series of 50 tests was continued until the engine repeatedly failed to start at the particular test temperature. The lowest temperature at that point marked the minimum starting temperature limit for this engine with wide-open throttle. Cold-Start Tests With Closed Throttle A series of cold-start tests was conducted with the throttle nearly closed in an attempt to increase methanol evaporation in the engine combustion chamber. The boiling point of any liquid is reduced by reducing the pressure. With the closed throttle, the vacuum developed by the fast downward movement of the piston on the intake stroke, was significantly increased. The pressure at the BDC marked the maximum vacuum available during the working cycle of the engine. With a closed throttle, the minimum cylinder pressure at BDC was measured to be 2. 7 psia. Methanol was injected at the BDC. In a typical test run, the engine was cranked for a maximum of 180 seconds with the electric motor provided on the engine stand. Tests were repeated at varying starting temperatures. To study the effect of increased cranking speed on the cranking time required to start the engine, a few tests were conducted at an increased cranking speed of 600 rpm, which was twice the normal 300 rpm cranking speed. CHAPTER VI OBSERVATIONS In this chapter, the results of experiments conducted to study the cold-starting behavior of engines fueled with methanol (M100) are presented. An in-depth analysis of all cold-start experimental data was accomplished. The analysis revealed a criterion for the successful cold-starting of methanol-fueled (M100) engines. Compression Tests Without Methanol Injection The data from the compression tests without injection are presented as plots of cylinder temperature versus cranking time. Figure 6.1 shows such a plot for the engine at a room temperature, about 20 °C. Figure 6.1 shows an average increase of about 20 oc in the cylinder temperature due to compression. Figure 6.2 shows the temperature rise from compression in the cylinder for different initial engine temperatures of 23, 9, 0, -10, -20, and -33 °C. From this plot it can be seen that for initial engine temperatures above 0 oc, the average temperature rise in the cylinder was approximately 20 °C. For initial engine temperatures below 0 oc, the average temperature rise in the cylinder was approximately 10 °C. This decrease in the average cylinder temperature rise can be related to the increased rate of heat transfer to the cylinder walls at lower engine temperatures. It should also be noted that during the first 20 seconds of cranking, cylinder temperature increases significantly and after that it remains almost constant. This behavior of cylinder temperature can be attributed to the fact that during the frrst 20 51 52 Cranking time (seconds) Figure 6.1 Plot of Cylinder Temperature Rise in Compression for Starting Temperature 23 ·c. 53 10 15 20 25 3 35 Cranking time (seconds) Figure 6.2 Plot of Cylinder Temperature Rise in Compression for Starting Temperatures 23, 9, 0, -10, -20, -33 ·c. 54 seconds of cranking, the rate of heat transfer to the cylinder is greater than the rate of heat transfer from the cylinder to the sidewalls. After first 20 seconds, equilibrium is established and average cylinder temperature stays constant. It is important to note that the thermocouple for engine cylinder temperature was located close to the sidewall of the cylinder in the combustion chamber. It is postulated that due to the position of the thermocouple, the measured temperature is a few degrees lower than the actual temperature within the cylinder. Compression Tests With Methanol Injection A series of tests were conducted to determine the possible cooling effect of cold methanol injection on the maximum cylinder temperature during compression. Figure 6.3 shows the effect of injection of methanol. In this test, methanol was injected after 50 seconds of cranking. An average drop of about 8 °C to 9 °C in the maximum cylinder temperature was observed. Cold-start Tests With Wide-Open Throttle A series of cold-start tests were conducted with wide-open throttle position. The results of these tests are presented in Table 6.1. It was found that the engine failed to start at temperatures below -6°C. Figures 6.4 through 6.7 show the plots of cylinder temperature versus cranking time for starting temperatures of 5°C, 0°C, -6°C, and -11 °C. The tests were repeated to ensure accuracy. 55 20r------~======~ ICompression Test With Methanol Injection I 15 ...... ·-·. --.-----.-----.--.-----.--.------.--.------.-----.-----.--.--.------.-----.--.------sudden injection of methanol () I 0 ···· ·····················································\································.-························ eO 0 "'0.._, ~ 3 ~... 8. E £... 0 "'0 .5 >. u -1 30 0 Cra.nk.ing time (seconds) Figure 6.3 Effect of Sudden Injection of Methanol on Cylinder Temperature. 