Influences of High Swirl Ratio on the Nature Gas/Air Mixing and Combustion of a Low-Speed Dual-Fuel Marine Engine
Taking a X92DF super large-bore low-speed two-stroke dual-fuel marine engine as the research object,the nature gas/air mixing process and combustion characteristics were analyzed based on the three-dimensional numerical simulation method,and the influence of in-cylinder swirl intensity of scavenging and combustion processes on mixing quality and flame propagation was studied.The results showed that the abnormal combustion occurs in the local high concentration area due to the uneven distribution of the in-cylinder mixture concentration before the top dead center(TDC),leading to obvious pressure oscillation in the cylinder.By analyzing the influences of different swirl intensities on the mixed quality of natural gas/air in the cylinder,it is suggested that the area of high concentration of natural gas before TDC is obviously reduced with the increase in swirl intensity of scavenging process and the mixed quality of natural gas and air is improved.Meanwhile,the jet flame formed by the prechambers are propagated in the main combustion chamber and the combustion speed of the natural gas in the cylinder is accelerated with the increase of the swirl intensity in the cylinder.Further analysis shows that the improvement of the mixing quality in the cylinder effectively avoids the occurence of the local abnormal combustion and reduces the pressure oscillation.Finally,a strategy of improving mixture quality and reducing pressure oscillation is proposed,which provides a certain theoretical basis for the popularization of liquefied natural gas on the marine engine.
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