Experimental and low-dimensional numerical study on the application of conventional NOx reduction methods in pulse detonation combustion

Abstract

Although research interest in pressure gain combustion (PGC) remains high, information on pollutant emissions from detonation-based devices such as pulse detonation engines is sparse, especially lacking extensive experimental parameter studies. Nevertheless, available results indicate potentially very high exhaust levels of nitrogen oxides (NOx) due to the significantly increased combustion temperatures and pressures induced by the detonation wave. To counter this issue, this study applies conventional NOx reducing measures in the form of fuel-lean mixtures and nitrogen dilution (emulating exhaust gas recirculation) to a pulse detonation combustor in multi-cycle operation. Their impact on the exhaust gas composition is measured and compared to numerical predictions by two available simplified models. To allow for a broader range of comparison and better assess the capabilities of these numerical models, emissions from fuel-rich and oxygen-enriched mixtures are measured as well. Experimental results confirm high levels of NOx up to several thousand ppm for near-stoichiometric, undiluted mixtures. When conventional NOx reduction measures are applied, significant NOx abatement can be achieved, with further reduction potential primarily limited by unsuccessful deflagration to detonation transition (DDT). Comparison with numerical results shows that simplified models allow for good qualitative agreement and can also deliver good quantitative predictions over a wide range of conditions if a suitable heat-loss model is chosen.