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    ROCKET FUEL IN OUR CARS

    USE OF TOLUENE AS AN AUTOMOTIVE FUEL ADDITIVE

    NOORANI TUFEL,

    B.E. III , MECHANICAL,

    L.J.I.E.T, AHMEDABAD

    Abstract:

    Gasolines sold at our service stations typically have an octane rating between about 87 & 93, & fuels ofsuch octane values are satisfactory for most automotive engines. However for high performance engines

    in particular, fuels of even higher octane ratings are required. Octane is a measure of a gasolines

    antiknock performance its ability to resist knocking, which is a metallic rattling or pinging sound that

    results from uncontrolled combustion in the engines cylinders. It may prevent engine damage. If a

    gasoline is used with too low of an octane rating than is required by an engine, then engine knock may

    result. Heavy and prolonged knocking or pinging may cause power loss and may damage the engine. As

    is well known, the production of fuels of progressively higher octane values is progressively more

    difficult to achieve. In particular, fuels of octane value at or above 100 are highly desired &

    correspondingly the most difficult to produce, particularly for unleaded fuels. Usage of such regular

    fuels in our S.I. , I.C. Engines thus reduces the performance of the engine & hence doesnt give requiredC.R. & thereby exhausts that pollute the environment. The following paper refers to a fuel additive

    component TOLUENE that helps to increase the octane rating of the fuel & thereby increasing C.R. to

    the required level in the engine.

    ______________________________________________________________________________

    Tags: Gasoline, Octane Rating, Compression Ratio, Toluene, Fuel, Performance, I.C. Engine

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    Background of Invention:

    For many years it has been customary to utilize separate chemicals to deal with various fuel problems.

    For example, it has been common to use kerosene to remove carbon deposits from an engine, to add

    alcohol to gasoline to render its moisture content miscible therewith & to add a highly volatile

    component to provide a quick start to a sluggish engine. It is also well-known that the octane number of

    gasoline may be increased by using increasingly-branched olefins, or aromatic hydrocarbons.

    This invention relates to liquid fuels of high octane rating in particular gasoline of octane rating @ or

    above 100 using Toluene as a key additive. For a high compression engine to run on low octane fuel, the

    engine management system will need to retard the ignition timing to prevent preignition or pinging.

    Retarding the ignition timing means that the firing of the spark plug is delayed until a later moment in

    the compression stroke. It does not take much to see that a later onset of combustion means that the

    combustion is less complete, which in turn mean less power and poorer fuel economy. It is possible that

    the casual driver will still come out ahead in terms of saving money by using low octane fuel, but the

    retarded ignition advance also means a rougher running engine and a much duller throttle response. Thus

    octane boosting is not necessarily of interest to all motorists but rather the enthusiasts.

    For turbocharged or supercharged engines, insufficient octane will also lead the engine management

    system to curtail the amount of boost which in turn defeats the purpose of these engines.

    Detailed Description of the invention:

    The incorporation of toluene provides a rich super charging fuel additive, as well as a solvent. Its anti

    knock properties are also well known. Toluene is a pure hydrocarbon (C7H8). i.e. it contains only

    hydrogen and carbon atoms. It belongs to a particular category of hydrocarbons called aromatic

    hydrocarbons. Complete combustion of toluene yields CO2 and H2O. This fact ensures that the entire

    emission control system such as the catalyst and oxygen sensor of your car is unaffected. There are no

    metallic compounds (lead, magnesium etc), no nitro compounds and no oxygen atoms in toluene. It is

    made up of exactly the same ingredients as ordinary gasoline. In fact it is one of the main ingredients of

    gasoline.

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    Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114.

    (R+M)/2 is how ordinary fuels are rated in the US. Note that toluene has a sensitivity rating of 121-

    107=14. This compares favorably with alcohols which have sensitivities in the 20-30 range. The more

    sensitive a fuel is the more its performance degrades under load. Toluene's low sensitivity means that it

    is an excellent fuel for a heavily loaded engine.

    Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit

    volume. Thus combustion of toluene leads to more energy being liberated and thus more power

    generated. This is in contrast to oxygenated octane boosters like ethanol or MTBE which contain less

    energy per unit volume compared to gasoline. The higher heating value of toluene also means that the

    exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive

    turbocharger vanes. In practical terms this is experienced as a faster onset of turbo boost.

