GASOLINE: Part 1
( check this forum section for other parts)

Gasoline is blend of many different hydrocarbons, all derived from crude oil. Gasoline has been around since approximately the late 1800's. Since that time, gasoline has gone through many changes in formulations and intended applications. For example, early 1900 cars used 40-60 octane fuel. 1960's cars needed octane values over 100 by comparison, as some Chevy, Ford, Mopar and Pontiac factory race cars were using up to 13:1 compression ratios! High compression was nice in the 60's as it made prodigious amounts of horsepower on the same cubic inch engine compared to one with less compression. In addition, high octane gas was abundant and their was little concern about pollution and the atmosphere compared with today.

Aside from powering factory race cars, most gasoline has to work in everyday cars going to and from work, start and stop, starting in sub zero weather, driving at 100+ temperatures and extended periods of storage. This is why gasoline is made from many different chemicals, as it must work over a broad range of situations. In addition, additives are used to provide icing protection, anti-wear properties, corrosion inhibitors, detergents and sometimes dyes. All of these are needed to protect your engine so it will last hundreds of thousands of miles under various conditions.

AIR/FUEL RATIO:

Gasoline is mixed with the air from your carburetor and distributed through the intake system to the chamber. It ignited with a spark and orchestrated with precise timing of intake and exhaust valves in relation to the piston stroke. All engines need a specific air/fuel ratios or amount of gas per volume of air your engine needs to work properly. For general purposes, it has been agreed that a ratio of around 14.0:1 (14.0 parts air to 1 part gas) is typical for carburated engines, using a non-oxygenated gasoline. The oxygen in air is what provides the explosive force when mixed with gas and set off with a spark. The interesting thing about the air we breathe is, it is only approximately 21% by volume Oxygen (remember this for later). The majority is Nitrogen, thank god, because it keeps everything from catching fire, oxidizing and rusting. Non-oxygenated gasoline contains 0% by volume of Oxygen in the chemical formula and therefore your engine must get all of its Oxygen from the intake system.

Deviating or going up and down on the air/fuel ratio will have an effect on power output and will also affect knocking. Leaning the mixture will require higher octane values. Each 1.0 increase in leaning (15.0) will require an increase of 2.0 (R+M/2) octane points. Mid to late 70's cars with EGR and lean calibrated Q-jets fall into this category. Timing will also have an effect as the timing is increased, the tendency to knock is increased. Typically, late 70's cars have lazy advance curves and limited total timing. However, higher cylinder temperatures and lean jetting will cause problems on lower octane gas with lean air/fuel ratios. Computer controlled newer cars will automatically adjust this ratio along with the timing for optimum performance for given conditions and octane used.

* To help with knocking on high performance cars with higher compression ratios, run air/fuel ratios richer (14.0:1) this will reduce chance of knocking.

OCTANE:

The topic of octane produces more controversy than any other pertaining to fuels.

It has been explained in various ways many accurate and some not so accurate. In a nutshell, octane is the resistance to knock during combustion. Knocking is when the fuel will auto-ignite under heat and pressure after the spark and causes extreme forces by having multiple flames fronts within the chamber. Many factors effect knocking in addition to octane, air inlet temperature, cylinder head temperature, air/fuel ratio, engine load, plug heat range and compression ratio. There are others I am sure but these are the primary.

The octane value of a fuel is measured under very specific and controlled conditions. A company (very close to my home in Wisconsin) manufacturers a single cylinder octane test engine with a variable compression ratio (4:1-18:1) that is used for the ASTM test. Ironically, the standard single engine design uses a longer stroke than bore similar to a 455 Pontiac! This device burns a test fuel while increasing the compression by moving the head and measuring ultra sonic vibrations in the chamber on a test apparatus that measures sound waves. Predictable knocking patterns at specific compression ratios on various fuels are assigned an octane value.

