Kinetic Modeling of NOx Formation and Consumption during Methanol and Ethanol Oxidation

This work presents a newly developed model for the oxidation of methanol and ethanol and their fuel interaction with NOx (NO and NO2) chemistry in jet-stirred and flow reactors, freely propagating and burner-stabilized premixed flames, as well as shock tubes. This work takes into account a very recent study on NO formation in pure methanol and ethanol burner-stabilized flames (Combust. Flame, 194, 363–375, 2018), augmented with so far unpublished experimental data. The paper mainly focuses on fuel interaction with nitrogen chemistry and NO formation in laminar premixed flames but also considers the formation and reduction of nitrogen oxides depending on the conditions of the surrounding gas phase. In agreement with previous experimental work, we find that doping of fuel blends with NO shifts the onset of fuel oxidation to lower temperatures depending on the gas conditions. The model suggests that the reactivity promoting effect of NO is mainly due to the net increase of OH radical concentrations, which causes increased fuel oxidation via the NO/NO2 interconversion reaction channel, NO+HO2⇋NO2+OH, NO2+H⇋NO+OH, NO2+HO2⇋HONO+O2, followed by the thermal decomposition of HONO. In burner-stabilized premixed ethanol flames, NO is mainly formed via a NCN pathway for all equivalence ratios, while for methanol flames the NCN pathway is only favored at rich conditions and the N2O pathway is favored at lean conditions.