喷孔面积和喷氢压力对PFI氢内燃机混合气形成及燃烧的影响

发布时间：2017-12-27 10:16

本文关键词：喷孔面积和喷氢压力对PFI氢内燃机混合气形成及燃烧的影响　出处：《华北水利水电大学》2016年硕士论文　论文类型：学位论文

【摘要】：当今世界能源危机和环境污染日趋严重,内燃机的代用燃料研究成为热点课题。氢气因其储量大、燃烧清洁、热效率高的特点,在燃料电池和内燃机领域有着广泛的应用,被称为21世纪的最终能源。但其在应用于内燃机过程中易出现回火、早燃等异常燃烧现象,阻碍了氢内燃机的发展。由于异常燃烧的诱因多发生在混合气形成过程中,且混合气形成质量的好坏对缸内的燃烧与排放有重要影响,因此如何改善混合气的形成质量显得尤为重要。本研究基于一台改装的PFI(进气道预混式)发动机,建立了完整的三维模型。利用AVL-fire软件分别模拟怠速转速(1000r/min)、最高扭矩转速(4500r/min)、最高功率转速(6000r/min)三种工况下,不同喷孔面积、喷氢压力对缸内混合气的形成质量及燃烧过程的影响。通过模拟揭示了进气道及缸内混合气速度场、浓度场、湍动能等的变化规律,并基于这些规律总结出两种参数对引起氢内燃机早燃和回火趋势的影响。结果表明,3mm喷孔直径不能满足中高转速时喷氢量的要求,在进气门关闭时缸内当量比太小,增大至5mm能显著提高混合气当量比。增加喷射压力有利于形成更均匀的混合气,使燃烧放热反应更加快速合理。0.2MPa喷氢压力需要超过5mm的喷孔直径去匹配,而增大喷孔直径和喷氢压力会使NO排放量增加,排放性变差。减小喷孔面积和喷氢压力会使喷出的氢气在进气道的滞留量和从缸内回流出的氢气量增大,增加了发动机早燃和回火的概率。综上所述,选择5mm的喷孔面积和0.3MPa的喷氢压力,可以在较小的异常燃烧概率下,达到强动力性、优经济性、低排放性的要求。
[Abstract]:Nowadays, the energy crisis and environmental pollution in the world are becoming more and more serious, and the research of alternative fuel for internal combustion engines has become a hot topic. Hydrogen has been widely used in the field of fuel cell and internal combustion engine because of its large reserves, clean combustion and high thermal efficiency. It is known as the final energy in twenty-first Century. However, the abnormal combustion phenomena such as tempering and early combustion are easy to occur during the application of internal combustion engines, which hinders the development of hydrogen internal combustion engines. Because the cause of abnormal combustion occurs mostly in the process of gas mixture formation, and the quality of mixed gas has great influence on the combustion and emission of the cylinder. Therefore, how to improve the formation quality of the mixed gas is particularly important. Based on a modified PFI (intake port premixed) engine, a complete three-dimensional model is established in this study. AVL-fire software was used to simulate the effects of idle speed (1000r/min), maximum torque speed (4500r/min) and maximum power speed (6000r/min) under three working conditions. The effects of different nozzle area and hydrogen pressure on the formation quality and combustion process of cylinder mixture were also simulated. The variation rule of velocity field, concentration field and turbulent kinetic energy in the inlet and cylinder is revealed by simulation. Based on these rules, the influence of two parameters on the trend of early combustion and tempering of hydrogen internal combustion engine is summed up. The results show that the diameter of 3mm orifice can not meet the requirement of hydrogen injection at middle and high speed. When the inlet valve closes, the equivalence ratio of cylinder is too small, increasing to 5mm can significantly increase the equivalence ratio of gas mixture. Increasing the injection pressure is beneficial to the formation of a more uniform gas mixture, which makes the combustion exothermic reaction more rapid and reasonable. The injection pressure of 0.2MPa needs to match the diameter of the jet hole of 5mm, and the increase of the diameter of the nozzle and the pressure of the hydrogen spray will increase the emission of the NO, and the emission is worse. Decreasing nozzle area and hydrogen injection pressure will increase the amount of hydrogen injected into the intake port and the amount of hydrogen flowing back from the cylinder, and increase the probability of early ignition and tempering. To sum up, the choice of 5mm orifice area and 0.3MPa hydrogen injection pressure can meet the requirements of strong power, good economy and low emission under a small probability of abnormal combustion.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK401

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