Characterization of Engine Control Authority on HCCI Combustion as the High Load Limit is Approached

In this study the authority of the available engine controls are characterized as the high load limit of homogeneous charge compression ignition (HCCI) combustion is approached. A boosted single-cylinder research engine is used and is equipped with direct injection (DI) fueling, a laboratory air handling system, and a hydraulic valve actuation (HVA) valve train to enable negative valve overlap (NVO) breathing. Results presented include engine loads from 350 to 650 kPa IMEPnet and manifold pressure from 98 to 190 kPaa. It is found that in order to increase engine load to 650 kPa IMEPnet, it is necessary to increase manifold pressure and external EGR while reducing the NVO duration. While both are effective at controlling combustion phasing, NVO duration is found to be a coarse control while fuel injection timing is a fine control. NOX emissions are low throughout the study, with emissions below 0.1 g/kW-h at all boosted HCCI conditions, while good combustion efficiency is maintained (>96.5%). Net indicated thermal efficiency increases with load up to 600 kPa IMEPnet, where a peak efficiency of 41% is achieved. Parametric investigations reveal that increasing exhaust gas recirculation (EGR) at a constant intake manifold pressure (MAP) and increasing MAP at a constant external EGR rate both retard combustion phasing. It is also found that combustion phasing becomes increasingly sensitive to NVO duration as engine load increases. Finally, comparisons are made between commonly used noise metrics. It is found that compared to the AVL combustion noise meter, ringing intensity (RI) significantly underestimates combustion noise under boosted HCCI conditions.