    The racing gasoline contains octane boosters. The worst case scenario is buying leaded racing gasoline

    without knowing it. Unleaded racing gasoline may still contain damaging octane boosters like MMT or

    methanol. Very high alcohol content will lead to fuel line erosion, accelerated fuel pump wear, very

    poor fuel economy and possibly lower performance, as alcohols have a less impressive MON rating than

    aromatics.

    It takes smaller quantities of toluene to achieve the same octane boost compared to 100 octane racing

    gas. I have not seen unleaded racing gas for sale that exceeds the octane rating of toluene. Octane ratings

    can be very easily calculated by simple averaging. For example, the tank of an Audi A4 1.8TQ is 15.6

    gallons. Filling it with 14.6 gallons of 92 Octane and 1 gallon of toluene (114 Octane) will yield a fuel

    mix of:

    (14.6 * 92) + (1 * 114) / 15.6 = 93.4

    The Audi A4 1.8T is a good example of a car that has very high octane needs if it has been modified to

    produce more turbo boost. The base compression ratio of this car is a very high 9.5:1 and when an

    additional 1 bar (14.7 psi) of turbo boost is applied on top of it, the resulting effective compression ratio

    is way beyond what 92 or 93 octane fuel can ever hope to cope with. Most modified 1.8Ts running

    without octane enhancement are running with severely retarded ignition timing and boost.

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    It has been found that octane values of 100 or more can be achieved with the components specified

    above by the following a specific equation i.e. the octane formula

    OV = 7.427B + 0.3476I + 0.92922A + 1.07801T + 0.095M + 0.06170BI 0.06967BA 0.06973BT

    O.O5728BM + 0.005692IA + 0.005671IT + 0.01705IM - 0.000311AT + 0.01189AM + 0.00912TM

    Where

    OV is the Octane Value, B= concentration of butane in volume percent, I= concentration of iso pentane

    in volume percent, A= concentration of alkylate in volume percent, T= concentration of Toluene in

    volume percent, M= concentration of MTBE in volume percent

    (Here applying the octane formula other components in the fuel are ignored.)

    In preparing compositions of the invention it is preferred that the concentrations of butane, iso pentane,

    & alkylate be no more than 5% volume, 15% volume, & 90% volume respectively primarily because

    higher concentrations cause volatility problems. Toluene is preferably present in concentrations no more

    than about 60% volume because higher levels of aromatics in the fuels may cause problems with

    elastomeric components &/or driveability. MTBE is preferably present in concentrations tend to create

    air/fuel ratio difficulties &/or fail to comply with current EPA requirements as to the maximum

    concentration of oxygenates permitted in the fuel.

    When the fuel composition consists of the four or five ingredients specified above, the octane formula

    has been found to be accurate within about 1.. (Refer Table 1)

    Usually 0.5, & at the most 0.3 octane unit. In other words it has been found that some fuels having a

    predicted octane rating between 100 & 101 may have octane value in the 99 & 100 or even as high as

    101 or 102. Likewise some fuels having a predicted octane value in the 99 or 100 range may have an

    actual value at or above 100. (Refer Table 2)

    The liquid fuel compositions of the invention are fuels & may therefore be used as such. The preferred

    fuels are those which are suitable for combustion in automotive Spark Ignition Engines & even more

    preferably the fuels confirm to the requirements of gasoline, & more preferably to unleaded gasoline &

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    most preferably of all to the requirements of racing gasoline (As used herein, the term unleaded means

    a concentration of lead in the fuel is no greater that 0.05 gm of lead/gal.)

    To obtain the maximum energy from the gasoline, the compressed fuel/air mixture inside the

    combustion chamber needs to burn evenly, propagating out from the spark plug until all the fuel is

    consumed. This would deliver an optimum power stroke. In real life, a series of pre-flame reactions will

    occur in the unburnt "end gases" in the combustion chamber before the flame front arrives. If these

    reactions from molecules or species that can auto ignite before the flame front arrives, knock will occur.

    Simply put, the octane rating of the fuel reflects the ability of the unburnt end gases to resist

    spontaneous auto ignition under the engine test conditions used. If auto ignition occurs, it results in an

    extremely rapid pressure rise, as both the desired spark-initiated flame front, and the undesired auto

    ignited end gas flames are expanding. The combined pressure peak arrives slightly ahead of the normal

    operating pressure peak, leading to a loss of power and eventual overheating. The end gas pressure

    waves are superimposed on the main pressure wave, leading to a saw tooth pattern of pressure

    oscillations that create the "knocking" sound.