56 Table 6.1 Results of Wide-Open Throttle Cold-Start Tests Run Engine Air Methanol Result Temp. Temp. Temp. No. oc oc oc Start/No Start 1 4 17 17 Start 2 0 0 0 Start 3 0 -10 18 Start 4 -5 17 -1 Start 5 -6 15 -5 Start 6 -6 -20 -11 Start 7 -8 0 -5 No Start 8 -10 -5 -16 No Start 9 -11 -13 25 No Start 10 -11 -15 -15 No Start 11 -13 -18 18 No Start 12 -17 10 15 No Start 13 -16 10 16 No Start 57 ---1 Wide-Open Throttle Cold-start Test 1-----·------·------·- 80 70 ... 60 ~ 50 ...... ] >. 40 u 30 20 -101 +-----,-----~----~--L-~----~----~----~--~----~ 0 10 20 30 40 50 60 70 80 90 Cranking time (seconds) Figure 6.4 Cylinder Temperature Plot for Cold-start at 5 oc Starting Temperature With the Throttle in a Wide-open Position. 58 ------~Wide-Open Throttle Cold-start Test ~------·---····---- ..... --· -- ...... -- ...... --- ...... -- ...... -- .. -- .. - -~ 1 bO u ~ 90 ... ---- ...... --- ...... --- .. ·...... 80 70 60 50 40 30 20 10 -10+-----~----~----~~--~----~----~----~----~----~ 0 10 20 30 40 50 60 70 80 90 Cranking time (seconds) Figure 6.5 Cylinder Temperature Plot for Cold-start at 0 ·c Starting Temperature With the Throttle in a Wide-open Position. 59 ror------======~--~~ IWide-Open Throttle Cold-start Test I 50 . ----- ...... -- ...... -- .... -· --- ...... -----...... -- ...... -- G 40 ...... -- ... -...... --.--.... -- ...... -----.---...... ------.--.... --.-----.-----...... ---- toil 8.._.. ~::s 30 ·······························-·············································································-······· . -..~ 8. E ~ 20 ·························-···········-············································································· ..C) ] >. u 0 10 20 30 40 50 60 70 80 90 Cranking time (Seconds) Figure 6.6 Cylinder Temperature Plot for Cold-start at -5 ·c Starting Temperature With the Throttle in a Wide-open Position. 60 20~------~ IWide-Open Throttle Cold-start Test I 15 -----··-·····-····--·--··-·--·--·-··------·-·-··--··-·······--····--····-··-··--·-··--·--·--·-··--·--··-·--··-···· u- bil s 5 ·············-- ~ ...::I ... "'8. E £... 0 ] >. u -1 10 30 40 0 Cranking time (seconds) Figure 6.7 Cylinder Temperature Plot for Cold-start at -11 oc Starting Temperature With the Throttle in a Wide-open Position. 61 Cold-start Tests With Closed Throttle A series of cold-start tests were conducted with the throttle in a closed position. The results of these tests are presented in Table 6.2. In this series of tests, the cylinder pressure at the BDC (on the compression stroke) was significantly reduced. With closed throttle, the lowest cylinder pressure at the BDC was measured to be 2.7 psia. By injecting methanol at this low in-cylinder pressure, the mole percent of methanol vapor increased significant! y. Successful cold-starts were achieved at temperatures as low as -38°C, with the -38°C value being the limit of the refrigeration apparatus rather than that of the engine. A detailed analysis of the results achieved at this extremely low temperature is presented in the next section. The results of this series of tests with closed throttle are presented in Table 6.2. Figure 6.8 is a plot of cylinder temperature versus cranking time for a successful start at -38°C engine temperature. The methanol temperature was -28°C and the intake air temperature was -36°C. Figure 6.9 is a plot of intake manifold pressure versus cranking time for the same test (at -38 °C). Similar plots of cylinder temperature and intake manifold pressure for various engine starting temperatures of -30°C, -25°C, -20°C, and -10°C are presented in Figure 6.10 through 6.17. The tests were repeated to ensure accuracy. 62 Table 6.2 Results of Cold-start Tests With Closed lbrottle Run Engine Air Methanol Result Cyl. Pressure Temp. Temp. Temp. AtBDC No. oc oc oc Start/No Start Psia 1 -38 -38 -20 Start 2.7 2 -30 -25 -22 Start 3.0 3 -30 -30 0 Start 6.0 4 -28 -20 -33 Start 4.0 5 -28 -20 -20 Start 3.3 6 -25 -25 -22 Start 3.8 7 -25 -20 -20 Start 3.0 8 -23 -20 -18 Start 2.9 9 -22 -25 -22 Start 3.2 10 -20 -20 -20 Start 3.0 11 -20 -20 -10 Start 3.0 12 -10 -10 -10 Start 4.0 63 -----~ Closed Throttle Cold-start Test ~------1 ······-····························------·------· 90 80 u -bO 70 ~ ...._,0 60 ~ a 50 ...cu 8. 40 E ...... £... ~ "'0 .5 >. u 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Cranking time (Seconds) Figure 6.8 Cylinder Temperature Plot for Cold-start at -38 ·c Starting Temperature With the Throttle m a Closed Position. 64 20.------~ I Closed Throttle Cold-stan Test j 18 .. ..______J ...... 16 .. ····---· ------··-. ·- -··---.-----.--.. ------·------·-. ·---·---.------.-----. ·--·------·------·· 4 2 -- .. -. --.-----.-----.--.----- Average intake manifold pressure at BDC = 2.7 psia 10 20 30 40 50 Figure 6.9 Intake Manifold Pressure Plot for Cold-start at -38 ·c Starting Temperature With the Throttle in a Closed Position. 