DEMONSTRATING DIESEL PILOT COMBUSTION OF METHANE-HYDROGEN BLENDS IN A SINGLE-CYLINDER COMPRESSION IGNITION RESEARCH ENGINE

Medium and heavy-duty (MHD) diesel engine applications are currently facing technical challenges in accomplishing decarbonization goals due to the lack of readily available technological solutions that can meet the large power density requirements needed. For example, while electrification may show promise for certain light-duty vehicle applications, the benefits are greatly reduced in energy-dense MHD vehicle applications and thus additional decarbonization pathways need to be considered. A promising strategy is the adoption of low/zero carbon fuels that can make use of the abundant number of traditional engine architectures available (and corresponding manufacturing supply chains) to meet both power requirements and decreased emissions requirements. Gaseous fuels of this type include green hydrogen and renewable methane, both of which exhibit characteristics that make them difficult to auto-ignite and combust through increased compression alone. For engines equipped with a direct injector, it is possible to fumigate these engines mainly with gaseous fuel blends in the cylinder head port and use a small volume of renewable diesel directly injected in the combustion chamber (i.e., a pilot injection) to ignite the fumigated gaseous blend mixture. This study builds upon previous work focusing on methane combustion with diesel pilot injection and introduces hydrogen blending, exploring the effects of such fumigated blends at varying start of injection timings and at a constant equivalence ratio. The fuel blend used in this investigation was a diesel pilot injection accounting for ≃2% of the total fuel volume; the other 98% was split between the gaseous fuels, methane and hydrogen, in varying volume blend ratios. The study found that the introduction of any amount of hydrogen reduced carbon dioxide and unburned hydrocarbon concentrations in the exhausted emissions stream when compared to a diesel pilot with pure methane. The presence of hydrogen overall also increased combustion efficiency, peak pressures, and shortened ignition delay time. All blend ratios with hydrogen saw advanced CA50 and shorted CA10 to CA90 duration. This study concluded that tri-fuel blends can be run in a compression ignition engine and a combination of the start of injection timings and volume fraction of hydrogen can be used to control efficiencies and emissions.