    The combination of intense pressure waves and overheating can induce piston failure in a few minutes.

    Knock and preignition are both favored by high temperatures, so one may lead to the other. Under high-

    speed conditions knock can lead to preignition, which then accelerates engine destruction.

    The fuel property the octane ratings measure is the ability of the unburnt end gases to spontaneously

    ignite under the specified test conditions. Within the chemical structure of the fuel is the ability to

    withstand pre-flame conditions without decomposing into species that will auto ignite before the flame-

    front arrives. Different reaction mechanisms, occurring at various stages of the pre-flame compression

    stroke, are responsible for the undesirable, easily-auto ignitable, end gases.

    During the oxidation of a hydrocarbon fuel, the hydrogen atoms are removed one at a time from the

    molecule by reactions with small radical species (such as OH and HO2), and O and H atoms. Thestrength of carbon-hydrogen bonds depends on what the carbon is connected to. Straight chain HCs such

    as normal heptane have secondary C-H bonds that are significantly weaker than the primary C-H bonds

    present in branched chain HCs like iso-octane.

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    The octane rating of hydrocarbons is determined by the structure of the molecule, with long, straight

    hydrocarbon chains producing large amounts of easily-auto ignitable pre-flame decomposition species,

    while branched and aromatic hydrocarbons are more resistant. This also explains why the octane ratings

    of paraffin consistently decrease with carbon number. (Refer Table 3)

    In real life, the unburnt end gases ahead of the flame front encounter temperatures up to about 700C

    due to piston motion and radiant and conductive heating, and commence a series of pre-flame reactions.

    These reactions occur at different thermal stages, with the initial stage ( below 400C ) commencing with

    the addition of molecular oxygen to alkyl radicals, followed by the internal transfer of hydrogen atoms

    within the new radical to form an unsaturated, oxygen-containing species. These new species are

    susceptible to chain branching involving the HO2 radical during the intermediate temperature stage

    (400-600C), mainly through the production of OH radicals. Above 600C, the most important reaction

    that produces chain branching is the reaction of one hydrogen atom radical with molecular oxygen to

    form O and OH radicals.

    The addition of additives such as alkyl lead and oxygenates can significantly affect the pre-flame

    reaction pathways. Anti-knock additives work by interfering at different points in the pre-flame

    reactions, with the oxygenates retarding undesirable low temperature reactions, and the alkyl lead

    compounds react in the intermediate temperature region to deactivate the major undesirable chain

    branching sequence.

    The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously

    ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes

    knocking in the engine. Knocking can damage an engine, so it is not something you want to have

    happening. Lower-octane gas (like regular 87-octane gasoline) can handle the least amount of

    compression before igniting.

    The compression ratio of your engine determines the octane rating of the gas you must use in the car.

    One way to increase the horsepowerof an engine of a given displacement is to increase its compression

    ratio. So a high-performance engine has a higher compression ratio and requires higher-octane fuel.

    The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a

    given engine weight that is what makes the engine high performance. The disadvantage is that the

    gasoline for your engine costs more.

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    The antiknock ability is related to the autoignition temperature of the hydrocarbons. Antiknock ability

    is _not_ substantially related to:-

    1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents,

    but high octanes.

    2. The flame speed of the conventionally ignited mixture, this should be evident from the

    similarities of the two reference hydrocarbons. Although flame speed does play a minor part,

    there are many other factors that are far more important. ( such as compression ratio,

    stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock

    additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate

    with octane.

    \What is the effect of Compression ratio?

    Most people know that an increase in Compression Ratio will require an increase in fuel octane for the

    same engine design. Increasing the compression ratio increases the theoretical thermodynamic efficiency

    of an engine according to the standard equation

    = 1 (1/compression ratio) ^ ( -1)

    Where = ratio of specific heats at constant pressure and constant volume of the working fluid (for most

    purposes air is the working fluid, and is treated as an ideal gas). There are indications that thermal

    efficiency reaches a maximum at a compression ratio of about 17:1

    The efficiency gains are best when the engine is at incipient knock, thats why knock sensors (actually

    vibration sensors) are used. Low compression ratio engines are less efficient because they cannot deliver

    as much of the ideal combustion power to the flywheel. For a typical carbureted engine, without engine

    management following results were obtained. (Refer Table 4)

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    FROM HONDA CIVIC TO FORMULA 1 WINNER.