The two most common values are, Research Octane RON and Motor Octane MON. The antiknock index is calculated by the average of the two, RON+MON/2. Both RON and MON use specific but different test parameters. The RON uses lower RPM, variable intake temperature, variable barometric pressure, and fixed timing. The MON uses higher RPM, fixed intake temperature and variable timing. An average of the two provides a good cross section of how a fuel will work under all conditions. Other octane values are tested as well as other tests to determine how the fuel will actually behave in the engine but the RON and MON are what most applies to our engines.

Increasing the compression ratio is the most common reason for using a higher octane fuel. Increasing compression will make more horsepower up to a point. The maximum effective compression ratio before you hit a point of diminishing returns is 16:1. This is about the compression that NHRA Pro Stock engines use for this reason. One important point is, as compression is increased from lower compression ratios (7:1 to 10:1) there is more brake thermal efficiency increase from lower than higher ratios. The point is, there is a bigger difference going from 7:1 to 10:1 than 10:1 to 13:1 compression. Turbos and blowers also have specific requirements as they increase cylinder pressure by artificial means.

As mentioned earlier, as compression ratios increased, the need for higher octane became important to reduce engine failures. Airplanes used in World War 1 really were the first to need higher octane. Shortly after, automotive engines were getting more powerful, more cubic inches and higher compression dictated the need for higher octane values.

During these years one of the most effective and economical means to increase octane was to use Tetra Ethyl Lead. Problem was, lead compounds are toxic by absorption, inhalation and even when burned. By the late 70's the EPA mandated reduction and elimination of TEL in gas. Similar replacements were used with limited success. This meant with lower octane fuel manufactured and the elimination of lead, auto manufacturers had to manufacture cars with lower compression ratios, something they were not used to doing! Compression ratios were dropped and timing curves were trimmed to function on 87 octane fuel and thus 70's cars got a bad rap by the press.

TEL:

The conditions of the MON rated octane value represent severe, sustained high speed, high load driving, like racing. For most fuels, including those with either lead or oxygenates, the motor octane number (MON) will be more applicable for racing applications. R+M/2 is more applicable for street driving. The MON will also be lower than the research octane number (RON). The following is a table showing the RON increase with the addition of TEL.

92 R+M/2 octane pump gas:

Lead g/l Research Octane Number

0 96
0.1 98
0.2 99
0.3 100
0.4 101
0.5 101.5
0.6 102
0.7 102.5
0.8 102.75

Keep in mind that the MON and the R+M/2 will be lower. This illustrates that TEL does not add a significant amount of octane. Other compounds are used as well.

As previously mentioned, there are many factors that dictate how much octane an engine needs. This value is effected by more than mechanical compression ratio. It is primarily affected by cylinder pressure and valve opening and closing in relation to mechanical compression.

Most G.M engines calculate to less compression than the factory literature or repair manuals state. If you think you have a 10.75:1 G.M engine, you don't! That does not mean you don't need good fuel, but rather your requirement might be actually for a 10.0:1 engine. Because of the aforementioned reasons, there is no easy way to determine the octane value for a given engine. The standard ASTM test engine changes barometric pressure, intake temperature, variable timing and variable compression ratio to determine octane values!

PUMP GAS:

Today, pump gas is of very high quality and has some inherent advantages over race fuels for street cars. Back in the early 1980's, the EPA began to mandate in certain regions of the country that gas manufacturers or terminals use oxygenated fuels. The single and primary reason, as far as the EPA is concerned is, reduced emissions. A secondary benefit is, in the case of Ethanol, it is a renewable resource as it is fermented from corn, distilled and dehydrated. This oxygenate is very popular here in the mid west.

