【作者】 林灵；

【导师】 魏远文； 黄海波；

【作者基本信息】 西华大学 ， 动力机械及工程， 2008， 硕士

【摘要】 随着发动机排放法规的日益严格和对发动机经济性的要求越来越高,HCCI燃烧技术在内燃机节能和降低排放的潜力以及二甲醚（DME）作为一种高效率清洁的柴油机代用燃料,引起了人们的关注。HCCI是一种新的燃烧模式,它不同于传统的点燃式内燃机和压燃式内燃机,HCCI具有高热效率、低PM和NOx排放的特点。目前,国内外许多研究者做了关于二甲醚HCCI燃烧模式的化学动力学和燃烧机理的实验和模拟计算研究。本文是以前人的研究成果为基础,应用Chemkin软件对二甲醚进行了HCCI燃烧模式的燃烧氧化机理数值模拟研究和排放特性实验研究。研究结果表明,二甲醚氧化着火燃烧过程可以划分为四个阶段:反应链诱发阶段;活性基积累;低温反应阶段;高温反应阶段。第一阶段的反应引导期放出的热量很少;第二阶段活性基的产生速率比消耗速率大,同时产生大量的热能,这导致了气缸内温度和压力的上升;第三阶段和第四阶段所有物质的反应速率空前提高,DME和CO被氧化的同时产生HO₂,燃烧放热达到最高。二甲醚主要通过以下两种途径氧化消耗:DME裂解:CH₃OCH₃（+M）→产物;二甲醚脱H反应:CH₃OCH₃+HO₂→产物和CH₃OCH₃+H→产物。在二甲醚氧化机理研究的基础上,本文又利用Chemkin软件,模拟计算了进气温度、过量空气数、转速和进气压力等燃烧边界条件对二甲醚燃料HCCI燃烧模式的影响。同时又对二甲醚均质压发动机的燃烧进行了变参数模拟研究。研究表明,进气温度、过量空气数、发动机转速能改变燃烧时刻和燃烧压力;进气压力虽然能改变燃烧压力提高发动机动力性能,但是它基本不改变燃烧时刻,不能作为控制燃烧时刻的一种手段。在ZS1100柴油机的基础上对其进行改造后,形成了可以进行纯柴油燃烧试验、柴油&DME混合燃料双模式燃烧试验和纯DME燃料HCCI燃烧试验。利用五成分废气分析仪,气相色谱仪对台架试验的排放进行了检测和分析。实验结果显示,二甲醚HCCI燃烧模式能同时降低NOx和碳烟,但HC和CO却显著增加。气相色谱仪在线分析发现,DME的非常规排放中只有甲醛峰,其他微量目标检测物质的峰没有出现,故需进一步改进尾气采集方式和检测手段。更多还原

【Abstract】 With the increasingly strict regulations of the engine emission and the significantly greater economical demands for engine, HCCI combustion mode technology has been drawn more and more attention because of its potential in saving energy and reducing emission, and also because dimethyl ether （DME） is an alternative fuel of high-efficient clean diesel. Homogeneous charge compression ignition （HCCI） is a new combustion mode. Different from combustion in spark ignition （SI） and compression ignition（CI） engine, HCCI has the advantage of higher thermal efficiency but low PM and NOx emission.Nowadays, many domestic and foreign researchers have experimented and simulated on DME HCCI combustion model of the chemical kinetics and mechanism of combustion. This paper is based on previous researchers’ achievements,with Chemkin software to do the simulating research on the characteristics of DME HCCI combustion mechanism and the emission.It’s found that the combustion process of DME can be divided into four stages: solicitation stage of series reaction;active accumulation stage;lower temperature reaction （LTR）;high temperature reaction （HTR）.At the first stage, the reaction chains are induced and only a little heat is released. At the second stage, the producing rate is faster than the consuming one and a large amount of energy was released, resulting in the rise of in-cylinder pressure and temperature. At the third and fourth stage, all kinds of reacting rates are very fast and at the same time, the oxidation of DME and CO creates HO2, and the released heat reaches its summit. DME was cracked by two combustion ways: DME split: CH₃OCH₃ （+M）→middle product and DME dehydrogenation Reaction: CH₃OCH₃ + HO₂→middle and product CH₃OCH₃ + H→product.Based on the mechanistic research on DME oxidation, the Chemkin software was used again to simulate the impact of the combustion-border conditions such as inlet temperature, excess air coefficient, rotating speed and air pressure on HCCI combustion of DME fuel. Experiment was also made on the characteristics of DME HCCI model engine’s emission. It shows that inlet temperature, excess air amount and rotating speed can change the time and pressure it costs. Although the pressure of inlet air can change the combustion pressure and improve engine performance, it can not change the combustion time, so it isn’t an effective way to control the comb -ustion time. Results show that DME HCCI combustion model can reduce NOx and soot, but CO and CH significantly increased.The ZS1100 diesel engine have been reconstructed to perform the pure diesel combustion test and the mixed fuels（diesel and DME） test and the pure DME HCCI combustion test. The five-exhausted-componect analyser and Gas Chromatography （GC） have been used to detect and analyze the emission of Engine test-bed. The GC on-line analyses proved only formaldehyde but no other trace of minim material in the emission. Thus further improvements of collecting and inspecting exhaust emission are needed.更多还原