NO_x emission characteristics of hydrogen internal combustion engine

In order to investigate the NO_x emission of hydrogen internal combustion engines. A test system for four-cylinder intake port-fuel-injection hydrogen internal combustion engine (H₂ICE) is established to study the effect of fuel-air equivalence ratio, ignition advance angle, engine speed and exhaust gas recirculation on NO_x emission. Experimental results show that the fuel-air equivalence ratio is the key factor to NO_x emission, NO_x emission concentration is always higher than 8000×10^-6 when the fuel-air equivalence ratio is larger than 0.8 and lower than 500×10^-6 when the fuel-air equivalence ratio is smaller than 0.5. The ignition advance angle and engine speed also play important roles on NO_x emission formation. EGR is an useful method to reduce NO_x emission concentration at large fuel-air equivalence ratio especially when engine speed is low and EGR ratio is high.