Characterization of Partially Premixed Combustion

TLDR

Partially Premixed Combustion (PPC) offers the potential to simultaneously reduce NOx and soot in diesel engines. This study seeks to delineate the operating range and conditions necessary for PPC. The authors evaluated emission and in‑cylinder data from engine experiments to characterize PPC. The results show that low compression ratio, high EGR, and near‑stoichiometric operation enable simultaneous NOx and soot reduction at 8, 12, and 15 bar IMEP, but this requires longer ignition delay, lower combustion temperature, higher HC and CO, and reduced efficiency; increasing inlet pressure expands the PPC operating range.

Abstract

Partially Premixed Combustion (PPC) provides the potential of simultaneous reduction of NOx and soot for diesel engines. This work attempts to characterize the operating range and conditions required for PPC. The characterization is based on the evaluation of emission and in-cylinder measurement data of engine experiments. It is shown that the combination of low compression ratio, high EGR rate and engine operation close to stoichiometric conditions enables simultaneous NOx and soot reduction at loads of 8bar, 12bar, and 15bar IMEP gross. The departure from the conventional NOx-soot trade-off curve has to be paid with a decline in combustion efficiency and a rise in HC and CO emissions. It is shown that the low soot levels of PPC come along with long ignition delay and low combustion temperature. A further result of this work is that higher inlet pressure broadens the operating range of Partially Premixed Combustion.