AUTOMOTIVE AND GENERAL REPAIR PRODUCTS:GASOLINE.

GASOLINE

Gasoline is a mixture of petroleum hydrocarbons (organic molecules com- posed of carbon and hydrogen) that in general contain chains of four to twelve carbons. It is primarily used as a motor vehicle fuel, although it is also used as a solvent in industry. The first cars were fueled by kerosene, but they knocked and were notoriously unreliable and needed constant repair. Scientists realized that the premature ignition or knocking was attributable to vapors present in the hot engine. Gasoline from the distillation of coal tar eventually replaced kerosene as an automotive fuel, and when combined with antiknock agents such as tetraethyllead became a standard fuel for the automotive industry in the late 1930s. Concerns about environmental pollution from automobiles burning leaded gasoline paved the way for the unleaded gasoline formulations of the 1970s, and lead was completely removed from gasoline in the early 1990s with the advent of the Clean Air Act.

When gasoline is burned in an internal combustion engine, carbon di- oxide, water, and heat are produced. A gallon of gasoline contains approximately 13 million kilojoules of energy and is primarily made up of hydrocarbons with seven to eleven carbons. The gasoline vapor is ignited by the spark plug of the engine to drive the pistons, which transfer the energy to drive the automobile. Pollutants such as unburned gasoline hy- drocarbons as well as nitrogen-containing compounds are removed in the catalytic converter. The familiar octane number that consumers see at the gasoline pump refers to gasoline’s tendency to produce knocking in the engine. Isooctane is arbitrarily given a rating of 100 and n-heptane is given a rating of 0. When different hydrocarbons are blended or mixed with gasoline, the combustion in the cylinders of the engine is measured and compared with the octane scale. The higher the rating, the more efficient the combustion in the engine. Higher-octane gasolines are blended to produce very efficient combustion, which is why consumers pay more at the pump for high-octane gasoline.

Gasoline is extremely flammable in the liquid and vapor phases. It can accumulate a static charge through flow or agitation, potentially causing an explosion if the static is not dissipated. In addition to the physical hazards, gasoline is a carcinogen and causes central nervous system depression. The vapors are harmful if inhaled into the lungs. Coal tar also produces other fractions that include kerosene, diesel fuel, home heating oil, Vase- line, paraffin wax, and tar. These compounds all differ in the average length of their carbon chains, and their production depends on the frac- tional distillation of coal tar or crude oil.