Lean combustion and emission performance of a gasoline direct injection engine with active pre-chamber

Pre-chamber jet ignition technology can effectively improve flame propagation speed and in-cylinder combustion rate, so it is conducive to the improvement of thermal efficiency and fuel economy. While, studies on the key parameters of the influence of active pre-chamber on combustion and emissions are not systematic. The influence of the key parameters of injection control in active pre-chamber on combustion and emission is not clear at present. Thus, in this paper, an active pre-chamber jet ignition system was designed and used in a single cylinder GDI engine, and the effects of compression ratio and pre-chamber injection strategy on pre-chamber jet ignition were experimentally studied, as well as the comparison of pre-chamber jet ignition and conventional spark ignition. The results show that, at 2750 r/min, IMEP 11 bar operation point, lean burn can effectively reduce the fuel consumption and increase the thermal efficiency of gasoline engine. Adopting traditional spark plug system can extend the lean burn limit to excess air ratio of 1.5 with the gross indicated thermal efficiency (GITE) of 45% limited by unstable combustion, while resembling active pre-chamber system can achieve GITE of 46.5% with the excess air ratio of 2.0 with the help of much more stable combustion. And the NOx emission of active-pre-chamber system has been reduced by 78% compared by conventional spark plug system. Increasing the compression ratio to 14.8 can further reduce the indicated fuel consumption to 177 g/kWh, and increase the GITE to 48.5% and further reduce the NOx emission to lowest 0.53 g/kWh with the excess air ratio of 2.1. With the increase of pre-chamber injection pressure, the ignition stability increases, the combustion duration decrases, and thermal efficiency increases. With the increase of the pre-chamber injection duration, the ignition delay first decreases and then increases. When the injection duration increases to 800 μs, COV is greater than 3%. If the pre-chamber injection duration further increase, the COV increases, the combustion phasing retard, and the thermal efficiency decreases. With the increase of pre-chamber injection duration and pressure, the wetting wall fuel increases, which leads to the increase of PN emission.