Split Injection Strategy Optimization to Achieve Ideal Stratified-Charge Mixture and Reinforce Ultralean Burn in a High Compression Ratio Direct Injection Spark Ignition Engine

Ultralean burn is considered an effective way to enhance the thermal efficiency of direct injection spark ignition engines. Herein, under ultralean burn condition, the split injection strategy is induced to investigate the in-cylinder mixture distribution, combustion characteristics, and emissions by simulation in a high compression ratio engine model. First, the homogeneity index shows that compared with the single injection method, the split injection strategy shows better stratification of the mixture gas at the early stage of the compression stroke, which results in higher in-cylinder pressure and heat release. Meanwhile, the results of heat balance show that split injection shows a slight effect on ignition delay, but significantly shortens combustion duration and advances CA50, and thus the exhaust loss is decreased. Second, with the decrease of a second injection fuel mass, the rich mixture is formed near the spark plug, thus reducing the ignition delay and combustion duration. Third, the split injection strategy presents faster flame kernel growth and propagation. A larger flame area is observed with the second injection mass decreasing. Finally, as the second fuel injection mass is reduced, NOx emissions increases continuously, while the soot emission decreases.

Automated summary

This study investigates the effects of split injection strategy on in-cylinder mixture distribution, combustion characteristics, and emissions in a high compression ratio engine model under ultralean burn condition. The results show that split injection improves mixture stratification, increases in-cylinder pressure and heat release, shortens combustion duration, reduces exhaust loss, and promotes flame kernel growth and propagation. However, it also leads to higher NOx emissions and lower soot emissions as the second injection fuel mass decreases.