Mid-ranging control of a multi-cylinder HCCI engine using split fuel injection and valve timings

Abstract

Homogeneous charge compression ignition (HCCI), though a promising piston-engine strategy for the future, presents a significant control challenge due to the presence of cycle-to-cycle dynamics and the absence of a direct combustion trigger. Several actuators can be used for controlling HCCI, but each of them presents unique hurdles to practical implementation. This paper presents an approach for controlling HCCI with exhaust recompression that addresses these challenges using the principle of mid-ranging control. The controller is based on a physical, discrete-time model of HCCI presented in previous work. A split injection strategy is used, with the timing of a small pilot injection of fuel during recompression being used to control the phasing of combustion on a cycle-by-cycle basis. A slower valve motion, easily achievable on an engine equipped with cam phasers, is then used to keep the injection timing in the middle of its range of influence, maintaining the control authority to handle fast transients while respecting actuator constraints. The controller is seen to be effective in tracking desired load and phasing trajectories in simulation, and on a multi-cylinder engine testbed. In particular, the controller enables steady operation at low load conditions on the engine.