直喷汽油机采用不同缸内稀释技术的性能研究

Effect of Different In-Cylinder Dilution Technologies on Performance of a Direct Injection Gasoline Engine

针对一款4缸1.5 L废气涡轮增压缸内直喷汽油(GDI)发动机,进行了废气再循环(EGR)缸内稀释燃烧技术、空气缸内稀释燃烧技术与原机燃烧的经济性、排放特性对比试验研究。研究了不同缸内稀释技术对发动机性能和排放影响的变动规律,并对比分析了相同稀释率下、采用不同稀释技术时发动机的性能变化。结果表明:空气稀释率在49.5%时比油耗相比原机下降6.2%,而EGR稀释率在20.5%时经济性改善4.2%,在相同稀释率时,EGR稀释可采用更为提前的点火角实现更优的燃烧相位,但空气稀释所带来的多变指数提升使其经济性优于EGR稀释,且发动机燃烧系统对空气稀释程度具有更强的容忍性;NO x排放在空气稀释率为11.0%时达到峰值水平,随后随着稀释率的提高不断下降,而EGR稀释的NO x排放随着稀释率的提高持续大幅下降;空气稀释的CO排放水平远低于原机,EGR稀释的CO排放随着稀释率的增加而略有下降;对于HC排放,空气稀释的排放量低于EGR稀释,而当空气稀释率由49.5%增加为68.0%时,HC排放出现较大幅度上升。

A comparative test of fuel economy and emission characteristics was carried out on a 1.5 L turbocharged direct injection gasoline engine using different technologies of exhaust gas recirculation(EGR)and in-cylinder air diluted combustion.Results show that compared with the original engine,the use of an air diluted combustion system can reduce fuel consumption by 6.2% at an air dilution rate of 49.5%,while with the EGR system,fuel consumption can be improved by 4.2% at a dilution rate of 20.5%.At the same dilution rate,the EGR system can use a more advanced ignition timing to achieve a better combustion,while the polytrophic exponent increment caused by the air diluted combustion system makes the engine more economical than the EGR system,and the engine is more tolerant to air dilution.When the air dilution rate of the air diluted combustion system is 11%,the engine emissions reach the highest level,and then decrease with the increase of air dilution rate.As for the EGR system,as the dilution rate increases,NO x emissions continue to drop significantly.In addition,when using the air diluted combustion system,CO emissions will be much lower than the original engine,while for the EGR system,CO emissions slightly decrease with the increase of dilution rate.Moreover,the use of air diluted combustion system can make HC emissions lower than the EGR system,and when the air dilution rate increases from 49.5% to 68.0%,HC emissions will increase significantly.