Gasoline is a mixture of liquid hydrocarbons distilled from crude oil that is used as a fuel for internal-combustion engines. Gasoline was invented after discovery of crude oil in the late 1850s when various refining processes were developed to make the oil useable. Early types of gasoline were produced as a byproduct of the process used to make kerosene fuel for oil lamps. Since this was before the development of the internal combustion engine, much of this early gasoline was discarded because no one had any use for it.
When the automobile was invented, a new market was created for gasoline. At first, automobile engines used "straight-run" gasoline--the natural gasoline fraction produced by distilling crude oil--a process that removes gasoline from other compounds in crude oil.But this process alone yielded less than 15 barrels of gasoline from each barrel of oil. After the mass production of cars began in 1908, oil refiners could not keep up with the growing demand for gasoline. In 1913, just in time for World War I, a process was invented to increase the amount of gasoline produced from crude oil. William Burton, who worked for Standard Oil of Indiana, developed thermal cracking, a process by which heavy hydrocarbons are broken down by heat and pressure into the lighter compounds used in gasoline. Since Burton's discovery, this basic process has been greatly improved. During the 1930s, catalysts were introduced to promote chemical reactions during cracking. Catalysts such as aluminum, platinum, processed clay, and acids are added to petroleum to break down larger molecules so that it will possess the desired compounds of gasoline. Besides increasing gasoline yields, catalytic cracking produces a higher quality gasoline than does thermal cracking.
During World War II catalytic cracking and other new refining processes greatly increased the United States' output of gasoline. More than 80% of the aviation fuel used by the Allies during the war was supplied by the United States. In Europe, gasoline became extremely scarce, and the German army had to rely on cruder types of gasoline that were produced from coal and heavy oil. The hydrogenation process for making this fuel had been developed in the 1920s by Friedrich Bergius, a German chemist who later fled his native country. A similar process developed in 1923 is called Fischer-Tropsch synthesis, which produces gasoline and other liquids from coal-derived synthesis gas (hydrogen and carbon monoxide). Gasoline can be made from just about any substance containing hydrogen and carbon.
Today's gasolines are blended from hundreds of hydrocarbons, and different combinations are produced to meet the needs of different engines. For example, engines vary in how hard they compress the fuel mixture of gasoline vapor and air. Although higher compression improves the engine's performance, it can also cause the gasoline to ignite too soon, creating a metallic "knocking" or pinging sound in the engine. This means that the engine is not burning fuel efficiently, and severe knocking can actually damage the engine. A gasoline's resistance to knocking is measured by its octane rating; if the gasoline's performance is 90% as good as that of a reference fuel (pure iso-octane), it gets an octane number of 90. In the early 1900s, engine knock was recognized as a problem, and the auto industry began searching for a fuel that could withstand high pressures without knocking. While engineers experimented with different engine designs, chemists explored "additives"--substances that could be added to gasoline to prevent knocking. In 1921, a team of American chemists led by Thomas Midgley, Jr. and T. A. Boyd made a spectacular breakthrough at General Motors. After much trial and error, Midgley began a systematic study of promising compounds, based on the position of each compound's elements on the periodic table. "What had seemed at times a hopeless quest," he recalled, "rapidly turned into a fox hunt. Predictions began fulfilling themselves instead of fizzling." The essential compound turned out to be tetraethyl lead. When added to gasoline in minute amounts, tetraethyl lead prevents engine knock and increases the gasoline's octane rating. From 1920-1950, gasoline octane numbers increased from 55 to 85, allowing automakers to nearly double engine performance by using higher internal pressures.
Unfortunately, tetraethyl lead pollutes the air with poisonous lead compounds when the gasoline is burned, and today leaded gasoline is being phased out. Instead, new engines have been designed to run on lower octane gasoline, which is made of hydrocarbons that are resistant to knock. New additives have also been formulated to increase the octane numbers of unleaded gasoline. Other modern additives preserve fuel quality and prevent rust, ice, and deposits of burned solids in the engine and fueling system.Antioxidants are added to prevent the formation of gum in the engine. Gum is a resin formed in gasoline that can coat the internal parts of the engine and increase wear. During the 1970s, leaded gasoline became associated with another problem. When lead is present in exhaust fumes, it ruins the car's anti-pollution equipment. In 1970, the government required automakers to sharply reduce emissions of carbon monoxide and "unburned" hydrocarbons that are produced when the engine is out of tune. To meet these standards, automakers introduced catalytic converters--devices that are attached to the exhaust system just behind the manifold. Most converters use platinum or palladium metal catalysts that convert carbon monoxide and hydrocarbons to carbon dioxide and water vapor. The catalysts are easily poisoned by lead, however, which clogs their reactive surfaces. That is why most cars must now use unleaded gasoline.
The abundance of gasoline in the United States through most of the twentieth century has made many aspects of life convenient and pleasurable. People are able to travel greater distances to get to their jobs or to go on vacation. Farmers are able to produce more food by using gasoline-fueled machinery. But by the early 1970s, consumption of gasoline had grown so enormously that oil refiners began depending on imported oil. When foreign oil supplies were disrupted, gasoline supplies suddenly became limited. People waited for hours to fill up their tanks at service stations and gasoline prices skyrocketed from less than 40 cents a gallon to more than a dollar. Since then, automakers have introduced smaller cars that use less fuel. It was the gasoline shortages of the 1970s that made compact Japanese cars popular in the United States for the first time. For a time, the government also encouraged people to conserve gasoline by using public transportation, and states reduced highway speed limits. During the 1980s, these conservation measures were neglected, and higher speeds are now allowed on some stretches of highway. However, the government still requires automakers to continue increasing fuel economy and reducing pollutant emissions.
In the 1990s, concern about pollution is even greater and cleaner-burning gasoline formulas have been developed to meet increasingly stringent clean-air standards. These reformulated gasolines contain either corn-derived ethanol or natural-gas derivatives such as MTBE (methyl tertiary butyl ether). Both additives increase the oxygen content of the gasoline which causes it to burn more cleanly and evaporate more slowly. Another recent antipollution measure requires service stations to control the gasoline vapors released into the atmosphere during fueling operations. This involves anti-evaporation equipment which is built into the gas pumps.
This is the complete article, containing 1,193 words
(approx. 4 pages at 300 words per page).
