Closed-loop combustion control of homogeneous charge compression ignition (HCCI) engine dynamics

Homogeneous charge compression ignition (HCCI) is a hybrid of the spark ignition and compression ignition engine concepts. As in a spark ignition engine, a homogeneous fuel-air mixture is created in the inlet system. During the compression stroke the temperature of the mixture increases and reaches the point of auto ignition, just as in a compression ignition engine (or diesel). One challenge with HCCI engines is the need for good timing control of the combustion. Auto ignition of a homogeneous mixture is very sensitive to operating condition. Even small variations of the load can change the timing from too early to too late combustion. Thus a fast combustion timing control is necessary since it sets the performance limitation of the load control. As measurement for combustion timing feedback, the crank angle of 50% burnt has been used. This paper performs a comparative study of different cylinder-pressure based methods for estimating the crank angle of 50% burnt, CA50. The estimates are compared in terms of accuracy, robustness and feasibility for cycle-to-cycle real-time control. Dynamic models of CA50 are estimated using system identification as a means to find models relevant to engine control.