Natural gas–ammonia dual-fuel combustion in spark-ignited engine with various air–fuel ratios and split ratios of ammonia under part load condition

•28% of CO2 is reduced with 50% volume fraction of ammonia in a natural gas engine.•The amount of fuel required increases as increasing ammonia ratio at a certain operation condition.•Fuel NOx formation leads to high NOx emissions when using ammonia.•The initial burn duration dominantly affects the...

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