    There are many variables that will determine the power output of an engine. High on the list will be the

    ability of the fuel to burn evenly without knock. No matter how clever the engine, the engine poweroutput limit is determined by the fuel it is designed to use, not the amount of oxygen stuffed into thecylinder and compressed. Modern engines designs and gasolines are intended to reduce the emission of

    undesirable exhaust pollutants, consequently engine performance is mainly constrained by the fuel

    available.

    The Honda Formula 1 turbocharged 1.5 litre engine was only permitted to operate on 102 Research

    Octane fuel, and had limits placed on the amount of fuel it could use during a race, the maximum boostof the turbochargers was specified, as was an additional 40kg penalty weight. Standard 102 RON

    gasoline would be about 96 R+M/2 if sold as a pump gasoline. The normally-aspirated 3.0 litre engines

    could use unlimited amounts of 102RON fuel. The F1 race duration is 305 km or 2 hours, and it's

    perhaps worth remembering that Indy cars run at 7.3 psi boost.

    Engine Standard Formula One

    Year 1986 1987 1989

    Size1.5 litre 1.5 litre 1.5 litre

    Cylinders 4 12 12

    Aspirationnormal turbo turbo

    Maximum Boost- 58 psi 36.3 psi

    Maximum Fuel- 200 litres 150 litres

    Fuel91 RON 102 RON 102 RON

    Horsepower @ rpm92 @ 6000 994 @ 12000 610 @ 12500

    Torque (lb-ft @ rpm)89 @ 4500 490 @ 9750 280 @ 10000

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    EFFECT OF TOLUENE CONTENT:

    The octane number of fuel for formula 1 Racing is limited to a maximum number of RON 102.

    Adopting a higher Compression Ratio is expected to improve both power & B.S.F.C. However at the

    same time the possibility of Knocking becomes higher. Therefore the knocking properties of fuels

    determine maximum Compression Ratio. It sometimes appears that differences in fuel ingredients effect

    knocking properties even though the RON of the fuels is same. The development of a fuel with good

    knocking properties under high speed & boost conditions is essential for adopting a high Compression

    Ratio.

    The tank Capacity regulation limits fuel amount to 150 liters. & refueling during a race event is

    forbidden. In order to obtain a largely calorific in capacity is needed i.e. a dense fuel. Comparative

    evaluation of various fuels revealed that a fuel with toluene content is most favorable to meet the

    requirements. Knocking properties & effects on B.S.F.C. of the test fuels are shown

    Toluene content ratios were 30%, 60%, & 84% for each test fuel(Refer Table 5)

    Appropriate amounts of normal heptanes & isooctane were respectively mixed with Toluene to achieve

    a RON of 102. As Toluene has a heavier density when compared to paraffin fuels, a fuel containing

    much Toluene has a larger calorific value in capacity (Cal/cc). Observations were conducted under the

    engine operating conditions of 12,000 rpm, 2.5 bar intake air temperature of 70 C & an equivalent ratio

    of 1.15. The knock-limit ignition timing advances as the ratio of toluene increases in the fuel ingredients

    resulting in better B.S.F.C. In addition since the test fuels differ in density, Brake Specific Volumetric

    Fuel Consumption. B.S.V.F.C. (cc/kwh) was considered, & studies revealed that a fuel containing a

    higher ratio of Toluene in the fuel ingredients proved most effective. (Refer Table 6)

    SUMMARY:

    A high toluene content in fuel had a good effect on knocking properties & allowed advanced ignition

    timing, which resulted in improvement of B.S.F.C. Toluene had a good effect on improvement of brake

    Volumetric Specific Fuel Consumption because of its heaviness of its density.

    CONCLUSION:

    It should be mentioned that in the US, efforts are underway to reduce the aromatic content of gasolines

    in general as a higher aromatic content leads to higher benzene emissions. Benzene is an extremely toxic

    substance. However it should also be noted that the proportions that is being discussed in this FAQ is

    relatively small and in the grand scheme of things is probably insignificant. Moreover, the industrial

    standard for defining gasoline composition allows plenty of leeway in aromatic content and the

    proportions present in US gas is already lower than most other countries. I therefore feel that the

    information provided here is useful to a performance minded car enthusiast while not being significantly

    detrimental to the environment.

