| Abstract | The introduction of gaseous hydrogen (H₂) into the intake air of a heavy-duty diesel engine results in H₂-diesel dual-fuel (HDDF) combustion, which offers a near-term pathway to reduce CO₂ emissions in heavy-duty long-haul trucking. Since H₂ introduction impacts oxygen availability, combustion characteristics, and emissions simultaneously, it is imperative to appropriately optimize and control the input parameters including intake air pressure, diesel injection timing, and EGR ratio. This study investigates the impacts of these controlling parameters on the combustion characteristics, limiting factors, and emissions of an HDDF engine. Experimental tests were conducted on a 2.4 L, single-cylinder research engine under medium load and speed conditions (1200 rpm, 8 bar brake mean effective pressure) with varying H₂ fractions. The results show that engine performance and combustion parameters are not solely influenced by H₂ introduction. Instead, the key factor is how H₂ introduction affects combustion phasing and fuels equivalence ratio at various intake air pressures and diesel injection timings. The findings demonstrate that technical challenges in HDDF combustion, such as combustion harshness (indicated by maximum rate of pressure rise) and unburned H₂ (“H₂ slip”) can be addressed through coordinated control of intake air pressure, diesel injection timing, and EGR ratio based on H₂ energy ratio. At high H₂ energy ratios, adding 20% EGR effectively reduced combustion harshness by up to 40% and NOx emissions by 68%, with negligible impact on brake thermal efficiency and H₂ slip. At a given EGR level, precise control of combustion phasing and intake pressure enabled the introduction of 40% H₂ energy ratio, resulting in 40% reduction in CO₂ emissions and 55% reduction in particulate matter emissions, with no increase in NOx levels compared to the baseline diesel operation. These outcomes establish simultaneous adjustment of key engine control parameters as a practical strategy to maximize H₂ introduction while addressing technical challenges in HDDF combustion. This ensures comparable engine performance with significantly lower CO₂ emissions compared to conventional heavy-duty diesel engines. |
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