摘要
在一台采用废气再循环(exhaust gas recirculation,EGR)策略的当量燃烧天然气发动机上开展了不同挤气比、压缩比的活塞对燃烧、热效率和排放影响的对比试验研究。结果表明:在50%负荷与中低转速75%负荷下,增大EGR率拓展了爆震边界,使得主燃烧相位(CA50)提前,指示热效率提高;而在100%负荷及高转速75%负荷下,EGR率的增大对燃烧持续期的延长作用更为明显,且CA50后移,指示热效率降低。增大压缩比和适当增大挤气比有利于增强缸内湍流运动,加快天然气火焰传播速度,使CA50更靠近上止点,热功转换效率提高,最高指示热效率提高了0.24%,NOx和CH4排放分别升高了2.30 g/(kW·h)、0.55 g/(kW·h)。进一步增大挤气比会受到爆震的限制,最佳点火时刻推迟,燃烧定容度小,燃烧持续期延长,最高指示热效率下降了0.51%,NOx和CH4排放分别降低了2.20 g/(kW·h)、0.44 g/(kW·h),CO排放升高了0.36 g/(kW·h),因此挤气比存在一个优化的范围。
A comparison test of the effect of piston with different squish ratios and compression ratios on combustion thermal efficiency and exhaust emissions was carried out on a stoichiometric combustion natural gas engine with exhaust gas recirculation(EGR)strategy.Results showed that at the speed of 1400 to 1800 r/min and with 50%or 75%of rated load,increasing the EGR rate extended the knock boundary,thus advancing the angle of 50%mass fraction burned(CA50),and increasing the indicated thermal efficiency.At the speed of 2300 r/min and with 75%or 100%of rated load,increasing the EGR rate could significantly extend the combustion duration,thus retarding the CA50 and reducing the thermal efficiency.On the other hand,increasing the compression ratio and appropriately enhancing the squish ratio was beneficial to improve the turbulent motion in the cylinder and accelerate the flame propagation speed of natural gas,so that the CA50 was closer to the top dead center,which improved the thermal power conversion efficiency coupled to the increase of the highest indicated thermal efficiency by 0.24%and hence NOx and CH4 emissions by 2.30 g/(kW·h)and 0.55 g/(kW·h),respectively.Further increase in squish ratio would be limited by knock,resulting in delayed maximum brake torque timing and extended combustion duration,which would reduce the maximum indicated thermal efficiency by 0.51%and decrease NOx and CH4 emissions by 2.20 g/(kW·h)and 0.44 g/(kW·h),respectively,coupled to the increase of CO by 0.36 g/(kW·h).Therefore,there was a range of squish ratio that needs to be optimized.
作者
郑尊清
王献泽
王浒
朱赞
邓远海
韦钻国
ZHENG Zunqing;WANG Xianze;WANG Hu;ZHU Zan;DENG Yuanhai;WEI Zuanguo(State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China;Guangxi Yuchai Machinery Co. , Ltd. , Yulin 537000, China)
出处
《内燃机工程》
EI
CAS
CSCD
北大核心
2020年第4期1-8,共8页
Chinese Internal Combustion Engine Engineering
基金
国家重点研发计划项目(2018YFB0105900)。
关键词
天然气发动机
当量燃烧
挤气比
压缩比
热效率
natural gas engine
stoichiometric combustion
squish ratio
compression ratio
thermal efficiency
