Key Laboratory for Microstructural Material Physics of Hebei Province, School of Science, Yanshan University, Qinhuangdao, 066004, China.
School of Vehicle and Energy, Yanshan University, Qinhuangdao, 066004, China.
Chemosphere. 2022 Sep;303(Pt 3):135275. doi: 10.1016/j.chemosphere.2022.135275. Epub 2022 Jun 10.
The air-fuel mixture preparation in pilot spray-ignited natural gas engines is primarily dominated by piston bowl profiles and fuel injection strategy. Piston bowl geometry is regarded as the crucial point in controlling engine pollutant emissions. In the present work, the SAGE combustion model was applied coupled with a general reaction kinetic mechanism. The engine model was validated with experimental data achieved from a Cummins ISX 400 engine, and good agreement between predicted and measured in-cylinder pressure and heat release rate was obtained. The influence of various piston bowl designs, including Mexican-hat geometry, double-lip geometry, bow geometry, and toroidal geometry, on the combustion process, engine performance, and pollutant emissions of a high-pressure direct-injection natural gas engine have been studied and analyzed numerically. The present study confirms the benefit of the piston bowl design as a beneficial tool to enhance the performance and pollutant emissions of the pilot diesel-ignited natural gas engine. Results showed that different chamber shapes slightly influence the combustion initiation, and the difference in in-cylinder pressure presents noticeable as the combustion continues. A higher turbulent kinetic energy improves the flow movement and facilitates the mixture formation in the cylinder. However, the combustion behavior is unwished caused by the improper injection angle of natural gas. Increasing the recess depth of combustion chambers reduces NO formations at the price of sacrificing fuel economy. For the bow combustion chamber design, the NO emission declined by 31.1%, while the indicated specific fuel consumption increased by 5.5% compared with the original engine. Although the indicated mean effective pressure and specific fuel consumption of the optimal double-lip geometry almost remain the same, NO emissions can be reduced by 16.7% compared with the base design.
在预燃喷射天然气发动机中，空燃混合气的准备主要取决于活塞碗轮廓和燃料喷射策略。活塞碗几何形状被认为是控制发动机污染物排放的关键。在本工作中，应用了 SAGE 燃烧模型，并结合了通用反应动力学机制。该发动机模型通过康明斯 ISX 400 发动机的实验数据进行了验证，预测的缸内压力和放热率与测量值吻合良好。研究和分析了各种活塞碗设计（包括墨西哥帽几何形状、双唇几何形状、碗几何形状和环形几何形状）对高压直喷天然气发动机燃烧过程、发动机性能和污染物排放的影响。本研究证实了活塞碗设计作为提高预燃式柴油引燃天然气发动机性能和污染物排放的有益工具的优势。结果表明，不同的燃烧室形状对燃烧起始稍有影响，而在燃烧持续过程中，缸内压力的差异则表现得更为明显。较高的湍流动能可改善缸内的流动运动，促进混合气的形成。然而，天然气的喷射角度不当会导致燃烧行为不理想。增加燃烧室的凹陷深度可以降低 NO 的生成，但会牺牲燃油经济性。对于碗形燃烧室设计，与原始发动机相比，NO 排放量减少了 31.1%，而指示比油耗增加了 5.5%。虽然最佳双唇几何形状的指示平均有效压力和比油耗几乎保持不变，但与基础设计相比，NO 排放量可减少 16.7%。
