Strategy and potential of homogeneous lean combustion at high load points for turbocharged gasoline engines with direct injection and small displacement

In this paper, a homogeneous lean combustion concept for gasoline engines with direct injection, small displacement and turbocharging is investigated under high-load conditions. A representative operating point was selected for this purpose. The tests were carried out on a single-cylinder research engine. In particular, the influence of the center of combustion, charge motion and pressure ratio is discussed. It has been discovered that the center of combustion has a large influence on the stability of homogeneous lean combustion at high load points. The present investigations provide a method of how to achieve an early center of combustion in knock-limited load points of homogeneous lean combustion. Early centers of combustion enable a high air–fuel ratio with good, smooth running and low NO_x emissions. In addition to the high charge motion, operation with a positive scavenging gradient and valve overlap can be applied to flush the hot internal residual gas out of the combustion chamber, whereby knocking can be reduced. With the high air–fuel ratio, specific fuel consumption can be reduced substantially and high combustion efficiency can be achieved. The results can be leveraged as a basis for future developments in gasoline engines.