Cylinder-to-Cylinder Variations in a V6 Gasoline Direct Injection HCCI Engine

Despite the fact that homogeneous charge compression ignition (HCCI) has been demonstrated as a combustion technology feasible for implementation with different fuels in various types of engines, cylinder-to-cylinder variations (CTCVs) in multicylinder HCCI engines remain one of the technical obstacles to overcome. A reduction in CTCV requires further developments in control technology. This study has been carried out with regard to the overall engine parameters, involving geometric differences between individual cylinders, coolant paths through the engine, combustion chamber deposits, and also the differences in the inlet temperature distributions between the cylinders. Experimental investigations on the Jaguar V6 HCCI research engine with negative valve overlapping and cam profile switching show that the differences in the rate of pressure rise between the cylinders can be larger than 1 bar/CA deg and that the load differences can be as high as 5-10%. It has been found that some individual cylinders will approach the misfiring limit far earlier than the others. The complex interaction between a number of parameters makes the control of the multicylinder engine a serious challenge. In order to avoid these differences, an active cylinder balancing strategy will be required. It has been observed that spark assistance and split injection strategy deliver the best control for the cylinder balance. However, spark assistance is restricted to low loads and low engine speeds, while split injection requires a considerable effort to optimize its possible settings. This paper defines the most important parameters influencing cylinder-to-cylinder variations in the HCCI engine and aims to put forward suggestions that can help to minimize the effect of cylinder-to-cylinder variations on the overall engine performance.