Reducing combustion variation of late-phasing HCCI with cycle-to-cycle exhaust valve timing control

Abstract

A framework for modeling late-phasing homogeneous charge, compression ignition (HCCI) combustion shows that combustion instability can be represented as a negative real-axis pole in a discrete-time linearized system. A simple, nonlinear model of the HCCI process presented in previous work effectively captures decreases in heat transfer at late-phasing HCCI points. These decreases in heat transfer result in highly oscillatory responses of combustion phasing at late-phasing HCCI points. Root loci generated by linearizing the nonlinear model at different operating conditions illustrate that a system pole moves from the origin at a nominal case onto the negative real axis for the late-phasing case. Finally, simple proportional control of exhaust valve closing, based on output feedback, demonstrates sufficient reduction in drastic swings in combustion phasing and indicated mean effective pressure.