Combustion shaping using multivariable feedback control

Abstract

As high exhaust gas recirculation (EGR) is introduced for efficiency, the combustion duration and combustion delay is elongated due to slow fuel burn rates requiring flexible and robust management of both the combustion initiation and duration (what we call combustion shaping). Combustion shaping through cylinder pressure sensing and feedback control of spark advance (SA) and EGR-valve position can be used for spark ignited (SI) engines operating within highly dilute, high efficiency regimes even where the combustion variability (CV) limits controller bandwidth. Although EGR is directly related with combustion duration, spark advance affects the start and duration of combustion simultaneously. This input/output coupling suggests a multivariable controller that coordinates the actuators. Control of SA and EGR is investigated with a coupled linear quadratic Gaussian (LQG) controller and compared with a decoupled proportional-integral (PI) controller. Simulation of the closed-loop system uses a simple engine model derived from system identification. Gain tuning was performed aiming for fast response without overshoot and considering cyclic variability reduction through a Kalman filter. Comparison of the simulated controllers shows that the LQG controller has better transients and responds better to CV.