Modeling, design and implementation of a closed-loop combustion controller for an RCCI engine

Reactivity Controlled Compression Ignition (RCCI) is a promising low temperature combustion strategy with high thermal efficiency and effective means to control combustion phasing and heat release rate. Being a dual-fuel stratified combustion process, RCCI requires precise control over the injection timing of direct injected fuel and in-cylinder mixture reactivity gradient. This paper focuses on developing a real-time, model-based controller for adjusting combustion phasing of an RCCI engine. Optimum combustion phasing is achieved by controlling mixture reactivity and injection timing of higher reactive fuel. A control-oriented model (COM) is developed using physics-based equations to predict combustion phasing during steady-state and transient operating conditions. The experimental validation results show that the COM is able to predict combustion phasing with less than 2 crank angle degrees (CAD). The COM is used to design a Proportional-Integral (PI) controller to track the desired combustion phasing by adjusting dual-fuel mixing ratio and injection timing. The PI controller is experimentally implemented on an RCCI engine test bench. The experimental results show that the designed controller can follow the desired combustion phasing with an average tracking error of 2 CAD and rise time of three engine cycles.