Oxygenates, Ethanol, MTBE, ETBE and Methanol have the benefit of reducing HC emissions, raising octane, adding Oxygen to the fuel, and provide more anti-icing properties to the fuel. Ethanol is the most predominant, followed by MTBE, ETBE and Methanol. Current fuel formulations use approximately 3-4% by volume of Oxygen in the formula in the form of one of the above oxygenates. Remember what I said previously about air only containing 21% Oxygen. By using an oxygenated fuel, you are introducing more Oxygen to your engine without changing any engine components. An increase of 3-4% Oxygen does not seem like a lot, until you remember that air only contains 21% by volume. The ratio is 14:1 but you are still adding more Oxygen without changing any external or internal engine parts.

ENERGY CONTENT:

The theoretical energy content of gasoline when burned in air is only related to the hydrogen and carbon contents. The energy is released when the hydrogen and carbon are oxidized to form water and carbon dioxide. Important to note: The octane rating is not related to the energy content. The actual hydrocarbon and oxygenate compounds used in the gasoline will determine both the energy release and octane rating.

BTU's of a given fuel do not have much effect on the power produced by an internal combustion engine when compared at the correct stochoimetric A/F ratio. Example: Gasoline has a BTU/lb value of roughly 20,000 BTU's. Methanol has a BTU value of 8,600. Methanol can produce much more power than gasoline because of this increased Oxygen content, thus, changing its stochiometric ratio and creating a denser charge. However, much more fuel per pound must be consumed. Any time you can introduce more Oxygen into the engine, it's a benefit.

For years, racers have used Methanol as a race fuel because half the weight of a molecule of Methanol is, Oxygen, at 49%. Because of this, the air/fuel ratio is now 6:1 (6 parts air to 1 part fuel). You must burn roughly twice the amount of Methanol as gasoline because of this. Methanol lost acceptance by the EPA as it produces Formaldehyde emissions and it attacks epoxy which is sometimes used to secure rubber fuel hose to gas tanks and filler necks.

Ethanol, which is the primary EPA oxygenate, has an air fuel ratio of approximately 9:1. When 10% Ethanol is blended in gas, it can cause a loss of gas mileage and power because of this stochoimetric air/fuel ratio. Computer controller cars will notice this also. However, if compensated and properly jetted, Ethanol and MTBE can produce more power because of the increased Oxygen content even over race gas if you have a lower compression ratio.

RFG:

The primary objective from the EPA's standpoint was, Oxygenates caused an engine to run lean, reducing CO and HC emissions. However, they also have high a blending octane and can be used to replace high levels of aromatics in fuel. Oxygenates (contain oxygen), really do not provide much BTU/lb of energy.

For an engine that runs on RGF, more fuel is required to obtain the same power, thus, the power ratio is not identical to the energy content ratio. They also require more energy to vaporize.

Oxygen Content wt %

Methanol 49.9%
Ethanol 34.7%
Gasoline 0.0%

Older higher compression cars in stock tune, are going to have the most problem with pump gas. With 10.0:1 actual compression ratios, stock carbs and short duration camshafts they will be the most prone to problems on lower octane gas. This means the resto crowd will have most of the problems. Modified cars with lower compression (<10:1) longer duration cams, ram air systems and richer jetting, will be OK with pump gas. Ethanol blended gas compared to non-oxygenated gas, can provide additional problems as it will lean out the air/fuel mixture as discussed before. This is why I recommended jetting carbs richer when using Ethanol/MTBE blended pump gas.

The most important thing to remember is, higher octane on an engine that does not require higher octane, will absolutely be a waste of time and money and you might slow down as well! Race engines with higher compression's (>10.5:1) will require a product with higher octane than pump gas can offer. And this is just as important. If the octane requirement is not met, the engine will be subjected to very severe cylinder pressures which will be transmitted to the rest of the reciprocating parts. Most street cars are not going to need race gas or octane boosters. Timing and carb adjustments will make it possible to function with pump gas.

OCTANE BOOSTERS:

Most octane boosters are hydrocarbon solvents already present in gas. Some claim to be real lead. Others are products have been banned by the EPA.

