Addressing the challenge of ammonia slip and nitrous oxide emissions from zero-carbon fuelled engines through catalytic aftertreatment solutions

Addressing climate change demands, energy security and resilience has necessitated replacing conventional fossil-based fuels with zero and carbon-neutral fuels/energy carriers. The most immediate solution is the partial and progressive substitution of conventional fuels in transportation. The effects of partially substituting gasoline with ammonia/hydrogen (NH 3 /H 2 ) mixtures in a spark ignition (SI) engine are investigated in this paper. The utilization of NH 3 /H 2 mixtures is a promising avenue of research since they can be produced from on-board NH 3 reforming, utilising heat energy that is recovered from hot exhaust gases. Experimental results indicate that adding NH 3 /H 2 enabled stable engine operation at lean conditions (λ = 1.4), resulting in reduced carbon-based emissions due to the non-carbon nature of NH 3 /H 2 . Utilising an integrated approach that combined a hemispherical flame geometry model with a thermodynamic model, has revealed that the introduction of NH 3 /H 2 significantly enhanced the combustion speed during the initial phase and further improved combustion efficiency. However, nitrogen-based emissions such as NO and NO 2 increased. This work also assessed the performance of a conventional three-way catalyst (TWC) and a double-function ammonia slip catalyst (ASC) in mitigating emissions. The TWC effectively controlled carbon-based emissions and NO under stoichiometric conditions but exhibited reduced efficiency under lean conditions, especially with NH 3 present. The ASC demonstrated high NH 3 conversion efficiency even at low temperatures, making it suitable for engine start-up and warm-up phases. Under steady-state conditions with artificially increased NH 3 /NO X ratios, a significant reduction in NOx emission was achieved with the ASC. However, high NH 3 /NO X ratios increased nitrous oxide (N 2 O) formation and NH 3 slip. • A combined NH 3 /H 2 combustion study was carried out with a prototype catalyst aftertreatment system. • NH 3 /H 2 blend in gasoline enables lean combustion but raises NO X emissions. • Combustion models show H 2 boosts initial phase burn rates. • TWC lacks N-based abatement capacity in terms of lean and NH 3 presence. • ASC efficiency increases with temperature but worsens with decreasing NH 3 /NO X ratio.