Influence of inlet pressure, EGR, combustion phasing, speed and pilot ratio on high load gasoline partially premixed combustion

The current research focuses in understanding how inlet pressure, EGR, combustion phasing, engine speed and pilot main ratio are affecting the main parameters of the combustion (e.g. efficiency, NOx, soot, maximum pressure rise rate) in the novel concept of injecting high octane number fuels in partially premixed combustion. The influence of the above mentioned parameters was studied by performing detailed sweeps at 32 bar fuel MEP (c.a. 16-18 bar gross IMEP); three different kinds of gasoline were tested (RON: 99, 89 and 69). The experiments were ran in a single cylinder heavy duty engine; Scania D12. At the end of these sweeps the optimized settings were computed in order to understand how to achieve high efficiency, low emissions and acceptable maximum pressure rise rate. The least square optimization analysis showed that for all the three fuels at this load it is possible to achieve gross indicated efficiency higher than 54 %, maximum pressure rise rate below 15 bar/CAD, NOx below 0.25 g/kWh and soot below 1.50 FSN. Depending on the fuel type, the targets were achieved by using 46-52 % of EGR, single injection, combustion phasing between 2 and 4 TDC and lambda between 1.54 and 1.58.