65 ---1 Closed Throttle Cold-start Test ~------...... -...... --- ...... --- ... -· --- ... -- ... -- .. ------...... --- .. ------..... -...... --- ... -- --·------...... - ..... -- ... -- ... ----- 80 70 60 50 40 30 ------~ ------20 ------~-- 10 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Cranking time (seconds) Figure 6.10 Cylinder Temperature Plot for Cold-start at -30 OC Starting Temperature With the Throttle in a Closed Position. 66 --~Closed Throttle Cold-start Test l ...... -- ...... -- ...... ----- ...... ---- .. -- ...... -- .. --- ...... -- .. -- ...... -..... ------...... ------.. .. ~-.:..:--.:..:--.:..:-·.:..:--..:..::--..:..::--..:..::-·..:..::--..:..::--..:..::-·..:..::--:.:.:--:.:.:-·:.:.:--:..:..--:..:..-·:..:..--:..:.-:..:..·-:..:.- -:..:..-· :..:..--.:..:.-·.:..:.--.:..:..:..:.·.:..:--.:..:--.:..:--.:..:--..:.:--..:.:--..:.:-·..:.:--..:.:--:.:..;-.. --- -- .. ------.. ---- Average intake manifold pressure at BDC = 2.9 psia 30 40 150 160 170 1 0 Figure 6.11 Intake Manifold Pressure Plot for Cold-start at -30 ·c Starting Temperature With the Throttle in a Closed Position. 67 1 L...__C_lo_s_e_d_Thr_o_t_tl_e_C_o_l_d-_s_tar_t_T_e_s_t _J~ ______ ...... u bO ~ "0 '-" ~ .... 50 ....~ ..,.... 8. 40 e ....~ .... ~ "0 .5 u>. 20 30 Figure 6.12 Cylinder Temperature Plot for Cold-start at -25 oc Starting Temperature With the Throttle in a Closed Position. 68 -----~Closed Throttle Cold-start Test ~------ -- ...... -- ...... --- ...... 0 Figure 6.13 Intake Manifold Pressure Plot for Cold-start at -25 ·c Starting Temperature With the Throttle in a Closed Position. 69 r·------ ~~~~] Closed Throttle Cold-start Test ------···········································--·------····-·------at ------bO t) 90 "'0 80 -...0 .a 70 ...CQ 60 8.e £... 50 0 40 "'0 .5 >.. u 10 20 30 40 50 60 70 80 90 1 110 1 0 130 140 150 160 170 180 Cranking time (seconds) Figure 6.14 Cylinder Temperature Plot for Cold-start at -20 ·c Starting Temperature With the Throttle in a Closed Position. 70 ------~ Closed Throttle Cold-start Test ~--·--·--·-----·------·--·------·------· -- ...... -- ...... -- ...... -...... -- ...... ...... --- ...... ---- ...... ----- ... -- ... -- ...... -... --- ... -- .. -- .. ------...... ------...... -- .. ----- .. ------...... ---- ...... ·---- Figure 6.15 Intake Manifold Pressure Plot for Cold-start at -20 ·c Starting Temperature With the Throttle in a Closed Position. 71 [------...... - ... -- .. -- .. -- .. -- ...... -...... ----- .. -- .. -.... -- .. ------...... ---- ..... ---- ...... ---- ...... -...... ------...... ----- .. -- 1 90 80 70 60 50 40 ------30 -----·····-···· 20 10 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Cranking time (seconds) Figure 6.16 Cylinder Temperature Plot for Cold-start at -10 ·c Starting Temperature With the Throttle in a Closed Position. 72 18 -----~ Closed Throttle Cold-start Test 1------ "'2 16 -- ... -- .. ----- ...... -- .... -.. ------..... ------...... ------.. --- ...... -... ------...... --- ...... -- ...... ------... -- ...... ------... ---- ... .. ----- ... .. 12 -- 10 -- Average intake manifold pressure at BDC 4.1 psia 2 ------ = L------~ 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Cranking time (seconds) Figure 6.17 Intake Manifold Pressure Plot for Cold-start at -10 OC Starting Temperature With the Throttle in a Closed Position. 73 The Phenomenon of Cold-starting Methanol Engines For every fuel-air combination there exists a range of mole percent of fuel vapor air mixture in which the mixture will sustain combustion when exposed to a spark or a flame - the lower flammability limit (LFL) to the upper flammability limit (UFL). For methanol, the lower flammability limit is 6% and the upper flammability limit is 36%. By employing an innovative technique of direct in-cylinder injection of methanol with a closed throttle, successful cold-starts were achieved at temperatures as low as -38°C in less than 2 minutes of cranking time. To determine the criteria for these cold starts, a careful analysis of the experimental data was accomplished. It was determined that for a successful cold-start, the formation of a 6% mole percent of methanol vapor in air is required when there is spark. Calculation of Methanol Vapor Mole Percent in Air Figure 6.18 is a plot of % methanol vapor versus temperature for different pressures (2.2, 4, 6, 14.7, and 30 psia). 74 45 ...... : 40 ...... ;...... ~ ...... ~ ...... ;...... ~ .... . I I : : . . : : : 35 ::.: .::: ..:r:.: .. : .: .: -1·7\: .: :: ..:·I.: ..: ..:.: .:r: .:.-: .: .:·-+: .: -~30... . ------~------J~~~------L.I I .I ...... L .I ...... l.I ...... J.1 .I .I .I .I .I . 8. I I I I CIS : : : : > I I t I ...... --~--- ...... ,...... - 0 25 c:: j Me~anol · CIS . . . : : . : ~ 20 ········Flammabiiityf..imils·········:···· I I I I E I .I I .I -c:: . ~ . . u... 15 ...... ~---·······i·'l: ...... ~ ...... ; ~ . . 10 ·······---~---·······H·········r···· . .\1 . : : v 5 ...... -----~----~---. ~.---- ...... ~- , ... 10 20 30 40 0 Temperature (Deg. C) Figure 6.18 Plot of Percent Methanol Vapor for Various Temperatures and Pressures. 