Heavy duty hydrogen internal combustion engine emissions development to achieve ultra-low NOx

This paper presents the emissions development of a heavy-duty hydrogen internal-combustion engine (H₂ ICE) targeting ultra-low NOx with a design goal of 20–35 mg/hp-hr. The approach integrates precise air–fuel-ratio control, transient-response enhancements to minimize rich/lean excursions, and advanced thermal management of the engine and aftertreatment, including an electric heater to accelerate light-off and sustain activity at low-load/idle conditions. A diesel-derived aftertreatment system (ATS) is selected to maximize practicality and component commonality, and a unified controls strategy spanning the engine and ATS is implemented to ensure emissions compliance over EPA certification and in-use testing cycles. The aftertreatment solution space is evaluated for catalyst sizing and backpressure while demonstrating particulate matter control without the need for a filter. The paper concludes with emphasis on catalyst aging and durability relative to diesel benchmarks, including long-term thermal exposure, sulfur tolerance, and control robustness over life.