Parametric Study to Optimize Gasoline Compression Ignition Operation under Low Load Condition Using CFD 2021-01-0440

The effects of intake pressure (P_in), start of injection (SOI), injection pressure (P_inj), injection split ratio (Qsplit), internal and external exhaust gas recirculation rates were varied to optimize several key parameters at a partially pre-mixed combustion low load/low speed condition using CFD. These include indicated specific fuel consumption (ISFC), combustion phasing (CA50), maximum rate of pressure rise (MRPR), maximum cylinder pressure (P_max), indicated specific NOx (sNOx), indicated specific hydrocarbons (sHC) and Filter Smoke Number (FSN) emissions. Low-load point (6 bar indicated mean effective pressure (IMEP), 1500 revolutions per minute (RPM)) was selected where P_in varied between 1.25 and 1.5 bar, SOI between -100 and -10 crank angle degree (CAD) after top dead center (aTDC), P_inj between 100 and 200 bar, split ratio between 0 and 0.5, EGR between 0 and 45% and internal EGR measured by rebreathing valve height was varied between 0 and 4.5 mm.

The study concluded that both internal and external exhaust gas recirculation along with moderate intake pressure and relatively early SOIs (-70 to -40 CAD aTDC) were necessary to realize acceptable combustion performance while meeting the emissions targets at this speed/load point.