SAE J312-2001 Automotive Gasolines

Foreword-Automotive gasolines are used to fuel internal combustion spark-ignition engines. While gasolines discussed herein are used primarily in passenger car and highway truck service, they are also used extensively inoff-highway utility vehicles and farm machinery, two-stroke and four-stroke cycle marine engines, and other spark-ignition engines employed in a variety of different service applications.
Automotive gasolines are essentially blends of numerous hydrocarbons derived from petroleum. To produce gasoline, refiners initially use fractional distillation of the crude oil to segregate those hydrocarbons in the gasoline boiling range, with finished gasolines encompassing a boiling range of about 30 to 225℃ (86 to 437℉). They then use various processes to:
a. Increase the yield of gasoline from a barrel of crude oil by converting larger-molecule(higher-boiling) and smaller-molecule(lower-boiling) hydrocarbons to hydrocarbons in the gasoline boiling range; or
b. Convert low-octane hydrocarbons to high-octane hydrocarbons. The primary processes used by today's refiners are:
1. Catalytic cracking, which converts higher-boiling hydrocarbons into hydrocarbons in the gasoline boiling range.
2. Reforming, which converts low-octane hydrocarbons to higher-octane hydrocarbons.
3. Alkylation, which converts gaseous hydrocarbons to high-octane liquid hydrocarbons.
4. Isomerization, which upgrades the octane quality of light straightrun gasoline by converting straight-chain paraffins to their branched-chain isomers.
5. Hydrocracking, in which cracking occurs in the presence of both hydrogen and a catalyst, to produce a less olefinic gasoline component.
Reforming was increasingly used during the 1970s and 1980s to replace the octane numbers lost by the requirement for unleaded gasoline in modern automobiles and the resulting reduction and eventual elimination of lead antiknock usage. Oxygenates such as ethanol and methyl tertiary-butyl ether(MTBE) are now contributing significant octane benefits. In 1995, the U.S. gasoline pool consisted of approximately 35% reformate,34% catalytic crackate,12% alkylate,6% isomerate,6% butanes,3% MTBE,2% light straightrun,1% hydrocrackate, and 1% ethanol.(The term"pool"is often used to refer to the total of all gasoline produced in the country.)
Gasolines are blended to satisfy diverse automobile requirements. Antiknock rating, volatility, and other properties are balanced to provide satisfactory vehicle performance. Additives are used to provide or enhance specific performance features and have become increasingly important in late-model cars. Up to 10 vol% ethanol and up to 15 vol% ethers are used as blending agents in gasoline, as discussed in Section 9.

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