[~JC~]

Gasoline

Gasoline, also called petrol, is a petroleum-derived liquid mixture consisting mostly of hydrocarbons and enhanced with benzene or iso-octane to increase octane ratings, used as fuel in internal combustion engines.

Most Commonwealth countries, with the exception of Canada, use the term "petrol" (abbreviated from petroleum spirit). The term "gasoline" is commonly used in North America where it is commonly shortened in colloquial usage to "gas". This should be distinguished in usage from genuinely gaseous fuels used in internal combustion engines such as liquified petroleum gas. The term mogas, short for motor gasoline distinguished automobile fuel from aviation gasoline, or avgas. The word "gasoline" can also be used in British English to refer to a different petroleum derivative historically used in lamps; however, this use is now uncommon. The Spanish language uses the word gasolina.

History
Pharmaceutical
Before internal combustion engines were invented in the mid-1800s, gasoline was sold in small bottles as a treatment against lice and their eggs. At that time, the word "Petrol" was a trade name. This treatment method is no longer common because of the inherent fire hazard and the risk of dermatitis.

In the US, gasoline was also sold as a cleaning fluid to remove grease stains from clothing. Before dedicated filling stations were established, early motorists would buy gasoline in cans to fill their tanks.

The name 'gasoline' is similar to that of other petroleum products of the day, most notably petroleum jelly (a highly-purified heavy distillate) which was branded "Vaseline." The trademark 'Gasoline,' however, was never registered, and thus became generic.

Gasoline was also used in kitchen ranges and for lighting, and is still available in a highly-purified form ('camping fuel' is one term) for use in lanterns and stoves used by outdoorsmen.

During the Franco-Prussian War of 1870–71, pétrole was stockpiled in Paris for use against a possible Prussian attack on the city. Later in 1871, during the revolutionary Paris Commune, rumours spread around the city of pétroleuses, women using bottles of petrol to commit arson against city buildings.

It is also used as a psychoactive inhalant.

Etymology
The word "gasolene" was coined in 1865 from the word gas and the chemical suffix -ine/-ene. The modern spelling was first used in 1871. The shortened form "gas" was first recorded in American English in 1905. Gasoline originally referred to any liquid used as the fuel for a gasoline-powered engine, other than diesel fuel or liquefied gas. Methanol racing fuel would have been classed as a type of gasoline.

The word "petrol" was first used in reference to the refined substance as early as 1892 (it previously referred to unrefined petroleum), and was registered as a trade name by English wholesaler Carless, Capel & Leonard. Although it was never officially registered as a trademark, Carless's competitors used the term "Motor Spirit" until the 1930s.

Bertha Benz used chemist shops to purchase the gasoline for her famous drive from Mannheim to Pforzheim in 1888. In Germany, gasoline is called Benzin. The usage does not derive from Bertha Benz, but from the chemical benzene.

World War II and octane ratings

World War II Germany received nearly all of its oil from Romania and set up huge distilling plants to produce gasoline from coal. In the US the oil was not "as good" and the oil industry had to invest heavily in various expensive boosting systems. This turned out to have benefits: the US industry started delivering fuels of increasing octane ratings by adding more of the boosting agents and the infrastructure was in place for a post-war octane agents additive industry. Good crude oil was no longer a factor during wartime and by war's end, American aviation fuel was commonly 130 to 150 octane. This high octane could easily be used in existing engines to deliver much more power by increasing the pressure delivered by the superchargers. The Germans, relying entirely on "good" gasoline, had no such industry, and instead had to rely on ever-larger engines to deliver more power.

However, German aviation engines were of the direct fuel injection type and could use methanol-water injection and nitrous oxide injection, which gave 50% more engine power for five minutes of dogfight. This could be done only five times or after 40 hours run-time and then the engine would have to be rebuilt. Most German aero engines used 87 octane fuel (called B4), while some high-powered engines used 100 octane (C2/C3) fuel.

This historical "issue" is based on a very common misapprehension about wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being always greater. So, for example, a common British aviation fuel of the later part of the war was 100/125. The misapprehension that German fuels have a lower octane number (and thus a poorer quality) arises because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number for their fuels. Standard German high-grade aviation fuel used in the later part of the war (given the designation C3) had lean/rich octane numbers of 100/130. The Germans would list this as a 100 octane fuel while the Allies would list it as 130 octane.

