Experimental and Numerical Study of the Effect of High Steam Concentration on the Oxidation of Methane and Ammonia during Oxy-Steam Combustion

Abstract

The effect of high H 2 O concentration during oxy-steam combustion on the oxidation of methane and ammonia was investigated both experimentally and numerically. Comparison experiments between O 2 /N 2 and O 2 /H 2 O atmosphere were performed in a flow reactor at atmospheric pressure covering fuel-rich to fuel-lean equivalence ratios and temperatures from 973 to 1773 K. Experimental results showed that the presence of high H 2 O concentration dramatically suppressed CO formation at temperatures above 1300 K. High H 2 O concentrations inhibited NO formation under stoichiometric and fuel-lean conditions but enhanced NO formation under fuel-rich conditions. The chemical kinetic mechanism, which was hierarchically structured and updated, satisfactorily reproduced the main characteristics of CO and NO formation. High H 2 O concentrations significantly alter the structure of radical pool and subsequently the formation of CO and NO. Ultralow CO concentrations above 1300 K are attributed to the enhancement of CO + OH ⇄ CO 2 + H by high OH radical concentrations. NO suppressions under stoichiometric and fuel-lean conditions are caused by strong suppression of NH 2 + O ⇄ H + HNO in the pathway NH 2 → HNO → NO. This suppression is due to the lack of O radicals. By contrast, NO enhancement under fuel-rich conditions is caused by the significant enhancement of NH 2 + OH ⇄ NH + H 2 O in the pathway NH 2 → NH → HNO → NO. This enhancement is due to the fairly high OH concentration in the O 2 /H 2 O atmosphere.