添加剂对微型内燃机甲醇燃烧影响的机理分析

Analysis of additive effects on methanol combustion mechanism in miniature IC engine

针对电热塞点火微型内燃机燃用甲醇(CH_3OH)燃料时失火率高、循环变动大等问题,提出了采用双氧水(质量分数30%H_2O_2)和硝基甲烷(CH_3NO_2)改善微空间甲醇燃烧的方法,并进行试验测试.试验结果显示,甲醇添加双氧水未能改善燃烧,并使燃烧恶化,加重失火;而甲醇添加硝基甲烷可改善甲醇燃烧,使得循环变动显著降低,并提高了燃烧稳定性.燃烧动力学分析表明,双氧水和硝基甲烷2种添加剂存在类似的助燃机理,都是通过贡献羟基(OH),改善着火性能以及燃烧稳定性.双氧水通过H_2O_2分解产生自由基OH,而硝基甲烷通过自身分解产生CH_3和NO_2并与HO_2/H反应产生OH,从而改善微空间甲醇燃烧.由于试验中双氧水质量分数较低,在添加H_2O_2的同时,混合气中水分增加,降低了初始混合气温度,一定程度上抑制了燃烧,使得双氧水丧失助燃效果.

Aiming at the high misfire rate and large cyclic fluctuations existing in glow-plug ignition miniature internal combustion（ IC） engine fueled with methanol（ CH_3OH）,a method for adding hydrogen peroxide solution（ 30 wt% H_2O_2） and nitromethane（ CH_3NO_2） was proposed to improve the combustion characteristics of methanol in micro space and experiments were conducted to test their effects. The results showthat the hydrogen peroxide solution fails to improve the combustion and makes it worse,meanwhile increases the misfire events. However,compared with hydrogen peroxide solution,the nitromethane can significantly reduce the cyclic fluctuations and improve the combustion stability. The combustion dynamics analysis indicates that these two kinds of additives have a similar combustion-supporting mechanism. By contributing hydroxyl（ OH）,both of them are conducive to improving the ignition performance and the combustion stability. Hydrogen peroxide solution provides OH by the decomposition of H_2O_2. By self-decomposition of nitromethane producing CH_3 and NO_2,then reacting with radical HO_2/ H to generate OH,thus it is beneficial to the combustion of methanol in micro space. Due to the lowmass fraction of hydrogen peroxide solution in the experiment,the adding of H_2O_2（ active ingredient） causes a substantial increase of the moisture in methanol-air mixture simultaneously,making the initial temperature of the mixture lower and inhibiting the combustion,thus leading to hydrogen peroxide solution to lose the combustion-supporting effect.