Experimental and numerical study of hydrogen addition in a natural gas heavy duty engine for a bus vehicle

• A multi cylinder heavy duty engine was fuelled with natural gas/hydrogen blends.
• A faster combustion was observed with hydrogen at 20 and 40% by volume.
• A specifying engine modelling was used to extend the experimental investigation.
• A negligible effect of combustion speed on thermal efficiency was proven.

Hydrogen added to natural gas improves the process of combustion with the possibility to develop engines with higher performance and lower environmental impact. In this paper experimental and numerical analyses on a multi cylinder stoichiometric heavy duty engine, fuelled with natural gas–hydrogen blends, are reported. Some constrains on hydrogen content and maximum load achievable have limited the scope of investigation. A specific modelling of the reference engine was developed to extend the study at full load condition and at higher hydrogen content. The results showed a higher combustion speed when hydrogen content in the fuel is increased. However, the positive effect of shorter combustion duration on thermal efficiency is mitigated by higher wall heat loss, due to higher combustion temperatures. Therefore lower CO2 emissions are due only to the substitution of natural gas with hydrogen, making crucial the way of hydrogen producing to have a benefit on well-to-wheel CO2 emissions.