Fuels and Lubricants 11/2/05

FUELS AND LUBRICANTS 11/2/05

Introduction

A fuel is any substance that is burned or reacted to provide heat and other forms of energy. In 2000, an estimated 40% of the energy needs of the United States were supplied by oil or petroleum fuels. The rest was provided by natural gas (approximately 23%), coal (23%), nuclear power (8%) and other renewable sources (6.3% percent). In 2000, the US consumed a total of 1.0 x 1017 kJ of energy. This value corresponds to an average daily energy consumption per person of 1.0 x 106 kJ, which is roughly 100 times greater than the per capita food-energy needs. In addition to energy, petroleum is the source of numerous organic chemicals used to manufacture drugs, clothing, and many other products.

Petroleum deposits are widely distributed throughout the world, but they are found mainly in North America, Mexico, Russia, China, Venezuela, and of course, the Middle East. Petroleum was formed in the Earth’s crust over the course of millions of years by the anaerobic (without oxygen) decomposition of animal and vegetable matter by bacteria. Unrefined petroleum, a viscous, dark-brown liquid, is often called crude oil. Crude oil is a complex mixture of compounds consisting mainly of hydrocarbons (compounds containing only hydrogen and carbon), a small amount of organic compounds containing sulfur, nitrogen, and oxygen, and some metallic compounds containing vanadium, nickel, iron and copper. Table I gives the percent by mass of the most common elements in a representative sample of crude oil. The graph shows the cost of crude oil over the past 30 years.

Average crude oil prices over the past 30 years $70.00 Table I: Percent Composition of Crude Oil $60.00 Carbon 83.0 - 87.0% $50.00 Hydrogen 10.0 - 14.0% $40.00 Nitrogen 0.1 - 2.0% $30.00 Oxygen 0.05 - 1.5% $20.00 Sulfur 0.05 - 6.0% cost ($) per barrel $10.00 $0.00 1975 1980 1985 1990 1995 2000 2005

Table I indicates that crude oil consists largely of hydrocarbons. Hydrocarbons are an extremely broad class of organic compounds, and we’ll only be focusing on a few specific types in our discussion of fuels and lubricants. The next section provides some basic terms and definitions pertaining to hydrocarbons.

Hydrocarbon Background Information

Alkanes are hydrocarbons that contain carbon-carbon single bonds (no multiple bonds) and have the general chemical formula of CnH2n+2. The table below provides the parent names for alkanes as a function of the number of carbon atoms. Alkanes can be classified as a straight-chain, branched, or cyclic depending on their structure. Examples of each are presented below.

1 Table II: Simple Alkanes a. Straight-chain Alkanes: # of C atoms Parent Name H H H H H H H HCC H HCC C C C H 1 methane H H H H H H H 2 ethane Ethane Pentane 3 propane C H C 5H 12 2 6 4 butane CH3 CH3 CH3CH2CH2CH2CH3 5 pentane H H H H H H H H HCC C C C C C C H 6 hexane H H H H H H H H 7heptane Octane 8 octane C 8H 18 CH CH CH CH CH CH CH CH 9 nonane 3 2 2 2 2 2 2 3 10 decane

For the straight-chain alkanes it is important that you be able to translate between the parent name (see Table II), the Lewis structure, and the molecular formula. Notice that the molecular formula can be written with the carbon atoms and their connected hydrogen atoms shown explicitly like in CH3CH2CH2CH3, or, in a more condensed way as in C4H10. For drawing the Lewis structures, follow the guidelines that carbon atoms form 4 Moo bonds and hydrogen forms only one bond. The simplest alkane is methane, CH4, a principle component of natural gas and classified as a greenhouse gas. Animal flatulation accounts for 17% of global methane emissions. A single cow is estimated to produce 600 L of methane every day.

b. Branched Alkanes:

