Gasoline is one of the most important fuels used for transportation. Most gasoline is used in engines that move automobiles and light trucks. Gasoline engines also power other vehicles and machines, including airplanes, motorboats, tractors, and lawn mowers. People in the United Kingdom and some other countries call gasoline petrol because it is made from petroleum.
The widespread use of gasoline began in the early 1900’s, when the mass production of cars started. Gasoline-powered cars made travel easier. People no longer had to live near their jobs, and they could reach remote vacation spots more easily. Gasoline-powered farm machinery allowed for improved crop production.
Through the years, the increasing use of gasoline gave rise to a gigantic industry employing millions of people. However, the use of gasoline has also caused serious problems. For example, transporting petroleum and the manufacture and use of gasoline contribute heavily to air and water pollution. To solve these problems, gasoline manufacturers are developing gasolines that cause less pollution.
Gasoline production
Gasoline can be produced by many processes, and it can be made from anything containing the two elements carbon and hydrogen. However, substances that contain additional elements must first be processed to separate out the hydrocarbons, organic compounds that contain only hydrogen and carbon. Gasoline is a blend of hydrocarbons, plus small amounts of other elements. Each hydrocarbon burns differently in an engine. See Hydrocarbon . Most gasoline is made by separating and chemically changing the different compounds in petroleum. This process is called refining. See Petroleum (Petroleum as a fuel) .
Some gasoline comes from the “natural” gasoline fraction (part) of petroleum. Gasoline manufacturers remove this natural gasoline, also called casinghead gasoline, from the petroleum. The refiners then blend the natural gasoline with gasoline produced using various refinery processes. The gasoline used in automobiles contains only a small proportion of natural gasoline.
Engine requirements.
Gasolines are made with different formulas because all engines cannot run smoothly on the same formula. Engines differ according to how much they compress (squeeze) the mixture of evaporated gasoline and air within their cylinders. High-compression engines squeeze the fuel and air more than low-compression engines do. When an engine compresses the gasoline and air mixture, the temperature of the mixture rises. In a process known as autoignition or preignition, the rise in temperature may ignite the gasoline before the piston is ready to receive the power from the burning gasoline. The gasoline mixture may explode suddenly, causing a “knocking” or “pinging” sound. This action wastes power and can damage an engine.
To run smoothly, a high-compression engine needs a gasoline more resistant to knocking than does a low-compression engine. A gasoline’s ability to resist knocking is called its antiknock quality. The octane number of a gasoline indicates the antiknock quality of the fuel.
As an automobile engine ages, deposits form in its combustion chamber. Such deposits cause engines to require gasoline with a higher octane number for knock-free operation. Thus, older cars often need higher-octane fuels.
Octane ratings.
Engineers determine a gasoline’s octane number by comparing its resistance to knocking with the antiknock performance of reference fuels. The reference fuels used to measure antiknock performance are mixtures containing two hydrocarbons called isooctane and normal heptane.
A gasoline’s octane number equals the percentage of isooctane in a reference fuel that has the same antiknock quality as the gasoline. For example, if a gasoline knocks as much as a reference fuel containing 90 percent isooctane, its octane number is 90. Octane numbers above 100 are measured with a reference fuel containing pure isooctane and chemical antiknock compounds, such as methylcyclopentadienyl manganese tricarbonyl (MMT).
Typically, automotive engineers measure octane number in two ways. Thus, every gasoline has two octane numbers: a research octane number (RON) and a motor octane number (MON). The RON is determined in a special one-cylinder engine in a laboratory. The MON is determined in the same test engine but under conditions more like those found in an ordinary engine. The RON is the higher of the two octane numbers. The MON is typically about 10 less than the RON. For example, a gasoline with a RON of 95 may have a MON of 85. The octane number quoted on the pump at a gas station is usually the average of the RON and the MON.
Gasoline blends.
Every brand of gasoline is a blend of different refinery streams (fluid refinery products) and additives. The blend changes daily, depending on refinery conditions, so that the gasoline has a constant octane number. Manufacturers also blend gasolines to make engines run better at various altitudes, in different climates, and during different seasons. For example, in summer or in hot climates, refiners prepare blends containing few hydrocarbons that boil at low temperatures. The summer heat turns such hydrocarbons into a vapor. If the gasoline contained too many of these hydrocarbons, the resulting vapor could cause vapor lock, an interruption in the flow of gasoline to the engine.
