Effects of In-Cylinder Mixing on Low Octane Gasoline Compression Ignition Combustion

Gasoline compression ignition (GCI) engines have been considered an attractive alternative to traditional spark ignition engines. Low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and in the volatility range of gasoline fuels. In this study, we have investigated the effect of different injection timings at part-load conditions using light naphtha stream in single cylinder engine experiments in the GCI combustion mode with injection pressure of 130 bar. A toluene primary reference fuel (TPRF) was used as a surrogate for the light naphtha in the engine simulations performed here. A physical surrogate based on the evaporation characteristics of the light naphtha has been developed and its properties have been implemented in the engine simulations. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from -50° to -11 ° CAD aTDC. The effect of SOI on mixing and combustion phasing was investigated using detailed equivalence ratio-temperature maps and ignition delay times. Both experimental and computational results consistently showed that an SOI of -30° CAD aTDC has the most advanced combustion phasing (CA50), with the highest NOx emission. The effects of the SOI on the fuel containment in the bowl of the piston, the ignition delay time, combustion rate and emissions have been carefully examined through the CFD calculations. It was found that the competition between the equivalence ratio and temperature is the controlling parameter in determining the combustion phasings.