Single Cylinder Research Engine Multi-Spark Ignition System

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Single cylinder research engine multi-spark ignition system

Andreas Lius

Master of Science Thesis TRITA-ITM-EX 2018:498 KTH Industrial Engineering and Management Machine Design SE-100 44 STOCKHOLM

Examensarbete TRITA-ITM-EX 2018:498

Encylindrig forskningsmotor med konfigurerbart tändsystem

Andreas Lius Godkänt Examinator Handledare 2018-06-19 Andreas Cronhjort Ola Stenlåås, Richard Adolfsson Uppdragsgivare Kontaktperson Scania CV AB Ola Stenlåås Sammanfattning I detta projekt presenteras ett arbete där en serieproducerad 5 cylindrig motor med gasdrift modifieras till drift på enbart en cylinder. En konceptstudie genomförs där för och nackdelar vägs mot varandra där sedan ett koncept implementeras. Tidigare lösningar har använts där avaktivering av cylindrar uppnåtts genom att ta bort komponenter till gasväxlingssystemet och med hål borrade i kolvarna. Motorn är tänkt att vid ett senare skede installeras i en test-cell på avdelningen för förbränningsmotorteknik på Kungliga Tekniska Högskolan. Oönskat kompressionsarbete i avaktiverade cylindrar minimeras genom att låta dessa ventilera mot atmosfären. Detta sker genom att plocka bort insugsventilerna och igentäppning av ventilstyrningar. Ventilation mot atmosfären sker med hjälp av ett modifierat insug. Ett system för att ta hand om olja som annars skulle ha förbränts i de avaktiverade cylindrarna konstrueras. Med denna lösning behöver inte den roterande massan modifieras vilket annars hade påverkat motorns balansering. Ett kapacitivt tändsystem där gnistenergi kan ändras under drift implementeras. Tändsystemet är uppbyggt av två stycken tändenheter och tändspolar som är kopplade till samma tändstift. Denna lösning tillåter bättre kontroll när multipla gnistor under en cykel är önskvärt. Motorn är tänkt att använda en experimentell styrning av tändning vilket kräver att tiden från när en gnista önskas till gnistinitiering minimeras. För kontroll av bränsle och tändning i ett initialt skede installeras ett eftermarknads motorstyrsystem. Detta styrsystem ansluts till motorns standard sensorer. Styrsystemet kan ändra relevanta driftparametrar under drift genom ett grafiskt gränssnitt, systemet inkluderar återkoppling för luft-bränsleblandning samt skyddsfunktioner för okontrollerad självantändning. Standardsystemet för avgasåterledning modifieras för att kunna styras av tidigare nämnt styrsystem. Hjälpaggregat och andra komponenter ej nödvändiga för drift i testcell demonteras. Motorn förbereds även så att en högtryckspump för direktinsprutning kan monteras i framtiden.

Master of Science Thesis TRITA-ITM-EX 2018:498

Single cylinder research engine multi-spark ignition system

Andreas Lius Approved Examiner Supervisor 2018-06-19 Dr. Andreas Cronhjort Dr. Ola Stenlåås, Richard Adolfsson Commissioner Contact person Scania CV AB Dr. Ola Stenlåås Abstract In this project, a 5-cylinder SI port-injected engine is converted to single cylinder operation by deactivating four of the cylinders. A concept generation process resulted in four different concepts where one of them was chosen to be implemented. Previous setups have been used before where cylinders have been deactivated by drilling holes in the piston.

Unwanted compression work for the deactivated cylinders is minimized by allowing ventilation to the atmosphere. The inlet valves are removed and the inlet guides plugged. A modified intake connects the deactivated cylinders to the atmosphere. To manage the oil in the deactivated cylinders which otherwise would be combusted is routed to a manifold and finally a catch tank. With this setup, the rotating assembly is untouched thereby retaining the stock engine balance.

A capacitive ignition system where the spark energy can be altered during operation is implemented. The ignition system is comprised of two separate ignition units and coils which is connected to the same spark plug. This setup allows full control of when the second spark is released when operated in a multi-spark mode. The system has been designed to minimize the time from spark demand to spark initiation. This is to prepare for future use where an experimental control algorithm will be used which doesn’t use traditional look-up tables.

In an initial stage, the fuel and spark will be controlled by an aftermarket engine control unit. The system is installed using the standard sensors on the engine. The control unit can alter relevant parameters during operation using a graphical user interface. The system incorporates closed- looped lambda and knock control for safe operation. The stock exhaust gas recirculation system is incorporated with the engine control unit.

Auxiliary units and other components not necessary for single operate are removed. The engine is also prepared to accommodate a high-pressure pump for future direct injection.

FOREWORD

This project has been a journey where many lessons was learned. The learning outcomes from this project stretches far beyond the scope of the project. As a gearhead where engines have been a central part of my life since childhood I am very thankful for doing my thesis at Scania. I would like to thank my main supervisor Ola Stenlåås for the support during the project. I would also like to thank Richard Adolfsson for the support and all the interesting discussions regarding engines. The project has been carried out at the NMEG/NMEO group and I would like to thank both groups. A special recognition goes to Anders Forslund who always made time available to discuss various problems. A big thank also goes to my fellow friends and thesis workers here at Scania, Rohan Sharad Kittur, Sotirios Tsironas, Jacob Arimboor Chinnan, Laura Horváth, Marcus Holmgren, Arvid Isaksson and Jonas Johansson.

Andreas Lius

Södertälje, May 2018

NOMENCLATURE

Notations Symbol Description

λ Air-fuel equivalence ratio

Abbreviations

AFR Air Fuel Ratio CAD Crank Angle Degree(s) CAN Controller Area Network CDI Capacitive Discharge Ignition CI Compression Ignition CNG Compressed Natural Gas DIY Do-It-Yourself DPF Diesel Particulate Filter ECU Engine Control Unit EGR Exhaust Gas Recirculation EMC Electromagnetic compatibility FPGA Field Programmable Gate Array LNG Liquefied Natural Gas NOx Nitrogen Oxides OEM Original Equipment Manufacturer OHV Over Head Valve PID Proportional Integral Derivative (controller) PTFE Polytetrafluoroethylene PWM Pulse Width Modulation RFI Radio Frequency Interference SAE Society of Automotive Engineers SCR Selective Catalytic Reduction SI Spark Ignition TIG Tungsten Inert Gas XML Extensible Markup Language

TABLE OF CONTENTS

SAMMANFATTNING (SWEDISH) 1

ABSTRACT 3

FOREWORD 5

NOMENCLATURE 7

TABLE OF CONTENTS 9

1 INTRODUCTION 13

1.1 Background 13

1.2 Purpose 15

1.3 Research questions 15

1.4 Deliverables 15

1.5 Delimitations 16

2 FRAME OF REFERENCE 17

2.1 Ignition system 17

2.1.1 Inductive ignition 17

2.1.2 Capacitive-discharge ignition 19

2.1.3 Inductive and capacitive ignition system comparison 20

2.2 Engine knock 20

2.3 Engine Control Unit 21

2.3.1 Aftermarket engine control units 21

2.3.2 Aftermarket ignition units 22

2.4 Air charge measurement 22

2.4.1 Thermal sensing 22

2.4.2 Speed-density 23

2.4.3 Other methods 23

2.5 Exhaust gas recirculation 23

2.6 Single-cylinder engine for research purposes 24

2.6.1 Cylinder deactivation & decompression 25

3 IMPLEMENTATION 26

3.1 Base engine specifications 26

3.2 Requirements 27

3.2.1 Cylinder deactivation requirements 27

3.2.2 Ignition requirements 27

3.2.3 Engine control unit requirements 27

3.2.4 Air handling requirements 27

3.3 Concept selection 28

3.3.1 Cylinder deactivation concept selection 28

3.3.2 Ignition system concept selection 33

3.3.3 Engine control unit concept selection 38

3.4 Concept implementation 39

3.4.1 Cylinder deactivation implementation 39

3.4.2 Ignition system implementation 40

3.4.3 ECU synchronisation 43

3.4.4 Air handling modifications 43

3.4.5 ECU implementation 45

3.4.5.1 ECU configuration 45

3.4.5.2 CAN & Heat release preparation 47

3.4.6 EGR preparation 47

3.4.7 Other modifications 49

3.4.7.1 Cooling system 50

3.4.7.2 Transmission plate 50

4 VERIFICATION 52

4.1 Ignition system 52

4.2 Synchronisation 53

4.3 Oil pressure 54

5 DISCUSSION AND CONCLUSIONS 55

5.1 Discussion 55

5.1.1 Cylinder deactivation 55

5.1.2 Ignition system 55

5.1.3 Engine control 55

5.1.4 Scope of thesis project 56

5.2 Conclusions 56

6 RECOMMENDATIONS AND FUTURE WORK 57

6.1 Recommendations 57

6.1.1 Oil pressure relief valve 57

6.1.2 Knock calibration 57

6.1.3 Manifold pressure sensor 57

6.1.4 Spark plug wear 57

6.1.5 Crankcase ventilation 57

6.1.5 Piston ring-pack 58

6.2 Future work 58

6.2.1 Oxygen sensor pressure correction 58

6.2.2 In-cycle spark event control 58

6.2.3 EGR system 59

7 REFERENCES 60

1 INTRODUCTION

1.1 Background The internal combustion engine in its current form has been used extensively due its relatively simple design and the availability of a suitable fuel source to run it. During its infancy, the development focused on power output and reliability, but in modern times with higher fuel prices the focus has shifted to efficiency and emissions (Heywood, 1988).

The reciprocating internal combustion engine can be differentiated into two groups depending on the inherent combustion process and how the fuel is introduced. Both groups can also be used in either two or four stroke applications (Johansson, 2014).

The first type relies on heat to initiate the combustion process, this heat is generated during the compression stroke. The engines are typically called compression ignited (CI) engines (Johansson, 2014). Modern engines based on this combustion process can under certain circumstances achieve a fuel efficiency close to 50% (EMMA-MAERSK, 2018).