The names and structures of the branched alkanes are H C CH H H3C H 3 3 CH3 H H more complicated than those of the straight-chain alkanes and C C C C H C C CH H C C CH are somewhat beyond the scope of our current discussion. It 3 3 3 3 H H H H is important that, given a Lewis structure of an alkane, you are 2,2,4-trimethylpentane 2-methylpentane able to classify it as straight-chain or branched. Isomers are (a.k.a. isooctane) (a.k.a. isohexane) compounds that have the same molecular formula, but different structures. In other words they have the same number and type of atoms, but the atoms are arranged differently. Notice that the branched alkanes shown above are each isomers of straight-chain alkanes. 2,2,4-trimethylpentane is an isomer of octane (both have the molecular formula, C8H18) and 2-methylpentane is an isomer of hexane (C6H14). c. Cyclic Alkanes: H H H H C We won’t focus much on cyclic alkanes in our discussion here. Notice that the H H C C generic formula for cyclic alkanes becomes CnH2n rather than the CnH2n+2 that is mentioned H C C H C above. This is because in going from a straight-chain alkane to a cyclic alkane, the two end H H hydrogens must be removed so that the ends of the chain can be tied together with a carbon- H H carbon bond to make a loop. cyclohexane

d. Other Hydrocarbons: Alkenes are hydrocarbons that contain carbon-carbon double bonds. The simplest alkene is

2 ethene or ethylene with the formula, C2H4. Alkynes contain carbon-carbon triple bonds with the simplest alkyne being C2H2, ethyne or acetylene. Hydrocarbons that contain any multiple bonds (double or triple) are known as unsaturated hydrocarbons, while those with only single bonds are known as saturated hydrocarbons. Another common class of hydrocarbons that contains a ring structure is the aromatic hydrocarbons. Aromatic hydrocarbons are not cyclic alkanes because alkanes contain only single bonds between carbons, and the aromatic hydrocarbons feature multiple bonds. Benzene is the prototypical aromatic hydrocarbon and it is shown below. There are other more complicated aromatics that contain benzene rings. One might conclude, based on the Lewis structure of benzene shown below, that benzene consists of alternating single and double bonds with the single bonds being longer than the stronger double bonds. However, experiments show that all of the bonds in benzene are the same length. Benzene has more than one valid Lewis structure (i.e., there is resonance). Thus, the best description of the structure of benzene is a hybrid (average) of the two resonance contributors.

Aromatic Hydrocarbons: Benzene’s resonance contributors: H H H H H C H H C C H H C C C C C H C H H C H C C C C C C C C C H C H H C C H C C C C H H H H C H H C H H H Benzene Naphthalene

Fractional Distillation of Petroleum

The refining of petroleum begins with the separation of the crude oil into groups of compounds with distinct boiling point ranges. Since crude petroleum contains literally thousands of hydrocarbon compounds, separation of the crude into pure compounds is neither feasible nor necessary. Rather, the petroleum fractions that are obtained are often mixtures of hundreds of hydrocarbons with boiling points within certain ranges. The physical properties of petroleum fractions determine their eventual end use. Table III lists common fractions obtained from crude oil with their approximate boiling ranges. Those compounds containing sulfur and nitrogen are generally undesirable in commercial petroleum products and are often removed by additionally refining the petroleum fractions obtained through distillation.

Table III: Petroleum Fractions Fraction Carbon Atoms in chain Boiling Pt. Range (°C) Uses

Natural gas C1-C4 -161 to 20 Fuel and cooking gas

Petroleum ether C5-C6 30-60 Solvent for organic compounds

Ligroin C7 20-135 Solvent for organic compounds

Gasoline C6-C12 30-180 Automobile fuels

Kerosene C11-C16 170-290 Rocket and jet engine fuels, domestic heating

Heating Fuel Oil C14-C18 260-350 Domestic heating and fuel for electricity production

Lubricating Oil C15-C24 300-370 Lubricants for automobiles and machines

Paraffins C20 and up Low-melting solids Candles, matches

Asphalt C30 and up Gummy residues Surfacing roads, fuel

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To accomplish the separation, the dark brown, thick crude oil is heated to about 400oC to convert it into a mixture of hot vapor and fluid that is fed into the bottom of a fractional distillation tower. The distilling tower is divided into horizontal zones of different temperatures. The unvaporized, liquid portion of the feed is drawn off at the bottom of the tower as the tar and asphalt fractions. In the distillation tower the temperature decreases the further up the tower the vapor goes. Therefore, different components condense at various points within the tower; the volatile, lower boiling petroleum fractions remaining in the vapor phase longer than the less volatile, higher boiling fractions. After condensing, the liquid fractions are drawn off and collected. The lightest, most volatile hydrocarbons do not condense and are drawn off at the top of the tower as gases (See Figure I).

