Parametric study and optimization of the main engine calibration parameters and compression ratio of a methane-diesel dual fuel engine

The increasing energy demand together with the severe emission legislation of the transportation sector requires effective solutions for automotive propulsion systems. Several studies are conducted to further develop the internal combustion engines and they are mainly oriented to the application of alternative combustion concepts combined with the use of alternative fuels. The main concerns are the efficiency, the pollutant, and the carbon dioxide (CO2) emissions. In this framework, the potential of the Dual Fuel (DF) concept is demonstrated. The methane - diesel DF application permits the reduction of the CO2 emissions and the diesel fuel usage while improving the NOx - PM trade-off compared to the conventional diesel combustion (CDC). The paper investigates the effects of the engine calibration parameters on the DF combustion characteristics, regulated emissions, and global performances. The parametric analysis was performed while varying the compression ratio (CR), the methane substitution ratio, fuel injection pressure, diesel pilot quantity, combustion phasing, Exhaust Gas Recirculation (EGR) and the Air-Fuel ratio (A/F). The tests were conducted utilising a modern combustion system architecture applied on a single cylinder engine. The analysis is performed at low-medium operating conditions that are more critical for the application of the advanced combustion concepts. In particular, four engine operating test points were selected, two engine speeds (1500, 2000 rpm) and loads (3, 7 bar of imep). The results show a significant impact of the CR, EGR and A/F ratio variables on the unburned hydrocarbons reduction (up to 40%) compared to the DF baseline. Benefits in terms of CO2 and particles distributions are shown with respect to the CDC. The CH4 slip on greenhouses gas (GHG) and the emissions and fuel consumption estimation over the New European Driving Cycle (NEDC) are considered. The information reported in this paper has a relevant impact on the development advanced combustion engines running under natural gas - diesel dual fuel combustion mode and transferable in modern light-duty engines, giving as output the main engine calibration parameters and CR that most influence the efficiency and pollutant emissions formation in a DF engines.