Combustion characteristics of a direct injection engine fueled with natural gas/hydrogen blends

The experimental investigation to combustion characteristics and heat release process in a direct injection spark-ignited engine fueled with natural gas/hydrogen blends was executed. For a fixed fuel injection duration, the results show that the heat release rate decreases with the increase of φ(H₂) (the hydrogen volume fraction) as φ(H₂) is smaller, and increases with the increase of φ(H₂) as φ(H₂) is over 10%. So only φ(H₂) reaches a certain level, the combustion can be improved. The flame development duration, the rapid combustion duration and the total combustion duration increase with the increase of φ(H₂) when φ(H₂) is less than 10% and decrease when φ(H₂) increases from 10% to 18%. The crank angle of the center of heat release curve moves apart from the top-dead-center with the increasing φ(H₂) and gets near the top-dead-center as φ(H₂) reaches to 18%. The maximum cylinder gas pressure, the maximum mean gas temperature, the maximum rate of pressure rise and the maximum heat release rate decrease with the increase of φ(H₂) when φ(H₂) is less than 10%, and they increase with the increase of φ(H₂) when φ(H₂) increases from 10% to 18%. The investigation shows that the influences of hydrogen addition on natural gas/hydrogen mixture combustion are more obvious at low engine speed than those at high engine speed.