75 The following empirical equation was used to determine the methanol vapor mole percent in air. ...... eq.(6.1) % (mf>v,,po, =mole percent of methanol vapor Pc =critical pressure of methanol= 1153.6 psia P, = total pressure, psia r = temperature at which mole percent of methanol vapor is being sought, oc A1 = 7.51334 A2 = 6468.101 A3 = 396.2652 Investigation of Cold-starts at Temperatures Below -l0°C An important prerequisite to achieve ignition in an internal combustion engine is availability of a combustible fuel vapor-air mixture rich enough to initiate ignition, near the spark plug. Equation 6.1 was used to determine the methanol vapor mole percent in air at the time of spark. The total cylinder pressure at the time of spark was calculated to be approximately 30 psia. 76 In accordance with the flammability limits, the 6% to 36% methanol vapor-air combination will ignite in air, when exposed to a spark. To determine the minimum % methanol vapor required to achieve cold-starts, plots of percent (%) methanol vapor versus cranking time were prepared. For a particular cold-start test, the mole percent of methanol vapor was determined using the cylinder temperature and pressure data for variables T and P, respectively in equation 6.1. It is important to note that in equation 6.1, P, and T represent the pressure and temperature in the engine cylinder. The pressure data recorded in the cold-start test data files represented the pressure in the intake manifold measured downstream of the throttle valve. Thus, this pressure is not representative of the actual cylinder pressure over the engine cycle. The valve timing specification for this Kawasaki engine indicates that the inlet valve closes 69° (from Table 4.1) after BDC, when the piston is on the compression stroke. At the BDC position, the pressure measured by the pressure sensor in the intake manifold is considered to be reasonably representative of the actual cylinder pressure. The pressure data at the BDC from the raw data files was used to calculate the methanol vapor mole percent at the time of methanol injection. The ignition timing specification for this engine indicates that, the spark occurs at 10° BTDC, which is 101° crank angle degrees after the inlet valve closes. Thus, at the time of spark, the pressure measured by the pressure sensor in the intake manifold does not represent the actual pressure in the cylinder. The pressure in the cylinder at the time of spark was determined by calculations. The calculated value for cylinder pressure was determined based on the pressure at the time of inlet valve closing and the change in cylinder volume from the 77 inlet valve closing to spark. The pressure in the cylinder at the instant of spark was found to be approximately 30 psia. Figure 6.19 shows a plot of the% methanol vapor at the time of spark and cylinder temperature versus cranking time for a cold-start at -38°C. From Figure 6.19 it can be seen that the engine started when mole percent of methanol vapor available at spark reached 6%. Figures 6.20 and 6.21 show plots of mole percent of methanol vapor at spark and cylinder temperature versus cranking time for starts at - 20°C and 0°C. From these plots it is noted that the engine started when mole percent of methanol vapor available at spark reached 6%. Several such plots for cold-starts at different temperatures were examined. It was found that the value of 6% methanol vapor mole at spark marked the minimum requirement to achieve a successful start at any given engine starting temperature. To validate this observation the mole percent of methanol vapor (at spark) achieved in unsuccessful cold-start tests was examined. In cold-start tests with wide-open throttle, the engine failed to start at temperatures below -6°C. Figures 6.22 and 6.23 show plots of the mole percent of methanol vapor (at spark) and cylinder temperature versus cranking time for unsuccessful cold-starts (with wide-open throttle) at -8°C and -11 °C. From these plots it is obvious that the mole percent of methanol vapor available at spark never reached 6% and the engine failed to start. A complete investigation of all cold-start experiments revealed that the engine invariably started if the mole percent of methanol vapor available at spark reached 6%. Table 6.3 represents the overall summary of results for all cold-start experiments. 78 72.------~~--70 66 -1 Closed Throttle Cold-start Test l------60 60 ------ ...... g .s ~ -10 u -20 -30 -24 10 20 30 0 70 80 90 1 110 1 Cranking time (Seconds) Figure 6.19 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at -38 OC Starting Temperature With the Throttle in a Closed Position. 79 72:.------~--~72 66 -1 Closed Throttle Cold-start Test 1------· j 66 60 60 54 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ] - 54 ~ 48 ------~~ - 48 f ~ - 42 ------~ - 42 - ; 36 ··-··-··-··-·· ·····--··-·· ··· · ··-·------·····---· -- · --· --- ~S-tart_a_t6.,...91-o ..... 