Investigations of multiple injection strategies for the improvement of combustion and exhaust emissions characteristics in a low compression ratio (CR) engine

The experimental analysis was conducted for a better understanding of the combustion stability and reduction of exhaust emission in low compression ratio (CR) engine. The combustion stability was analyzed in terms of combustion pressure, the rate of heat release (ROHR), the indicated mean effective pressure (IMEP), and coefficient of variation of indicated mean effective pressure (COVIMEP), and formation of exhaust emissions such as CO, HC, NOX, and soot was measured and compared in the low compression ratio single cylinder CI engine.It was revealed that maximum value of combustion pressure (Pmax) in two pilot injections was increased to almost the same level of single injection combustion although its maximum rate of heat release (ROHR) was decreased to 47.2% compared to single injection combustion. It was also observed that two pilot injections improves combustion efficiency, and these injection strategies operate engine more stably in low compression ratio engine, based on the results of increased IMEP (2.1%) and decreased COVIMEP (5.7%). Moreover, in multiple injection combustion, more CO formation and less HC emission were observed during combustion process, and remarkable simultaneous reduction of NOX up to 58.7% and soot up to 25% can be achieved in low compression ratio engine.

► Effect of multiple injection strategies on the reduction of exhaust emission were analyzed in low CR engine.
► Two pilot combustions show the best performance among different injection strategies.
► It increase IMEP (2.1%) and decrease COVIMEP (5.7%).
► Remarkable simultaneous reduction of NOX (58.7%) and soot (25%) can be also achieved.