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

ABSTRACT

This work presents a newly developed model for the oxidation of methanol and ethanol and their fuel interaction with NO_x (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 Flame, 194, 363–375, 2018), augmented with so far unpublished experimental data.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+O_2, 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.

KEYWORDS:

• NO
• NO₂
• NO_x
• methanol
• ethanol
• kinetic model
• nitrogen chemistry

Acknowledgments

We thank the Graduate Research School of the BTU Cottbus-Senftenberg for providing the travel Grant to attend the conference “Joint Meeting of the German and Italian Sections of the Combustion Institute”, 23–26 May 2018, Sorrento, Italy. The authors would like to acknowledge Myles D. Bohon, author of “PLIF measurements of non-thermal NO concentrations in alcohol and alkane premixed flames” (Combustion and Flame, 194, 363-375, 2018), for providing additional experimental data for this work and for fruitful discussions.

Supplementary material

Supplemental data for this article can be accessed here.