The other type of engine is the spark ignited (SI) engine where an electrical discharge in the combustion chamber ignites the fuel mixture. While the combustion process limits the fuel efficiency to a lower level compared to the CI engine, it is widely used as it can be made in various sizes suitable for personal transport. The SI engine is typically exposed to a lower level of mechanical stress than the CI engine and can use a less expensive system for exhaust treatment compared to a CI engine, thus making it cheaper to purchase than an equivalent CI engine. To manage exhaust emission in an SI engine a three-way catalyst can be used. For an equivalent CI engine, a more complex system as selective catalytic reduction (SCR) and diesel particulate filter can be used (DPF) (Johansson, 2014).

The CI engine has typically been favored in heavy duty applications where fuel economy is highly prioritized. Modern legislations regulating the emissions from heavy duty vehicles are becoming more stringent and thus necessitates further developments of the engines (Blumberg et al, 2008). One type of engine out emission which is strictly regulated in the European Union and other countries is Nitrogen oxides (NOx) (The European Commission, 2011). Three-way catalysts used in SI-engines are relatively cheap and very effective, but they require stochiometric conditions for effective operation. For engines operating with lean mixtures such as CI engines different methods need to be implemented (Reif and Dietsche, 2014). One method of solving the problem is by using an exhaust treatment system, but using such a system increase the already complex nature of a modern internal combustion engine and also effect the fuel efficiency. Commonly used exhaust treatment system also requires an additional liquid to be injected in the exhaust system and thus necessitates another fluid to be stored on the vehicle besides the main fuel (Johansson, 2014). This type of system relies on accurate dosing of the liquid to maximize system efficiency (Chi and DaCosta, 2005). For a case where the liquid runs out before refilling the system will cease to function (Johansson, 2014).

The drawbacks on the CI engine has fueled the development of the SI engine to be used for heavy duty applications (Middleton, Neumann and Khatri, 2007). In certain areas, especially urban ones the use of CI engines have been reduced in favor for SI engines due to political initiatives to reduce particulate emissions (The Paris Public Transport Authority, 2014). This trend can be seen in various countries and seem to be growing. This development in certain areas has already made the SI engine the only option unless the latest technology in CI engines are utilized (The City of Oslo,

2018). The use of SI engines in long haulage has also been recognized by the European Union “Clean Power for Transport” commission to increase with better availability of LNG (Liquified Natural Gas) (Kofod and Stephenson, 2013). Modern heavy-duty trucks with SI engines and using LNG can in certain operating conditions have a range of 1100 km (Scania AB, 2017).

One of the mechanisms which limit the fuel efficiency of the SI engine is called detonation or knocking. Knocking is when the fuel mixture in the combustion chamber is auto-ignited i.e. ignited by heating rather than the spark-plug and the resulting flame front (Heywood, 1988). In a CI engine, this is not an issue as the fuel is not premixed. But in an SI engine which typically uses a premixed blend of air and fuel this imposes a problem. When knocking occurs in an SI engine the premixed fuel mixture is auto-ignited and result in a rapid pressure increase. Knock can be generated by either the compression heat or the increase pressure due to ongoing combustion initiated by the sparkplug which has not reached the end-gas (Heywood, 1988). The knocking phenomena will result in pressure oscillations which can be observed in a pressure trace. Knocking will increase the heat flux in the combustion chamber beyond its designed capabilities resulting in damage (Johansson, 2014). The increased heat flux is due to the pressure oscillations which breaks down a thin thermal boundary layer which otherwise protect the combustion chamber (Tsurushima et al, 2002).

If the phenomena is not counteracted the temperature will increase in the combustion chamber and the probability of the following cycle to self-ignite increases, thus countermeasures need to be implemented (Heywood, 1988).

Typically, the condition where the highest efficiency of a SI is found is at the limit where knock occurs. As modern engines are capable at operating at relatively high engine speeds, anti-knock methods must be activated quickly if knock is sensed. One method to counteract is by retarding the ignition timing and thereby reducing the peak pressure (Johansson, 2014).

Previous methods for controlling and counteracting knock has typically been achieved on a cycle- to-cycle basis. Multiple novel approaches have been used to mitigate knock at an in-cycle basis. This has been achieved using either in-cylinder pressure readings or ionic-current measurement during the combustion cycle. On method relied on either ionic-current or pressure sensing during the combustion event and when knock was detected additional fuel was injected in cycle to lower the combustion temperature (Liu et al, 2016).

Ongoing research with CI is focused on in-cycle control using in-cylinder pressure and fast computing using FPGA’s (Field Programmable Gate Arrays). Such methods enable adjustments to the combustion process in-cycle for increased efficiency and reduced emissions (Jorques Moreno, Stenlåås and Tunestål, 2018).

For research purposes and development in the early stages single-cylinder engines are typically used. Compared to a full multi-cylinder engine a single-cylinder engine offers multiple advantages such as better access for combustion diagnostics. Another advantage is that modifications can be implemented in a short time span (Snyder, Lahti and Moskwa, 2006).

As a single-cylinder consumes less air than a full scale multi-cylinder version the air delivery needs to be controlled. Another issue is that inter-cylinder dynamics is lost and therefore impact the applicability of results gained from a single-cylinder engine. One for example is the reduced frequency in combustion events which result in greater variation of the rotational speed. One way to minimize such effects is to use a flywheel with higher polar moment of inertia, but such a solution will greatly affect the transient response (Moskwa et al, 2009).

1.2 Purpose The aim of this thesis work is to deliver a single cylinder engine where parameters related to the ignition and fuel system can be adjusted. Why these parameters need to be adjusted will be presented below.

The work encompasses multiple subjects which need to be addressed.

The research engine in question will be based on an already existing engine platform sourced from an automotive manufacturer. As the research engine will be based on a multi-cylinder platform necessary modifications need to be carried out to adapt it for its intended purpose.

The ignition system should be capable to alter the ignition timing cycle to cycle and to provide multiple sparks in a controlled manner during a combustion event. The system should also be capable of altering the ignition energy for every spark. This is because the spark energy needed to ignite a mixture changes with factors such as charge density, mixture and EGR dilution.

In some instances where the mixing is far from ideal multi-spark might be incorporated where the initial spark fails to ignite the mixture.

The fuel system will be adopted for CNG, to evaluate mixing properties the gas will be injected at different locations.

1.3 Research questions 1. Evaluate different modification alternatives to convert a multi-cylinder engine to single- cylinder operation in a test cell with a special emphasis on the ignition system.

2. Evaluate necessary engine control requirements in terms of ignition control and knock countermeasures. The ignition system requirements include parameters such as control of spark energy, timing and multi-spark functionality. Another requirement includes fast execution of the spark e.g. time from trigger to spark execution. A method for the ignition to be triggered from two different sources has to be evaluated, e.g. by an engine control unit and an external FPGA. Knock countermeasures should be evaluated so to allow for safe engine operation by novice operators.

3. Evaluate modification alternatives to modify a EGR-system intended for multi-cylinder operation to single-cylinder operation.

1.4 Deliverables A running single cylinder SI engine designed for CNG fuel and adopted to be commissioned in a KTH test-bench will be delivered. This imply that several tasks listed below must be carried out:

1. Be adapted to test-bench support-systems for fuel delivery, data-acquisition, remote control, cooling, charge-air, exhaust system, electrical power, EGR and electromagnetic interference.

2. Deactivation of unused cylinders.

3. An experimental ignition system where the ignition timing and energy can be altered.

4. The ignition system should be capable of generating a spark as fast as possible when demanded, i.e. the time from spark demand to actual spark initiation should be minimized.

5. The ignition system should be capable producing multiple sparks when demanded.

6. Adjust quantity and injection timing accurately cycle to cycle by sequential port fuel injection.

7. Be capable of injecting from multiple locations upstream the intake valve. To fulfil these deliverables a variety of tasks needs to be carried out.

The engine in question will as mentioned earlier be based on a multiple cylinder engine, this necessitates that some modifications must be carried out such as cylinder deactivation. The ignition and fuel system should be controlled by some aftermarket engine control unit which include an interface to control necessary parameters. The engine in question is supposed to be commissioned in a test-bench at KTH, therefore it is necessary to evaluate and document the support-system capabilities to modify the engine accordingly.

1.5 Delimitations The thesis work is limited to 20 weeks of work and therefore the project should be limited in agreement with the supervisor and commissioner. The delimitations of the project have been defined in the list below.

1. An external adjustable charge-air system will not be a part of this thesis, but preparations to accommodate charge-air will be carried out.

2. A fully controllable EGR system together with a secondary air estimation method will not be included. Accommodations for EGR will be carried out such as EGR valve and cooler for future implementation.

3. Accurate calibration of engine parameters will not be carried out.

4. This thesis will focus on the ignition system while another thesis worker focus on the fuel and air-handling system.

2 FRAME OF REFERENCE

2.1 Ignition system In an SI engine, the combustion process ideally is initiated by a spark in the combustion chamber. Once the spark initiates the adjacent fuel mixture combusts and a flame propagates throughout the chamber and ideally combusts all of the fuel mixture (Reif and Dietsche, 2014).

For a spark to initiate the voltage over the electrode-gap must be sufficiently large. The voltage required depends on the electrode gap, air-fuel mixture and the density at the moment of ignition (Reif and Dietsche, 2014).

The electrical power to the ignition system is typically externally supplied by a battery or a capacitor (Heywood, 1988). For well-functioning engine operation, the spark must be initiated at the correct time instance with respect to the crankshaft position. In a typical ignition system, the voltages might exceed 10 kV (Reif, 2015).

As a modern SI engine can operate over a large span of operating conditions the demand on the ignition system will vary. Richer fuel mixtures and higher density will increase the threshold for spark initiation and thus require more energy. In static and ideal conditions 0.2 mJ can be sufficient to initiate flashover and flame propagation. In real scenarios with a running engine the spark energy can be in the range of 30-100 mJ for a regular car (Reif and Dietsche, 2014). In automotive drag racing where highly oxygenated fuels are used which necessitates rich air to fuel mixtures spark energy can reach up to 800 mJ (MSD Performance, 2018). In cases when running on lean mixtures with CNG it has been reported that cycle-to-cycle variation is reduced when increasing ignition energy (Polcyn, Lai and Lee, 2014). Generally, the minimum required ignition energy is found at stagnant stochiometric mixture conditions (Heywood, 1988). When using lean mixtures of CNG it has been shown that increasing the spark duration can help extending the lean limit. It has also been reported that using multi-spark strategy will extend the lean and dilution limit (Dahlström, Tunestål and Johansson, 2013).