After the war the US Navy sent a Technical Mission to Germany to interview German petrochemists and examine German fuel quality. Their report entitled Technical Report 145-45 Manufacture of Aviation Gasoline in Germany chemically analyzed the different fuels and concluded that "Toward the end of the war the quality of fuel being used by the German fighter planes was quite similar to that being used by the Allies".

Chemical analysis and production

Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend.

The bulk of a typical gasoline consists of hydrocarbons with between 5 and 12 carbon atoms per molecule.

Many of these hydrocarbons are considered hazardous substances and are regulated by OSHA. The MSDS (Material Safety Data Sheet) for unleaded gasoline shows at least fifteen hazardous chemicals occurring in various amounts from 5% to 35% by volume of gasoline. These include big names like benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1% by volume), trimethylbenzene (up to 7% by volume), MTBE (up to 18% by volume) and about 10 others. Ref: (Tesoro Petroleum Companies, Inc. [5])

The various refinery streams blended together to make gasoline all have different characteristics. Some important streams are:

Reformate, produced in a catalytic reformer with a high octane rating and high aromatic content, and very low olefins (alkenes).
Cat Cracked Gasoline or Cat Cracked Naphtha, produced from a catalytic cracker, with a moderate octane rating, high olefins (alkene) content, and moderate aromatics level. Here, "cat" is short for "catalyst".
Hydrocrackate (Heavy, Mid, and Light), produced from a hydrocracker, with medium to low octane rating and moderate aromatic levels.
Virgin or Straight-run Naphtha (has many names), directly from crude oil with low octane rating, low aromatics (depending on the crude oil), some naphthenes (cycloalkanes) and no olefins (alkenes).
Alkylate, produced in an alkylation unit, with a high octane rating and which is pure paraffin (alkane), mainly branched chains.
Isomerate (various names) which is obtained by isomerising the pentane and hexane in light virgin naphthas to yield their higher ocatane isomers.
(The terms used here are not always the correct chemical terms. They are the jargon normally used in the oil industry. The exact terminology for these streams varies by refinery and by country.)

Overall a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), aromatics and olefins (alkenes). The exact ratios can depend on

1. the oil refinery that makes the gasoline, as not all refineries have the same set of processing units.
2. the crude oil used by the refinery on a particular day.
3. the grade of gasoline, in particular the octane rating.

Currently many countries set tight limits on gasoline aromatics in general, benzene in particular, and olefins (alkene) content. This is increasing the demand for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce the benzene content.

Gasoline can also contain some other organic compounds: such as organic ethers (deliberately added), plus small levels of contaminants, in particular sulfur compounds such as disulfides and thiophenes. Some contaminants, in particular thiols and hydrogen sulfide, must be removed because they cause corrosion in engines.


Volatility

Gasoline is more volatile than diesel oil, Jet-A or kerosene, not only because of the base constituents, but because of the additives that are put into it. The desired volatility depends on the ambient temperature: in hotter climates, gasoline components of higher molecular weight and thus lower volatility are used. In cold climates, too little volatility results in cars failing to start. In hot climates, excessive volatility results in what is known as "vapour lock" where combustion fails to occur.

In the United States, volatility is regulated in large urban centers to reduce the emission of unburned hydrocarbons. In large cities, so-called reformulated gasoline that is less prone to evaporation, among other properties, is required. In Australia, the volatility limit changes every month and differs for each main distribution center, but most countries simply have a summer, winter and perhaps intermediate limit.

Volatility standards may be relaxed (allowing more gasoline components into the atmosphere) during emergency anticipated gasoline shortages. For example, on 31 August 2005 in response to Hurricane Katrina, the United States permitted the sale of non-reformulated gasoline in some urban areas, which effectively permitted an early switch from summer to winter-grade gasoline. As mandated by EPA administrator Stephen L. Johnson, this "fuel waiver" was made effective through 15 September 2005 . Though relaxed volatility standards may increase the atmospheric concentration of volatile organic compounds in warm weather, higher volatility gasoline effectively increases a nation's gasoline supply because the amount of butane in the gasoline pool is allowed to increase.

