Abstract:
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 intakemanifold. In order to reduce the emissions of nitrogen oxides when compared against dieselcombustion, dual fuel engines begin the injection process early in the combustion cycle.However, at early injection timings dual fuel engines exhibit high emissions of both unburnedhydrocarbons (HC) and carbon monoxide (CO). This work discusses the emissions optimizationprocess to reduce emissions for two different fueling types, diesel-propane and poly-oxymethylene dimethyl ether (POMDME)-propane, on a single cylinder research engine (SCRE)based upon a PACCAR MX-11 heavy-duty engine while maintaining combustion and fuelconversion efficiencies.The parameters swept during this optimization process include start of injection, percentenergy substitution, a second injection and its timing, the split ratio – or the ratio of commandedduration of the first injection to that of the second, a coupled injection sweep, rail pressure, andintake pressure. These parameters were varied at a fixed gross indicated mean effective pressure(IMEPg) of 5 bar to represent low load operation as well as a fixed engine speed of 1339 rpm("B speed" of the SCRE). During all experiments a global limit of 1 g/kWh was set on theindicated specific NOx emissions, as well as a maximum pressure rise rate of 10 bar/deg, and acoefficient of variation of IMEPg at or below 5%. Using these limits and the emissions tradeoffsbetween HC, CO and NOx, this work was able to demonstrate diesel-propane emissionsimprovements of HC and CO of 86.4% and 66.8% respectively when compared to the baseline, while POMDME-propane emissions showed improvements in HC and CO of 90.9% and 86.2%respectively. Additionally, POMDME emissions demonstrated zero measurable filter smokenumber during all engine operations. A preliminary life cycle analysis of using both dual fuelcombinations have been compared against traditional diesel operation as well as battery poweredoperation and is found within the appendix of this work.