Typically, the ignition is set in relationship with the crankshaft position. The position where the ignition occurs is called ignition timing, and timing is usually set at the point where the engine generates maximum torque. In some instances, there might be a limit to where the ignition timing can be set due to engine knock or emissions regulations (Heywood, 1988).

An improperly working ignition system where misfires occurs can lead to increased emissions, poor performance and damage of the catalytic converter (Reif and Dietsche, 2014). For proper function, it is therefore necessary to have ignition system which can produce a spark at all operating conditions while keeping a safety margin for wear and tear of the system (Reif, 2015).

2.1.1 Inductive ignition This type of ignition system has been in use for a long time and have been improved over the years for a more reliable operation. Early designs were based on mechanical moving parts while newer designs rely on solid state electronics (Heywood, 1988) (Reif, 2015). The system is still commonly used in modern cars today (Dahlström, Tunestål and Johansson, 2013).

The basic design uses a battery, coil, breaker, sparkplug and necessary wiring (Heywood, 1988). The coil is made up of a primary winding and a secondary winding. The secondary winding is

17 typically made of a thinner wire comparing to the primary, the secondary winding also has higher number turns. Typical turns ratio lies between 1:50 – 1:150 for commonly used coils (Reif, 2015).

The basic operation of the systems relies current flowing through the primary winding creating a magnetic field within the iron core of the coil. When the flow of current in the primary stops a voltage potential is induced in the secondary winding in excess of 15 kV. If the secondary winding is connected with a sparkplug and if the voltage is exceeding the spark threshold a spark will be initiated (Heywood, 1988), see Figure 1. When the primary current is switched on a voltage in the secondary winding is induced with reversed polarity compared to when the primary current is switched of. This voltage can exceed 1-2 kV and therefore initiate a spark, to prevent this a diode in the secondary winding is used (Reif, 2015). The spark can last between roughly 0.1 to 2 ms. The point where ignition commence is called the flashover, see Figure 2. The point of flashover depends on several factors such as air/fuel mixture, density, the velocity of the flow and electrode geometry/material/gap distance. The spark sequence can be divided into two phases, the spark head and the spark tail. The spark head is represented by the initial flashover where the voltage is at the highest. The second phase is called the spark tail where the voltage decreases, the spark tail lasts for the duration of the spark. As only a limited amount of energy can be stored in the coil the energy is divided between the two spark phases. If a sparkplug is worn and thus requiring a higher voltage for flashover, less energy is left for the spark tail and thus resulting in a shorter spark duration (Reif, 2015).

Figure 1. Inductive ignition system.

Figure 2. Spark event with flashover highlighted with blue arrow and spark duration with black arrow.

The switching of the primary current can be achieved by different mechanisms, both mechanical and solid state. Early system relied on breaker points and a cam synchronized to half the engine speed. Modern systems rely on transistors to provide switching of the primary voltage (Reif, 2015).

A drawback with the inductive ignition system is the time required to charge the coil might limit the system to only one spark per cycle. This might not be sufficient at certain operating conditions where the spark might be extinguished or located in an unfavorable region. In such a situation, it might be necessary to have a sequence of multiple spark events (Piock et al, 2010).

The charging time of the coil is called the dwell period and exists because of inductance and resistance in the primary winding. Over charging a modern coil could potentially damage it by excessive thermal loading. Current starts to flow in the primary before moment of ignition to account for the dwell time, at the moment of ignition the primary current is cut. The dwell time depends one several factors and one is the operating system voltage (Reif, 2015).

2.1.2 Capacitive-discharge ignition The capacitive-discharge ignition (CDI) system works in a similar fashion as the inductive system but with a slight modification. In an inductive system, the ignition coil has two major functions, transform the lower primary to a higher voltage in the secondary side and to store the ignition energy. In a CDI system, the energy is stored in a capacitor rather than in the coil. The advantage of using this principle is that the capacitor is typically much faster in storing the energy. The use of a capacitor as a storage medium gives the system a fast discharge of the energy resulting in a strong spark of short duration (Heywood, 1988).

The CDI has been recognised as a system with no or negligible delay between trigger input and spark discharge. Due to the fast nature of the system it is capable of generating multiple sparks within one combustion cycle (Liu et al, 2017) or in applications with engine speeds in excess of 20000 rpm (Shimasaki et al, 2004). The use of CDI ignition also aids the use of ionic-current measurement over the sparkplug for in cycle combustion diagnosis such as misfire or knock detection system (Johansson, 2014). In an induction ignition system, it might not be possible to use ionic-current measurement during the discharge period which is typically longer than the of the capacitor discharge in a CDI system. In a CDI system, the short ignition period enables ionic- current measurement short after flashover for combustion diagnosis (Shimasaki et al, 2004).

CDI ignition systems have been in use in automotive racing environments for some time due to its capability of high spark frequency. Another advantage is the higher available spark voltage which is necessary when extreme cylinder pressures and rich mixtures are used, such in automotive dragracing (Motec, 2018).

There are also exists versions of CDI ignition systems which can generate a customized ignition event. In such a system, a large capacitor is used and rather than fully discharge during one spark event, the system can be pulsated to create a spark with longer spark duration (Dahlström, Tunestål and Johansson, 2013). Using a system of this kind the spark energy can be adjusted for unfavourable operating conditions. Some systems intended for industrial gas engines have a reported output energy of 600mJ deliverable in one combustion event (Altronic. LLC, 2014).

There are some systems which combine the advantages of inductive and capacitive ignition systems. Systems like this generate a first spark according to the operating principle of the inductive ignition system, and for a second spark a capacitor is discharged (PerTronics, Inc, 2016).

2.1.3 Inductive and capacitive ignition system comparison To illustrate the capabilities of the inductive and capacitive-discharge ignition system their advantages and disadvantages are condensed in Table 1.

Table 1. Inductive ignition system vs. CDI Inductive ignition system CDI Advantages Less complex High spark frequency Inexpensive Multi-spark capability Robust Short charging time Longer spark duration Higher voltage over spark gap Widely used in automotive applications Disadvantages Typically limited to one spark event More complex Lower voltage over spark gap More expensive Longer charging time Safety concerns (Charged capacitor)

2.2 Engine knock In SI engines, there can be situations where the combustion is initiated by something other than the spark. Under certain instances the combustion process might be ignited by hot surfaces such as valves or other complex geometries. This type of ignition might not be of any danger for the engine other that the combustion initiation time is not controlled (Johansson, 2014).

During engine knock a portion of the trapped mixture auto-ignites and thus generates a rapid pressure increase. In regular controlled SI combustion, the pressure increase is not as rapid as the combustion occurs at the flame front which travels at a limited speed (Johansson, 2014). The autoignition can be initiated by the compression heat but also of the pressure increase of an ongoing combustion. During a knock event, the rapid pressure increase will lead to pressure waves which will reflect on the surfaces in the combustion chamber leading to pressure oscillations. If a pressure transducer is connected these oscillations will be clearly visible on a crank angle resolved pressure trace (Johansson, 2014).

Knock is one of the phenomena’s which limits the SI engine efficiency. In SI engines, typically the ignition is controlled in such a way that peak combustion pressure is achieved at a crank angle location where maximum torque lies. If engine knock is occurring at this operating point the ignition point is retarded so the peak combustion pressure becomes lower (Heywood, 1988).

Different strategies can be used to counteract and control knock such as ignition timing retardation, EGR, mixture change etc. The strategy of ignition timing has been described above, another is the use of EGR. With EGR introduced in the intake charge, the gas acts like an inert gas occupying space and thus lowering the peak combustion temperature (Johansson, 2014).

The mixture can also be altered to reduce the risk of knock. In applications with a three-way catalyst the mixture highly affects the performance of the catalyst and thus render this method not useful (Johansson, 2014). This method is typically used in automotive racing where emissions is of lower importance (Bell, 2002).

Models to predict knock has been developed which calculate the ignition delay of the unburned mixture in the combustion chamber. The models typically calculate the accumulated heat during the compression stroke and together with the required activation energy knock can be predicted. For these models to accurately predict knock onset coefficients obtained from either complex

20 simulations or experimental data are needed. A drawback of these type of models is the inability to predict the cycle-to-cycle variations found in a SI-engine (Kozarac et al, 2015).

2.3 Engine control unit Modern internal combustion engines employ a controller for the engine and accessories. Stricter legislation for emissions and fuel consumption has pushed the development of the controllers to meet current requirements (Reif and Dietsche, 2014).

A modern engine control unit (ECU) uses sensor inputs to calculate an output which is then sent as a signal to an actuator. Typically, the ECU receives a torque demand which is then used to calculate the suitable actuator outputs to meet the torque demand while regulating emissions and fuel efficiency (Reif and Dietsche, 2014).

The ECU can be comprised of one or more microcontrollers. Engine calibration parameters can be stored as look-up tables, characteristic curves and algorithms. To account for deviations some of the tables can be adaptive and updated during the duration of operation (Reif and Dietsche, 2014).

Sensor inputs are typically sampled by analogue to digital converters. Basic sensor inputs for a SI engine include accelerator-pedal position, air mass flow, throttle valve position, crankshaft and camshaft position etc (Reif and Dietsche, 2014).

Modern ECU’s also include advanced diagnostics to evaluate sensor inputs to ensure proper engine operation (Reif and Dietsche, 2014). This functionality is required in some countries to control functionality and that the engine has been untampered (Transportstyrelsen, 2015). Typical diagnostic algorithms can make plausibility checks to ensure correct operation, and if an error is detected models can be used for continued engine operation but with lower power output e.g. limp- home (Reif and Dietsche, 2014).

2.3.1 Aftermarket engine control units In applications where there can be a need for full control and real-time adjustments a standalone engine management might be considered. These systems can be employed by automotive enthusiasts to upgrade an older engine with carburettor fuelling and distributor ignition. There are many variants available which offer various functions to be altered. One advantage of the standalone system is the ability and ease for real time adjustments of parameters such as ignition timing and fuel quantity (Banish, 2007).

