Air-to-fuel ratio regulation during SI to HCCI combustion mode transition using the LQ tracking control

The combustion mode transition between spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustions of an internal combustion (IC) engine is challenging due to the distinct engine operating parameters over the two combustion modes and the cycle-to-cycle residue gas dynamics during the mode transition. The control problem becomes even more complicated for a multi-cylinder engine without camless valve actuation. This paper studies the combustion mode transition problem of a multi-cylinder IC engine with dual-stage valve lift and electrical variable valve timing (VVT) systems. Hardware-in-the-loop (HIL) simulations were used to develop and validate the proposed control strategies. The HIL simulation results show that smooth combustion mode transition can be realized utilizing the hybrid combustion mode in a few engine cycles and in-cylinder air-to-fuel ratio during the mode transition needs to be regulated to the desired level. This paper presents a model based linear quadratic tracking strategy to track the desired air-to-fuel ratio by controlling the engine throttle. The HIL simulations demonstrated the effectiveness of the developed control strategies. As a result, it is feasible to have a smooth combustion mode transition with dual-stage valve lift and electrical VVT systems.