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The removal of tetraethyl lead (TEL) from U.S. automotive gasoline has caused concern within the general aviation (GA) community because of possible legislated environmental or supply restrictions on TEL, an essential ingredient in existing high octane aviation gasolines (avgas). At the same time, the GA industry which was besieged by numerous product liability suits in the past has seen a resurgence since the passage of the GA Revitalization Act in 1994. Because aircraft typically remain in service for many years, the survival of the industry may well depend on the availability of a high octane unleaded gasoline that provides a safe level of power and antiknock performance to the existing fleet. This paper describes the tools and techniques used by one team to develop fuels that provide the required antiknock quality while meeting most of the other criteria of the existing specification for high octane avgas: ASTM D 910, Standard Specification for Aviation Gasolines.

The oxides of nitrogen (NOx) produced during combustion in an automobile engine play a major role in atmospheric chemistry and therefore need to be reduced by modifying vehicle engine designs and fuels of tomorrow. In a combustion chamber of a spark ignited engine, NOx is formed as atmospheric nitrogen competes with fuel molecules to couple with oxygen in the extremely hot burned gases behind the proceeding flame front (Zeldovich type) and as reactions occur directly in the combustion flame zone (“prompt” type). Since little nitrogen is present in the fuel, the fuel contribution to the overall NOx emissions is minor. Certain combustion chamber deposits have been shown to increase NOx emissions by thermally insulating the combustion chamber and taking up chamber volume, thus slightly increasing the compression ratio of the engine and raising the combustion gas temperature.

To gain a better understanding of the exhaust emissions impact of olefins in a low aromatic, full boiling range gasoline, an evaluation of the before and after catalyst emissions of three highly olefinic refinery streams and three highly paraffinic refinery streams, blended 50/50 in motor alkylate, was conducted using a 3.1 L GM engine. The test fuels were also selected to consider the effects of volatility in addition to olefin concentration. The fuels were evaluated under three steady state engine operating conditions. The results of the tests indicate essentially only small differences in the before and after catalyst total hydrocarbons (THC) between the pairs of highly olefinic streams and the highly paraffinic streams at relatively the same volatility level, for two of the test conditions (2400RPM-light and moderate/heavy loads. The ozone forming potentials (OFP) for these fuels, across all three speed and load conditions, also show relatively small differences.