Simulation Research on Ultra-Lean Constant-Volume Combustion Initiated by Spark-Ignited Micro-Fuel-Jet 2022-01-0432

In the ultra-lean combustion mode, the combustion temperature is relatively low, which is expected to avoid the high-temperature NOx generation. And it also can use excess air to fully oxidize CO, HC and Soot, to achieve cleaner combustion. But at the same time, ultra-lean combustion has difficulties in ignition and flame propagation.

This paper used CONVERGE to simulate the combustion process and products of a new ultra-lean combustion mode, which ignited the ultra-lean premixed fuel/air mixture with the spark-ignited micro-fuel-jet, in a constant-volume vessel with a 6-hole GDI injector. The differences of combustion processes and products were simulated for two spark-ignition positions, including ‘on’ the micro-jet spray and ‘between’ two micro-jet sprays. It was found that the combustion duration (the time for burned-fuel-ratio from 10% to 90%) could be shortened by about 14.3% if igniting ‘on’ the micro-jet spray, but the amount of NO_x generated would increase about 21.0%. Meanwhile, compared with the homogeneous premixed combustion with traditional spark ignition at the same global fuel/air ratio, the new ultra-lean combustion mode with igniting ‘on’ the micro-jet spray had lower CO and NO_x emissions, reduced by 49.5% and 23.3% respectively. In addition, the three ultra-lean ignition methods all have extremely low Soot products. The heat release of this new mode was more concentrated with combustion duration shortened by about 20.2%, which would be beneficial to achieve more efficient and cleaner combustion.