Spatio-temporal evolution of harmonic disturbances on laminar, non-premixed flames: Measurements and analysis

Abstract

This paper analyzes the dynamics of harmonically forced, non-premixed flames, both experimentally and computationally. Prior theory has made a number of predictions on how wrinkles on non-premixed flamelets are excited by flow disturbances, convect axially, and evolve in disturbance magnitude, including setting up interference patterns in wrinkle disturbance magnitude. The objective of this study was to obtain measurements from forced flames to determine if these features are present, and to compare the gain/phase of these wrinkles with predictions using the measured velocity field as inputs.High speed PIV data was taken on a coflowing methane-air diffusion flame, equipped with speakers for harmonic forcing, over a variety of flow velocities, forcing frequencies, and forcing amplitudes. These measured velocity fields were used as inputs to a Z -equation solver, and the resulting space-time dynamics of iso-Z surfaces were extracted from the Z field solutions. Both experimental and numerical results show that flame wrinkles propagate axially at the mean flow velocity, a result consistent with previous analytical findings. These wrinkles start with near zero magnitude at the fuel tube lip and grow with downstream distance, until peaking at some axial location. Further downstream, the wrinkle magnitude modulates, indicative of interference effects which have been previously predicted in analytical studies.

A Review of Environmentally Friendly Approaches in Fire Extinguishing: From Chemical Sciences to Innovations in Electrical Engineering

“…In practice, the sound pressure increases linearly only in a certain range, depending on the electrical power applied to the sound source, and the combustion may have a discontinuous pattern [ 34 , 35 , 36 ]. Some works have described unpredictable wrinkling [ 37 , 38 ] or bifurcation [ 39 , 40 ] of the flame.…”

Experimental Investigation of Amplitude-Modulated Waves for Flame Extinguishing: A Case of Acoustic Environmentally Friendly Technology

“…Some research carried out showed that an increase in the average mass loss rate of fuels was observed with increasing sound pressure. Unpredictable flame wrinkling was reported in [48], [49], and its bifurcation was described in [50], [51]. From the analysis of research papers [52], [53], it can be inferred that the average flow effect is a significant factor in flame control.…”

Analysis of Flame Suppression Capabilities Using Low-Frequency Acoustic Waves and Frequency Sweeping Techniques

“…The process of flame stream rupture due to acoustic waves is described in [51]. Wrinkling of the flame is presented in [52,53], and its bifurcation in [54,55].…”