燃气预喷对高压直喷天然气船机的影响研究

针对高压直喷(HPDI)天然气双燃料低速船机的燃料喷射系统,研究了不同的天然气预喷策略对发动机燃烧特性及性能的影响,探究了适用于低速船机燃烧系统的天然气喷气规律。利用计算流体力学(CFD)软件Converge建立了HPDI天然气双燃料的单缸机仿真模型,与试验数据进行标定后,计算得到了不同预喷间隔及预喷比例下发动机燃烧性能和排放数据。分析计算结果表明,预喷策略的采用影响了燃烧过程中预混燃烧的比例,从而影响了燃烧放热相位及燃烧等容度。预喷比例相比预喷间隔对燃烧过程的影响更显著,后者在较大预喷比例下才会明显影响缸内燃烧放热过程。合理优化预喷策略可控制预混燃烧程度,从而同时改善NOx排放和油耗。不同的预喷策略使得缸内碳烟分布区域不同;与无预喷算例相比,采用预喷策略的算例最终碳烟排放量偏高。

Influence of Gas Pre-Injection Strategies on Combustion and Emission Characteristics of a Pilot-Ignited High-Pressure Direct-Injection Natural Gas Marine Engine

For the fuel injection system of a pilot-ignited direct-injection natural gas engine, the influence of different natural gas pre-injection strategies on the combustion and emission characteristics of the engine was studied to explore the potential of natural gas pre-injection to improve the combustion system of low speed marine engines using a single-cylinder simulation model established by a Converge software. The combustion and emission data were verified by experiments and calculated at different pre injection intervals and pre-injection ratios. Results show that the use of pre-injection strategy affects the proportion of premixed combustion in the combustion process, thus affecting the exothermic phase and isovolumetric combustion. Moreover, the pre-injection ratio has a more significant influence on the combustion process than the pre-injection interval, and the latter only affects the combustion exothermic process at a larger pre-injection ratio. In terms of emissions, the optimized pre-injection strategy can control the premixed combustion so as to achieve simultaneous improvement of NOx and fuel consumption. On the other hand, different pre-injection strategies allow different soot distributions in the cylinder. Compared with non-pre-injection solution, the use of pre-injection strategies leads to higher soot emissions.