The simplicity and the ease of adjustments has made the standalone engine control unit useful for research purposes where full control of parameters is necessary (Baeta et al, 2005). In some instances where full control is needed a standalone engine control is the only option as the original manufacturer of the engine control unit has incorporated encryption algorithms to stop the stored data from being read or edited (Valle et al, 2004). Some original equipment manufacturers also provide aftermarket standalone engine control units for automotive racing and other purposes (Bosch Engineering GmbH, 2018). The range of standalone engine control units range from relatively simple systems which can control four-cylinder engines to 12-cylinder engines with advanced features such as traction control and Controller Area Network interface (MaxxECU, 2017). Modern standalone engine control units can support features such as drive-by-wire throttle, turbocharger boost-control, closed-loop combustion control using a wideband oxygen sensor,

21 sequential fuel injection and ignition. The systems can also control both inductive and capacitive- discharge ignition systems (MaxxECU, 2017).

2.3.2 Aftermarket ignition units Aftermarket standalone ignition system are available for many different applications. Applications can vary from automotive enthusiasts who want to upgrade the ignition system from a breaker- point system to a transistorised system (MSD Performance, 2018) to systems for large stationary engines (Altronic, 2014). These systems are commonly used in automotive racing where high charge-density and nitrous-oxide are used (Motec, 2018).

The ignition systems can be retrofitted to older engines, and by using either a hall-effect or magnetic pickup sensor and a slotted disc on the crankshaft, camshaft or both synchronisation can be established (Altronic, 2014).

These aftermarket ignition systems are used in automotive motorsport where power output can reach 6000 horsepower (Bell, 2002). In these setups ignition energy can exceed 1.5J for every combustion event with a spark duration up to 26 CAD (MSD Performance, 2018).

2.4 Air charge measurement Legislation regarding emission and fuel consumption today require accurate measurements on air entering the engine. Accuracies of 2-3% of the measured or estimated value for the air mass is needed. A modern SI engine can have a span of 1:100 between the air mass flow at idle and full power. And due to the reciprocating nature of a piston engine the flow is pulsating (Bosch, 2014).

2.4.1 Thermal sensing For measurement or estimation there are multiple methods available, on is called the hot-wire/film anemometer. The hot-wire anemometer uses a thin metallic wire which is heated by a current flow. The exposed wire is then cooled by the flow by conduction and convection. The resistance increases with temperature and thus a relationship can be established. The method requires the wire to be heated to a higher temperature than the passing airflow, to ensure long-term function deposits on the wire are regularly burned-off. One drawback of the method is the incapability to sense flow direction (Reif and Dietsche, 2014).

The hot-film anemometer operates by the same principle as the one mentioned above. A metallic film rather than a wire is used, this might reduce the thermal inertia and thus the response. Due to the different design, the burn-off operation can be omitted (Reif and Dietsche, 2014).

A further evolution is the micromechanical hot-film sensor. Using this method two temperature sensors and heating elements are utilized. A heating element is placed between two temperature sensors, where one is upstream the flow and the other downstream. In a stationary condition, the temperature sensed by both sensors would be the same, but in a flow the upstream sensor would sense a different temperature than the one downstream. The difference in temperature can be used to estimate the airflow and flow direction (Reif and Dietsche, 2014).

2.4.2 Speed-density The speed-density method is an estimation method where the intake manifold pressure and temperature together with the engine speed are used. With temperature and pressure reading the density in the manifold can be calculated. Together with the density and the volumetric efficiency of the engine an estimation of the trapped air mass in the cylinder can be made (Pachner and Beran, 2016). The volumetric efficiency can be described as the ratio of air flow into the engine and the displaced volume. The volumetric efficiency describes the performance of engine intake system for pumping. For engines without forced induction this efficiency lies in the 80-90% region (Heywood, 1988).

The Speed-density method can be used in conjunction with the thermal-sensing devices for EGR estimation. In such a setup, the EGR-rate can be calculated as the difference between the speed- density estimate and thermal sensor reading (Pachner and Beran, 2016).

The Speed-density is widely used due to its simple nature. The drawback is that the volumetric efficiency for the operating range have to be known. An advantage of the system is that it can be non-intrusive. Most standalone aftermarket engine control units use the Speed-density method due to its less complex nature (Banish, 2007).

2.4.3 Other methods Other methods for measuring airflow include differential pressure methods such as an Orifice plate and pitot-tube (Reif and Dietsche, 2014). Another method uses an ultrasonic flowmeter which can operate according to two different principles. One principle is according to the Doppler effect and one called transit-time (LaNasa, Upp and Upp, 2014).

2.5 Exhaust gas recirculation EGR in SI engines can be used for both knock control and as a NOx countermeasure. The methods introduce exhaust gas into the air charge to lower combustion temperature. Exhaust gas is suitable as it is inert and has a high specific heat capacity. The introduction of exhaust gas will lower the volumetric efficiency. For knock control the lowered temperature of the end gases reduces the risk for auto-ignition. As a NOx countermeasure, the reduced peak temperature can be lowered below the temperature threshold for thermal NOx. An advantage is that the use of EGR can be done at stochiometric conditions and therefore will not impede the three-way catalyst (Johansson, 2014).

The EGR system can typically be implemented using two different approaches. One method is the so called high-pressure system where exhaust gases are diverted upstream the turbocharger turbine through a cooler and then mixed downstream the throttle. The other system routes exhaust gases downstream the three-way catalyst through a cooler which is then mixed upstream the turbocharger compressor (Ogata, 2017). Both systems utilize a valve (EGR-valve) to control the exhaust flow.

The high-pressure setup has the drawback of higher exhaust backpressure which might lead to an increase in hot residual exhaust gases and thus knock (Alger et al, 2013).

The other setup called the long route is better suited to the SI engine. In this setup one advantage is the reduced pumping loss, but it is more difficult to control compared to a short route setup. In the short route setup, the ducting system is relatively short whereas in the long-route it is as name suggest, longer. Due to the longer ducting, there will be a significant lag of the system. If the lag

23 is not considered for ignition timing knock can occur. The system is also suspect to water condensation and fouling (Liu et al, 2016). The setup can be suitable for downsizing applications as all exhaust energy is available for the turbocharger turbine. Cooling capacity can be reduced as the exhaust is cooler downstream the turbine (Wheeler et al, 2013).

For low load, the throttle is used to regulate the amount of air entering the cylinders. When EGR is used the pressure difference over the throttle is reduced as exhaust gases are drawn into the cylinders. An advantage with EGR is reduced heat loss to the walls in the combustion chamber due to reduced peak temperature. Another advantage but of lower importance is “a reduction in the degree of dissociation in the energy to be converted to sensible energy near TC” (Heywood, 1988).

Higher dilution percentages typically need higher ignition energy, multi-spark capability or an extended spark duration for stable combustion (Alger et al, 2011). The increased effort on the ignition system using dilution is due to an increased breakdown voltage which in turns lower the spark duration. EGR also cause the combustion rate to decrease and thus affecting combustion stability (Ogata, 2017).

In an ~1.6L displacement engine using long route EGR the dilution limit could be extended from ~15% to ~25% going from a 70mJ single discharge ignition system to a multi-spark system with 300mJ divided over 10 sparks. This study was for a set coefficient of variance of the indicated mean effective pressure at 2% (Ogata, 2017). A study using a ~2.0L direct injection engine using long route EGR has reported that an 10% increase in EGR rate corresponds to an 3% increase in the effective fuel octane number in the 0-20% range for EGR rate (Hoepke et al, 2012).

2.6 Single-cylinder engines for research purposes Single-cylinder engines have been used in research for a long time. For research purposes, it can be sufficient with a single cylinder engine compared to a multi cylinder. Due to the nature of a single-cylinder engine access to the combustion chamber can be improved for experiments. As less hardware are used modifications are typically easier to implement and thus less costly. Using single-cylinder engine as a research base for a multi-cylinder engine has some disadvantages which can be difficult to mitigate. One problem is that the dynamics from the other intended cylinders is lost (Snyder, Lahti and Moskwa, 2006).

Another issue which arise when using a single-cylinder engine is the increased time between power-stroke. This will result in increased fluctuations in the rotational speed. To counteract this a large flywheel can be used (Lahti and Moskwa, 2002). The use of large flywheels can enable for steady-state operation but heavily limits the possibility for transient operation (Snyder, Lahti and Moskwa, 2006). Efforts has been made to limit the phenomena with a dynamometer which mimics the missing cylinders (Lahti and Moskwa, 2002).

Attempts has been made to mitigate the effects of the problems related to the gas dynamics with single-cylinder operation with a prototype intake manifold by removing air with multiple solenoid valves to replicate multi-cylinder dynamics. In cases where not a system is used large intake plenums can be used reduce pressure fluctuations (Snyder, Lahti and Moskwa, 2006).

There has also been studies and attempts to replicate the cooling multi-cylinder engine in a single- cylinder by controlling the flow over the liner. Using such a system cold-start emission can be better replicated in a single-cylinder engine (Klick et al, 2007).

2.6.1 Cylinder deactivation/decompression In certain cases, a multi-cylinder can be converted to single-cylinder operation just by deactivating the cylinders which is of no interest (Goyal et al, 2017). To minimize the compression and expansion work one method utilized is to drill strategic holes in the pistons of the deactivated cylinders. Another method to deactivate cylinders is to deactivate the valvetrain (Persson, 2008).

The advantage of using a multi-cylinder to single-cylinder operation is that the balanced nature of a multi-cylinder rotating assembly can be retained. For the deactivated cylinders, there is also the possibility to use a steel plate rather than a cylinder head (Vressner, 2007).

3 IMPLEMENTATION

The body of the thesis work including concept generation, selection and implementation will be presented in this chapter.

3.1 Base engine specifications The engine commissioned for the current project is a turbocharged and intercooled inline 5 cylinder using port injection and capacitive discharge ignition. The engine was produced in 2012 and has been aged in a truck intended for research, see figure 3. Due to the inherent design of a 5 cylinder two balance shafts are used to reduce vibrations. The engine is of an OHV (Over-head- valve) design with a centrally/block mounted camshaft. The engine is originally designed for CI but converted to SI. In its previous installation it was coupled to an automatic transmission.

Detailed information is given in table 2 below.

