废气再循环系统参数对柴油机燃烧特征的影响

Effects of Exhaust Gas Recirculation System Parameters on Combustion Characteristics of Diesel Engines

为进一步优化柴油机燃烧过程,减少燃烧污染物排放.围绕EGR(exhaust gas recirculation,废气再循环技术)废气组分和废气温度等系统参数对柴油机燃烧特征的影响机制,采用试验与模拟相结合方法,分别研究了通入废气、N_2、CO_2时以及不同EGR废气温度时对柴油机燃烧过程的影响,阐明了燃烧关键中间产物的生成规律.结果表明,(1)通入CO_2时,柴油机的缸内最大爆发压力和放热率峰值最低,滞燃期最长,燃烧持续期最短,·OH、H_2O_2、CH_2O·和CO等关键中间组分的生成规律与通入N_2时相反.(2)通入N2时,柴油机的缸内最大爆发压力和放热率峰值最高,滞燃期最短,燃烧持续期最长并;并且通入N_2时,·OH的峰值最高,形成时刻最早,H_2O2、CH_2O·以及CO的峰值均有所降低且形成时刻提前.(3)随着废气温度增加,缸内最大爆发压力降低,放热率曲线由单峰向双峰分布发展,放热率峰值有较大幅度的降低,滞燃期缩短,燃烧持续延长,缸内·OH、H_2O_2、CH_2O·以及CO的峰值均有所降低,并且生成的区域范围变窄.(4)废气成分中,CO_2对燃烧过程和关键中间产物的影响最大,是阻滞燃烧反应的主要气体成分,通过控制EGR废气成分和温度可以有效改善柴油机燃烧过程,拓宽EGR技术的工况使用范围.研究显示,EGR废气成分对燃烧中间产物的自由基衍化历程影响较大,有必要进一步开展EGR废气成分预处理研究,精确控制EGR废气温度,有助于改善燃烧过程,控制排放污染物中间产物的生成历程和排放量.

In order to optimize the combustion process of diesel engines and to reduce the emissions of pol lutants,the effects of exhaust gas composition and temperature during exhaust gas recirculation （EGR） on combustion characteristic of diesel engines were systematically studied by combing experiments and simulations. In particular,we examined the influence of N 2 , CO2 and different EGR exhaust gas temperature on the combustion process of diesel engines. The results showed that,compared with exhaust gas and Nz,the engine obtained maximum cylinder explosion pressure,lowest heat release rate peak,longest combustion delay period and shortest combustion duration byadding CO2. The engine obtained maximum cyl inder explosion pressure,maximum heat release rate,minimum combustion delay period and longest combustion duration by adding N 2. Compared with EGR,the OH free ra dical,which is formed first,reached the highest peak with the single inlet of N 2,whereas the peaks of H 2O2, CH2O＊ and CO free radicals were reduced s l ightly and formations were moved forward. When CO2 was introduced into the engine,the formation of key intermediate components such as ？OH, H 2O2, CH 2O＊ and CO was contrary to the N 2. When exhaust gas was introduced into the engine,the combustion characteristic parameters, the c r it ical intermediate component generation and generation time of the diesel engine were between N 2 and CO2. W ith the increase of EGR exhaust temperature, the maximum cylinder explosion pressure decreased,the heat release rate curve developed from a single peak to double peak, the peak value of heat release rate decreased g reatly,the ignition delay period was shortened, the combustion duration was prolonged, the peak values of ？0H,H202 , CH20＊ ,free radical and CO were decreased and the range of the generated region was shortened. The inlluence of C02 on the combustion process and the key intermediate products was greater than N2. Because C02 is the main component of the gas combustion reaction, the combustion process of diesel engines can be improved effectively and the working range of EGR can be widened by controlling the composition and temperature of EGR exhaust gas.