Stabilization of lifted hydrogen jet diffusion flame in a vitiated co-flow: effects of jet and coflow velocities, coflow temperature and mixing

TL;DR

This study uses numerical simulations to analyze how jet and coflow velocities, temperature, and mixing influence the stabilization and lift-off height of hydrogen jet flames in a vitiated co-flow, revealing auto-ignition as the stabilization mechanism.

Contribution

It provides detailed numerical insights into the effects of flow parameters and mixing on hydrogen flame stabilization, using advanced turbulence-chemistry interaction modeling.

Findings

Lift-off height is highly sensitive to coflow temperature.

Mixing model constant CΦ=4 aligns best with experimental data.

Auto-ignition is identified as the stabilization mechanism.

Abstract

The present paper reports on the numerical investigation of lifted turbulent jet flames with H2/N2 fuel issuing into a vitiated coflow of lean combustion products of H2/air using conditional moment closure method (CMC). A 2D axisymmetric formulation has been used for the predictions of fluid flow, while CMC equations are solved with detailed chemistry to represent the turbulence-chemistry interaction. Simulations are carried out for different coflow temperatures, jet and coflow velocities in order to investigate the impact on the flame lift-off height as well as on the flame stabilization. Furthermore, the role of conditional velocity models on the flame has also been investigated. In addition, the effect of mixing is investigated over a range of coflow temperatures and the stabilization mechanism is determined from the analysis of the transport budgets. It is found that the lift-off height is highly sensitive to the coflow temperature, while the predicted lift-off height using the mixing model constant, i.e., C{\Phi}=4, is found to be the closest to the experimental results. For all the coflow temperatures, the balance is found between the chemical, axial convection and molecular diffusion terms while the contribution from axial and radial diffusion is negligible, thus indicating auto-ignition as the flame stabilization mechanism.