Addressing the challenge of ammonia slip and nitrous oxide emissions from zero-carbon fuelled engines through catalytic aftertreatment solutions
M. Wu, Alexis Cova‐Bonillo, Pedro Gabana, George Brinklow, Nikhil Dilip Khedkar, J.M. Herreros, Soheil Zeraati Rezaei, A. Tsolakis, Paul Millington, S. Alcove Clave, A. York
Abstract
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.