Figure I: Distillation Tower

Lowest Boiling Natural Gas Fractions

Petroleum Ether

Ligroin

Gasoline

Kerosene/Jet Fuels

Heating Oil

Lube Oil Crude Oil Paraffins Highest Boiling Fractions Asphalt

For more information about oil refining, go to http://science.howstuffworks.com/oil-refining.htm.

Pictures of distillation towers which can be hundreds of feet tall.

4 Thermochemistry of Combustion: The main purpose of the combustion of the fuels obtained from the distillation described above is to generate heat or supply power in engines. One of the most important uses of thermochemical measurements and calculations is assessing materials as potential energy sources. Combustion of a hydrocarbon is defined as the reaction of the substance with oxygen according to the following stoichiometry:

CxHy + (x + (y/4)) O2 x CO2 + (y/2) H2O

As discussed in your textbook, the standard heat of combustion, ∆H°comb, is defined as the enthalpy change for the reaction of one mole of a substance with oxygen to form water and carbon dioxide under standard conditions (1 atm and a specified temperature, usually 25oC). The values of ∆H°comb can be obtained by the following methods:

1. Measured in a calorimetry experiment (as done in Experiments 12F or 30A) 2. Calculated using standard heats of formation, ∆H°f (“products minus reactants”). 3. Estimated using average bond dissociation energies.

For instance, the reaction of methane with oxygen is exothermic and produces 890.3 kJ of heat per mole of methane and is defined by the following balanced equation (eq. 1):

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l) ∆H°comb = –890.3 kJ/mol (Eq. 1)

One way to compare the efficiency of different fuels is to look at the specific enthalpy (also called fuel value in the textbook), which is the enthalpy of combustion per gram of the substance (Table IV). A fuel with a high specific enthalpy releases a large amount of heat per gram when burned. This value is important in applications (e.g. rocket engines, airplanes, etc.) where the mass of the fuel is a significant consideration. Note that the specific enthalpy is related to other terms such as fuel value and energy content which are typically listed as positive values of energy released per gram of fuel. The enthalpy density is defined as the enthalpy of combustion per liter and is important in applications where the volume of the fuel is significant. The families presented are the alkanes which contain all single bonds between carbon atoms, the aromatics which contain benzene rings in their structures and the alkenes which are compounds containing at least one double bond. Notice that the specific enthalpy (kJ/g) is fairly consistent for a family of compounds. This is not surprising given their fairly consistent carbon to hydrogen ratios in compounds of the same structural family.

Similarly, heats of combustion and specific enthalpy values can be obtained for the mixtures of compounds used in different fuel applications (Table V). Notice, that in an application where weight is important, hydrogen is an excellent choice due to its high heat output per gram. However, in an application where the volume is important, such as in a car, hydrogen is not the best choice as it has a relatively low enthalpy density (heat of combustion per milliliter) (-9.9 kJ/mL for hydrogen as compared to -33.6 kJ/mL for octane).

5 Table IV: Heats of Combustion for Select Fuels: molecular Heat Family Fuel weight of Combustion Specific Enthalpy (g/mol) (kJ/mol) (kJ/g) alkanes n-hexane 86.18 -4163.1 -48.30

n-heptane 100.20 -4816.9 -48.03

n-octane 114.23 -5471.8 -47.90

2-methylhexane 100.20 -4810.0 -48.00

2,2-dimethylhexane 114.23 -5458.61 -47.79

cyclohexane 84.16 -3919.0 -46.57 aromatics benzene 78.11 -3267.5 –41.82

toluene 92.14 -3910.4 -42.43

alkenes 1-heptene 98.19 -4658.0 -46.42

cyclohexene 82.14 -3752.4 -45.68

Safety Considerations: To understand the fire hazards Table V associated with many organic compounds and petroleum fuels it Specific is important to recognize that certain conditions must be met Fuel Enthalpy before combustion can occur. (kJ/g) Hydrogen –141.9 Flammable Limits: Flammable limits are defined as the upper and lower concentrations of fuel vapors in air that will burn once Natural Gas –53.1 a suitable ignition source is introduced. If the fuel vapor Liquified petroleum –49.8 concentration is either too rich (the ratio of fuel to oxygen is too high) or too lean (the ratio of fuel to oxygen is too low) burning Aviation petroleum –46.0 will not continue when the ignition source is removed.

