The effect of fuel injection on NOx emissions and undesirable combustion for hydrogen-fuelled piston engines

In order to determine the potential of direct cylinder injection for hydrogen-fuelled engines, an experimental study was performed with an ASTM-CFR engine. Both the standard Otto head and the standard diesel head were used. Measurements were made of power output, thermal efficiency, and oxides of nitrogen emissions. The feasibility was investigated of a scheme in which injection of gaseous hydrogen starts late in the compression stroke, ignition occurs as soon as possible thereafter, and combustion rate is determined by injection rate. This scheme prevents undesirable combustion phenomena such as pre-ignition, high rates of cylinder pressure rise, and high amplitude pressure waves in the cylinder. Furthermore, it obviates flashback into the carburetor. The potential of hydrogen as a low pollution fuel was investigated by operating the Otto head engine on both hydrogen and indolene, and by comparing the resulting NO_x, emissions. Hydrogen yielded very low NO_x emissions provided the fuel-air equivalence ratio was less than 0.5, and provided the hydrogen and air were well mixed. For equivalence ratios greater than 0.5, hydrogen yielded NO_x emissions that were higher than those obtained with indolene. The timing of hydrogen injection was found to have a significant effect on NO_x emissions. With an unthrottled air intake and hydrogen injection at equivalence ratios between 0.3 and 0.8, indicated mean effective pressures ranged from 0.3 to 0.78 MPa. Corresponding indicated thermal efficiencies ranged from 43 to 31%. By decreasing the equivalence ratio to 0.1, the IMEP could be reduced to 0.07 MPa, thus providing an indicated load range of more than a factor of 10.