Numerical Investigation into Effects of Fuel Physical Properties on GCI Engine Performance and Emissions

In this study, the effects of eight physical fuel properties on gasoline compression ignition (GCI) combustion and emissions are computationally investigated. The examined properties are density, heat of vaporization, surface tension, viscosity, specific heat of capacity, Reid vapor pressure, thermal conductivity, and critical temperature. Here, the effects of these properties on indicated specific fuel consumption, 50% burn (CA.50), maximum pressure rise rate, maximum pressure (P-max), specific NOx, specific hydrocarbons, and filter smoke number emissions are studied using a multidimensional computational fluid dynamics (CFD) code. Two different engine load points are studied in this work. The first is a partially premixed low-load case (6 bar indicated mean effective pressure (IMEP)) where different starts of injection (SOIs) are tested. The second is a high-load 20 bar IMEP engine operating point at a fixed SOI. The numerical CFD spray, combustion, turbulence, heat transfer, and evaporation models are calibrated using low-load engine and spray experimental data. At low-load engine operating conditions, it is found that most of the physical properties affect the combustion and emissions at different magnitudes. In general, density, heat of vaporization, critical temperature, specific heat of vaporization, and viscosity are the most influential physical properties at these low-load conditions. At high-load conditions, the effects of the physical properties on the engine combustion and emissions are considerably lower compared with those at low load. Similar to low-load conditions, the density is the most influential among the other physical properties. A detailed analysis is performed to explain how the different physical properties affect the combustion and emissions in the GCI engine operation mode.