Reducing cyclic dispersion in autoignition combustion by controlling fuel injection timing

Model-based control design for reducing the cyclic variability (CV) in lean autoignition combustion is presented. The design is based on a recently proposed control-oriented model that captures the experimental observations of CV. The model is extended here to include the effect of the fuel injection timing, which is an effective way of influencing the combustion phasing. This model is only stable for certain amounts of residual gas. For high amounts, runaway behavior occurs where the combustion phasing occurs increasingly earlier. For low amounts, a cascade of period-doubling bifurcations occurs leading to chaotic behavior. This complex dynamics is further complicated with significant levels of noise, which creates a challenging control problem. With the aim at controllers feasible for on-board implementation, a proportional controller and a reduced-order state feedback controller are designed, with feedback from the combustion phasing. The controllers are evaluated by simulations and the results show that the CV can be significantly reduced, in an operating point of engine speed and load, for a wide range of residual gas fractions.