Analysis of chemical pathways for n-dodecane/air turbulent premixed flames

TL;DR

This study investigates how turbulence affects chemical pathways in n-dodecane/air flames, finding that integrated heat release pathways are largely unaffected by turbulence, while local pathways vary significantly with flame topology and temperature.

Contribution

It provides a detailed comparison of turbulence effects on chemical pathways in n-dodecane flames using DNS data, highlighting the relative insensitivity of integrated pathways and the localized pathway alterations.

Findings

Integrated heat release pathways are insensitive to turbulence.

Pathways in positively-curved regions show larger alterations.

Peak activity shifts to higher temperatures with increased turbulence.

Abstract

This paper analyzes turbulence-chemistry interactions for an n-dodecane-air flame, focusing on the degree to which fuel oxidation pathways change in turbulent flames relative to their corresponding laminar flames. This work is based on a lean n-dodecane-air flame DNS database from Aspden et al. (Proc. Combust. Institute, 36 (2017) 2005-2016). The relative roles of dominant reactions that release heat and produce/consume radicals are examined at various turbulence intensities and compared with stretched flame calculations from counterflow flames and perfectly stirred reactors. These results show that spatially integrated (i.e. integrated heat release or radical production rate metrics averaged over the entire flame) chemical pathways are relatively insensitive to turbulence intensity and mimic the behavior of stretched flames. In other words, the contribution of a given reaction to heat release or radical production, integrated over the entire flame, is nearly independent to turbulence. Localized analysis conditioned on topological feature of the flame and on temperature is also performed. The former analysis reveals that much larger alteration of pathways occurs in the positively-curved regions of the flame. The latter localized analysis shows that peak activity in the low temperature (i.e. below 1200K) region shift towards higher temperatures with increases in Karlovitz number. This result is particularly interesting given that prior work with lighter fuels showed the opposite behavior suggesting a disparate response of the reactions involved in the fuel oxidation process to increased turbulence.