Automotive gasoline –45.8 Ignition Temperatures: Autoignition temperature is the Kerosene –46.3 minimum temperature at which a solvent will ignite when the liquid is dropped on the surface of a hot plate (with no other Diesel –45.3 ignition source present). In contrast, the lowest temperature at which a vapor-air mixture above a liquid will ignite when a suitable ignition source (such as a flame or spark is introduced) is the flash point. Chemicals with higher flash points are generally less flammable or hazardous than those with lower flash points. Both of the above mentioned ignition temperatures will vary with the exact method by which they are measured and, therefore, any reported value must be considered as approximate. Table VI lists some of the characteristics of common solvents. Gasoline is designed for use in an engine which is driven by a spark. The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. The fuel should not pre-ignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high autoignition temperature. (from http://en.wikipedia.org/wiki/Flash_point)

6 Diesel is designed for use in a high-compression engine. Air is compressed until it has been heated above the autoignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low autoignition temperature. (from http://en.wikipedia.org/wiki/Flash_point)

Autoignition Temp (°C) Flash point (°C) Gasoline ~257°C < - 45°C Diesel ~210°C > 62°C

Table VI: Flammability Characteristics of Select Organic Solvents Flammable Limits boiling point autoignition flash point Solvent (oC) lower upper temp (oC) (oC)

Acetone 56 2.6 12.8 465 -20.0 Benzene 80 1.3 7.1 498 -11.0 Cyclohexane 81 1.3 8.0 245 -20.0 Diethyl ether 35 1.9 36.0 160 -45 Ethanol 79 3.3 19.0 363 13.0 Methane -162 5.3 15.0 537 -188 Butane -0.5 1.9 8.5 405 -60 Propane -42 2.2 9.5 432 -104 Hexane 68 1.1 7.5 223 -22.0 Isohexane 69 1.2 7.0 264 -32 Octane 126 1.0 6.4 220 15 Isooctane 99 1.0 6.0 418 -40 Isopropanol 82 2.0 12.0 399 12.0 Toluene 111 1.2 7.1 480 4 (Note: The flammable limits are measured as percent by volume in air.)

The volatility of a substance is related to how readily it evaporates. Substances with high vapor pressures (such as gasoline) evaporate more quickly than substances with low vapor pressures (such as oils). Liquids that evaporate quickly are known as volatile liquids. Many organic solvents such as acetone and ether are very volatile and ignition of their vapors can be a serious fire hazard. In addition, vapor pressures (and hence volatilities) increase significantly with increasing temperature which can enhance the possibility of fires (such as on a hot carrier deck or hot engine room). A final consideration of the fire hazards of fuels and organic solvents is that their vapors are generally more dense than air and can travel across a bench top or table and collect on the floor and in other low areas. If there is a source of ignition in these areas (e.g., a flame, electric motor, thermostatically controlled equipment, etc.), a flash fire can result. Asphyxiation can also result if the gases displace air. 7

Knocking and Octane Rating: One consequence of the autoignition temperature relates to the condition in automobiles known as knocking. Generally, straight chain hydrocarbons have lower autoignition temperatures than branched chain hydrocarbons. Gasoline has a relatively high autoignition temperature and, therefore, requires an ignition source (a spark from a spark plug) to initiate combustion. However, as the engine becomes hot during use, ignition of the fuel can occur before the spark ignites the fuel. This premature ignition produces a “knocking” or “pinging” sound and robs the engine of power, and if it continues, the engine may be damaged. Since straight chain hydrocarbons in the gasoline boiling range have lower autoignition temperatures they have a greater tendency to produce knocking than do the branched chain compounds of similar molecular weight (refer to Table VI).

To determine the octane number for different grades of gasoline, the knocking characteristics of the gasoline are compared to mixtures of 2,2,4-trimethylpentane (also known as isooctane or simply octane) and n-heptane. Heptane knocks considerably and is arbitrarily assigned an octane number of zero. Whereas, 2,2,4-trimethylpentane burns smoothly and is assigned an octane number of 100. Thus, a gasoline with an 87-octane rating has knocking characteristics matching those of a mixture of 87% 2,2,4-trimethylpentane and 13% n-heptane. Since the octane rating system was established other fuels have been determined to be more knock resistant than isooctane and they have octane numbers above 100. For example, methyl tertiary butyl ether (MTBE), benzene, and toluene have octane numbers of 113, 106 and 120, respectively.

