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The engine and its exhaust flow behaviors are investigated in a turbo-charged gasoline direct injection engine under simulated cold-fast-idle condition. The metrics of interest are the exhaust sensible and chemical enthalpy flows, and the exhaust temperature, all of which affect catalyst light off time. The exhaust sensible enthalpy flow is mainly a function of combustion phasing; the exhaust chemical enthalpy flow is mainly a function of equivalence ratio. High sensible and chemical enthalpy flow with acceptable engine stability could be obtained with retarded combustion and enrichment. When split injection is employed with one early and one later and smaller fuel pulse, combustion retards with early secondary injection in the compression stroke but advances with late secondary injection. Comparing gasoline to E85, the latter produces a lower exhaust temperature because of charge cooling effect and because of a faster combustion.

The fuel effects on HCCI operation in a spark assisted direct injection gasoline engine are assessed. The low load limit has been extended with a pilot fuel injection during the negative valve overlap (NVO) period. The fuel matrix consists of hydrocarbon fuels and various ethanol blends and a butanol blend, plus fuels with added ignition improvers. The hydrocarbon fuels and the butanol blend do not significantly alter the high or the low limits of operation. The HCCI operation appears to be controlled more by the thermal environment than by the fuel properties. For E85, the engine behavior depends on the extent that the heat release from the pilot injected fuel in the NVO period compensates for the evaporative cooling of the fuel.