Octane rating

The most important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to premature detonation which causes knocking. It is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are a number of different conventions for expressing the octane rating therefore the same fuel may be labeled with a different number depending upon the system used.
(We will come back to this issue of octane later)

Energy content

Gasoline contains about 34.6 megajoules per litre (MJ/l) or 131 MJ/US gallon. This is an average, gasoline blends differ, therefore actual energy content varies from season to season and from batch to batch, as much as 4% more or less than the average, according to the US EPA.

A high octane fuel such as LPG has a lower energy content than lower octane gasoline, resulting in an overall lower power output at the regular compression ratio an engine ran at on gasoline. However, with an engine tuned to the use of LPG (ie. via higher compression ratios such as 12:1 instead of 8:1), this lower power output can be overcome. This is because higher-octane fuels allow for a higher compression ratio - this means less space in a cylinder on its combustion stroke, hence a higher cylinder temperature which improves efficiency according to Carnot's theorem, along with fewer wasted hydrocarbons (therefore less pollution and wasted energy), bringing higher power levels coupled with less pollution overall because of the greater efficiency.

The main reason for the lower energy content (per litre) of LPG in comparison to gasoline is that it has a lower density. Energy content per kilogram is higher than for gasoline (higher hydrogen to carbon ratio). The weight-density of gasoline is about 737.22 kg/m3.

Different countries have some variation in what RON (Research Octane Number) is standard for gasoline, or petrol. In the UK, ordinary regular unleaded petrol is 91 RON (not commonly available), premium unleaded petrol is always 95 RON, and super unleaded is usually 97-98 RON. However both Shell and BP produce fuel at 102 RON for cars with hi-performance engines. In the US, octane ratings in fuels can vary between 86-87 AKI (91-92 RON) for regular, through 89-90 (94-95) for mid-grade (European Premium), up to 90-94 (RON 95-99) for premium unleaded or E10 (Super in Europe).

Additives

Lead
The mixture known as gasoline, when used in high compression internal combustion engines, has a tendency to ignite early (pre-ignition or detonation) causing a damaging "engine knocking" (also called "pinging" or "pinking") noise. Early research into this effect was led by A.H. Gibson and Harry Ricardo in England and Thomas Midgley and Thomas Boyd in the United States. The discovery that lead additives modified this behavior led to the widespread adoption of the practice in the 1920s and therefore more powerful higher compression engines. The most popular additive was tetra-ethyl lead. However, with the discovery of the environmental and health damage caused by the lead, and the incompatibility of lead with catalytic converters found on virtually all US automobiles since 1975, this practice began to wane in the 1980s. Most countries are phasing out leaded fuel; different additives have replaced the lead compounds. The most popular additives include aromatic hydrocarbons, ethers and alcohol (usually ethanol or methanol).

In the U.S., where lead was blended with gasoline (primarily to boost octane levels) since the early 1920s, standards to phase out leaded gasoline were first implemented in 1973. In 1995, leaded fuel accounted for only 0.6 % of total gasoline sales and less than 2,000 tons of lead per year. From January 1, 1996, the Clean Air Act banned the sale of leaded fuel for use in on-road vehicles. Possession and use of leaded gasoline in a regular on-road vehicle now carries a maximum $10,000 fine in the United States. However, fuel containing lead may continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines until 2008. The ban on leaded gasoline led to thousands of tons of lead not being released in the air by automobiles, and resulted in lowering levels of lead in people's bloodstreams.[citation needed]

A side effect of the lead additives was protection of the valve seats from erosion. Many classic cars' engines have needed modification to use lead-free fuels since leaded fuels became unavailable. However, "Lead substitute" products are also produced and can sometimes be found at auto parts stores.

Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion, and to allow easier starting in cold climates.

In some parts of South America, Asia and the Middle East, leaded gasoline is still in use. Leaded gasoline was phased out in sub-Saharan Africa with effect from 1 January, 2006. A growing number of countries have drawn up plans to ban leaded gasoline in the near future.

