Understanding the negative temperature coefficient phenomenon in methane-air mixtures at high pressures

TL;DR

This study evaluates various micro-kinetic models for methane oxidation at high pressures, revealing the key role of C2 formation in the negative temperature coefficient phenomenon, which is crucial for designing advanced reactors.

Contribution

The paper critically compares multiple reaction mechanisms and identifies the dominant pathway responsible for negative temperature coefficient behavior in methane oxidation.

Findings

C2 formation via recombination drives negative temperature coefficient behavior

Steam addition influences reaction pathways and system stability

High pressure impacts the reaction dynamics significantly

Abstract

Design and operation of advanced reactors such as fuel reformers require reliable micro-kinetic models that capture the dynamics of the reaction. The negative temperature coefficient phenomenon causes a reduction in mixture temperature for increasing inlet temperatures. However, micro-kinetic models available in the literature have not been critically evaluated for their ability to capture this phenomenon. Consequently, the ability to predict system behavior for particular application situations, such as in the presence of certain diluents or at high pressures, is largely missing. In this work, we adapt multiple reaction mechanisms from literature and compare them for methane oxidation over a wide range of pressures and temperatures. Using reaction path analysis and sensitivity analysis, we find that the C2 formation through the recombination pathway is chiefly responsible for negative temperature coefficient behavior. With this insight, the dependence of steam addition and pressure on is also discussed.