Performance and emissions of a pilot ignited direct injection natural gas engine operating at slightly premixed combustion mode

Due to the increased attention on energy saving and carbon emission reduction, the research on techniques for the improvement of engine efficiency has become more attractive. Slightly premixed combustion mode has been considered as an effective method for raising thermal efficiency. In this paper, the performance and emissions of a pilot ignited direct injection natural gas engine operating at slightly premixed combustion mode were evaluated by experiments and compared to those of mixing-limited combustion mode. The results indicated that brake thermal efficiency could be improved by up to 1.1% to 3.6% when slightly premixed combustion mode is utilized at different engine loads. At BMEP higher than 6.5 bar, adoption of slightly premixed combustion mode could cause NOx emissions to rise by more than 7.3% while at BMEP lower than 13.0 bar, significant increases in THC emissions may be accompanied. It is also revealed that using slightly premixed combustion mode could reduce CO emissions by more than 35.2% at BMEP higher than 6.5 bar and reduce soot emissions by more than 55.8% at all engine loads. Moreover, the effects of the injection parameters are highly dependent on engine load, which means that the trends for thermal efficiency and emissions are different at different engine loads.

Automated summary

This study evaluated the performance and emissions of a pilot ignited direct injection natural gas engine operating at slightly premixed combustion mode, finding that this mode can improve brake thermal efficiency and reduce CO and soot emissions at different engine loads. However, it also showed that NOx and THC emissions could be impacted by the adoption of slightly premixed combustion mode. The effects of injection parameters on engine performance were found to be highly dependent on engine load, leading to different trends in thermal efficiency and emissions.