LNT as an effective solution to minimize NOx emissions of hydrogen combustion engines

Hydrogen-powered internal combustion engines (HICE) offer a longterm solution to ensure a more sustainable mobility service. NOx-free combustion is not feasible since high combustion temperatures and lean operation result in nitrogen oxides formation, which can be reduced to a minimum by an intelligent controlled combustion process in lean operation and with exhaust gas recirculation. However, to comply with the Euro VII climate targets, the implementation of an aftertreatment system is required. The lean NOx trap (LNT) is a well-known solution that provides an alternative for NOx conversion in internal combustion engines other than the selective catalyst reduction (SCR) system. This solution can offer robustness and low operation complexity, optimizing the already low exhaust gas NOx emissions. In this paper, an LNT installed on a HICE was experimentally investigated. The LNT loading behaviour, when submitted to the hydrogen engine exhaust gases, was demonstrated. The LNT operation was assessed, being the loading operation demonstrated and an overview of the regeneration process conducted. For regeneration, a rich lambda setpoint is necessary. The influence of the NOx concentration and space velocity on the loading capacity was evaluated graphically. Regulated European cycles were conducted utilizing precise, energy-efficient, and compliant internally developed controls. After being freshly regenerated, the LNT provided a highly efficient operation, showing a NOx conversion efficiency of over 80 %. Moreover, the potential of this exhaust aftertreatment solution was further confirmed by performing consecutive cycles. It was concluded that the LNT is a robust, suitable, and a promising approach for the deNOx strategy, allowing hydrogen combustion engines to comply with current and future emission regulations.