Numerical Study on the Combustion and Emission Characteristics of a Pre- Chamber Engine Fueled with Hydrogen Enriched Compressed Natural Gas

In order to investigate the effects of hydrogen enrichment on the combustion and emission formation processes of large medium-speed natural gas engines ignited by pre-chamber turbulent jets, a computational fluid dynamic method coupled chemical kinetics was applied to calculate the in-cylinder processes of a 6ACD320 type natural gas engine fueled with different hydrogen fraction(from 0 to 30% in volumetric fraction). The numerical results show that the hydrogen enrichment enhances the formation of active radicals such as O and OH, which accelerates the in-cylinder flame propagation, leading to higher heat release rate. As a result, several decreases in the indicated specific fuel consumption accompanying with some slight increases in the indicated thermal efficiency of the engine are obtained. Concerning the emission characteristics, the CO, THC and NHMC emissions decrease, while the NOx emissions increase with the increase of hydrogen enrichment. Moreover, it is found that for the turbulent jet ignition gas engine, the effect of hydrogen enrichment on increasing the in-cylinder flame propagation is more effective in the latter half of the combustion process. While in the initial half of the combustion process, the effect of turbulent disturbances generated by the flame jets seems to be more dominant in promoting the flame propagation. Considering both the performances and the emissions of the engine, a proper volumetric fraction of hydrogen should be 10%. © 2021, Editorial Office of the Transaction of CSICE. All right reserved.