甲醇/正庚烷双燃料均质充量压缩着火燃烧

在单缸发动机上进行了甲醇/正庚烷双燃料均质充量压缩着火(HCCI)燃烧的试验研究,采用详细化学反应机理分析了它们的反应过程和中间产物历程.研究表明,甲醇和正庚烷浓度的变化主要通过影响第一阶段放热量和放热时刻,进而影响高温着火时刻.正庚烷当量比不变时,随着甲醇浓度增加,低温反应放热量减小,燃烧始点推迟;当总燃料当量比不变,增加正庚烷比例时,低温反应时刻提前,峰值放热率增加;正庚烷当量比和总燃料当量比之比在0.8左右时,高温着火时刻发生在上止点附近,此时气缸压力和峰值放热率最大.对排放影响因素分析表明,CO排放更多取决于燃烧温度,而HC主要取决于甲醇比例.数值模拟发现,OH摩尔分数在10-6数量级才触发冷焰反应,甲醇浓度的变化引起低温阶段nC7ket和OH最大浓度及时刻的改变,从而影响低温和高温反应.

Study on the Methanol/n-Heptane Duel Fuel Homogeneous Charge Compression lgnition Combustion

This paper reported the experimental study of methanol/n-heptane HCCI combustion which was conducted on a single-cylinder engine.At same time,a zero-dimensional thermodynamic model couple with detail chemical kinetics was used to simulate the combustion process.The experimental results show that,the low-temperature reaction which can be adjusted by fuel properties plays important effect on the high-temperature reaction.For the same n-heptane equivalence ratio,the ignition timing delays and the heat release in the cool flame decreases with the increase of the methanol concentration.For the same total fuel(equivalence) ratio,the ignition timing advances and the heat release in the cool flame increases with the increase of n-heptane concentration.As a result,the combustion occurrs near the top dead center when the mole ratio of n-heptane to total fuel is about 0.8.Moreover,CO emissions strongly depend on the maximum combustion temperature,while HC emissions are mainly determined by the mole ratio of n-heptane to total fuel.The simulation results reveal that the cool flame reaction occurrs when the OH concentration is about 10~(-6).The effect of methanol addition on HCCI combustion was mainly attributed to the changing of nC7ket and OH concentrations.