MMT

Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used for many years in Canada and recently in Australia to boost octane. It also helps old cars designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems.

There are currently ongoing debates as to whether or not MMT is harmful to the environment and toxic to humans. However, US Federal sources state that MMT is suspected to be a powerful neurotoxin and respiratory toxin.

Dye

Sometimes dyes are added to fuel for identification. However there are different systems in use and this has led to confusion. In the United States the most commonly used aircraft gasoline, avgas, or aviation gas, is known as 100LL (100 octane, low lead) and is dyed blue. Red dye has been used for indentifying untaxed (non-highway use) agricultural diesel. The UK uses red dye to differentiate between regular diesel fuel, (often referred to as DERV), which is undyed, and diesel intended for agricultural and construction vehicles like excavators and bulldozers. Red diesel is still occasionally used on HGVs which use a separate engine to power a loader crane. This is a declining practice however, as many loader cranes are powered directly by the tractor unit.

Oxygenate blending

Oxygenate blending adds oxygen to the fuel in oxygen-bearing compounds such as MTBE, ethanol and ETBE, and so reduces the amount of carbon monoxide and unburned fuel in the exhaust gas, thus reducing smog. In many areas throughout the US oxygenate blending is mandatory. For example, in Southern California, fuel must contain 2% oxygen by weight. The resulting fuel is often known as reformulated gasoline (RFG) or oxygenated gasoline. The federal requirement that RFG contain oxygen was dropped May 6, 2006.

MTBE use is being phased out in some states due to issues with contamination of ground water. In some places it is already banned. Ethanol and to a lesser extent the ethanol derived ETBE are a common replacements. Especially ethanol derived from biomatter such as corn, sugar cane or grain is frequent, this will often be referred to as bio-ethanol. A common ethanol-gasoline mix of 10% ethanol mixed with gasoline is called gasohol or E10, and an ethanol-gasoline mix of 85% ethanol mixed with gasoline is called E85. The most extensive use of ethanol takes place in Brazil, where the ethanol is derived from sugarcane. Over 3,400 million US gallons (13,000,000 m³) of ethanol mostly produced from corn was produced in the United States in 2004 for fuel use, and E85 is fast becoming available in much of the United States. The use of bioethanol, either directly or indirectly by conversion of such ethanol to bio-ETBE, is encouraged by the European Union Biofuels Directive. However since producing bio-ethanol from fermented sugars and starches involves distillation, ordinary people in much of Europe cannot ferment and distill their own bio-ethanol at present (unlike in the US where getting a BATF distillation permit has been easy since the 1973 oil crisis.)


Health concerns

Many of the non-aliphatic hydrocarbons naturally present in gasoline (especially aromatic ones like benzene), as well as many anti-knocking additives, are carcinogenic. Because of this, any large-scale or ongoing leaks of gasoline pose a threat to the public's health and the environment, should the gasoline reach a public supply of drinking water. The chief risks of such leaks come not from vehicles, but from gasoline delivery truck accidents and leaks from storage tanks. Because of this risk, most (underground) storage tanks now have extensive measures in place to detect and prevent any such leaks, such as sacrificial anodes. Gasoline is rather volatile (meaning it readily evaporates), requiring that storage tanks on land and in vehicles be properly sealed. The high volatility also means that it will easily ignite in cold weather conditions, unlike diesel for example. Appropriate venting is needed to ensure the level of pressure is similar on the inside and outside. Gasoline also reacts dangerously with certain common chemicals; for example, gasoline and crystal Drāno (sodium hydroxide) react together in a spontaneous combustion.

Gasoline is also one of the sources of pollutant gases. Even gasoline which does not contain lead or sulfur compounds produces carbon dioxide, nitrogen oxides, and carbon monoxide in the exhaust of the engine which is running on it. Furthermore, unburnt gasoline and evaporation from the tank, when in the atmosphere, react in sunlight to produce photochemical smog. Addition of ethanol increases the volatility of gasoline.

Through misuse as an inhalant, gasoline also contributes to damage to health. Petrol sniffing is a common way of obtaining a high for many people and has become epidemic in many poorer communities such as with Indigenous Australians. In response, Opal fuel has been developed by the BP Kwinana Refinery in Australia, and contains only 5% aromatics (unlike the usual 25%) which inhibits the effects of inhalation.