Most of us have a pretty big gas tank in our Corvette's. It would take a lot of little 8 oz. bottles to actually provide any measurable increase. Claims that, "adding a 8 oz. bottle of our octane booster will raise octane 4 points". Actually, they mean .4 points.
Sunoco did a test a couple of years ago and tested the major products on the market. None of them raised octane when used be the manufactures recommendation. In fact a couple actually lowered it. Only when dosing 4X the recommended volume, one product raised it a few points. The problem was they were only now up to 96-97 octane and had surpassed the cost of a tank of race gas.

Some of the products claim they will minimize valve seat recession. They do this by adding a heavy weight oil that gets introduced to the chamber via the gas and lubes the valves. Valve seat recession is primarily a problem in sustained high speed operation (racing, autobahn, etc.) Test data shows a 1970 engine operated at 70 MPH averaged 1.5 mm of seat recession in 7,500 miles per year. However, this is 7,500 miles at 70 MPH.
Gas line antifreeze products are typically used by us northern and mid western people. These products are typically, Ethyl, Methyl or Isopropyl Alcohol. If you are using Ethanol blended gas, using these products would be a total waste of money, as there is more alcohol already in your tank than you are adding from an 8 oz. bottle.

I am not stating that none of the products work. The better products under the right conditions might provide some advantage to a car owner that has problems with knocking. What I am saying is, the additional octane provided is less than you think, meaning your car does not require as much octane as you think. Additionally, there are thousands of people out there that are adding fuel additive's that do not need to.

AV GAS:

Products are usually formulated for a specific application. The automotive engineer or aircraft engineer usually has a pretty good idea what will work best for the engine design. This is why you have auto gas, AV gas and race gas.

The density of AV gas is much less than automobile gas or race gas. Thus, for every gallon of AV gas passed through your carb jets, you have less fuel per pound compared to pump gas/race gas. This will lean out the air/fuel ratio and produce less power if jetted for pump gas.

AV gas has a different vapor pressure than pump gas. It contains a lighter fraction of solvents that can cause or lead to vapor lock in an automotive engine that uses a heated intake plenum. This might not be problem for a race car but a street car running in hot weather, it will cause hesitation or vapor lock.

A mild race car (11:1) might be an OK application for true high octane AV gas. If the owner is going to take the time to specifically jet the carb to run on the AV gas, he might be OK. However, all out race motors running 12:1 actual compression ratios are going to need more than the typical 100 LL octane. The common available AV gas (100 LL) will not be enough octane for a race motor.

If you need to raise your octane, as you fall into one of the above mentioned categories, do the following. Current high octane, unleaded fuel and many race gas formulations increase octane by cranking up the T&X content. Most race gas formulations use Toluene or Xylene to achieve the octane boost.

Typical T&X content of 92 octane pump gas.
Typical T&X content of race gas.



Toluene 9% by vol.
Toluene 27% by vol.

Xylene 8% by vol.
Xylene 1% by vol.

Total T&X 17%
Total T&X 28%

Adding 10% Toluene by volume to your gas tank will achieve the same thing. Toluene has a RON+MON/2 of 118 so it is very effective. Caution, do not spill on you paint or you will be sorry. Toluene is a major constituent in lacquer thinner and enamel reducers. *Toluene is available from most hardware stores and will boost octane a lot more than a little 8oz. bottle of a flash in the pan product.

one should look at the amount of energy (heat) released in the burning of a particular fuel. This is described by the specific energy of the fuel. This quantity describes the amount of power one can obtain from the fuel much more accurately. The specific energy of the fuel is the product of the lower heating value (LHV) of the fuel and molecular weight of air (MW) divided by the air-fuel ratio (AF):

Specific Energy = LHV*MW/AF

For example, for gasoline LHV= 43 MJ/kg and AF=14.6, while for methanol LHV= 21.1MJ/kg (less "heat" than gasoline) and AF=6.46 (much richer jetting than gasoline). Using the above formula we see that methanol only has a 10% higher specific energy than g asoline! This means that the power increase obtained by running methanol, with no other changes except jetting, is only 10%. Comparing the specific energy of racing and premium pump gas you can see that there is not much, if any, difference. Only alcohol s (such as methanol or ethanol) have a slightly higher specific energy than racing or pump gas.