36 ~ ~ > 30 ··································-·-----·-··························------· ...... 30 - ~ ~ •:-····· 24 -5u ~ e - ~ ----- 18 ...c 1 § 12 If - \~,;. 6 ______::;:~~;;;;~t-1~~:::::::::::~~:~~ :::::::::::::::::::::: ~6 ------r ..;~---~--;,.---r- _____ ;___ ~ ------1 Cylinder temperature t------12 ~~;:.a;=~~~r ------:-····· ...... ······-·······-··------·······--········-··-·····-··-······-·······-· -18 -24 10 20 30 40 50 70 80 90 1 110 1 140 150 160 170 1 0 Cranking time (Seconds) Figure 6.20 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at -20 ·c Starting Temperature With the Throttle in a Closed Position. 80 102 170 96 Closed Throttle Cold-start Test 90 [~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 150 84 ... - ...... - ...... - ...... - ...... -- ...... - ...... -...... _ -_ -_ ~=.. = ~,=.i_;;~_,,·_l:,· · __· ~-· -_· · __· ~-· -_· · __· ~_· l..:\. ~~ ~-t·:·~,t_~~~_L_· :_= ·~_!-_·-__~ ~-- --···._·~~-· -_· ·· __·~ -· -_··-__· ~-·· __· ·:_·-~_·. 78 ...... T - 130 72 ...... ]r.{ -· _1: ___ ...... ::-~ ----· ...... -- ... -- ...... -.. ~ u - ~ . '-' 66 ------1 Percent Methanol Vapor at Spark 1------·-~-- ...... --:-- ...... cO ... 110 ~ 0 8.., 60 -----.--.------.------.--.------.------.--.-----~ 1r------.----- ·--·------.------'-' > ~ 54 -- ...... --- ...... +-- ...... 90 0 :: a., c., 48 -5 & ~ ...... ,..... ~-~~------·············· ...... 70 E E __ ..... Cylinder temperature ~ c ············· -- ·····-············· ...... r------. ... ~ Start at 6% .g 0 ... :: 50 .5 :·: ~ ...... -- ...... ------.. -- ...... -...... :...... >- .}}::::·:: u ...... -- ...... -...... ~: ·· · ...... - ...... 30 :::::~· ...... --- ...... -...... -...... - ~:~· 10 .&r----~----~--~~--~-----r----~----~--~-----+-10 10 20 30 40 50 60 70 80 90 Cranking time (Seconds) Figure 6.21 Plot of Percent Methanol Vapor and Cylinder Temperature for Cold-start at 0 ·c Starting Temperature With the Throttle in a Wide-open Position. 81 7~------5 IWide-open Throttle Cold-start Test I 0 -..._,~ ... j Cylinder temperature 8.. ~~4 ------··r--,~v ------5 i ~ ~,:}j!:'}tL:,L______Percent Methanol Vapor at Spark ------~ 3 ... ~ ."0s >- -10 u 1 ------·------ H-----,-----~----.-----.----.----~-----r----~----+-15 10 20 30 40 50 60 70 80 90 Cranking time (Seconds) Figure 6.22 Plot of Percent Methanol Vapor and Cylinder Temperature for an Unsuccessful Cold-start at -8 OC Starting Temperature With the Throttle in a Wide-open Position. 82 Wide-<>pen Throttle Cold-start Test Cylinder temperature u -~ - tab - u ~ 0 > -u ] B eu I .g'"' .s ->. -10 u Cranking time (Seconds) Figure 6.23 Plot of Percent Methanol Vapor and Cylinder Temperature for an Unsuccessful Cold-start at -11 ·c Starting Temperature With the Throttle in a Wide-open Position. 83 The Mechanism for a Successful Cold-start From the analysis of cold-start tests with closed throttle it was observed that the engine consistently started at any given temperature; while for cold-starts with open throttle, the engine failed to start at temperatures below -6 °C. For cold-starts with the throttle in a wide-open position the cylinder temperature did not increase after the initial rise in cylinder temperature due to compression heating. An analysis of the effect of throttle position on the in-cylinder vaporization of methanol was carried out to explain the physical mechanism behind starts at temperatures as low as -38°C with throttle in closed position. In this analysis it was assumed that the at any given time during the run, the air-methanol vapor mixture was in equilibrium. The analysis revealed that with closed throttle, the average value of in-cylinder mole percent of methanol vapor increases significantly. Various factors and processes that led to a successful cold-start with closed throttle were identified. It was observed that a typically successful cold-start with closed throttle involved the following five (logically) inter-related phases: (1) compression heating (1-2), (2) localized burning of methanol vapor mist (2-3), (3) first fire (3-4), (4) continuous firing for about 5 seconds (4-5), (5) and start at 6% methanol vapor mole percent (5-6). 84 Figure 6.24 shows a plot of cylinder temperature and methanol vapor percent (at spark) versus cranking time for a cold-start at -38°C with the throttle in the closed position. Figure 6.24 identifies the five phases of a successful cold-start. From Figure 6.9 for cold-start at -38°C, with the throttle in the closed position, the average pressure inside the cylinder at BDC is approximately 2.7 psia. Methanol was injected directly inside the cylinder at the BDC when the cylinder pressure was 2.7 psia. The amount of methanol vaporized in the air at BDC was calculated using Equation 6.1. The cylinder temperature data and the cylinder pressure at BDC (2.7 psia) were used as the variables rand P, in Equation 6.1. For cold-starts with wide-open throttle, the pressure inside the cylinder at BDC was found to be approximately 10 psia. Figure 6.25 is a plot of mole percent of methanol vapor for different cylinder pressures (2. 