Flame diagnostics based on measurement of diffusive-thermal oscillations characteristics

In this work, we review our recent advances in developing a flame diagnostic method by measuring the diffusive-thermal oscillations characteristics of premixed burner stabilized flames. One of the key factors affecting the accuracy of the method was identified as the formation of a secondary diffusion flame over the primary premixed combustion front. This diffusion flame can be successfully suppressed by organizing a shielding N2 co-flow around the main burner. However its effect on flame dynamics is not obvious. Here, we conduct for the first time a detailed experimental study of the two-dimensional dynamics and structure of the methane-air burner stabilized flames by using the Laser Induced Fluorescence of the OH radical. It is demonstrated that near the boundary of the onset of diffusive-thermal instability flame oscillations are one-dimensional if the N2 co-flow is configured correctly. This mode is thus ideally suited for testing detailed reaction mechanisms using numerically efficient one-dimensional simulation codes. The oscillations deviate moderately from one-dimensional if the parameter values are shifted away from the boundary of stability. ... mehrFurther applications of the method and ways to advance it are discussed.
Novelty and significance statement: This work presents a novel approach to obtaining reliable experimental data for validating and verifying detailed reaction mechanisms of various types of fuels. The approach is based on studying the dynamic characteristics of flames stabilized on a flat porous burner operating in a diffusive-thermal oscillation regime. As a case study, the two-dimensional dynamics and structure of a rich pulsating methane-air flame were investigated for the first time using laser-induced fluorescence (LIF) of OH. The proposed method enables the acquisition of a large amount of new, high-precision experimental data for subsequent comparison with predictions from detailed reaction mechanisms and for their verification. The applicability of computationally effective one-dimensional modeling of oscillating flames is confirmed once the precise control of the system parameters is provided. The conditions necessary to preserve the pulsating flame in a flat one-dimensional regime are outlined, which is crucial for the effective implementation of the proposed method.