Table 2: Engine specifications OC9 G05 L01 Displacement 9.29L Max power 340 hp Peak torque 1600 Nm # Cylinders 5 EGR Water-cooled short-route Cylinder diameter 130 mm Stroke 140 mm Compression ratio 12,6:1 Firing order 1-2-4-5-3 Ignition Coil-on-plug CDI, centrally mounted plug # Valves 4/Cylinder Lubrication Wet-sump with heat exchanger and piston cooling

Figure 3. Truck the mentioned engine is sourced from.

3.2 Requirements

Requirements related to the single cylinder engine is presented below.

3.2.1 Cylinder deactivation requirements The requirements were established in conjunction with the commissioner as:

1. One cylinder active, either #1 or #5. Other cylinders shall be deactivated. 2. Unwanted friction and compression work should be minimized. 3. Use as many production parts as possible i.e. reduce the number of custom parts. 4. Minimize the amount of work.

3.2.2 Ignition requirements The requirements were established in conjunction with commissioner as:

1. Quick execution i.e. minimize the time from when a spark is demanded to actual spark delivery. 2. Multi-spark functionality, i.e. the ignition system should be capable to generate multiple sparks within an effective time period. 3. Consider and minimize RFI/EMC, i.e. implement countermeasures to limit radio and electromagnetic interference generated by the ignition system. 4. Configurable spark energy, i.e. The spark energy delivered from the ignition system shall be configurable to some extent. 5. Capable of being triggered from an external source such as an FPGA, i.e. the ignition system shall be capable to generate a spark when triggered from something other than an ECU.

3.2.3 Engine control unit requirements The requirements were established in conjunction with commissioner as:

1. Configurable, i.e. parameters such as ignition timing and fuel quantity can be altered. 2. Camshaft synchronisation i.e. be able to generate a spark on the correct stroke and support sequential fuel injection. 3. User friendly interface, i.e. individuals not familiar to the engine control system can at some extent use it. 4. Include fail-safe functionality, i.e. the engine will shut down or notify if some parameter is out of bound. 5. E-throttle support i.e. control of a drive-by-wire throttle. 6. Closed-looped lambda control, i.e. fuel control by lambda feedback. 7. Knock-control by spark retard, i.e. retard ignition timing if engine knock is occurring.

3.2.4 Air handling requirements The requirements were established in conjunction with the commissioner as:

1. Capable of being operated with external compressed air. 2. Capable of being operated with EGR. 3. Use as many production parts as possible i.e. reduce the number of custom parts. 4. Minimize the amount of work.

3.3 Concept selection The concept selection for the cylinder deactivation, ignition system and ECU is presented in detail below.

3.3.1 Cylinder deactivation concept selection Four different concepts regarding different methods to deactivate cylinders where generated. Advantages, disadvantages and work amount for all methods was identified and documented in table 3. The four concepts are presented below together with a table highlighting the advantages and disadvantages. The first concept uses the stock heads complete with valves but without the valvetrain, i.e. removing the corresponding pushrods and rocker arms. Holes drilled in the piston minimize pumping work. Blocking plates on the intake and exhaust ports together with the valves prohibit any foreign object to enter the cylinder and prevent crank house gases to leak into the test cell, see figure 4.

Figure 4. Cylinder deactivation concept number one

Table 3. Advantages, disadvantages and work needed for concept one. Advantages Disadvantages Work needed - Relatively easy to - Oil mist in - Removing pistons and implement. combustion chamber, drilling holes. - No major impact on i.e. risk for - Deactivate valvetrain engine balance. autoignition. on unused cylinders. - No need for major - Impact on piston - Crankcase ventilation custom parts. strength. or scavenging (to - Engine block torqued - Oil system minimize risk of as designed. considerations autoignition). - Previously used (plugging piston - Plug or redirect piston solution. cooling nozzle). cooling nozzles. - Hardpoints for - Inhibits access to - Manufacture blocking accessories retained. activated cylinder. plates for intake and - Compression work exhaust ports. due to size limitations of the drilled holes in the piston.

The second concept uses a custom steel plate rather than the stock heads to cover the pistons and liners, see figure 5. This plate can be designed to accommodate a “combustion” volume large enough to accept additional weights. Such weights can be useful when using a Bowditch piston in an optical access configuration. The weights can then be bolted on to the pistons in the deactivated cylinders to minimize unbalance caused by the additional mass of the Bowditch piston. Compression work is minimized as in the previous concept with holes drilled in the pistons. Advantages, disadvantages and the corresponding work involved is listed in table 4.

Figure 5. Cylinder deactivation concept two. Table 4. Advantages, disadvantages and work needed for concept two. Advantages Disadvantages Work needed - Prepared for future - Oil mist in - Removing pistons and optical access. combustion chamber, drilling holes. - No major impact on i.e. risk for - Deactivate valvetrain engine balance. autoignition. on unused cylinders. - Previously used - Impact on piston - Crankcase ventilation solution. strength. or scavenging (to - Improved access to - Oil system minimize risk of activated cylinder. considerations autoignition). (plugging piston - Plug or redirect piston cooling nozzle). cooling nozzles. - Water cooling - Manufacture blocking considerations. plate for unused - Custom parts needed. cylinders. - Block not torqued as - Sourcing suitable designed. studs or bolts for steel - Compression work plate. due to size limitations of the drilled holes in the piston. - Hardpoints for various accessories lost.

The third concept uses a similar setup as the previous concept but with the major difference that no holes in the pistons are drilled. Compression work is minimized by connecting the deactivated cylinders to a manifold which can be ventilated to the atmosphere, see figure 6. For this concept, an automotive air filter is connected to the manifold to prevent any dust or foreign object to enter the cylinders. Advantages, disadvantages and the corresponding work involved is listed in table 5.

Figure 6. Cylinder deactivation concept three. Table 5. Advantages, disadvantages and work needed for concept three. Advantages Disadvantages Work needed Oil system Deactivate valvetrain - Prepared for future - - optical access. considerations on unused cylinders. - No impact on engine (plugging piston - Manufacture blocking balance. cooling nozzle). plate with manifold - Improved access to - Water cooling for unused cylinders. activated cylinder. considerations. - Sourcing suitable - Less amount of oil - Custom parts needed. studs or bolts for steel mist in combustion - Block not torqued as plate. designed. chamber - Hardpoints for various accessories lost.

The fourth and final concept retains the stock cylinder heads on the deactivated cylinders. To minimize compression work, the intake valves are removed allowing the cylinders ventilation to the atmosphere. The ventilation is done by sectioning of the stock intake manifold to connect the unused cylinders and connecting a pipe with an air filter. The intake valve guides are plugged to prevent oil or crank house gases entering the deactivated cylinders, see figure 7. Advantages, disadvantages and the corresponding work involved is listed in table 6.

Figure 7. Cylinder deactivation concept four. Table 6. Advantages, disadvantages and work needed for concept four. Advantages Disadvantages Work needed Oil system Deactivate valvetrain - Less oil mist in - - combustion chamber. considerations on unused cylinders. - No impact on engine (Valvetrain oil - Plug unused valve balance. consumption). guides. - Engine block torqued - Reduced access to - Modify stock intake. activated cylinder. as designed. - Hardpoints for accessories retained. The selection process was carried out in conjunction with supervisors where the advantages, disadvantages and the needed work was considered. At this stage, it was decided that there were no plans for the future to convert to optical access. In cylinder pressure measurement can be carried out in the future using special cast heads. Using these heads in-cylinder pressure sensors can be used without modifications to improve access. A major factor when deciding the concept was the workload, therefore concept four was selected. With this concept, no custom steel plate has to be manufactured, and there is no need to remove the pistons. Using this concept, the compression work would be kept at a minimum as the cylinder can ventilate through the inlet valves. A manifold to connect the deactivated cylinders is also already available in the form of the stock manifold which can be sectioned off. The necessary modifications needed to the cylinder head are plugging inlet valve guides and one oil channel for the valvetrain. With this method, the engine block and liners are clamped as designed, therefore any unwanted deformation of the engine block is avoided. Previous trials by the engine manufacturer without balance shafts ended with a cracked bellhousing, due to this it was decided to retain the balance shafts. The piston cooling nozzles was retained for the deactivated cylinders. If plugged the by-pass valve regulating the oil- pressure is too small to accommodate the extra flow.

3.3.2 Ignition system concept selection Four different concepts or solutions for an ignition system was generated, all system was based on a capacitive design. The inductive ignition system was ruled out early due to its mode of operation. One of the requirements was quick execution, and with an inductive system the coils typically need to be charged for 0.5 to 3 ms depending on the coil and primary voltage. In a regular installation, this impose no problem as the ignition timing is known beforehand and the dwell time is considered to generate the spark at the correct crank angle. For the continuation of this project the ignition event will in some instances be determined using other methods than predefined look- up tables. For this reason, the time from when a spark is demanded and an actual spark is generated must be minimized. In Figure 8 typical dwell times has been represented as CAD as a function of engine speed. From Figure 8 it can be seen that if a coil requires 2 ms of dwell at 2000 rpm, more than 20 CAD will pass before ignition can occur. In a case where dwell time cannot be considered the delay will be too long.

Figure 8. Typical dwell times represented in CAD as a function of engine speed.

For the multi-spark functionality, the ignition system must be capable of generating a minimum of two sparks when demanded. The release of these sparks should be controlled, i.e. the following spark should only be released when demanded. For an effective multi-spark operation, the second or following sparks should be released relatively short after the initial spark. This require a relatively high ignition frequency, in Figure 9 the multi-spark capability for different ignition frequencies as a function of engine speed has been plotted.

Figure 9. Multi-spark capability as a function of engine speed and ignition frequency.

From figure 9 it can be seen that at an ignition frequency of 1400 Hz is required if two sparks should be generated within 20 CAD for the entire engine speed. The first solution is using the stock ignition system which is of the capacitive type. The stock system uses pencil coils for each cylinder. The advantages and disadvantages of using the stock ignition system together with specifications is listed in table 7 below. The stock ignition system has previously been used in conjunction with an aftermarket ECU triggered by analog signals, but by doing this functionality as spark mode selection and misfire detection are lost. When triggered by analog signals the system is designed to generate a spark on the falling edge with a delay of 12 µs.

