SAE J312 pdf download
SAE J312 pdf download.Automotive Gasolines.
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 °C (86 to 437 °F). 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 hy&ocarbons in the gasoline boiling range; or
b. Convert low-octane hydrocarbons to high-octane hydrocarbons. The primary processes used by todays 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. lsomerization. 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 1 970s and 1 980s to replace the octane numbers lost by the requirement for unleaded gasoline in modem 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 ci 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 specitic performance features and have become increasingly important in late-model cars. Up to 10 vOI% ethanol and up to 15 vol% ethers are used as blending agents in gasoline, as discussed in Section 9.
3. Antiknock QuaIit114’’—The antiknock quality of an automotive gasoline is of pnme importance. If antiknock quality is too low, knock occurs. Knock results in a high-pitched metallic rapping noise. In addition to being audibly annoying, severe knock can cause burning of piston crowns and other engine damage. There is also evidence that knock increases the rate of engine wear. The potential durability, power, arid fuel economy of a given engine is realized only when the gasoline antiknock quality is adequate. However, except br some vehicles equipped with knock sensors, there is no advantage in using a gasoline having antiknock quality higher than the engine requires. Section 11 contains additional details on knock sensors and other engine design factors affecting octane number requirement.
Knock depends on complex physical and chemical phenomena highly interrelated with engine design, engine operating conditions, and atmospheric conditions. It has not been possible to completely characterize the antiknock performance 01 gasoline by a single measurement. The antiknock performance of a gasoline is intimately related to the engine in which it is used and to the engine and transmission operating conditions. Furthermore, this relationship varies from one engine design to another and will be different among engines 01 the same design due to normal production variations.
The antiknock quality of a gasoline is measured by several methods, These employ single-cylinder laboratory engines and more realistic, but much less precise, multicylinder engines in cars on the road. The American Society for Testing and Materials (ASTM) has standarzed the following two single-cylinder methods: ASTM D 2699 and ASTM D 2700.
Both of these test procedures employ a variable-compression-ratio engine. The Motor method operates at a higher speed and Inlet mixture temperature than does the Research method. They relate the knocking characteristics of a test gasoline to standard fuels, which are blends of two pure hydrocarbons—isooctane (2,2,4-trimethylpentane) and n-heplane. These blends are called primary reference fuels. By definition, the octane number of isooctane is 100 and the octane number of n-heptane is zero. At octane levels below 100, the octane number of a given gasoline is the percentage by volume of isooctane in a blend with n-heptane that knocks with the same intensity at the same compression ratio as the gasoline when compared by one of the standardized engine test methods. The octane number of a gasoline greater than 100 is based on the milliliters of tetraethyllead required to be added to isooctane to produce knock with the same intensity as the reference gasoline. The number of milliliters of tetraethyllead in isooctane is conveled to octane numbers greater than 100 by use of tables published by ASTM.