The gasoline fraction obtained directly from the fractional distillation of petroleum has too low an octane number to be an effective automobile fuel as it contains too high a percentage of straight chain hydrocarbons. A major objective of the petroleum refinery is to raise the octane number. This is accomplished by many of the post-distillation processes (catalytic reformer, cracking units, and alkylation units) that come in to play after the crude oil fractions have been separated in the distillation tower (Figure 1). The purpose of these units is to convert a percentage of the straight chain hydrocarbons into branched hydrocarbons and aromatic compounds, which increases the octane number of the fuel.

Alternatively, specific compounds can be added to unleaded gasoline as octane enhancers. Prior to 1975 the most commonly used octane enhancer was tetraethyl lead. However, this compound is no longer used as it deactivates catalytic converters and lead is known to be toxic. Some of the more common octane enhancers currently in use are the following (octane numbers in parenthesis): toluene (118), methyl alcohol (107), ethyl alcohol (108), tertiary-butyl alcohol (113), tertiary-butyl methyl ether (116). Additionally, gasolines that have compounds such as tertiary-butyl ether or any of the alcohols added to them tend to burn more completely and reduce carbon monoxide emission. The Clean Air Act of 1990 mandates the use of oxygenated gasolines during winter months in cities with high levels of carbon monoxide pollution.

For more information about: gasoline, go to http://auto.howstuffworks.com/gasoline.htm. how car engines work, go to http://auto.howstuffworks.com/engine.htm. octane ratings, go to http://en.wikipedia.org/wiki/Octane_rating. turbochargers, go to http://auto.howstuffworks.com/turbo.htm.

8 Jet fuels next… Jet Fuels: Common jet fuels are JP-4, JP-5 and JP-8 and the newly formulated JP-8+100. All airplanes used to burn JP-4, but the Navy and Air Force have switched fuels. All of these fuels have about the same specific enthalpy (approximately –43 kJ/g) but JP-4 is more flammable than JP-8, and both JP-4 and JP-8 are more flammable than JP-5. The Navy uses JP-5 since shipboard use requires a greater degree of safety. JP-8+100 is a new product that contains an additive package designed to increases the temperature range over which the fuels remains thermally stable by 100°F. While commercial aircraft still use JP-4, the Navy now uses JP-5, and the Air Force uses JP-8+100. There is much research currently underway to find a single fuel that meets the requirements of all DoD aircraft. This results in much greater flexibility in refueling in joint operations. In addition, it is hoped that the same fuel could even be used for non-aviation applications (heating units, motor vehicles, etc.).

From a chemistry standpoint, the composition of jet fuels is quite similar to that of diesel fuel, kerosene or light distillates including home heating oil. Jet fuels are characterized by their high flash points, which makes them relatively safe to transport, store and handle when compared with gasoline. JP-5 can also be used for maritime gas turbine engines. Thermal stability is of particular importance in military aircraft fuels because the fuel is often circulated for engine cooling purposes. Thus, in addition to the principle issue of good combustibility, the fuel must have the additional attribute of being an effective heat sink. Sometimes these issues are in conflict with each other. For example, the greater thermal stability of JP-5 comes with the consequence of a greater likelihood of engine stalls.

For a history of jet fuels, go to http://www.airbp.com/airbp/public/generalinterest/jethistory.html.

Rocket Fuels: The fuels used in spacecraft, in most cases, are different than the petroleum fuels discussed to this point as they are designed for very different environments and conditions. A rocket fuel should have a high specific enthalpy (enthalpy of reaction/gram of substance). Additionally, as the fuel must react in the absence of air, a rocket must carry an oxidizer as well as the fuel. Since the rocket is propelled by the ejection of gases from its engines, a desirable rocket fuel produces a large amount of heat and a large volume of gases when it is burned. Due to the high specific enthalpy it is reasonable to expect that hydrogen and oxygen are an ideal fuel-oxidizer combination (eq. 2)

o H2 (g) + ½ O2 (g) → H2O (g) ∆H = -242 kJ/mol (or -141.9 kJ/g) (Eq. 2)

This reaction was used with the Apollo spacecraft missions in the third stage of the Saturn V rockets. This reaction is also used to boost the space shuttle into its proper orbit while firing the solid rocket booster. The solid booster rockets of the space shuttle use the reaction of aluminum powder (the reducing agent) with ammonium perchlorate (NH4ClO4, the oxidizing agent) in the presence of the catalyst iron oxide (Fe2O3). One of the reactions that can occur is shown in eq. 3. The solid products from this reaction (Al2O3 and AlCl3) form the thick, white cloud observed during liftoff of the shuttle.