Table 7. Stock ignition system Advantages Disadvantages Specifications - Well documented - Limited spark energy. Firing frequency: 670 performance. Hz (Continuous) - Limited ignition - Multiple spark modes Primary voltage: 400V frequency. (Single & multi-strike). Secondary voltage:< - Misfire detection (Ionic - Triggered using CAN- 40kV sensing) protocol. Ignition energy: ~30mJ - Breakdown voltage - Spark modes only (Secondary)

recording capability selectable using CAN- - Reprogrammable protocol. - EMC compliant - Triggered on falling - Availability edge when using analog signal

The second solution is using an aftermarket ignition system designed for either automotive racing or industrial engines. Evaluating all available aftermarket ignition systems would be too comprehensive for this thesis, because of this only systems from relatively known manufactures was been evaluated. The systems evaluated can be found in table 8-12 below.

Table 8. Information for the Altronic VariSpark ignition system. Altronic VariSpark Advantages Disadvantages Specifications - Multi-strike - Separate trigger Secondary voltage: <50kV capability. solution. Ignition energy: 130-1780 mJ - Selectable primary - Engine speed limited (Primary) ignition energy. to 2500 rpm. - Configurable spark - No Swedish profiles. distributor. - Spark profiles - Designed for large selectable using industrial engines. axillary output. Table 9. Information for the M&W Pro-10E ignition system. M&W Pro-10E Advantages Disadvantages Specifications - Multi-strike - No Swedish suppliers. Secondary voltage: >44kV capability. (Using M&W coils) - Selectable primary Primary voltage: 460-540V ignition energy Ignition energy: 115-150 mJ (115/150 mJ). (Primary) Ignition frequency: 1200 Hz - Ignition frequency. - Selectable trigger edge (falling/rising). - Price (~2500 SEK) Table 10. Information for the Autronic 500R ignition system. Autronic 500R Advantages Disadvantages Specifications - Multi-strike capability - Price (~10000 SEK). Primary voltage: 350-500V (Special order - Few suppliers. Ignition energy: 100-125 mJ version). - Triggered on falling (Primary) - Two separate ignition edge. Ignition frequency: 1500 Hz outputs - Selectable primary ignition energy. - Ignition frequency.

Table 11. Information for the Motec CDI Single channel ignition system. Motec CDI Single channel Advantages Disadvantages Specifications - Ignition frequency. - Multiple Swedish Primary voltage: 460V - Price (~4500 SEK) suppliers. Ignition energy: 115 mJ - Triggered on falling (Primary) edge. Ignition frequency: 1000 Hz

Table 12. Information for the MSD DIS-4 ignition system. MSD DIS-4 Advantages Disadvantages Specifications - Multi-spark - Multiple Swedish Primary voltage: 460-480V functionality. suppliers. Ignition energy: 165-175 mJ - Price (6000 SEK) - Triggered on falling (Primary), up to 2100 mJ in a edge. multi-strike sequence. Ignition frequency: ~470 Hz Secondary voltage: <43kV (Using MSD coils) The third concept relies on using multiple ignition boxes which is connected to the same spark plug, see figure 10.

Figure 10. Ignition system concept three.

The inspiration for this concept is provided by the Southwest Research Institute (Alger et al, 2011) and results in a doubled ignition frequency. This solution will give full control of when the second spark is generated as two different capacitors are used. Two coils are used which are connected to one sparkplug using a device with diodes. Such a device is available for automotive racing where redundant ignition systems are used. The concept can use different types of ignition boxes, the only limiting factor is the coil selector with diodes which has a limit on the secondary voltage. The advantages, disadvantages and specifications of the third concept is listed in table 13.

Table 13. Information for the third concept ignition system. Third concept Advantages Disadvantages Specifications - Multi-spark - Bulky Dependent on ignition unit functionality. - Triggered on falling - Price. edge. - Firing frequency. - Expandable. - Uses of the shelf/automotive racing components

The fourth concept was to build a very simple capacitive ignition system using a large capacitor. In such a system, the discharge would be controlled using transistors. The ignition energy can either be altered by discharging the capacitor for a longer duration or charge the capacitor to a higher voltage. The concept would then be controlled using an open-source microcontroller such as an Arduino. This concept was not evaluated in depth as it was quickly realized that it would consume too much time and effort. The advantages, disadvantages and specifications of the fourth concept is listed in table 14.

Table 14. Information for the fourth concept ignition system. DIY (Do-it-yourself) ignition system Advantages Disadvantages Specifications - Price. - Time consuming Virtually unlimited - Configurable. - Potentially dangerous - Firing frequency. (large capacitor). - Expandable. - EMC/RFI - Uses of the shelf electronic components.

The selection of a concept was carried out in conjunction with the commissioner. The third concept was selected as it was deemed to be realizable within the time frame of the thesis and that it can be expanded. As quick execution was a critical requirement for the ignition system two ignition units which can be triggered by the rising edge of the signal (0-5V) was chosen. Many of the ignition units are triggered on the falling edge to mimic the behavior of an inductive ignition system. The ignition units chosen for the third concept are designed for automotive racing and can be set to be triggered on the rising edge. Therefore, the only time delay for the ignition system is the time to increase the voltage from ~0.5V to 1.6V for a 10mA analog trigger signal.

The stock ignition system was deemed unsuitable as the configuration is optimized for 5 & 6- cylinder use and integration with the Scania ECU. The system has multi-spark capability but the secondary spark is delivered after a set time interval. The software for the unit can be rewritten by the supplier (Svenska Elektromagneter) to suit the project requirements better, but it is still limited to the discharge of a 2uF capacitor. The system would be suitable in conjunction with the third concept if it can be reconfigured to be triggered on the rising edge.

The second solution was concluded to be unable to fulfill the requirements adequately. The Altronic VariSpark has multiple suitable features such as fully configurable spark profiles, but it uses a separate trigger system unsuitable for quick execution.

The third concept can be used with any of the aftermarket ignition systems presented, but some of the units are not suitable for this project. The Motec, Autronic and MSD ignition system was deemed unsuitable as they are configured to be triggered on the falling edge of the trigger signal. The Autronic offers a high ignition frequency and has two separate ignition outputs, but the price and trigger edge exclude the system. The Motec unit is reasonable inexpensive but is excluded due to the trigger edge and ignition frequency. The MSD ignition system can generate up to 12 sparks during one sequence, but there is no control of how these are delivered and the trigger edge excludes the system.

The fourth concept was deemed unsuitable as it would require too much time to implement without any guarantees of proper function.

The finalized ignition system will be based on the third concept using two M&W Pro-10E ignition units and coils, see figure 11 and table 15. The deciding factor was the price of the components and that the ignition boxes can be configured for rising edge triggering, a feature not found in any other evaluated ignition system.

Figure 11. M&W Pro-10 ignition unit

Table 15. Information for the finalized ignition system. 2x M&W Pro-10E using MSD Automatic Coil Selector Specifications Secondary voltage: >44kV (Using M&W Ignition energy: 115-150 mJ or 115mJ + coils). 80mJ (Primary) using built in multi-spark Primary voltage: 460-540V. function with 0.4ms separation. Ignition frequency: 2400 Hz (Continuous).

3.3.3 Engine control unit concept selection The selection of a suitable engine control unit was left to the student focusing on the fuel system. The requirements related to the ignition system was that it should support triggering a capacitive ignition system. The system chosen is from a Swedish supplier called MaxxECU which previously has been used at Scania in predevelopment. The ECU supports capacitive ignition system where the ECU can be set to assume no delay between triggering and spark initiation. The ignition can be disabled using the ECU configuration software in real time, thereby allowing easy switching control of the ignition.

3.4 Concept implementation The implementation of the concepts presented in the previous chapter will be presented.

3.4.1 Cylinder deactivation implementation To realize the cylinder deactivation, concept the engine was dismantled to a “long block” i.e. everything disassembled except the engine block and rotating assembly. The inlet valves where removed and the valve guides plugged by TIG (Tungsten-Inert-Gas) welding. The valvetrain mechanism in the cylinder head is lubricated by one oil feed from the main oil gallery. This oil feed was drilled, tapped and plugged by a threaded M6 rod, see figure 12. To prevent the rod from unthreading during operation a thread locking compound was used.

Figure 12. Unmodified head (left) and modified head (right). Red arrows highlighting plugged valve guides and blue arrow plugged oil feed.

The camshaft is supported in the engine block and have two rocker arms for each cylinder, access is possible by removing two cover plates beneath the intake manifold. The rocker arms rotate around a shaft with hydrodynamic journals which is mounted to the engine block. The rocker arms are actuated by the camshaft through a hydrodynamic roller bearing which in turn pushes the pushrods, see figure 13. For the deactivated cylinders, all related valvetrain components in the engine block was removed.

Figure 13. Engine block unmodified valvetrain.

Oil feed for the removed valvetrain was done by a M10 bolt and a crush washer to prevent internal oil leakage, see figure 14.

Figure 14. Engine block modified valvetrain. Blue arrows highlight pressurised oil feed which have been plugged.

Cylinder number one and two share a common rocker arm support shaft, this leaves two oil channels open for cylinder number two rocker arms. These holes where plugged by careful TIG- welding to avoid any distortion, see figure 15.

Figure 15. Rocker arm support shaft, welded oil feed holes highlighted by blue arrows.

3.4.2 Ignition system implementation The stock ignition system uses a pencil coil to connect the coil and spark plug, this will not work with the ignition system in this project as external coils will be used. A stock pencil coil was modified where the coil was removed and replaced with a lathed PTFE adaptor. The adaptor uses a standard SAE plug connector, a plastic fork secures the assembly on the sparkplug, see figure 16. A 5000Ω resistor is incorporated in the connector to limit RFI.

Figure 16. sparkplug connector.

The ignition units can be configured in three different modes, 115 mJ single spark, 150 mJ single spark or multi-spark with a 115 mJ primary spark and an 80 mJ secondary spark. When using the multi-spark option the second spark is delivered 0.4ms after the first spark. Switching between the modes are controlled by the ECU which grounds output wires from the ignition units, switching between the modes can be done in real time. Different modes can be set independently for each ignition unit. Rising edge trigger selection is done by a jumper wire between two wires on the ECU. To minimize RFI the coils and coil selector are mounted as close to the spark plug as possible. Wiring on the primary side uses twisted pair with grounded shielding for RFI and EMC reasons as these passes near other sensor wiring. High tension leads are made to length with the correct connectors using components typically used for automotive racing. A schematic of the ignition system is provided in Figure 17.

