Promotion and inhibition of oxidation of rich hydrogen-air mixtures by nitric oxides (NO and NO2) during adiabatic self-ignition

Abstract

The tracer method was used to numerically study the effect of nitric oxides (NO and NO2) on the oxidation of rich hydrogen-air mixtures during adiabatic self-ignition at low and high initial temperatures and a pressure of 0.1 MPa. At low temperatures, the added NO interacts with HO2 to form NO2, and NO2 then interacts with H to form NO. When NO2 is added at the same temperatures, a two-stage mechanism takes place: NO formed by the reaction NO2 + H is not involved in the reaction until NO2 is almost completely consumed. In the temperature range 900–1200 K, NO2 inhibits self-ignition through participation in the reaction with H, leading to the replacement of part of the completely branched chain H → (O, OH) → 3H by the unbranched chain H → OH → H. At low initial temperatures, NO effectively promotes hydrogen oxidation due to replacement of the unbranched chain H → HO2 → H2O2 → OH → H by a chain with branching.