Feasibility and Calibration Considerations for Selection of Combustion Control Features

Abstract

Improving modern downsized turbocharged engines requires not only the use of optimized engine components but also the implementation of control algorithms that minimize certain performance indicators such as fuel consumption. This paper proposes a two-input two-output (TITO) tracking control problem to achieve the optimal combustion process while minimizing indicated specific fuel consumption (ISFC) by means of adjusting spark advance (SA) and maximizing the levels of external exhaust gas recirculation (EGR). We show that at a fixed engine speed and various intake manifold pressures, the optimal combustion phase that maximizes piston work is fairly independent of EGR levels. If the crank angle of 50% mass fraction burned (CA50) is used as the combustion phasing indicator, this paper shows that the crank angle duration from spark advance to CA50 can be used as the second output of the TITO system without causing directionality or infeasibility problems. Feasibility of the integral control problem using (SA, EGR) as inputs and (CA50, CA50+SA) as outputs is discussed and a simple combustion model is proposed to account for the mean behavior and the cycle-to-cycle combustion variability.