Performance and emissions characteristics of hydrogen-diesel heavy-duty engines: The influence of engine control parameters

The introduction of gaseous hydrogen (H 2 ) into the intake air of a heavy-duty diesel engine results in H 2 -diesel dual-fuel (HDDF) combustion, which offers a near-term pathway to reduce CO 2 emissions in heavy-duty long-haul trucking. Since H 2 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 H 2 fractions. The results show that engine performance and combustion parameters are not solely influenced by H 2 introduction. Instead, the key factor is how H 2 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 H 2 (“H 2 slip”) can be addressed through coordinated control of intake air pressure, diesel injection timing, and EGR ratio based on H 2 energy ratio. At high H 2 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 H 2 slip. At a given EGR level, precise control of combustion phasing and intake pressure enabled the introduction of 40% H 2 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 H 2 introduction while addressing technical challenges in HDDF combustion. This ensures comparable engine performance with significantly lower CO 2 emissions compared to conventional heavy-duty diesel engines. • Boost pressure and diesel timing control can offset the combustion and emission impacts of adding H 2 to a diesel engine. • Adding 40% H 2 reduced CO 2 by 40% and PM by 55% in a heavy-duty engine with independent boost, timing and EGR control. • Controlling diesel timing and boost pressure in combination achieved comparable BTE and NOx as diesel engines with 40% H 2 . • Introducing 20% EGR reduced H 2 -diesel combustion harshness by 40% and NOx emissions by 68%. • Over 99% of the introduced H 2 participated in the combustion for overall equivalence ratios above 0.4.

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