NOx reduction strategies in scramjet combustors

The chance for future long range high speed commercial transport leads to a more comprehensive investigation of its environmental impact to ensure in advance that this development is sustainable. Although scramjet engines mostly use hydrogen as fuel consequently avoiding the particulate, CO and CO2 emissions, the high temperatures within these engines are critical for the NOx, water vapour and OH emissions. Altitudes associated with hyper/supersonic flight, i.e., 20 000-30 000 m, correspond closely to the maximum ozone density: there, NOx emissions can catalyze ozone destruction. Thus reduction of the NOx emissions remains of primary concern, being responsible for the ozone layer depletion. In this context, this paper investigates a strategy for the NOx reduction in supersonic combustion engines, in particular focusing on the impact of the combustor pressure and equivalence ratio on the nitrogen oxide emissions.