Controlling combustion phasing variability with fuel injection timing in a multicylinder HCCI engine

Reduction of combustion phasing cyclic variability (CV) in homogeneous charge compression ignition (HCCI) engines operating lean with late autoignition is experimentally demonstrated. A three-state discrete time model developed in [1] is used for controlling the fuel injection timing and is applied to a multicylinder engine. A key objective of this work is to reduce cyclic variability without advancing the mean combustion phasing. Specifically, if late combustion phasing can be made less variable without advancing the operating point then areas where high CV is typically encountered could be made less variable. Examples include load transition down, when the residual temperature drops more rapidly than can be manipulated by the valve timing, or during mode transitions. Experimental results are presented to gauge the effectiveness of two control schemes, namely proportional and state feedback which have been tuned using the three-state model. Each of these controllers have been augmented with an integrator to maintain the late combustion phasing requirement. This is also done to draw a fair comparison of the controllers ability to reduce CV. The controllers are tested at various levels of CV and it is found that simple control can reduce the standard deviation of combustion phasing an average of 17% over open loop behavior. In addition, because of the simplicity of the control, this offers a viable solution for commercial applications.