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    TABLE 1

    Note: All the fuel compositions had actual octane ratings of 100 or more & all were within 0.5

    unit of the predicted octane rating.

    TABLE 2

    Fuel StateHeat of Combustion

    MJ/kg

    Research

    Octane

    Motor

    Octane

    n-heptanel 44.592 0 0

    g 44.955

    i-octanel 44.374 100 100

    g 44.682

    toluenel 40.554 124* 112*

    g 40.967

    2-methylbutene-2 44.720 176* 141*

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    TABLE 3

    Name Octane value

    Paraffins 50-100

    Benzene 26

    Toluene 93

    Xylene >100

    Cyclo pentane 70

    Di-isobutylene 64

    Hexene-2 -26

    TABLE 4

    Compression Ratio Octane Number RequirementBrake Thermal Efficiency

    @ Full throttle

    5:1 72 -

    6:1 81 25 %

    7:1 87 28 %

    8:1 92 30 %

    9:1 96 32 %

    10:1 100 33 %

    11:1 104 34 %

    12:1 108 35 %

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    TABLE 5

    TEST FUEL SPECIFICATIONS

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    FIGURE 1

    EFFECT OF TOLUENE CONTENT RATIO ON KNOCK LIMIT IGNITION TIMING & FUEL

    CONSUMPTION

    B.S.V.F.C. Brake Specific Volumetric Fuel Consumption (cc/kwh)

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    TABLE 6

    COMPARATIVE ANALYSIS OF OCTANE BOOSTERS

    Name of Octane BoosterRank

    Results ( in RON )@ baseline octane

    96.8

    Amount of increase

    in octane no.(+),

    in RON

    AmountRequired

    NF Octane BoosterRacing Formula, 1 99.6 2.8

    250 ml treats

    80 litres

    Nulon Pro Strength

    Octane Booster, 1 99.6 2.8500 ml treats

    60 litres

    Toluene,2 99.3 2.5

    20 litres treats100 litres

    Amsoil Series 2000Octane Boost, 3 98.8 2.0

    354ml treats 57

    litres

    ELF HTX 330 Racing

    Fuel Stabilizer, 4 98.6 1.81000 ml treats

    50

    NOS Octane Booster

    Racing Formula, 5 98.6 1.8355ml treats 60

    litres

    VP C5 Fuel Additive,6 98.1 1.3

    355ml treats 75litres

    Super 104+ OctaneBooster, 7 97.5 0.9

    473ml treats 83

    litres

    Wynns Octane 10+

    Power Booster, 897.6

    0.8325ml treats 60

    litres

    STP Octane Booster9 97.4 0.6

    350ml treats 57litres

    PowerFuel Super StreetNitro Based,

    1197

    0.2

    946 ml treats

    35 litres

    PowerFuel Max Race

    Nitro Based, 10 97 0.2946ml treats 35

    litres

    Material courtesy of Fast Fours Magazine Nov/Dec 1999.

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    REFERENCE MATERIALS

    1) GASOLINE FAQ

    2) Mc LAREN HONDA TURBO, A TECHNICAL APPRAISAL BY IAN BAMSEY

    (ISBN 0-85429-840-1, published 1990)3) CHEVRONS EXCELLENT MOTOR GASOLINES TECHNICAL REVIEW

    4) AGENCY FOR TOXIC SUBSTANCES FAQ ON TOLUENE

    5) TOXIC CHEMICALS IN YOUR ENVIRONMENT AUSTRALIA FAQ ON TOLUENE

    6) EXXON CHEMICALS AMERICA

    7) RECICLADORA TEMMARY DE MEXICO RECUCLING PROCESSOR

    8) MODERN PETROLEUM TECHNOLOGY - ANY EDITION.

    9) EDITOR, G.D.HOBSON, WILEY. ISBN 0 471 262498 (5TH=1984).

    10) HYDROCARBON FUELS.

    11) E.M.GOODGER, MACMILLAN. (1975)

    12) ALTERNATIVE FUELS

    13) E.M.GOODGER, MACMILLAN. ISBN 0-333-25813-4 (1980)

    14) SAE TECHNICAL PAPER SERIES 890877,

    15) HONDA FORMULA ONE TURBO CHARGED V6 1.5L ENGINE

    16) UNITED STATES PATENT 61234742

    17) U.S. PATENT 4812146

    SOURCE

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