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Results from two separate emission test programs using a fifteen fuel test matrix in which ten key fuel properties were independently varied have shown that changes in gasoline distillation characteristics, olefin content and Reid vapor pressure (RVP) can produce major changes in total tailpipe exhaust emissions. All other variables examined, including oxygen content and aromatic content of the fuels, did not directly affect the tailpipe output of carbon monoxide, nitrogen oxides, or hydrocarbon emissions. From these results a generalized mathematical model was produced which predicts tailpipe emission changes from key fuel properties. The model was verified in a separate, 13 vehicle study.

The five noncyclic hexane homologs were mixed and tested for their octane qualities. The mixtures of normal hexane with the branched homologs, as well as a few of the combinations of branched species, had statistically significant higher octane quality than would be expected if the compounds responded in the CFR octane test engines as a linear combination of the individual components. It is hypothesized that this positive interaction is a reflection, of the formation of intermediates, via intermolecular hydrogen abstraction reactions, which are not able to progress along branching pathways during the combustion process. The formation of these intermediates delays the low temperature reaction kinetics, making the reaction mixture more knock resistant than expected.

In 1985 the U.S. Environmental Protection Agency instituted regulations which have ultimately limited the lead content of leaded gasolines to 0.1 grams of lead per gallon. There is currently very little test work on the potential for exhaust valve seat recession while running an engine with a cast iron head without hardened exhaust valve seats on gasoline at this lead level. Therefore, we have examined valve seat recession from low lead fuels. The test program described here evaluates test conditions and additives which can affect exhaust valve seat recession in mid-1960s vintage heads. Cylinder heads produced after the early 1970s had induction hardened exhaust valve seats and were not susceptible to exhaust valve seat recession. Specifically, tests were run in which lead, air/fuel ratio and engine hardware (valve rotators) were varied and evaluated for contribution to the valve recession process.