7 psia at injection with closed throttle, 10 psia at injection with wide-open throttle, and 30 psia at spark) versus cylinder temperature for the same cold-start test at -38°C. Figure 6.25 identifies the first three phases of a successful cold-start. A frrst frre was identified when during the run due to a spontaneous fire, cylinder temperature increased and never droped back to the temperature at which that spontaneous frre was spotted. A start was considered successful only if the engine frred and sustained combustion (without assistance of the starter) for a period of 10 to 15 seconds. As for the frrst frre a start is identified when during the continous frring phase, due to a spontaneous fire the cylinder temperature increases and then never drops below the temperature at which the spontaneous frre was spotted. Figure 6.26 identifies a start for a closed throttle cold-start test at -25°C. Each of the five phases for the start at -38°C (with closed throttle) is discussed below. 85 l~r------~~~96 90 1 - 2 Compression heating 80 ...... (). 84 2 - 3 Localized burning of methanol vapor mist 78 3 - 4 First fire 72 G 60 ······· 4 - 5 Continous firing 66~ cO ~ 60'"' 54 ~> 48 0; 42 -5 ~ 1: ------;~::~::.;~~~:-~-~~~~-~~--~:.~~------~-~~~-~~~- ~:~~ __ :~___/_: _: ·· 36 ...e 4 30 ~ ~ 24~ 18 12 6 0 .O+~r-~--~~--,--,--,-~--~~~~----~--r--.--r--.--+~ 10 20 30 40 0 60 70 80 90 100 110 120 130 140 150 160 170 180 Cranking time (Seconds) Figure 6.24 Phases of a Successful Cold-start at -38 OC With the Throttle in a Closed Postion. 86 . 1 - 2 Compression heating ...... • .• t • i------·-----~------~---- 2 - 3 Methanol vapor mist burning • I I ------·-----I 1 I I f I r~~~~~----·~ ··:··••••• ...... r••• 5 1 Cylinder Temperature (Deg.C) Figure 6.25 Plot of Percent Methanol Vapor Versus Cylinder Temperature Showing Various Phases of a Successful Cold-start at -38 ·c With the Throttle in a Closed Postion. 87 110 100 90 u 80 70 . .._1 ------·. 60 . ~ .,.J so f 40 Gl~ 4.1 ]"" u~ -10 I ::1 · ~ -- ~ - ••I I m l • m : l m -~ - · : --~- ml m - ~ m ~ : m ml m m l I ~ -- . ··· I 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 % 97 98 99 100 Cranking time (seconds) Figure 6.26 A Start for a Closed Throttle Cold-start Test at -25°C 88 Compression Heating Phase ( 1-2) Figure 6.24 shows a l6°C temperature nse achieved in the first phase of compression heating (1-2). lhls l6°C temperature rise was achieved during the frrst 5 seconds of cranking. The temperature did not increase any more on further compression. Figure 6.25 depicts the corresponding rise in mole percent of methanol vapor at injection with closed throttle {1-2) and at spark (1'-2'). It is apparent from Figure 6.25 that the mole percent of methanol vapor for injection with closed throttle is significantly higher than for injection with wide-open throttle. With increase in cylinder temperature, the mole percent of methanol vapor for injection with closed throttle increased at a much faster rate than for injection with wide-open throttle.At the end of the compression heating phase, the mole percent of methanol vapor at injection reached 6%, when the cylinder temperature reached -22°C. Localized Burning of Methanol Vapor Mist (2-3) After the initial compression heating, a slow rise in the cylinder temperature was observed for cold-starts with closed throttle. This temperature rise is marked by phase 2-3 in Figure 6.24. The corresponding rise in the mole percent of methanol vapor at injection at with closed throttle is marked by 2-3 in Figure 6.25. This temperature rise after the initial compression heating phase was not observed for cold-starts with wide open throttle, indicating the direct effect of the throttle position on the cylinder temperature for the second phase (2-3). From Figures 6.24 and 6.25 it can be seen that at the end of the compression heating phase (1-2), the mole percent of methanol vapor 89 at injection reached 6% when the cylinder temperature reached -22°C. Once the mole percent of methanol vapor at injection reached 6%, the cylinder temperature increased continuously due to the localized burning of small droplets of liquid methanol, which can be attributed to the cycle-to-cycle increase in the amount of average methanol vapor mole fraction available in the cylinder. The mole percent of methanol vapor available at the time of injection is compressed along with droplets of liquid methanol suspended in air as the piston moves up on the compression stroke. It is assumed that upon compression, some methanol vapor condenses in the air. Due to the rapid movement of the piston, the time available for condensation of methanol vapor is too short for complete condensation to take place. Thus, the resulting mixture consists ofsupersaturated vapor with small droplets