Usage and pricing

The United States uses 360 million US liquid gallons (1.36 gigalitres) of gasoline each day. Western countries have among the highest usage rates per person. Some countries, e.g. in Europe and Japan, impose heavy fuel taxes on fuels such as gasoline. Because a greater proportion of the price of gasoline in the United States is due to the cost of oil, rather than taxes, the price of the retail product is subject to greater fluctuations (vs. outside the U.S.) when calculated as a percentage of cost-per-unit, but is actually less variable in absolute terms).

Stability

When gasoline is left for a certain period of time, gums and varnishes may build up and precipitate in the gasoline, causing "stale fuel." This will cause gums to build up in the cylinders and also the fuel lines, making it harder to start the engine. Gums and varnishes should be removed by a professional to extend engine life. Motor gasoline may be stored up to 60 days in an approved container. If it is to be stored for a longer period of time, a fuel stabilizer may be used. This will extend the life of the fuel to about 1-2 years, and keep it fresh for the next uses. Fuel stabilizer is commonly used for small engines such as lawnmower and tractor engines to promote quicker and more reliable starting.

TO BE CONT

[~JC~]

Octane rating

The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. It's a measure of anti-detonation of a gasoline or fuel.

Knock resistance

Engine knocking or 'pinking (pinging)' is compression detonation of fuel in the power stroke of the engine. Knocking occurs when the air-fuel mixture autoignites all at once (or sometimes perhaps when the flame front goes supersonic because of early ignition timing), before the flame front from spark plug ignition can reach it. The explosive reaction causes combustion to stop before the optimum timing, causing a decrease in performance. A fuel such as ethanol, with a high autoignition temperature that burns reasonably fast and thus does not need early ignition timing, will most often have high practical value knock resistance.

Definition of octane rating

Octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline, for example, has the same octane rating as a mixture of 87 vol-% isooctane and 13 vol-% n-heptane. This does not mean, however, that the gasoline actually should contain these chemicals in these proportions. It simply means that it has the same autoignition resistance as the described mixture.

A high tendency to autoignite, or low octane rating, is undesirable in a gasoline engine but desirable in a diesel engine. The standard for the combustion quality of diesel fuel is the cetane number. A diesel fuel with a high cetane number has a high tendency to autoignite, as is preferred.

Measurement methods

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-95 (regular) in Europe.

The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, Avgas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116). Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition.

Octane ratings above 100

By definition, the maximum octane number is 100, i.e. 100% of the solution. For substances with higher shock resistance, the octane performance (note: not octane number) is an extrapolation of the octane performance chart. Some sources mention adoption of the performance number (PN) scale in US in 1943. Anecdotal evidence suggests that before adoption of such widely accepted standard many producers assigned arbitrary numbers for everything above 100.

Examples of octane ratings

The octane ratings of n-heptane and iso-octane are exactly 0 and 100, by definition. For some other hydrocarbons, the following table gives the road octane numbers as stated in. See references for another source

2-methylheptane 23
n-hexane 25
2-methylhexane 44
1-heptene 60
n-pentane 62
1-pentene 84
n-butane 91
cyclohexane 97
benzene 101
toluene 112

Effects of octane rating

Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation (pre-ignition = engine knock) as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

A simple explanation is the carbon bonds contain more energy than hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content on a volume basis (per liter or per gallon). The reason for this is that ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl radical for a H hydrogen which transforms the gas ethane (C2H6) (which is an alkane) into ethanol (which is an alcohol). Note that to a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

In the case of alcohol fuels, like Methanol and Ethanol, since they are partially oxidized fuels they need to be run at much richer mixtures than gasoline. As a consequence the total amount of fuel burned per cycle counter balances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred max power air fuel mixture of 12.5:1, it will release approximately 19,000 BTU (about 20 MJ) of energy, where ethanol run at its preferred max power mixture of 6.5:1 will liberate approximately 24,400 BTU (25.7 MJ), and Methanol at a 4.5:1 AFR liberates about 27,650 BTU (29.1 MJ).

