Influences of stoichiometry on steadily propagating triple flames in counterflows

TL;DR

This study investigates how variations in stoichiometry affect the behavior and structure of triple flames in counterflow configurations, revealing dominance of one premixed wing and providing a simple predictive model.

Contribution

It introduces a numerical analysis of triple flames with non-symmetric stoichiometry and demonstrates a simple kinematic model for predicting flame shape and velocity.

Findings

Asymmetry in stoichiometry causes one premixed wing to dominate.

The diffusion flame becomes weaker when stoichiometry departs from 1/2.

A kinematic balance model accurately predicts flame shape and speed at low stretch.

Abstract

Most studies of triple flames in counterflowing streams of fuel and oxidizer have been focused on the symmetric problem in which the stoichiometric mixture fraction is $1/2$. There then exist lean and rich premixed flames of roughly equal strengths, with a diffusion flame trailing behind from the stoichiometric point at which they meet. In the majority of realistic situations, however, the stoichiometric mixture fraction departs appreciably from unity, typically being quite small. With the objective of clarifying the influences of stoichiometry, attention is focused on one of the simplest possible models, addressed here mainly by numerical integration. When the stoichiometric mixture fraction departs appreciably from $1/2$, one of the premixed wings is found to be dominant to such an extent that the diffusion flame and the other premixed flame are very weak by comparison. These curved, partially premixed flames are expected to be relevant in realistic configurations. In addition, a simple kinematic balance is shown to predict the shape of the front and the propagation velocity reasonably well in the limit of low stretch and low curvature.