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Fuel-air mixing in a direct-injection SI engine was studied to further improve full-load torque output. The fuel-injection location of DI vs. PFI results in different heat sources for fuel evaporation, hence a DI engine has been found to exhibit higher volumetric efficiency and lower knocking tendency, resulting in higher full-load torque output [1]. The ability to change injection timing of the DI engine affects heat transfer and mixture temperature, hence later injection results in lower knocking tendency. Both the higher volumetric efficiency and the lower knocking tendency can improve engine torque output. Improving volumetric efficiency requires that the fuel is injected during the intake stroke. Reducing knocking tendency, in contrast, requires that the fuel is injected late during the compression stroke. Thus, a strategy of split injection was proposed to compromise the two competing requirements and further increase direct-injection SI engine torque output.

For several years, a single-cylinder, spark-ignited engine without catalyst has been operated at Ford on single-component fuels that are constituents of gasoline as well as on simple fuel mixtures. This paper presents a review of these experiments as well as others pertinent to understanding hydrocarbon emissions. The engine was run at four steady-state conditions which are typical of normal operation. The fuel structure and the engine operating conditions affected both the total HC emissions and the reactivity of these emissions for forming photochemical smog in the atmosphere. These experiments identified major precursor species of the toxic HC emissions benzene and 1,3-butadiene to be alkylated benzenes and either straight chain terminal olefins or cyclic alkanes, respectively. In new data presented, the primary exhaust hydrocarbon species from MTBE combustion is identified as isobutene.

Multidimensional modeling is used to study air-fuel mixing in a direct-injection spark-ignition engine. Emphasis is placed on the effects of the start of fuel injection on gas/spray interactions, wall wetting, fuel vaporization rate and air-fuel ratio distributions in this paper. It was found that the in-cylinder gas/spray interactions vary with fuel injection timing which directly impacts spray characteristics such as tip penetration and spray/wall impingement and air-fuel mixing. It was also found that, compared with a non-spray case, the mixture temperature at the end of the compression stroke decreases substantially in spray cases due to in-cylinder fuel vaporization. The computed trapped-mass and total heat-gain from the cylinder walls during the induction and compression processes were also shown to be increased in spray cases.