Gasoline

Gasoline or petrol is a liquid mixture primarily used as fuel in internal combustion engines. It is petroleum-derived, and consists mostly of aliphatic hydrocarbons, enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene to increase its octane rating.
Gasoline is a mixture of hydrocarbons, although some may contain significant quantities of ethanol and some may contain small quantities of additives such as methyl tert-butyl ether as anti-knock agents to increase the octane rating or as an oxygenate to reduce emissions. The hydrocarbons consist of a mixture of n-paraffins, naphthenes, olefins and aromatics. Naphthenes, olefins and aromatics increase the octane rating of the gasoline whereas the n-paraffins have the opposite effect.Most current or former Commonwealth countries use the term "petrol", abbreviated from petroleum spirit. In North America, the word "gasoline" is the common term, where it is often shortened in colloquial usage to simply "gas." It is not a genuinely gaseous fuel (unlike, for example, liquefied petroleum gas, which is stored under pressure as a liquid, but returned to a gaseous state before combustion). The term petrogasoline is also used.
In aviation, mogas, short for motor gasoline, is used to distinguish automobile fuel from aviation gasoline, or avgas. In British English, "gasoline" can refer to a different petroleum derivative historically used in lamps, but this usage is relatively uncommon.

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" for gasoline was first recorded in American English in 1905 and is often confused with the older words gas and gases that have been used since the early 1600s.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 in 1892 (it was previously used to refer to unrefined petroleum), and was registered as a trade name by British wholesaler Carless, Capel & Leonard at the suggestion of Frederick Richard Simms.Carless's competitors used the term "motor spirit" until the 1930s, but never officially registered it as a trademark.It has also been suggested that the word gasoline was coined by Edward Butler in 1887.

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 in the United States by Occupational Safety and Health Administration. The Material Safety Data Sheet for unleaded gasoline shows at least fifteen hazardous chemicals occurring in various amounts. These include 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 ten others.The various refinery streams blended together to make gasoline all have different characteristics.

Density

The density of gasoline is 0.71–0.77 kg/l (0.71–0.77 g/cm3),(in English units, approx. 0.026 lb/cu in or 6.073 lb/U.S. gal or 7.29 lb/imp gal) which means it floats on water. This may be advantageous in the event of a spill. It is flammable and can burn while floating over water.
As an example, 65l of mogas (the maximum allowed in microlight aircraft in some countries) weighs about 50kg. This is a significant proportion of the payload: an Ikarus C42 has an empty weight of 270kg, so with full fuel the passenger(s) and any baggage must total no more than 130kg (290 lb).

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 final control of volatility is often achieved by blending with butane. The Reid Vapor Pressure (RVP) test is used to measure the volatility of gasoline. 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, because the liquid fuel has changed to a gaseous fuel in the fuel lines, rendering the fuel pump ineffective and starving the engine of fuel.
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 summer petrol volatility limits are set by State Governments and vary between capital cities. 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

An important characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to the abnormal combustion phenomenon known as pre-detonation (also known as knocking, pinging, spark knock, and other names). Deflagration is the normal type of combustion. Octane rating 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.
The octane rating became important in the search for higher output powers from aero engines in the late 1930s and the 1940s as it allowed higher compression ratios to be used.

World War II and Octane Ratings

During World War II, Germany received much of its oil from Romania. From 2.8 million barrels (450,000 m3) in 1938, Romania’s exports to Germany increased to 13 million barrels (2,100,000 m3) by 1941, a level that was essentially maintained through 1942 and 1943, before dropping by half, due to Allied bombing and mining of the Danube. Although these exports were almost half of Romania’s total production, they were considerably less than what the Germans expected. Even with the addition of the Romanian deliveries, overland oil imports after 1939 could not make up for the loss of overseas shipments. In order to become less dependent on outside sources, the Germans undertook a sizable expansion program of their own meager domestic oil pumping. After 1938, the Austrian oil fields were made available, and the expansion of Nazi crude oil output was chiefly concentrated there. Primarily as a result of this expansion, the Reich's domestic output of crude oil increased from approximately 3.8 million barrels (600,000 m3) in 1938 to almost 12 million barrels (1,900,000 m3) in 1944. Even this was not enough.
Instead, Germany had developed a synthetic fuel capacity that was intended to replace imported or captured oil. Fuels were generated from coal, using either the Bergius process or the Fischer-Tropsch process. Between 1938 and 1943, synthetic fuel output underwent a respectable growth from 10 million barrels (1,600,000 m3) to 36 million. The percentage of synthetic fuels compared with the yield from all sources grew from 22% to more than 50% by 1943. The total oil supplies available from all sources for the same period rose from 45 million barrels (7,200,000 m3) in 1938 to 71 million barrels (1.13E+7 m3) in 1943.
By the early 1930s, automobile gasoline had an octane reading of 40 and aviation gasoline of 75-80. Aviation gasoline with such high octane numbers could only be refined through a process of distillation of high-grade petroleum. Germany’s domestic oil was not of this quality. Only the additive tetra-ethyl lead could raise the octane to a maximum of 87. The license for the production of this additive was acquired in 1935 from the American holder of the patents, but without high-grade Romanian oil even this additive was not very effective. 100 octane fuel, designated either 'C-2' (natural) or 'C-3' (synthethic) was introduced in late 1939 with the Daimler-Benz DB 601N engine, used in certain of the Luftwaffe`s Bf 109E and Bf 109F single-engined fighters, Bf 110C twin-engined fighters, and several bomber types. Some later combat types, most notably the BMW 801D-powered Fw 190A, F and G series, and later war Bf 109G and K models, used C-3 as well. The nominally 87 octane aviation fuel designated 'B-4' was produced in parallel during the war.
In the USA 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 octane, and 150 octane was available in limited quantities for fighters from the summer of 1944. This high octane could easily be used in existing engines to deliver much more power by increasing the pressure delivered by the superchargers.
In late 1942, the Germans increased the octane rating of their high-grade 'C-3' aviation fuel to 150 octane. The relative volumes of production of the two grades B-4 and C-3 cannot be accurately given, but in the last war years perhaps two-thirds of the total was C-3. Every effort was being made toward the end of the war to increase isoparaffin production; more isoparaffin meant more C-3 available for fighter plane use.
A common misconception exists concerning wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being greater. The misunderstanding that German fuels had a lower octane number (and thus a poorer quality) arose because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number. Standard German high-grade 'C-3' aviation fuel used in the later part of the war had lean/rich octane numbers of 100/130. The Germans listed this as a 100 octane fuel, the Allies 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.”

Energy Content

Gasoline contains about 34.8 MJ/L or 132 MJ/US gallon. This is about 9.67 kWh/L or 36.6 kWh/US gallon. This is an average; gasoline blends differ, therefore actual energy content varies from season to season and from batch to batch, by up to 4% more or less than the average, according to the US EPA. On average, about 19.5 US gallons (16.2 imp gal/74 L) of gasoline are available from a 42-US-gallon (35 imp gal/160 L) barrel of crude oil (about 46% by volume), varying due to quality of crude and grade of gasoline. The remaining residue comes off as products ranging from tar to naptha.