Cycle-by-cycle variations of a spark ignition engine fueled with natural gas-hydrogen blends combined with EGR

Cycle-by-cycle variations of a spark ignition engine fueled with natural gas-hydrogen blends combined with EGR were investigated. The effects of EGR ratio and hydrogen fraction on cycle-by-cycle variations of the engine were analyzed. The results show that, with the increase of EGR ratio, the maximum pressure rise, the maximum rate of pressure rise and the indicated mean effective pressure are decreased and cycle-by-cycle variations are increased. Weak interdependency is presented between the above parameters and their corresponding crank angles with the increase of EGR ratio. For a given EGR ratio, combustion stability is promoted and cycle-by-cycle variations are decreased with the increase of hydrogen fraction in the fuel blends. Non-linear relationship is presented between indicated mean effective pressure and EGR ratio. Slight influence of EGR ratio on indicated mean effective pressure is observed at small EGR ratio while large influence of EGR ratio on indicated mean effective pressure is demonstrated at high EGR ratio. Increasing engine speed decreases cycle-by-cycle variations due to the enhancement of air flow in cylinder. Increasing hydrogen fraction can maintain low cycle-by-cycle variations at high EGR ratios.