Combustion and Flame

TLDR: In this paper, an experimental system was designed to stabilize steady counterflow methane diffusion flames at elevated pressures, up to 3 MPa, and the replacement of nitrogen with helium as inert was found to be critical to stabilize well behaved flames with respect to steadiness, laminarity, adiabaticity, one dimensionality and flame thickness.

Abstract: An experimental system was designed to stabilize steady counterflow methane diffusion flames at elevated pressures, up to 3 MPa. In contrast with the much more common coflow configuration, the counterflow one is advantageous for the following reasons: the suppression of buoyancy instabilities that typically plague coflow flames at high pressures; the one-dimensionality of the flame, that enables computational modeling with very large chemical kinetic mechanisms; and the high level of control that it provides on soot loading. Above 0.8 MPa, the replacement of nitrogen with helium as inert was found to be critical to stabilize well behaved flames with respect to steadiness, laminarity, adiabaticity, one-dimensionality and flame thickness. Scaling and experimental considerations allowed for the identification of acceptable operating conditions in terms of pressure and strain rate and yielded a synthetic representation of a domain of diffusion flames of good quality. Such a graph can inform the design of a high-pressure counterflow system with respect to the selection of burner geometry, diagnostic techniques and experimental conditions, allowing for the experimentalist to sidestep costly and time consuming trial and error. Measurements by thin-filament pyrometry and numerical simulations confirmed the proposed scaling.