of liquid methanol suspended in air. The spark occurs at 10° crank angle degrees before TDC. By the time the spark occurs, most of the vapor delievered to the cylinder during injection has condensed. Thus, the mole percent of methanol vapor available at spark is still too low to initiate a combustion. However it is postulated that some of the smaller methanol droplets are caught up in methanol vapor mist were available near the spark plug. Some of these droplets of liquid methanol, along with methanol vapor mist, burn promoting a small rise in cylinder temperature in every engine cycle. Even though localized burning of methanol vapor mist and individual droplets is achieved, the flame front does not propagate since the average in-cylinder mole percent of methanol vapor is below the LFL, or in other words, the flame front did not propagate because there was not enough vapor having a local 6% mole fraction present near the spark plug . It is important to realize 90 that this localized burning is the only factor that contributes to the continuous increase in the cycle-to-cycle cylinder temperature after the initial increase that occur during the first 10 to 15 seconds of compression. With higher cylinder temperatures, the mole percent of methanol vapor at BDC during injection increases successively. This promotes an increase in the average methanol vapor mole fraction in the cylinder. It is evident from Figure 6.25 that if the same test (at -38°) was performed with the throttle in the wide-open position, the mole percent of methanol vapor (at injection) at the end of the compression heating phase would have been only 1%. With wide-open throttle, the cylinder temperature would have to reach 0°C before any localized burning of methanol vapor mist could occur. This is shown by state point 6 in Figure 6.25. This means that a temperature rise of about 38°C would be required for the mole percent of methanol vapor (at injection) to reach 6% at the end of compression heating phase. It may be recalled that the compression test data revealed that the maximum temperature rise achieved in pure compression was only about 15°C. For starting temperatures below Q°C, the temperature rise during compression was reduced to 10°C. From these data it can be concluded that for cold-starts with wide-open throttle, a successful cold-start cannot be achieved for temperatures below -l0°C. For cold-starts with the throttle in a wide-open position, the engine failed to start below -6°C, which supports this hypothesis. 91 First fire This phase of a successful cold-start is difficult to isolate from the methanol vapor mist burning phase. It is discussed separately to explain the nature of a successful cold start. The factor determining a good first fire is found to be the existence of densely packed liquid methanol droplets and supersaturated methanol vapor close to the spark plug. When this condition is satisfied, the supersaturated methanol vapor and droplets of methanol will burn which causes an increase of about 15°C in cylinder temperature. The first fire invariably occurred when the quantity of mole percent of methanol vapor reaches 12% or above at a given cylinder temperature. For cold-starts at different temperatures, all of the first fires were obseved in the 12-26% methanol vapor range. For most of the successful cold-starts with closed throttle, first fires were observed at cylinder temperatures around -10°C and -5°C. A temperature rise of about 10°C to 15°C was observed in frrst fues for cold-starts at different temperatures. For some cold-starts, moderate frres were observed before first frre, as shown in Figure 6.24. Continuous Firing In this phase of a successful cold-start, the engine frred continuously for every cycle and cylinder temperature increased continuously. This phase is represented as phase 4-5 in Figure 6.24. Typically this phase lasted for about 15 to 20 seconds, until the mole percent of methanol vapor reaches 6% and the cylinder temperature reaches 19 oc. Compared to the cycle-to-cycle cylinder temperature rise achieved in the localized 92 methanol vapor mist burning phase (2-3 ), the cycle-to-cycle cylinder temperature rise achieved in this phase was much larger. The sharp temperature rise achieved in this phase can be attributed to the fact that for this entire phase, the quantity of avearge mole percent of methanol vapor above 6% was significantly higher than the local burning phase. The Start The fmal phase of cold-start can be identified by a cylinder temperature rise of about 100°C over a short period of 8 to 10 seconds. This phase is represented by phase 5-6 in Figure 6.24. A start was considered successful only if the engine fired and sustained combustion (without assistance of the starter) for a period of 10 to 15 seconds. From Figure 6.24 and 6.25 it can be seen that the engine started instantaneously, when the methanol vapor available at spark (30 psia) reached 