Performance and Emissions of a Hydrogen Dual-Fuel Engine Using Diesel and HVO as Pilot Fuels

A comprehensive experimental study of hydrogen–diesel dual-fuel and hydrogen-hydrotreated vegetable oil (HVO) dual-fuel operations was conducted in a single-cylinder diesel engine (bore 85.0 mm, stroke 96.9 mm, and compression ratio 14.3) equipped with a common rail fuel injection system and a supercharger. The hydrogen flow rate was manipulated by varying the hydrogen excess air ratio from 2.5 to 4.0 in 0.5 increments. Hydrogen was introduced into the intake pipe using a gas injector. Diesel fuel and HVO were injected as pilot fuels at a fixed injection pressure of 80 MPa. The quantity of pilot fuel was set to 3, 6, and 13 mm³/cycle. The intake and exhaust pressures were set in the range of 100–220 kPa in 20 kPa increments. The engine was operated at a constant speed of 1,800 rpm under all conditions. The pilot injection timing was varied such that the ignition timing was constant at the TDC under all conditions. The results demonstrated that smoke was lower when HVO was used as the pilot fuel than when diesel fuel was used, and that knocking occurred at lower excess air ratios of hydrogen when diesel fuel was used as the pilot fuel than when HVO was used. This is owing to the longer ignition delay of diesel fuel compared to that of HVO. The wider distribution of diesel fuel compared to that of HVO accelerates the chemical reactions in the premixed mixture, leading to autoignition. In addition, misfiring occurred when diesel fuel was used under low boost pressure operating conditions. This was attributed to differences in the ignition properties of the pilot fuel. These results demonstrate that HVO can be operated over a wider load range and at a wider hydrogen excess air ratio than diesel fuel operation.