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The effects of augmented mixing through the use of an auxiliary gas injection (AGI) were investigated in a direct-injection gasoline engine operated at a 22:1 overall air-fuel ratio, but with retarded injection timing such that the combustion was occurring in a locally rich mixture as evident by the elevated CO emissions. Two AGI gas compositions, nitrogen and air, were utilized, the gas supply temperature was ambient, and a wide range of AGI timings were investigated. The injected mass was less than 10% of the total chamber mass. The injection of nitrogen during the latter portion of the heat release phase resulted in a 25% reduction in the CO emissions. This reduction is considered to be the result of the increased mixing rate of the rich combustion products with the available excess air during a time when the temperatures are high enough to promote rapid oxidation.

The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high-speed engines. The overly lean overall air-fuel ratio (Φ≺0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single-cylinder engine based on a production General Motors 1.9L 4-cylinder high-speed diesel engine.