6% - the LFL of methanol. CHAPTER Vll CONCLUSIONS Conclusions In this research project, a reliable and economical mechanism for cold-starting methanol fueled (MlOO) engines was identified and successfully tested. The proposed cold-starting technique of "The Use of Compression Heating to Improve In-Cylinder Methanol Vaporization" failed to achieve successful cold-starts below -6 °C. By employing an innovative technique of "Direct In-Cylinder Injection of Methanol at Sub Atmospheric Cylinder Pressures," successful cold-starts were achieved at temperatures as low as -38 °C without using any external heat source. The -38 °C starting temperature value was the limit of the refrigeration apparatus used in the rather than that of the engine. The criteria for cold-starting methanol fueled (MlOO) engines at extremely low temperatures were determined. Analysis of the cold-start experimental data provided a unique insight as to the general nature of successful cold-starting with methanol fueled (MlOO) engines. The literature on cold-start research identifies cold-start temperatures (without using high energy in-cylinder heating devices) no lower than -5 °C. The data obtained from this research indicates that cold-starts can be achieved at temperatures as low as -38 °C, a significant improvement in an important limitation on the use of methanol fueled engines. For cold-start tests with wide-open throttle, the engme failed to start at temperatures below -6 °C. It was found that for these tests, the maximum mole percent 93 94 of methanol vapor (relative mole fraction in the air) achieved at spark was only 3%, which is not sufficient to support ignition. The proposed cold-starting technique of "The Use of Compression Heating to Improve In-Cylinder Methanol Vaporization" failed to achieve sufficient in-cylinder methanol vaporization. To achieve a combustible fuel vapor-air mixture at spark, methanol injection at sub-atmospheric cylinder pressures was employed. By keeping the throttle in a closed position, cylinder pressures as low as 2.7 psia were achieved at bottom dead center and starts were achieved at temperatures as low as -38 °C. With closed throttle, the mole percent of methanol vapor increased significantly which promoted localized burning of supersaturated methanol vapor mist the most critical factor that led to engine starts at extremely low temperatures. It is important to mention that the engine consistently started when the mole percent of methanol vapor at spark reached 6% - the lower flammability limit of methanol. Hence, it was concluded that the principal criterion for a successful cold-start is the formation of a 6% methanol vapor mole fraction in the air when there is spark. It was found that the in-cylinder mole percent of methanol vapor can be increased more effectively by injecting methanol at very low cylinder pressures than by increasing the in-cylinder temperatures. This fact explains the limitation of the technique of "just preheating the engine, the air or the fuel" as a cold-starting technique. Suggestions for Future Research The technique of "direct in-cylinder injection of methanol at sub-atmospheric cylinder pressures" is suggested as a potential solution for the MlOO cold start problem. 95 It is further suggested that the following measures be exercised while implementing the suggested technique with either a single-cylinder or a multi-cylinder engine for assisting in cold-starting: ( 1) The cylinder pressure at spark initiation is a significant factor in determining whether a start will be achieved. Low cylinder pressure at spark initiation could possibly ensure rapid starts at very low ambient temperatures. Here, it must be mentioned that a very precise and fast-response control mechanism would be required for accurate and timely control of cylinder pressure throughout the working cycle of the engine. Spark advance is one technique that would result in lower cylinder pressures at spark. (2) "Pre-heating the Engine" will improve the cold-start performance in conjunction with the suggested technique of "Direct In-Cylinder Injection of Methanol at Sub Atmospheric Cylinder Pressures,". If the heat of compression is used to "heat the engine," the engine should be cranked without fuel for about 10 to 15 seconds, until the cylinder temperature reaches its maximum value. A compression release device could be actuated after initial compression to achieve the low cylinder pressures required for improvement in the in-cylinder methanol vapor mole percent. (3) Higher cranking speeds are strongly recommended for achieving rapid starts. REFERENCES 1. U.S. Department of Energy's "Progress Report One : Context and analytical framework," January 1988. 2. N. Iwai et al., "A study on cold Startability and Mixture Formation of High Percentage Methanol Blends," Paper 880044 Society of Automotive Engineers, 1988. 3. Dempsey, A.B. 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