Τesting and modeling of a passive SCR system for hydrogen engines

Heavy-duty vehicles powered by hydrogen internal combustion engines (H2 ICEs) present a compelling solution for sustainable transportation.. When optimized for ultra-lean operation, H2 ICEs are capable of meeting the most stringent contemporary legislative emission standards. However, achieving optimal drivability necessitates occasional to an enriched operating mode, thereby presenting significant challenges in maintaining ultra-low emissions. In this context, the implementation of advanced exhaust after-treatment technologies becomes essential to ensure near-zero tailpipe emissions with minimal impact on fuel efficiency and drivability. This paper investigates the potential of a passive Selective Catalytic Reduction (SCR) exhaust configuration for a heavy-duty hydrogen (HD H₂) engine, employing testing and modeling of a Lean NOx Trap, utilized as an ammonia (NH₃) generator, in conjunction with a downstream Selective Catalytic Reduction system. We underscore the complexities associated with defining inlet boundary conditions—including exhaust flow rate, temperature, and composition—during transient engine operation. To address this challenge, an advanced engine model is used, providing the feed gas conditions for targeted steady-state and transient testing protocols on a synthetic gas bench (SGB). Based on the test results, we isolated the underlying phenomena, calibrating the Lean NOx Trap (LNT) and Selective Catalytic Reduction (SCR) kinetic models with a focus on NOx/NH₃ storage, deNOx efficiency, and NH₃ generation during LNT regeneration events. Utilizing a fully transient SGB test, the catalysts are subjected to transient conditions resembling real world driving cycles and to validate the fidelity of the catalyst models. The combined engine and aftertreatment model allows a comprehensive evaluation of the passive SCR technology potential for a heavy-duty hydrogen engine.