Other oxygen-bearing fuels, besides the alcohols and nitromethanes, such as the new ELF fuel, will also produce slightly more power once the bike is rejetted. However, at $15.00 to $20.00 at gallon for the fuel the reportedly minor (1% - 2%) improvement is hardly worth the cost for the average racer.

The real advantage of racing gasolines comes from the fact that they will tolerate higher compression ratios (due to their higher octane rating) and thus indirectly will produce more power since you can now build an engine with a higher compression rati o. Also, alcohols burn cooler than gasoline, meaning even higher compression ratios are possible with them, for even more power.

The bottom line here is that, in a given engine, a fuel that doesn't knock will produce the same power as most expensive racing gasolines.

However, it sometimes happens that when you use another fuel, the engine suddenly seems to run better. The reasons for this are indirect: First, the jetting may be more closely matched to the new fuel. Secondly, the new fuel may improve the volumetric e fficiency (that is, the "breathing") of the motor. This happens as follows: Basically a fuel that quickly evaporates upon contact with the hot cylinder wall and piston crown will create additional pressure inside the cylinder, which will reduce the amount of fresh air/fuel mix taken in. This important--but often overlooked--factor is described by the amount of heat required to vaporize the fuel, described by the 'enthalpy of vaporization' (H), or 'heat of vaporization' of the fuel.

A high value of H will improve engine breathing, but the catch is that it leads to a different operating temperature within the engine. This is most important with two-strokes, which rely on the incoming fuel/air mix to do much of the cooling--even mode rn water-cooled two-strokes rely on incoming charge to cool the piston. For two-strokes a fuel that vaporizes, drawing a maximum amount of heat from the engine, is essential--the small variations in horsepower produced by different fuels is only of second ary concern.

Also important is the flame speed: Power is maximized the faster the fuel burns because the combustion pressure rises more quickly and can do more useful work on the piston. Flame speed is typically between 35 and 50 cm/sec. This is rather low compared to the speed of sound, at which pressure waves travel, or even the average piston speed. It is important to note that the flame propagation is greatly enhanced by turbulence (as in a motor with a squish band combustion chamber).

The most amazing thing about all this is that you can get the relevant information from most racing gasoline manufacturers. Then, just look at the specification sheet to see what fuel suits you best: Hot running motors and 2-strokes should use fuels wit h a value of "H" that improves their cooling, while more power (and more heat) is obtained from fuels with a high specific energy.

By the way, pump gas has specific energies which are no better or worse than most racing gasolines. The power obtained from pump gas is therefore often identical to that of racing fuels, and the only reason to run racing fuels would be detonation probl ems, or, since racing fuels are often more consistent than pump gas--which racers call "chemical soup"--a consistent reading of the spark plugs and exhaust pipe.

Nitrous Oxide

Nitrous oxide ( N2O ) contains 33 vol% of oxygen, consequently the combustion chamber is filled with less useless nitrogen. It is also metered in as a liquid, with can cool the incoming charge further, thus effectively increasing the charge density. With all that oxygen, a lot more fuel can be squashed into the combustion chamber. The advantage of nitrous oxide is that it has a flame speed, when burned with hydrocarbon and alcohol fuels, that can be handled by current IC engines, consequently the power is delivered in an orderly fashion, but rapidly. The same is not true for pure oxygen combustion with hydrocarbons, so leave that oxygen cylinder on the gas axe alone

* I will stress this again, if you don't need it, higher octane fuel won't make a difference. In fact, the slower burn rate of higher octane solvents actually might slow the car down if you have a low compression motor.


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