3 NH4ClO4 (s) + 3 Al (s) → Al2O3 (s) + AlCl3 (s) + 6 H2O (g) + 3 NO (g) (Eq. 3)

The Apollo moon-landing module used methylhydrazine as a fuel and dinitrogen tetraoxide as the oxidizer (eq. 4). This takes advantage of the fact that the nitrogen-nitrogen bond in methylhydrazine is relatively weak, whereas, the nitrogen-nitrogen triple bond in the diatomic nitrogen (N2) product is very strong.

4 CH3NHNH2 (l) + 5 N2O4 (l) → 9 N2 (g) + 12 H2O (g) + 4 CO2 (g) (Eq. 4)

For more information about rocket fuels, go to http://en.wikipedia.org/wiki/Rocket_fuel or http://www- pao.ksc.nasa.gov/kscpao/nasafact/count2.htm.

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Lubricating Oils: The primary purpose of lubrication is separation of moving surfaces to minimize friction and wear. Lubricating oils are also obtained from distillation of petroleum and they are distinguished from other fractions of crude oil by their high boiling points (typically greater than 400oC) and high viscosity. Lubricating oils are primarily composed of mixtures of hydrocarbons containing 25 to 30 carbon atoms per molecule. Additionally, as much as 7-12% of an engine oil mixture consists of performance additives.

One of the most important properties of modern engine oils is viscosity. Viscosity is the oils’ resistance to flow and it is well established that the viscosity of an oil changes dramatically with temperature. The SAE Engine Oil Viscosity Classification System defines ten viscosity grades for engine oils. Within this grading system there are two series: those that contain the letter “W” (e.g. 10W and 15W) are considered to be the winter grades as they are generally recommended for cold temperature operation. Those without the “W” are not recommended for cold weather application and are sometimes referred to as “summer” grades. Multi-grade engine oils are specially formulated and include additives to produce an oil with excellent cold temperature flow properties and sufficient high temperature viscosities to protect the engine at high temperatures. These multi-grade oils have designations such as 10W30.

Viscosity and Structure: Viscosity, resistance to flow, is directly related to the intermolecular forces of attraction between molecules. Strong intermolecular forces will contribute to a higher viscosity. Because fuels and lubricants are usually non-polar compounds, the intermolecular forces of interest are London dispersive forces. These depend on polarizability, which will increase with molecular weight and surface area. Thus, a straight-chain hydrocarbon will have higher London forces than a branched structure of similar mass (η α M3.4).

Oils must be blended to achieve the range of viscosities that is needed under operating conditions. This multi-grade treatment is a good example of the importance of intermolecular forces. One of the ways in which this is accomplished is by the addition of silicone molecules of comparable molecular weight to the hydrocarbon oils. At low temperatures, these molecules tend to be attracted to themselves rather than the hydrocarbons so they “ball up” and provide little contribution to the viscosity of the system. Thus the viscosity is that of the smaller number in the SAE label. At higher temperatures, the effects of molecular motion (entropy) causes the silicone to unfold and the now- extended molecules drag through the hydrocarbon, which has the effect of increasing the relative viscosity at the higher temperature. The lubrication oil of turbine bearings and reduction gears on board ship is constantly filtered to remove foreign particles and is maintained at relatively low temperatures by constant circulation through a cooler. Since the oil is never subjected to extreme temperatures and contaminants found in auto engines, it seldom if ever, needs to be changed. Ships and submarines routinely monitor lube oil for impurities. Small samples of the oil are sent to labs for spectrometric analysis. Results from such analysis can pinpoint exact bearings or equipment suffering abnormal wear.

