Effects of the ignition timing retard and the compression ratio on the full-load performance and the emissions characteristics of a heavy-duty engine fuelled by hydrogen–natural-gas blends

Heavy-duty natural-gas vehicles contribute towards environmental improvement in the air quality of downtown areas because the particulate matter emissions are quite low and lean combustion facilitates improvement in the efficiency and reduction in the harmful emissions. However, because stronger emission regulations such as Euro VI cannot be satisfied using the current technology, new technology is required. Hydrogen–natural-gas blend engines have been investigated as an alternative in preparation for the hydrogen era. Such engines make further emission reductions and efficiency improvements possible by extending the lean-combustion limit. However, they do have some disadvantages such as the degradation in the full-load performance, which can limit the reduction in the nitrogen oxide emissions or the operation range because the extension of the lean-burn limit requires a larger amount of intake air even under a wide-open throttle operating condition. In the present study, the full-load performance and emissions characteristics of a hydrogen–compressed-natural-gas engine were evaluated using hydrogen–compressed-natural-gas fuel with a hydrogen content of 30 vol %. In order to achieve performance improvement, a spark timing retard strategy was employed, together with a change in the compression ratio. After examining the full-load performance for each parameter change, the emission characteristics were assessed to analyse the commercialization potential and feasibility of this hydrogen–compressed-natural-gas engine. For a higher compression ratio, the specified torque value could be achieved with spark timing retard; an excess air ratio of 1.8 was found to be preferable, and the nitrogen oxide emissions standard of Euro VI was satisfied.