A Comparative Study of Diesel– and POMDME–Propane Dual Fuel Combustion in a Heavy-Duty Single Cylinder Engine at Low Load

Dual fuel engines utilize two different fuels consisting of a high reactivity fuel (HRF) injected into the cylinder and a low reactivity fuel (LRF), typically fumigated into the intake manifold. To reduce engine-out emissions of oxides of nitrogen (NO_x), early start of injection (SOI) of HRF may be employed in dual fuel combustion, albeit at the expense of higher engine-out emissions of unburned hydrocarbons (HC) and carbon monoxide (CO). This study compares performance and emissions of diesel–propane and poly-oxy methylene dimethyl ether (POMDME)-propane dual fuel combustion for a heavy-duty single-cylinder research engine (SCRE) platform based on a production PACCAR MX-11 engine at a low load of 5 bar IMEPg and a constant speed (“B Speed”) of 1339 rpm. While POMDME-natural gas combustion has been explored in previous work, the novelty of the present work lies in the direct comparison of diesel–propane and POMDME–propane combustion for the same SCRE under fixed constraints of NO_x < 1 g/kWh, COV of IMEP < 5%, and a maximum pressure rise rate < 10 bar/CAD. By optimizing HRF injection parameters, boost pressure, and propane energy substitution, the present work demonstrates diesel–propane HC and CO emissions improvements of ~86% and ~67%, respectively, while POMDME–propane HC and CO emissions improved by ~91% and ~86% respectively, compared to the corresponding unoptimized baseline values. These improvements were obtained while achieving very low engine-out NO_x emissions (diesel–propane ~0.7 g/kWh, POMDME–propane ~0.1 g/kWh) and very good gross indicated fuel conversion efficiencies (diesel–propane ~51%, POMDME–propane ~48%). Additionally, POMDME–propane demonstrated near-zero measurable smoke emissions for all engine operating conditions.