Exhaust energy recovery via catalytic ammonia decomposition to hydrogen for low carbon clean vehicles

The work presented here, demonstrates the on-board exhaust assisted catalytic ammonia (NH₃) conversion to H ₂-N ₂ using either only exhaust heat (decomposition) or by direct reaction with part of the exhaust gas (reforming). The resultant H ₂-N ₂ gas mixture from the exhaust heat driven thermochemical energy recovery processes contains up to 15% more energy than the reactant NH ₃ (i.e. for 1 kW of NH ₃ used in the reaction up to 1.15 kW of H ₂ is produced). Experimental studies using a rhodium-platinum (Rh-Pt) catalyst and equilibrium calculations in Chemkin using Konnov's 0.6 and Nozari's reduced mechanisms have revealed that complete NH ₃ conversion occurs at typical gasoline direct injection (GDI) engine exhaust gas temperatures (450 °C–550 °C). By partially replacing gasoline in GDI engine with the resultant (H ₂-N ₂ products, up to 30% reduction in CO ₂ and fuels consumption can be achieved. Additional benefits can be gained under real engine operation when the benefits of reduced pumping losses, due to intake dilution with H ₂-N ₂ gas, are also considered. Furthermore, the work demonstrates additional benefits in CO ₂ life cycle for the NH ₃ use as an energy carrier in transportation and broader combustion power generation systems.