Effects of chemical reaction mechanism and NO<i>_x</i> formation pathways on an inter-turbine burner

Abstract

ABSTRACT One of the main challenges of future aircraft engines is to achieve low pollutant emissions while maintaining high combustion efficiencies and operability. The Flameless Combustion (FC) regime is pointed as one of the promising solutions due to its well-distributed reaction zones that yield low NO x emissions and oscillations. A dual-combustor configuration potentially facilitates the attainment of FC in the Inter-Turbine Burner (ITB). The development of such burner is dependent on knowledge regarding NO x formation and the parameters affecting it. It is known from the literature that the NO x formation mechanisms are different in FC. Therefore, in an attempt to clarify some of the mechanisms involved in NO x formation at relevant conditions, a chemical reactor network model developed to represent the ITB is explored. The role of prompt NO x was previously shown to be dominant at relatively low inlet temperatures and atmospheric pressure. In order to check these findings, five chemical reaction mechanisms were employed. All of them overpredicted NO x emissions and the overprediction is likely to be caused by the prompt NO x subset implemented in these mechanisms. Higher reactants temperatures and operational pressures were also investigated. Overall NO x emissions increased with temperature and the NO x peak moved to lower equivalence ratios. Operational pressure changed the emissions trend with global equivalence ratio. Leaner conditions had behaviour similar to that of conventional combustors (increase in NO x ), while NO x dropped with further increase in equivalence ratio due to suppression of the prompt NO x production, as well as an increase in NO reburning. These trends highlight the differences between the emission behaviour of the ITB with those of a conventional combustion system.