喷射模式及参数对甲醇-柴油双燃料发动机性能的影响

Impact of Injection Mode and Parameters on Methanol-Diesel Dual-Fuel Engine Performance

摘要

基于进气道喷射甲醇-柴油双燃料船用发动机，本文建立了三维数值仿真模型，研究了甲醇开阀和闭阀喷射模式以及关键喷射参数(喷射压力和喷孔直径)对发动机燃烧和排放特性的影响规律. 结果表明：甲醇喷射模式对缸内燃烧效率、油膜分布及排放具有显著影响，发动机燃烧效率与不同喷射模式下甲醇油膜质量存在密切联系．由于甲醇喷雾与进气气流协同作用，液滴更易蒸发，开阀喷射模式能够减少甲醇油膜质量，提高缸内甲醇燃烧质量和甲醇燃烧效率，使发动机整体燃烧效率和指示热效率增加．开阀喷射模式发动机指示热效率达到46.82%，闭阀喷射指示热效率低于39.00%．与闭阀喷射模式相比，开阀喷射模式下缸套甲醇油膜质量更多，沿缸套轴向的分布范围更广．同时，存在最佳甲醇喷射压力(即2.0 MPa)，该工况发动机燃烧持续期最短，甲醇油膜质量最小，甲醇燃烧质量最多，使发动机指示热效率比原工况提升0.96%，碳烟排放降低54.13%，但NO_x 排放增加29.25%．此时，甲醇油膜主要集中在缸套底部，缸套油膜质量和分布范围较小．此外，发动机指示热效率随着喷醇器喷孔直径增加而降低，当喷孔直径为0.20 mm 时，指示热效率比原工况提高0.76%，这可能归因于更短的燃烧持续期，发动机碳烟排放降低53.91%，NO_x 排放增加27.21%.

Abstract

Based on a port fuel injection methanol-diesel dual-fuel marine engine，a three-dimensional numerical simulation model was established to investigate the influence of the methanol injection mode and key injection parameters(injection pressure and nozzle diameter)on combustion and emission characteristics. The results demonstrated that the methanol injection mode significantly affected the in-cylinder combustion efficiency，film distribution，and emissions，with a strong correlation between combustion efficiency and the methanol film mass in different injection modes. Owing to the synergistic effect between methanol spray and the intake airflow，droplet evaporation was enhanced in the open-valve injection mode，which reduced the methanol film mass，improved the methanol combustion mass and efficiency，and consequently increased the overall combustion efficiency and the indicated thermal efficiency. In the experiment，the indicated thermal efficiency reached 46.82% in the open-valve injection mode，compared with less than 39.00% in the closed-valve mode. In contrast to the closed-valve injection mode，the open-valve mode resulted in a higher methanol film mass and wider axial distribution along the cylinder liner. Furthermore，an optimal methanol injection pressure(2.0 MPa)was identified，under which the combustion duration was the shortest，the methanol film mass was minimized，and the methanol combustion mass was maximized，resulting in a 0.96% improvement in indicated thermal efficiency，a 54.13% reduction in soot emissions，and a 29.25% increase in NO_x emissions compared with the baseline condition. Under this optimal pressure，the methanol film was primarily concentrated at the bottom of the cylinder liner，with a reduced mass and distribution range. Additionally，the indicated thermal efficiency decreased with an increase in the methanol injector nozzle diameter：at a nozzle diameter of 0.20 mm，the indicated thermal efficiency was improved by 0.76% compared with the baseline，which was attributed to the shorter combustion duration. Furthermore，soot emissions were reduced by 53.91%，whereas NO_x emissions increased by 27.21%.

关键词

甲醇-柴油双燃料发动机 / 喷射模式 / 甲醇油膜 / 燃烧效率 / 污染物排放

Key words

methanol-diesel dual-duel engine / injection mode / methanol film / combustion efficiency / pollutant emission

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基金资助

国家自然科学基金资助项目(52222604)

国家自然科学基金资助项目(T2341001)