【作者】 郑清平；

【导师】 张惠明；

【作者基本信息】 天津大学 ， 动力机械及工程， 2006， 博士

【摘要】 本文提出了一种新的压燃式天然气发动机燃烧系统。为了使高辛烷值的天然气实现压缩着火,该系统采用了高压缩比、电热塞助燃和燃烧室壁面喷涂隔热层等技术措施,并采用了进气预热。为了克服高辛烷值天然气在压缩着火和燃烧过程中出现的失火和敲缸现象,该燃烧系统采用了分隔室式燃烧室结构和天然气复合供气系统,从而实现了主、副燃烧室内的混合气浓度分层和温度分层,有效地控制了着火时刻及燃烧速度,拓展了发动机的运行范围。为了进一步改善发动机的起动性,扩展稀燃界限,增大高负荷运行范围,采用了助燃添加剂和热EGR的技术措施,取得了明显的效果。本文介绍了这一压燃式天然气发动机燃烧系统的研制和开发工作,其中包括新型燃烧系统的构思、燃烧室形状和隔热结构设计、复合供气系统设计、EGR系统设计、助燃添加剂供给系统设计等。本文介绍了作者对这一燃烧系统进行的模拟计算和燃烧机理分析。为对这一燃烧系统进行模拟计算,研究其燃烧机理和影响因素,首先建立了由23种物质和42个基元反应式组成的天然气化学动力学简化机理,并将该机理与CFD模拟软件相结合对压缩着火天然气发动机的燃烧过程进行了模拟计算。模拟计算结果表明,复合供气模式能够通过进气温度、进气终了缸内混合气浓度、电热塞温度、高低压供气量、高压喷气起始时刻等参数的优化组合在燃烧室内形成合理的混合气浓度分层和温度分层,实现了两级燃烧,扩大了发动机的运行范围。进气温度、电热塞温度及供气量等运行参数对压缩着火天然气发动机的着火和燃烧过程影响较大,它们主要是通过改变主、副室内混合气温度分层和浓度分层效果来影响着火和燃烧过程的;燃烧室几何形状对燃烧性能的影响主要是通过气流运动起作用的。涡流对着火的影响要强于湍流,湍流的主要作用在于促进提高燃烧速度,缩短燃烧持续时间。本文还介绍了作者在原理样机上进行的试验研究,试验结果与模拟计算相吻合。试验结果表明,进气道低压供气模式最容易起动,其次为复合供气模式,缸内高压供气模式难以起动。当压力升高率超过0.65MPa/℃A时,发动机出现轻微敲缸现象,而当压力升高率超过0.78MPa/℃A时,发动机出现较强烈的敲缸现象。发动机运行范围受到失火和敲缸的限制。二叔丁基过氧化物添加剂的加入由于能在较低的温度下分裂出自由基,同时又能在低温下放出热量,从而加快了连锁反应的速度,故对天然气的着火有明显的改善作用;采用热EGR可推迟着火时刻,降低燃烧速度,有利于克服发动机燃烧敲缸,扩大高负荷运行范围。更多还原

【Abstract】 In this paper, a new combustion system of natural gas fueled compression ignition engine is presented. In order to let high octane number natural gas to be compression ignited, measures like high compression ratio, glow plug heating, heat-isolating coating, as well as air inlet heating, are adopted in this system. In order to overcome misfiring and cylinder knocking caused by high octane number natural gas in the process of compression ignition and combustion, divided chamber and compound natural gas supply system are applied in this system, therefore the stratified concentrations and temperature distribution are realized while ignition timing and combustion rate are controlled effectively and operation range is broadened. In order to improve engine start-up performance, broaden the lean limit and increase operation range in high load condition, additive and hot Emission gas Recycling (EGR) are used in this system and an obvious effect is achieved.The developing work for natural gas fueled compression ignition engine is introduced in this paper, including concept design of new combustion system, structural design of combustion chamber and heat isolation, layout design of compound natural gas supply system, EGR system and combustion assistant additives supply system.The study of simulation and analysis of combustion mechanism referring the combustion system is introduced in this paper.In order to simulate the combustion process and investigate its combustion mechanism and affecting factors, a reduced kinetic dynamic mechanism of natural gas is established based on 23 species and 42 reactions. The mechanism is used to simulate combustion process through coupling with Computational fluid dynamics (CFD) software.The simulating results show that reasonable stratification of mixture concentration and temperature distribution can be formed in compound gas supply mode through controlling inlet air temperature, in-cylinder mixture concentration during the end of inlet stroke, glow plug temperature, gas supply volume and injection timing,so a two-stage combustion is realized and its operating range is broadened. Based on analysis, it is learned that inlet air temperature, glow plug temperature and natural gas supply volume have much influence on ignition and combustion process of natural gas fueled compression ignition engine. Their functions are activated更多还原