Combustion and emissions characteristics of a dual fuel engine operated on alternative gaseous fuels

Among the different efforts towards the reduction in pollutant emissions from direct injection (DI) diesel engines, the use of gaseous fuels as a partial supplement for diesel fuel has been proposed by many researchers. An experimental investigation was performed to investigate the influence of dual-fuel combustion on the performance and exhaust emissions of a DI diesel engine fueled with natural gas (NG) and biogas (BG). The engine was operated at a constant speed of 1750 rpm and at two different loads: low (∼3 N m) and high (∼28 N m), which were about 10% and 85% respectively of the rated torque output of the engine at 1800 rpm. In this work, the combustion pressure and the rate of heat release were evaluated experimentally in order to analyze the combustion characteristics and their effects on exhaust emissions including particulate matter (PM) for single-fuel (diesel) and dual fuel combustion modes. In dual fuel mode, the peak cylinder pressure was found to be similar to diesel at 75% of the rated output of the engine. About 27–30% higher maximum net heat release rates were obtained for NG and biogas fueling respectively compared to diesel fueling. Longer ignition delays but shorter combustion durations were characterized for dual fueling operations. Specific NOx emissions for dual fueling was always lower than diesel fueling case. Significantly lower specific PM emissions but sharply increased unburned hydrocarbons (UHC) emissions were measured for biogas–diesel dual fuel operations as compared to diesel fueling.