Retard to the Limit: Closed-Loop COVIMEP Control for Aggressive Exhaust Heating

During cold-starts, diesel engines equipped with aftertreatment systems typically use combustion phasing retard to increase exhaust gas enthalpy to hasten catalyst light-off, resulting in lower tailpipe emissions. Although later combustion phasing can help achieve faster catalyst light-off, combustion variability increases which can physically manifest as vibration and erratic engine behavior. To achieve faster catalyst light-off while remaining within combustion variability constraints, the premise of closed-loop control of Coefficient of Variation of IMEP (COVIMEP) to a target value using feedback from an in-cylinder pressure sensor has been explored. COVIMEP controllers have been designed using a model and validated via simulation and experiment at steady-state. The simulation and experimental results indicate that closed-loop COVIMEP control is a viable technique for retarding combustion phasing to the combustion variability limit at steady-state conditions.