Modeling nitrogen species from ammonia reciprocating engine combustion in temperature-equivalence ratio space

This paper explores nitrogen species formation in temperature (T)-equivalence ratio (ϕ) space under internal combustion engine-relevant conditions using zero-dimensional modeling. The analysis reveals that N₂O and NO are formed in a much larger region of ϕ-T space than in hydrocarbon combustion due to fuel chemical pathways. N₂O is formed over a large range of ϕ, primarily in low temperature regions that have significant levels of unburned NH₃. NO is formed over a large, high temperature, lean region. Further analysis shows that even when mixing burned gas with unburned NH₃ from engine crevices, N₂O is reduced to low levels in the expansion stroke after initially increasing due to the thermal de-NOx mechanism. This indicates that N₂O emissions measured from premixed engine combustion are likely from quenching near cold surfaces.