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The spark-ignited pre-chamber stratified combustion system is one of the most effective ways of expanding lean-burn ability and improving the performance of a natural gas engine. For these pre-chamber engines, the geometrical structure of orifices between the pre- and main chamber plays a significant role on the gas flow and flame propagation behaviors. The present study aims to investigate the effects of orifice number and diameter on combustion characteristics of a Shengdong T190 natural gas engine through CFD simulation. Various geometrical structures for the pre-chamber orifices were designed, offering variations in the number of orifices (4 to 8), and in the diameter of orifices (1.6mm to 2.9mm). A non-dimensional parameter β was employed to characterize the relative flow area of the orifices in the design. CFD simulations of combustion processes for these designs were carried out using a simplified chemical reaction kinetic mechanism for methane.

The intersecting hole nozzle, in which each orifice is formed by the converging of two or more child-holes, was proposed for the purpose of enhancing the internal turbulence in diesel nozzle, so as to promote the fuel atomization. In this paper, the internal flow characteristics of a cylindrical hole nozzle and two intersecting hole nozzles are studied by CFD simulation. The results show that, compared with conventional cylindrical hole nozzle, the internal flow of intersecting hole nozzles is characterized with slower rate of pressure decrease in the hole, none or very little cavitation, as well as about 20% to 30% higher discharge coefficients, especially under conditions of high injection pressure. Additionally, the setting of the blind hole as a disturbing domain in the intersecting hole nozzle results in more perturbation for internal flow, which will be beneficial for fuel atomization.