Comparison of Premixed Fuel and Premixed Charge Operation for Propane-Diesel Dual-Fuel Combustion

With the rising popularity of dual-fuel combustion, liquefied petroleum gas (LPG) can be utilized in high-compression diesel engines. Through production from biomass (biomass to liquid, BtL), biopropane as a direct substitute for LPG can contribute to a reduction in greenhouse gas emissions caused by combustion engines. In a conventional dual-fuel engine, the low reactivity fuel (LRF) propane is premixed with the intake air to form a homogeneous mixture. This air-fuel mixture is then ignited by the high reactivity fuel (HRF) in the form of a diesel pilot injection inside the cylinder. In the presented work, this premixed charge operation (PCO) is compared to a method where propane and diesel are blended directly upstream of the high-pressure pump (premixed fuel operation, PFO) in variable mixing ratios for different engine loads and speeds. Furthermore, the effects of internal and external exhaust gas recirculation are investigated for each operating mode. The results show that PCO allows higher propane ratios of up to 75 % at low loads, while PFO enables higher percentages of propane at medium and high loads (up to 50 %), allowing for a “reactivity on demand” approach. In addition, PFO shows significantly lower emissions of unburned hydrocarbons (-98.3 %) and carbon monoxide (-94.6 %) compared to PCO while soot emissions are reduced in both cases. The use of EGR allows nitrogen oxide emissions to be lowered to similar levels for both operation modes and shows benefits concerning unburned hydrocarbon (-73.5 %) and carbon monoxide (-62.9 %) emissions in PCO.