Figure 17. Ignition system setup schematic

The ignition unit was installed on an aluminium plate together with the ECU. The same plate also includes terminals for accessibility if the configuration is to be altered, see figure 18. Power to the ignition unit and the primary wiring is done with twisted and shielded wires, the shield is grounded to the engine block. To control the different ignition modes four general purpose outputs from the ECU are used. Control can be achieved by either an ON/OFF setting from the graphical user interface or look-up table with selectable axes.

Figure 18. Ignition unit and ECU

A platform was manufactured and mounted to the valve covers of cylinder two and three. This platform locates the ignition coil and coil selector. This setup allow for relatively short high tension leads and cable routing, see figure 19.

Figure 19. Ignition coil and coil selector

In the figures above only one ignition system is installed. The delivery of the second ignition system was delayed due to issues with the delivery. The platform in figure 19 can accept an additional coil by vertical stacking using spacers.

3.4.3 ECU synchronisation To enable sequential fuel injection the MaxxECU need a signal from the camshaft to determine the correct stroke. The MaxxECU can work with various OEM (Original equipment manufacturer) engine synchronisation systems, but it comes with no support for the Scania stroke synchronisation design. To enable synchronisation with the MaxxECU it is only required to have one signal for every camshaft revolution. The stock design uses a toothed disc riveted to the camshaft drive gear, see figure 20. All except one tooth was removed to enable the disc to work with the MaxxECU.

Figure 20. Unmodified trigger disc riveted to the camshaft gear.

The crankshaft uses a relatively common 60-2 trigger which the MaxxECU support therefore requiring no modifications. The sensors for the synchronisation is of the inductive type and has been used with MaxxECU previously.

3.4.4 Air handling modifications The intake manifold was modified and sectioned of for the deactivated cylinders. A cut between the intake runners for cylinder number one and two was done, a cover plate was then inserted and welded in place. A 70mm hole was drilled between the intake runners for cylinder number three and four. An aluminium pipe with an air filter was then welded to the hole. Unused ports previously occupied by various sensors was either plugged by bolts when possible or welded shut, see figure 21.

Figure 21. Modified and sectioned off intake manifold.

The inlet air temperature sensor is located near cylinder number five in the stock application. This part of the manifold is now used for ventilation and thus the sensor need to be relocated. The sensor was relocated to above the intake runner on cylinder number on a boss of the same thickness as in the stock location. The same boss also includes a connector for a pressure sensor in the ECU used for the speed-density estimation, see figure 22.

Figure 22. Boss incorporating temperature sensor and pressure outlet.

The current engine in the project uses different oil control rings than the engine in production. The rings in the current engine are designed for a thicker wall film. As there will be no combustion in the deactivated cylinders the oil will not be consumed. To account for the possibility of oil accumulation in the intake manifold a drainage system was manufactured. The drainage system connects the bottom of all the intake runners to a reservoir which can be emptied using a draincock, see figure 23.

Figure 23. Oil drainage system.

3.4.5 ECU Implementation Initial ECU configuration and preparation for heat release implementation is presented in the subchapters below.

3.4.5.1 ECU configuration The MaxxECU used in this project is designed for port injected liquid fuels (gasoline, ethanol or methanol) where the fuel pressure is either set constant (deadheaded fuel system) or constant pressure differential over the injector. No pre-sets are available for CNG, therefore requiring some modifications of the inputs.

Injector flow rate data is entered in cc/min for a pressure differential of 3bar. The injectors used in this setup specifies the flowrate as 10.4 kg/hour. This implies that the injectors must be recalculated for gasoline equivalents. The injectors where recalculated to gasoline equivalents using typical heating values for gasoline and methane to 294 cc/min at a 3bar pressure differential, see figure 24.

Figure 24. Injector setup.

Closed-looped lambda control can be achieved by activating the wideband oxygen sensor supplied with the ECU (Bosch LSU 4.2). A lambda target is specified for different operating points in a look-up table with manifold pressure and engine speed on the axes. As mentioned before no pre- set for CNG is available, therefore the AFR (Air fuel ratio) displayed in the ECU interface will be incorrect. If correct AFR should be displayed the lambda signal can be scaled and output using CAN, otherwise see table 16. For an initial setup lambda target was set to λ = 1, see figure 25. Gas quality must also be considered as typical CNG blends require a AFR of 16:1-16.5:1 for stochiometric combustion.

Table 16. Air fuel ratio & λ for gasoline and CNG Air Fuel Ratio λ Gasoline CNG 0.70 10.3 12.0 0.75 11.0 12.9 0.80 11.8 13.8 0.85 12.5 14.6 0.90 13.2 15.5 0.95 14.0 16.3 1.00 14.7 17.2 1.05 15.4 18.1 1.10 16.2 18.9 1.15 16.9 19.8 1.20 17.6 20.6 1.25 18.4 21.5 1.30 19.1 22.4 1.35 19.8 23.2 1.40 20.6 24.1 1.45 21.3 24.9 1.50 22.1 25.8 1.55 22.8 26.7 1.60 23.5 27.5

Figure 25. Lambda target look-up table, engine speed on horizontal axis and manifold pressure on vertical axis.

Throttle control is done by a 0-5V input signal which can be connected to the dynamometer controller. The throttle controller in the ECU incorporates a PID controller for feedback. The engine can be controlled without the 0-5V signal by modifying a look-up table in the ECU and enabling a pedal input override. In a dynamometer, the engine can be motored to the desired speed and then adjusting the table to achieve the desired load, this setup has been used previously at Scania. An example is given in figure 26 where at 1000 rpm the throttle is forced to a 50% open position.

Figure 26. An example of a target throttle position look-up table where no pedal or throttle input is used. Engine speed on horizontal axis and pedal position on vertical axis.

3.4.5.2 CAN & Heat release preparation For future heat release calculation, it will be necessary to accurately measure or estimate the amount of fuel entering the engine. The current setup uses port injection where the pressure differential over the injector is kept constant. In a stock configuration, the flow in the injector is critical for all operating points, i.e. not dependent on intake manifold pressure. The injection period can be transmitted from the MaxxECU using a CAN-protocol. MaxxECU support common CAN- protocols used in automotive applications i.e. CAN 2.0. The stock fuel rail incorporates a combined pressure and temperature sensor for density measurement. Using this information, the fuel quantity can be estimated for future heat release calculations. The injection period data can be scaled and offset to user preference in either the graphical user interface or editing a .XML file, see figure 27.

Figure 27. Graphical user interface for CAN setup.

3.4.6 EGR preparation The stock EGR system is a short route system which uses a water-cooled heat exchanger. Flow is controlled by a valve and driven by the pressure difference between exhaust and intake manifold. The valve is actuated by a pneumatic cylinder which in turn is feed by an air compressor powered by the crankshaft. The position of the valve is controlled by a proportional valve located on the bellhousing, the turbocharger wastegate is controlled by the same valve. The proportional valve is controlled by a 100Hz PWM (Pulse width modulation) 24V signal from the ECU. A sensor in the

EGR-valve actuator is used for positioning feedback. The stock air compressor is designed to cater a complete truck and was therefore removed. External air can be supplied using a quick connector, see figure 28.

Figure 28. EGR-valve, valve block and actuator. Actuator and position sensor highlighted with blue arrow, EGR-valve with green arrow, valve block red arrow and yellow arrow air connection.

The stock setup will not work with the aftermarket ECU used in this setup as it uses 24V and not 12V as the aftermarket ECU. To solve this a solid-state relay was used, the relay uses a 12V control signal. The relay can in turn pulse the valve block with an 24V external power supply. The control can be achieved by a look-up table in the MaxxECU where the axes are fully configurable, see figure 29. Feedback for the valve positioning was incorporated where the valve position is output as 0-100%.

Figure 29. Look-up table for EGR control, engine speed on horizontal axis and manifold absolute pressure on vertical axis.

Current is regulated to design specification of 400mA with a resistor in conjunction with a coil resistance in the solenoid of approx. 20Ω. A fly-back diode is used to protect from inductive loads, see figure 30. Function was controlled using a bench power supply.

Figure 30. EGR control circuit.

The stock EGR valve is of a butterfly type and has the disadvantage that it can’t fully seal when closed. Previous trials with the valve have revealed that when closed the area between the pipe and valve is equivalent to a circle with 4mm diameter. To prevent unwanted leakage when operated without EGR block off plates where manufactured, see figure 31. When using EGR the plates are removed and a pipe can be fitted.

Figure 31. Blocked off EGR-circuit.

3.4.7 Other modifications Modifications of the cooling system and transmission plate are presented in the subchapters below.

3.4.7.1 Cooling system The cooling system have been modified to suit single cylinder operation and test-cell operation. In the initial setup, the cooling system incorporated the (beside the base engine) turbocharger, air compressor, throttle, cabin heater, oil cooler, EGR-cooler and retarder. The cooling system have been simplified using standard parts typically used for engines in power generation which use less auxiliary equipment. There are four connections remaining where two connect to either a radiator or heat exchanger. The remaining connects to the overflow tank, see figure 32. The engine was equipped with a block heater which has been retained.

Figure 32. Schematic of simplified cooling system with flow directions.

3.4.7.2 Transmission plate For future studies, it was desired to prepare the engine for direct injection. This requires a high- pressure fuel pump. To accommodate a high-pressure pump used for diesel or ethanol the transmission plate must be replaced. The transmission plate is a steel plate bolted to the engine block which in turn the bellhousing is bolted to. The stock transmission plate on the engine only provides access to the crankshaft gear train for the air compressor. A transmission plate with provision for a high-pressure pump was sourced from a similar engine using diesel or ethanol.

The high-pressure pump will be installed at a later stage, requiring the opening to be blocked off. The high-pressure pump uses engine oil feed from the main oil gallery routed through the transmission plate, this has been blocked of by an O-ring seated in a milled pocket. The block off plate incorporating the O-ring can be seen in figure 33.

Figure 33. Block off plate for high-pressure pump location.

The connection for the previous air-compressor has been blocked-off using a plate otherwise used in marine applications or power generation, see figure 34.

Figure 34. Air-compressor block-off plate.

