A computational study of operating range extension in a natural gas SI engine with the use of hydrogen

•CNG fueled SI engine was studied by coupling the CFD to chemical kinetic model.•Operating range of engine extended about 20% by adding 30% H2 and 39% for 50% H2.•Combustion duration were 70, 47 and 45° CA for H2 fractions of 0%, 30% and 50%.•The Φ that maximum NOx occurred is nearly independent of the hydrogen fraction.•30% H2 reduced 10.2% CO2 emission approximately and 50% H2 led to 22.7% reduction.

The performance of a natural gas fueled spark ignition engine was studied to investigate the effect of hydrogen enrichment on the engine operating range and combustion characteristics. A validated multi-dimensional CFD model coupled with detailed chemical kinetics mechanism was used to study the combustion process in Hydrogen/CNG engine. Results indicated that misfiring occurs in equivalence ratios of about 0.61, 0.48 and 0.42 for hydrogen fractions of 0%, 30% and 50% respectively. Also, combustion durations were 70, 47 and 45° crank angle for hydrogen fractions of 0%, 30% and 50% respectively with same equivalence ratio (Ф = 0.625). Regarding the emission, the maximum amount of break specific NOx was detected around Ф = 0.83 (λ = 1.2), and this point is almost independent of the hydrogen fraction. It was found that hydrogen fraction decreases the emissions of CO, and HC and CO2. Adding 30% hydrogen reduced CO2 emission by10.2% while 50% hydrogen fraction led to 22.7% CO2 reduction.