Thermal Breakdown: Lubricating oils do not have unlimited lifetimes. They will change characteristics over time. One factor is thermal breakdown. Since oil is a blend of compounds, loss of a certain component of the oil will affect the viscosity. Oil is normally consumed in the operation of an engine and it is normal for the lighter weight, low viscosity fractions to be consumed at a higher rate. This results in a higher weight, higher viscosity fraction being left over. So oils will get heavier over time and lose the ability to function well, particularly in cold weather and cold starts.

10 Engine Oil Additives: Almost all lubricants contain chemical additives that improve the lubricating ability of the oils. The quality and quantity of the additives depend on the nature of the oil and the lubricants intended use. Typical automobile motor oil consists of 6 -14% additives. All of the additives contain hydrocarbon groups that make the additive soluble in the oil. The exact structure of the hydrocarbon group affects the way in which the additive functions and, often, a given additive will perform more than one function. The different kinds of engine oil additives are shown in Table VII. Detailed discussion is provided for only a few of the different types to illustrate the importance of intermolecular forces.

Table VII: The Types of Engine Oil Additives

additive class purpose mechanism of action

dispersants keep insoluble contaminants dispersed in the surround the insoluble contaminants and help them lubricant to dissolve

detergents prevent attack of metal surfaces by the acid by- These additives (1) neutralize organic acid that products of combustion and oxidation. Helps come from the oxidative breakdown of the oil, and keep metal surfaces free of deposits. (2) associate with the sludge to keep them dissolved in the oil. Both of these mechanisms keep the metal surfaces clean.

rust inhibitors prevents corrosion and rusting of metal parts in formation of protective film contact with the lubricant

wear inhibitors reduce friction and wear and prevent scoring additives react with the metal surface to form a and seizure sacrificial protective film. This inhibits the welding of the two surfaces and minimizes the Oxidation inhibit the decomposition of the lubricant and these additives have the ability to react with the inhibitors additives through oxidation free radicals that play a central role in the oxidative decomposition of the lubricant viscosity minimize the change in viscosity with modifiers temperature

friction reducers alter the coefficient of friction polar ends associate with the metal surface and the nonpolar end with the lubricant

foam inhibitors prevent lubricants from forming foams these additives reduce surface tension of air bubbles and cause them to collapse

For more information about oil grades, go to http://auto.howstuffworks.com/question164.htm. For more information about viscosity, go to http://en.wikipedia.org/wiki/Viscosity.

The World’s longest running experiment, which started in 1927, involves the pitch drop experiment. Pitch is a tar-like substance that is very viscous. How would you like run an experiment for 78 years? For more information, go to http://en.wikipedia.org/wiki/Pitch_drop_experiment or http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml (to see a live image).

11 Glossary of Terms

Alcohols – any of a class of organic compounds containing the hydroxyl group, OH, i.e., ethanol or ethyl alcohol

Aliphatic – any of a class of hydrocarbons that are not aromatic (i.e., contain no benzene rings) for example; alkanes, alkenes, and alkynes

Alkanes – any of a class of hydrocarbons that contain carbon-carbon single bonds (no multiple bonds), may be straight-chained, branched, or cyclic

Alkenes – any of a class of hydrocarbon compounds that contain at least one carbon-carbon double bond

Alkynes – any of a class of hydrocarbon compounds that contain at least one carbon-carbon triple bond

Aromatic – any of a class of hydrocarbons that contain at least one benzene ring structure (a six- membered ring of sp2-hybridized, or trigonal planar, carbons, not to be confused with cyclic alkanes which contain sp3-hybridized, or tetrahedral, carbons)

Cycloalkanes – hydrocarbons of the alkane family arranged in a loop or cyclic fashion

Ethers – any of a class of organic compounds containing an oxygen atom linking two hydrocarbon groups, R-O-R, i.e., ethyl ether, (C2H5)2O

Flashpoint - the temperature at which the material will sustain a flame briefly when a spark is passed through the vapor in equilibrium with the liquid

Hydrocarbons – compounds containing only hydrogen and carbon

Isomers – compounds that have the same molecular formula, but different structures

Olefins – any of a family of unsaturated, chemically active hydrocarbons, with one carbon-carbon double bond, i.e., ethylene, propylene

Saturated Hydrocarbons – any of a family of hydrocarbons with all carbon bonds satisfied, i.e., no double or triple bonds

Unsaturated Hydrocarbons – any of a family of hydrocarbons that have at least one double or triple carbon-carbon bond, for example, ethylene, acetylene.

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