4 VERIFICATION

Verification of ignition system and other features is presented in this chapter.

4.1 Ignition system Due to time constraints, the engine could not be started on CNG within the time frame of the thesis work. The ignition system can be tested without operating the engine. This is achieved by using a diagnostic feature in the ECU which can trigger a selected output at a desired frequency. The primary side current of the ignition coil was sampled at 100MHz using an oscilloscope. The ignition unit was configured to be triggered on the rising edge of the trigger signal. The trigger signal was logged with a probe using the previous mentioned oscilloscope, see figure 35.

Figure 35. Acquisition of primary side current and trigger signal, channel 1 (top trace) trigger & channel 2 (lower trace) primary current. From figure 34 the delay between trigger rising edge and capacitor discharge is in the region of 17µs. It can also be seen that there is some high frequency interference in the trigger trace during discharge. The current clamp outputs a voltage corresponding to 1V/10A, equating to a primary current of 26A. The time delay between rising edge and ignition event represented in CAD as a function of engine speed can be seen in Figure 36.

Figure 36. Ignition delay represented in CAD as a function of engine speed.

4.2 Synchronisation Synchronisation was configured by cranking the engine with the starter motor. As the ECU is built to work with a large array of synchronisation sensors with various output voltages some configuration was needed. The ECU features a built-in oscilloscope which can be used to determine the output voltage of the crankshaft and camshaft position sensor, for an illustration of the crankshaft position sensor output see figure 37. With the output voltages determined for both sensors the voltage sensing thresholds in the ECU can be set.

Figure 37. Typical voltage output from a crankshaft position sensor, the “missing tooth” corresponds to the plateau at ~105 ms. Correct synchronisation with the ECU was achieved using a timing light, see Figure 38. The ignition timing was locked to top dead centre in the ECU, the engine was then turned over by the starter motor. An offset term in the ECU was updated until the timing light reading showed the top dead centre mark. When this was done, the crankshaft position read by the ECU corresponds to the actual crankshaft position.

Figure 38. Timing light with inductive pick-up.

4.3 Oil pressure The engine oil system has been modified where more oil is routed through the pressure relief valve. For an initial evaluation if the pressure relief valve can support the extra flow the engine can be turned over using the starter motor. If the oil pressure greatly exceeds the pressure relief valve opening pressure modifications must be carried out. This can be elevated by bypassing some oil from a gallery in a controlled fashion back to the oil pan. The oil pressure was logged when turned over by the starter motor, see figure 39. The engine oil pressure peaked at 2 bar with an engine speed of ~190 rpm.

Figure 39. Engine oil pressure during cranking, log time ~15s, red arrow highlighting the peak recorded pressure of ~2 bar and the blue arrow highlighting the instantaneous pressure of 0.4 bar when the screen was captured.

5 DISCUSSION AND CONCLUSIONS

A discussion concerning the results and conclusions for the project is presented in this chapter.

5.1 Discussion Thoughts regarding the cylinder deactivation, ignition system and engine control will be discussed in the following subchapters.

5.1.1 Cylinder deactivation One goal of this project was to convert a multi-cylinder engine to a single cylinder research engine. A dedicated single cylinder engine originally intended for research would of course be desirable. Such a solution is typically very expensive and require custom parts. The engine presented in this project is based on an engine which currently is in series production. The result can be seen as a trade-off between cost and functionality. Multiple solutions to convert the engine was evaluated where one solution was decided to be implemented. Previous setups where a multi-cylinder engine has been converted used pistons with holes drilled in them the to reduce compression work. In this project, it was decided not to touch the rotating assembly and try another method to reduce compression work. Any detailed measurements to compare the friction work with the full engine could not be done due to time constraints and lack of test cell availability. The only qualitatively test carried out was that the engine can be turned over by grabbing the axillary belt pully when not on the compression stroke for the activated cylinder.

5.1.2 Ignition system Unforeseen delays with the delivery of the ignition system components resulted in that no multi- spark testing could be carried out within the time frame of the thesis. The design of the ignition system was inspired by the Southwest Research Institute (Alger et al, 2011) where a similar setup has been used with promising results. The system will give full control of when the first two spark events are initiated, the following events are limited by how fast the capacitors can be charged. One requirement was quick execution, this ruled out an inductive ignition system where it takes some time to generate the magnetic field. The execution time for the current ignition system was measured to 17µs. The ignition system in this thesis uses ignition units originally intended for automotive racing with relatively high ignition energy.

5.1.3 Engine control An aftermarket engine control unit system was installed, the system has been used at Scania previously with satisfactory results. Many features of the system could not be evaluated as the engine could not be started on CNG due to time constraints. Look-up tables calibrated for full engine operation cannot be used to a satisfactory level for initial setup as a different algorithm is used. The stock short route EGR system was retained, control of valve position can be done by the engine control unit. As the turbocharger has been removed, a valve in the test-cell exhaust system must be used to create a pressure difference to drive the EGR flow. An EGR system using a pump which can drive the EGR flow irrespective of the pressure difference would be more desirable but such a solution could not be implemented within the scope of the thesis.

5.1.4 Scope of thesis project It was initially intended that the engine would be started on CNG. As the project progressed this plan was discarded. It was decided that an initial start will occur after the engine has been transported to the university. An adequate function evaluation of the engine modifications has to be postponed until installed to a dynamometer.

Due to this the scope of the project plan have been updated and revised on multiple occasions after discussion with supervisors and commissioner.

5.2 Conclusions A multi-cylinder engine has been converted to single-cylinder operation. This was achieved by deactivating all cylinders except one. The balanced rotating assembly has been retained and unmodified. Compression work for the deactivated cylinders has been minimized by allowing them to ventilate against the atmosphere trough the intake channels. An aftermarket engine control system with closed-loop lambda and knock control have been installed. Parameters of interest such as ignition timing and fuel quantity can be altered in real time by a graphical user interface. An experimental capacitive based ignition system has been prepared. The ignition system feature two selectable ignition energies and a theoretical ignition frequency of 2400Hz. Ignition energy can be controlled by the ECU. The experimental system was designed to minimize execution time and for future control by an FPGA. The execution time of the experimental system was measured to 17µs.

6 RECOMMENDATIONS AND FUTURE WORK

Recommendations for the initial operation of the engine and future studies are presented in this chapter.

6.1 Recommendations Recommendations for the initial start where the engine can operate throughout a larger operating range is presented here.

6.1.1 Oil pressure relief valve The oil system has been modified where more oil now must be ventilated trough the pressure- relief valve. During initial start-up in a dynamometer or operating without load the oil pressure should be closely monitored. If the pressure greatly exceeds 6 bars at higher engine speeds and during operating temperature an extra bleed valve might be necessary to prevent damage of the oil system.

6.1.2 Knock calibration Due to time constrains the engine could not be operated in a dynamometer, therefore no initial knock calibration was carried out. Knock calibration should be carried out with an in-cylinder pressure transducer together with a charge amplifier and rotary encoder. Knock can then be induced by spark advance for various operating points and a suitable threshold can then be set in the ECU using the knock sensors.

6.1.3 Manifold pressure sensor The manifold pressure sensor used for the speed-density calculation has an upper absolute pressure capability of 400kPa. If higher inlet manifold pressures are to be used the stock sensor can be used. The stock sensor has an upper absolute pressure range of 500kPa, but using this some other sensor must be disconnected as all inputs in the ECU are currently occupied.

6.1.4 Spark plug wear The ignition system in this project will deliver more spark energy than the stock ignition system. Therefore, the spark plug wear will be accelerated and thus requiring more frequent spark plug inspection and replacement.

6.1.5 Crankcase ventilation The engine has been modified to be operated with an external air supply. Crankcase gases in the stock configuration pass through a separator and the remaining gas is inducted upstream the turbocharger compressor. If the crankcase system is routed in a similar fashion as in the stock application the external air will pressurize the crankcase. In the future installation gases from the separator should be routed to outside the test cell.

6.1.6 Piston ring-pack The engine used in this project uses oil-control rings which allows for a thicker oil film on the liners. If the engine will receive new liners and pistons in the future the production ring-pack should be used. The production ring-pack is designed for a thinner oil film as the gaseous fuel don’t wash the cylinders as a port injected liquid fuel. To prevent unwanted oil accumulation and crank case gas blow-by in the unused cylinders the rings could be tighter gapped as they are exposed to less heat.

6.2 Future work Features which was not possible to implement during the duration of the thesis work are presented below. Suggestions for future studies are also presented.

6.2.1 Oxygen sensor pressure correction If operated with high backpressure the exhaust oxygen measurement should be modified. The oxygen sensor equipped on this engine is pressure dependent. The ECU used in this project has no feature for pressure correction as it is typically used in automotive racing or enthusiast applications with less restrictive exhaust systems. The pressure dependency for lean and rich mixtures for a similar sensor (Bosch LSU 4.9) to the one used in this project (Bosch LSU 4.2) can be seen in figure 40.

To remedy such situation in the future a lambda meter from a vendor such as ETAS can be used. Such a device can take the raw signal together with a pressure signal and correct it before the ECU reads it.

Figure 40. Pressure dependency for the Bosch LSU 4.9 oxygen sensor, absolute pressure on the horizontal axis and sensor output error on the vertical axis.

6.2.2 In-cycle spark event control The Altronic Varispark ignition system mentioned in section 3.3.2 includes a feature for custom spark profiles. Such a system would be desirable for an engine with a wide operating range. If a fully configurable ignition system is implemented in the future it should try to include some similar feature like the Altronic Varispark. Such a system would can deliver just the required amount of spark energy at each operating point. If fast control can be achieved there should be a possibility

58 to some extent of controlling the duration of the different spark phases. With these features, it should be studied if the spark plug wear can be reduced. In the stock ignition system as with many other ignition systems especially capacitive based the operating point with the highest spark demand dictate the spark energy.

6.2.3 EGR system For accurate control of internal EGR a different setup compared to the one in this project should be implemented. If a short route system is used as in this project a negative pressure difference over the intake to exhaust must be maintained for EGR flow. This setup will cause higher rates of internal EGR due to the higher exhaust backpressure. If EGR is to be used while minimizing the internal EGR with the current camshaft profile a system using a pump for the EGR flow should be implemented.

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