Experimental and Numerical Evaluation of Nitrous Oxide in Lean Combustion of Alternative Fuels

摘要

NO_x which mainly refers to nitrogen dioxide (NO_2) and nitric oxide (NO) is considered as a major pollutant due to adverse effects on respiratory systems. Many studies on formation of NO_x in both mobile sources and stationary applications have been carried out. Nitrous oxide (N_2O), which is considered as a relatively new pathway of NO_x formation, is a strong absorber of infrared radiation in troposphere, thus is itself a greenhouse gas. There are few studies where the emission level of N_2O is studied for coal fueled burners, and gas fueled burner in high temperatures. The present work is focused on very low temperature lean combustion conditions. N_2O in the exhaust might be a concern in these cases because N_2O formation reaction rates are at their maximum at temperatures around 1250K. In this work, N_2O in the exhaust of a model gas turbine combustor is measured experimentally for (1) firing temperatures as low as 1200K, (2) different natural gas and hydrogen blends, (3) different levels of air preheat, and (4) different residence times. The experimental work is supported by chemical kinetics simulations using a chemical reaction network (CRN) to provide details regarding the emission formation rates. Reacting computational fluid dynamics are also applied to develop the CRN accurately. The results confirm that a simple CRN can provide reasonable predictions of CO, NO_x, and N_2O. Also, it was shown that the N_2O levels are always negligible for natural gas and hydrogen blends even in very low temperatures near the extinction limits.