Effect of hydrogen addition to intake air on combustion noise from a diesel engine

This study investigates the characteristics of combustion noise from a diesel engine with hydrogen added to intake air. The engine noise with hydrogen addition of 10 vol% to the intake air was lower than that with diesel fuel alone at late diesel-fuel injection timings. A transient combustion-noise-generation model was introduced to discuss noise characteristics based on energy conversion from combustion impact to noise via structure vibration. The results show that the maximum combustion impact energy had a predominant effect on the maximum engine noise power for each cycle. Therefore, the combustion noise largely contributed to the total engine noise in an early stage of the expansion stroke. The dependences of engine noise on the diesel-fuel injection timing for different hydrogen fractions are discussed considering the characteristics of maximum combustion impact energy for each frequency.

► 10 vol% H2 addition greatly decreased in combustion noise at late diesel-fuel IT.
► Cyclic variation for 10 vol% H2 addition was larger than that without H2 addition.
► Max combustion impact energy had a predominant effect on max engine noise power.
►  Max combustion impact energy at 830 Hz largely contributed to the total engine noise.