Increasing High Load Engine Power with Advanced Combustion Modes

Partially Premixed Combustion (PPC) approaches were applied in a single cylinder diesel research engine in order to characterize engine power improvements. PPC (dual fuel) and PPC (single fuel) are alternative advanced combustion approaches that generally result in lower engine-out soot and NOx emissions, with a moderate penalty in engine-out unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions. In this study, PPC was accomplished with a minority fraction of fuel (isobutanol, iso-octane and jet JP-5) injected into the intake manifold, while the majority fraction of jet JP-5 fuel was delivered directly to the combustion chamber near the start of combustion (SOC). Four compression ratios (CR) were studied. Exhaust emissions plus exhaust opacity and particulate measurements were performed during the experiments in addition to fast in-cylinder combustion metrics. It was seen that as CR increased, the soot threshold equivalence ratio decreased for conventional diesel combustion; however, this afforded an opportunity for increased levels of port fuel leading to a range of power increases from −2 to 27% as CR increased from 14 to 21.5. PPC allowed for these power increases (defined by a threshold opacity level of 3%) due to smaller particles (and lower overall number of particles) in the exhaust that influenced measured opacity less significantly than larger and more numerous conventional diesel combustion exhaust particulates. Carbon monoxide levels at the higher driven power levels were only modestly higher for the PPC combustion modes, although NOx was generally lower due to the overall enriched operation.