Research on cycle-by-cycle variations of an SI engine with hydrogen direct injection under lean burn conditions

Considering the improvement on combustion stability for hydrogen addition under lean burn conditions, cycle-by-cycle variations of a spark ignition gasoline engine with hydrogen direct injection were studied. Effect of hydrogen fraction of 10% on cycle-by-cycle variations for lean burn with various excess air ratio and throttle position was analyzed. The results showed that coefficient of variation in indicated mean effective pressure decreased firstly and increased afterward with the retard in ignition timing, confirming there existed a minimal cycle-by-cycle variations ignition timing for a specified excess air ratio and throttle position. It was also found that the peak cylinder pressure, the maximum rate of pressure rise and the indicated mean effective pressure increased, and their corresponding cyclic variations decreased after hydrogen addition. Interdependency between the combustion pressure parameters and their corresponding angles tended to become strongly correlated after hydrogen addition. Moreover, the pressure-derived combustion parameters and the indicated mean effective pressure decreased with the increase of excess air ratio, and coefficient of variation in both the gross indicated mean effective pressure and peak cylinder pressure increased under leaner conditions. This effect would be weakened with the enlargement of throttle position. The engine lean operating limit could be extended after hydrogen addition. (C) 2016 Elsevier Ltd. All rights reserved.