Gasoline additives.
Gasolines contain a number of additives. Special oxygen-containing chemicals called oxygenates make up one important group of additives. These chemicals have high research octane numbers and may make up as much as 85 percent of a gasoline. Oxygenates include such alcohols as ethanol, methanol, and isopropanol; and a group of compounds called ethers that include ethyl-tert-butyl ether (ETBE), methyl-tert-amyl ether (TAME), and diisopropyl ether (DIPE).
Gasolines also contain smaller amounts of a number of other additives. Antioxidants keep the gasoline from becoming gummy. Anti-icers prevent ice from clogging gas lines in winter. Antirust agents prevent tanks and fuel lines from rusting. Detergents and deposit modifiers clean off or prevent engine deposits caused by the burning of gasoline. Metal deactivators keep small amounts of metal impurities from changing the properties of the gasoline.
History
In the early days of the petroleum industry, during the late 1800’s, kerosene was by far the leading product of refineries. Refiners considered gasoline a useless by-product. The industry, when refining kerosene from crude oil, produced more gasoline than could possibly be used. Refineries threw away most of the gasoline. People used only small amounts of gasoline, then called stove naphtha, in cookstoves built to burn it.
Gasoline-powered automobiles
were first mass produced in 1908, and the demand for gasoline greatly increased. In 1913, refiners introduced a process that cracked (broke down) heavy fuel oils into the lighter ones that were used in gasoline.
As gasoline demand increased, industrialized countries imported more and more petroleum. In the early 1970’s, petroleum refiners had difficulty in meeting gasoline demand in many countries. In addition, political instability in the Middle East reduced the world’s petroleum production. To conserve gasoline, many countries reduced speed limits and encouraged their people to use public transportation. Manufacturers began to produce smaller cars with more fuel-efficient engines. For a time, such energy conservation efforts led to a lower demand for gasoline. But gasoline consumption rose again in the 1980’s.
Pollution control.
Many efforts have been made to control air pollution resulting from the exhaust fumes from gasoline engines. In the United States, the federal Clean Air Act of 1970 and amendments to the act in 1990 have led to many changes in the design of automobiles and the composition of gasoline. The 1970 act required sharp reductions of hydrocarbon and carbon monoxide emissions. To meet the emission standards, American automobile manufacturers in 1975 introduced devices called catalytic converters that reduce pollutants in automobile exhaust. At that time, tetraethyl lead, an antiknock compound, was widely used as an additive. Engines that burned tetraethyl lead released poisonous lead in their exhaust. The introduction of catalytic converters helped reduce lead emissions because cars with the converters required unleaded gasoline for the devices to function efficiently (see Catalytic converter ).
By the early 1980’s, all new U.S. cars had catalytic converters. Gasoline manufacturers eliminated lead in most gasoline consumed in the United States by the early 1990’s and added alcohols and ethers to increase octane ratings. Today, about 85 percent of all automobiles sold in the world have catalytic converters.
The 1990 amendments to the Clean Air Act ordered stricter regulations on motor vehicle emissions. They required retailers in areas with the worst carbon monoxide pollution to sell cleaner-burning gasolines. They also required that all gasolines sold contain detergents adequate to keep engines clean, so that cars maintained proper performance. In addition, the amendments encouraged the development of alternative clean fuels, such as liquefied natural gas and pure methanol, and the development of vehicles that produced extremely low emissions. In the early 2000’s, the U.S. gasoline industry began to phase out the use of methyl-tert-butyl ether (MTBE) after the widely used oxygenate was found in ground water.
Today, gasoline producers seek to reduce pollution by decreasing the amounts of certain toxic hydrocarbons, including compounds called olefins and aromatics, and the amounts of compounds containing sulfur. Reducing these chemicals lowers the octane number of gasoline, so the use of oxygenates to increase octane has become more important. High levels of oxygenates also help reduce the amount of carbon monoxide produced by burning gasoline, especially in older cars.
In the United States, the Environmental Protection Agency requires gasolines sold in many cities to contain high levels of oxygenates during cold weather months, when carbon monoxide problems are most serious. Many other countries, including Japan and most European nations, have made similar changes in the composition of gasoline.