To account for these differences, a measure called the fuel's specific energy is sometimes used. It is defined as the energy released per air fuel ratio.

Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure, which is a function of elevation and weather conditions.

Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved.

Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers and thus demand high-octane premium gasoline.

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly false—engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal.

Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pin-point if you can examine a print-out of the power-output (torque values) of an engine. On a typical high-rev'ving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the cylinder is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark, for example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load then the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted or what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 1 inHg (11 kPa/km). An engine that might require 93 octane at sea level may perform at maximum on a fuel rated at 91 octane if the elevation is over, say, 1000 feet. See also the APC article.

The octane rating was developed by the chemist Russell Marker. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.

U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.



TO BE CONT:

[~JC~]

Projected Octane ratings for specific Compression ratios:

Compression ~ Octane Number ~ Brake Thermal Efficiency
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 %


Remember this statement earlier in your reading: Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark, for example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp).


Octane Mixing Chart

Gallons of 100 Octane Racing Gasoline (Across)
Gallons of 92 Octane Station Gasoline (Down)
~~~~~~1. 2. 3. 4. 5. 6. 7. 8. 9. 10.~~~~~~~~~
1. 96.0 97.3 98.0 98.4 98.7 98.9 99.0 99.1 99.2 99.3
2. 94.7 96.0 96.8 97.3 97.7 98.0 98.2 98.5 98.7 98.8
3. 94.0 95.2 96.0 96.6 97.0 97.3 97.6 97.8 98.0 98.2
4. 93.6 94.7 95.4 96.0 96.4 96.8 97.1 97.3 97.5 97.7
5. 93.3 94.3 95.0 95.6 96.0 96.4 96.7 96.9 97.1 97.3
6. 93.1 94.0 94.7 95.2 95.6 96.0 96.3 96.6 96.8 97.0
7. 93.0 93.8 94.4 94.9 95.3 95.7 96.0 96.3 96.5 96.7
8. 92.9 93.6 94.2 94.7 95.1 95.4 95.7 96.0 96.2 96.4
9. 92.8 93.5 94.0 94.5 94.9 95.2 95.5 95.8 96.0 96.2
10. 92.7 93.3 93.8 94.3 94.7 95.0 95.3 95.6 95.8 96.0

Note: for unleaded engines only, Sunoco 100 and Unocal 100 are the only recommended fuels. Older engines that were produced prior to unleaded fuel or more modern engines heavily modified to handle lead fuel. Then there are several options available to you from various Mfg.'s such as 110, 112, & 116 octane ratings... Also of importance do not be fooled into Avaition Fuel. Yes, it has a high octane rating but is designed to be used at alititude where the air is less dense & colder...

What about those little bottles of Octane Booster sold at Auto parts stores?

Do they work? Sure! The good ones do. First, let's take a look at what a good octane booster will do to your gasoline. Please make note of that word "good," because there is a lot of trash out there on the market...

Octane boosters can be broken into three types based on their active ingredients. Methyl cyclopentadienyl manganese tricarbonyl (MMT) and ferosene are used in limited amounts in off-the-shelf boosters. The majority of commercial boosters use MMT. Another type of booster uses alcohols or aromatics as the active ingredient. Many racers use toluene as a home-style octane booster. Toluene, an aromatic circular hydrocarbon chain, is a regular component of pump gas and is available in various grades at chemical supply stores. Premium street gasoline carries roughly 3- to 5% toluene, which partially helps octane characteristics. Unocal's 100-octane race gas has almost 25% toluene.

The drawback to any of these additive ingredients is the diminishing effect they have on higher-octane fuels. Adding the same booster to 87-octane pump gas will yield a lot more octane gain than adding a bottle to 91-octane premium gas. Excessive concentrations of these additives also damage emissions-control hardware, such as spark plugs, injectors, oxygen sensors and catalytic converters. This is why most off-the-shelf boosters have an emissions-legal street formulation and an off-road formulation that exceeds the government-regulated concentration of MMT or ferosene.


WILL OCTANE BOOSTERS ADD HORSEPOWER?

