Analysis of Flame Structure and Interactions Between Chemical Reactions, Species Transport and Heat Release in Laminar Flames

TL;DR

This paper introduces a novel sensitivity-based method to analyze species interactions and heat release in laminar counterflow flames, revealing complex chemical and diffusion effects during auto-ignition of fuel mixtures.

Contribution

The study develops a new approach inspired by neural network sensitivity analysis to identify key species influencing heat release in combustion, applied to n-heptane and ethanol mixtures.

Findings

Ethanol addition inhibits low-temperature chemistry in n-heptane flames.

Ethanol-rich mixtures increase heat release rate through decomposition reactions.

Radicals like CH2O, C2H4, C3H6, and H2O2 play critical roles in heat release dynamics.

Abstract

A novel method for analyzing counterflow diffusion flames, inspired by Zurada's sensitivity approach for neural networks, is proposed to identify critical species influencing the heat release rate in combustion. By further analyzing concentration changes of selected key species and radicals, this method reveals complex interactions among them across regions with temperature. To illustrate this approach, the study investigates the mechanisms of auto-ignition of n-heptane and ethanol mixtures in a counterflow configuration under low strain rates. In mixtures where n-heptane is dominant, the inhibition of low-temperature chemistry (LTC) by addition of ethanol impacts the heat release rate in regions where the temperature is higher through the diffusion of specific radicals such as CH2O, C2H4, C3H6, and H2O2. In mixtures where ethanol is dominant, the high ethanol fractions in the mixture increase the heat release rate, primarily due to ethanol decomposition and its subsequent reactions. This method effectively quantifies and compares the influence of both chemical kinetics and species diffusion effects, providing detailed insights into the interactions among species across the reactive field when analyzing the counterflow configuration of complex fuel mixtures.