Abstract The objective of this study is to optimize the performance of a direct injection natural gas engine by using the newly developed many-objectives optimization genetic algorithm NSGA-III. A total number of 11 parameters are optimized simultaneously with respected to four optimization objectives, including the ISFC, NO, CH4 and Soot emissions. The main findings are as follows: More than half of the calculated cases in the Pareto front can meet the EURO V emission regulation. In addition, a larger EGR rate is needed in order to achieve a lower NO emission. The optimized natural gas spray angles are around 80° and 70°; the diesel spray angles are around 60°, 70° and 75°; the EGR rates are around 28% and 14%; the swirl ratios are around 1.6 and 0.5; the compression ratios are around 16.5 and 18.5; the azimuth angles are around −3° and 5°. The combustion modes of the optimized cases can be divided into three categories based on the difference between the natural gas and diesel injection timings. The high-temperature combustion regions in the NG PPCI (Partial Premixed Compression Ignition) combustion mode with open combustion chamber are widely distributed, which result in an obviously higher NO emission than the other combustion modes. However, its Soot emission is the lowest. For diesel PPCI and HPDI (High Pressure Direct Injection) combustion mode, the natural gas is mainly consumed through diffusion combustion. Therefore, the Soot emissions are relatively higher. However, as the ignition timing is postponed, their NO emissions are relatively lower.

中文翻译：

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不同燃烧模式下直喷天然气发动机的优化

摘要 本研究的目的是利用新开发的多目标优化遗传算法NSGA-III优化直喷天然气发动机的性能。针对四个优化目标，包括 ISFC、NO、CH4 和碳烟排放，同时优化了 11 个参数。主要发现如下： 在帕累托前沿计算的案例中，有一半以上可以满足欧五排放法规。此外，为了实现较低的 NO 排放，需要更大的 EGR 率。优化的天然气喷射角度在80°和70°左右；柴油喷射角度大约为60°、70°和75°；EGR率约为28%和14%；涡流比约为 1.6 和 0.5；压缩比约为 16.5 和 18.5；方位角约为 -3° 和 5°。根据天然气和柴油喷射时间的不同，优化案例的燃烧模式可以分为三类。NG PPCI（Partial Premixed Compression Ignition）燃烧室敞开式燃烧模式的高温燃烧区分布广泛，导致NO排放明显高于其他燃烧模式。然而，它的烟尘排放是最低的。对于柴油 PPCI 和 HPDI（高压直喷）燃烧模式，天然气主要通过扩散燃烧消耗。因此，烟尘排放量相对较高。然而，随着点火时间的推迟，它们的 NO 排放量相对较低。