No. This is a misconception. Octane in itself does not add power. However, an engine that's forced to run on fuel with a lower octane than what's needed will run hot, detonate, and eventually lose power. The proper octane level will let the engine run to its full potential, but won't transform it into something special.

SIDE EFFECTS OF OCTANE BOOSTERS

Will attack plastics, rubbers and some fiberglass. Discolor and attack most paints. Foam filters will deteriorate if cleaned in a booster-carrying gasoline. So will the glues holding the filter together. Some oils are affected by octane boosters. Most normal oils are not bothered, but if you have any doubt about your favorite brand, check with the manufacturer, to play it safe. Two-stroke users have to pay particular attention to this. Can make an engine run rich. Rejetting may be necessary. Are toxic to the skin, and the fumes can make you sick. Exposure to air can cause a 50-percent breakdown in effectiveness. Ultraviolet rays - that's plain old sunlight- will make octane boosters deteriorate. Will attack gas tank sealants and could plug up your entire fuel system if used together. Cost a lot of money. NOW...THE GOOD SIDE Don't let all of that scare you. Octane boosters have a real place in the world today. Here are some of the good things they can do: Better throttle response. You can actually feel it. Gets better mileage. Also, you can often lean out the carb slightly when using octane boosters, which will give improved mileage. Best performance possible from your engine, short of using race gas. Reduce detonation and pinging. Clean out deposits. A good booster will actually let the engine run cleaner and inhibit carbon build-up. Acts as a gasoline stabilizer when the machine is left to sit for a period. Gas stores longer with a good octane booster in the fuel. Lets you use whatever gas is available at the time. A good booster doubles as an emulsifier and can keep small amounts of water in suspension. Fuel system condensation is a very real problem, especially when the machine sits for long periods of time between use.

HOW TO TELL A GOOD OCTANE BOOSTER FROM A POOR ONE

The market is loaded with octane additives. Here's one rule of thumb: if the product comes in a clear or transparent bottle, don't even consider it. Ultra violet rays cause deterioration.

There should be specific directions on the label, i.e., how much octane booster to use to how much gas. And, there should be a listing of how many numbers the octane will be raised per ounce of booster used to each gallon of gas. A good octane booster will raise a gallon of gas by two-and-a-half numbers with one ounce added. If the label isn't specific, don't bother with the product.

Consider the cost per ounce. You can get a good octane booster to add 2-1/2 numbers per ounce per gallon for around 30 cents per ounce. Some of the cheaper products might not be as efficient as the more expensive ones.

Make sure the label has a toxicity warning. If it isn't toxic, it isn't going to work. And if it is toxic and there's not a prominent warning, this borders on criminal negligence. Some of the better octane boosters are aniline, nitro benzine and toluene. Additives like acetone and sulfurs can be very corrosive.

Better octane boosters also have metal deactivators in them. This lessens the corrosive action of the additive on brass. And, as you know, all of your jets are made of brass, as are a number of parts in the carb and fuel system. Traces of brass can destroy volatilities in the gas.

Here are a couple of brands that have been tested and passed and can be truly called octane booster... many others out there are a waste of money!

1. (NOS) Racing Formula octane booster
2. Outlaw's Super Concentrated Octane Booster

A good rule of thumb in purchasing an Octane booster is to purchase as fresh a date as possible, it must be in a metal container and have either MMT, alcohols, or aromatics as its active ingredient... a Bottle (12oz) to 15 Gallons of 91 octane fuel is all you should need... This should give you exatly what you need for any engine boosted or not that runs below a 11.1 compression or running boost on turbo/supercharged engines of around 6-8 PSI. If your beyond that compression then Race fuel is your only option... and at last count thats running about $7 a gallon...


Thank you

Hope this has been insightful and the thread is now open for discussions.

[~JC~]

Sunoco 100

Sold at the Sunoco Station
1240 N Orlando Ave, Winter Park, FL
(407) 647-2828

Sunoco 112

Sold at Sunoco Station
9400 E Colonial Dr
Orlando, FL 32817
(407) 658-0468

[Skippy]

Wow, that is going to take a long time to read all of that lol.

[Stormin]

Hey Kyle, can you limit JC"s ability to cut & paste ?? My eyeballs are SORE ! :rof

Thanks for the info JC.