高涡流比对低速双燃料船舶发动机天然气/空气混合及燃烧性能的影响

Influences of High Swirl Ratio on the Nature Gas/Air Mixing and Combustion of a Low-Speed Dual-Fuel Marine Engine

以X92DF超大缸径低速二冲程双燃料船用发动机为研究对象,基于三维数值计算分析了天然气和空气混合过程及燃烧特性,并研究了扫气和燃烧过程中缸内涡流强度对混合质量和火焰传播的影响。结果表明:由于上止点前缸内天然气和空气的混合气浓度分布不均,造成局部高浓度区域出现燃烧异常现象,导致缸内压力振荡幅度增大。通过分析不同涡流强度对缸内天然气/空气的混合质量的影响可以得出,随着扫气过程中涡流强度的增大,上止点前缸内天然气高浓度区域面积明显减小,表明天然气和空气的混合质量得到明显提高。同时,随着缸内涡流比的增加,加快了预燃室射流火焰在主燃烧室内的传播速度和缸内天然气的燃烧速度。进一步研究得出缸内混合质量的提高可以有效地避免局部异常燃烧现象和降低压力振荡。最后,提出一种改善缸内混合质量和减小压力振荡的策略,为液态天然气在船机上的普及提供了一定了理论基础。

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.