Effects of a split injection in a spray-guided direct-injection spark ignition engine under lean stratified operation

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Abstract
The effects of a split injection were investigated in a spray-guided direct-injection spark ignition engine under lean stratified operation. In-cylinder pressure analysis, exhaust emissions measurement and visualization of the spray and combustion were applied. From the results using a single-injection strategy, stratified combustion showed advanced and rapid combustion characteristics. However, the low work conversion efficiency and the high nitrogen oxide emissions were obstacles to stratified combustion. Furthermore, the smoke emissions were high as a result of the dominant mixing-controlled combustion. A dual-injection strategy was applied to control the level of stratified combustion by modifying the dwell time and the split ratio. With a split injection, the nitrogen oxide emissions and the smoke emissions were reduced because of the moderated combustion speed and the enhanced local homogeneity. The liquid phase of the stratified mixture and the luminous sooting flame were reduced significantly as well. However, a low combustion efficiency and a low indicated mean effective pressure resulted owing to the over-mixing effect when the portion of lean premixed combustion was increased. Via moderately controlled stratified combustion, a split injection could be an effective way to reduce the nitrogen oxide emissions and the smoke emissions with a reasonable indicated mean effective pressure and a reasonable combustion efficiency.

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