The Chemiluminescence and Structure Properties of Normal/Inverse Diffusion Flames

Abstract

The flame emission spectrometry was applied to detect the distribution of excited radicals in two types CH4/O2 coflow jet diffusion flames (normal and inverse diffusion flames). Combining the image analysis along with the spectrometry, the chemiluminescence and structure characteristics of these diffusion flames were investigated. The results show that the inverse diffusion flame (IDF) with relatively high inlet oxygen velocity is composed of two regions: a bright base and a tower on top of the base, which is quite different from the normal diffusion flame (NDF). The flame is divided into two regions along the flame axis based on maximum OH* position (Region I: initial reaction zone; Region II: further oxidation zone). The degree of the further oxidization taking place in Region II is obvious in accordance with OH* distribution, which is the main difference in reaction zone between fuel-rich condition and fuel-lean condition for NDFs. For IDFs, the change of OH* distribution with increasing equivalence O/C ratio ([O/C]e) in Region II is not conspicuous. More OH* and CH* are generated in IDFs, due to the inner high-speed O2 flow promoting the mixing of fuel and oxygen to a certain extent.

Comparative flame structure investigation of normal and inverse turbulent non-premixed oxy-fuel flames using experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals

“…the temperature profile of the inverse H 2 -flame [7] departed from the profile of the corresponding normal flame caused by differences in the H 2 ratio. Further, the investigation of an inverse and normal CH 4 -O 2 flame at a constant O/C ratio (not comparing flames at the same jet velocity) [9] found significantly different peak OH* chemiluminescence intensity and profiles in physical space along the burner central axis. For the present turbulent oxy-fuel NDF/IDF pair, the underlying flamelet structure is very similar due to negligible differential diffusion effects.…”

“…Whilst some studies of laminar air flames have found that inverse and normal diffusion flames are similar in structure [4,8], other authors have observed differences in the measured temperature in air combustion [7] and in the OH* chemiluminescence fields in oxy-fuel combustion [9]. To our knowledge, a similar comparison of turbulent normal and inverse diffusion flames has not been published.…”

“…In the present investigation, we focus on analyzing the differences between non-piloted IDFs and NDFs, extending previous laminar studies [4,[7][8][9] towards turbulent oxy-fuel flames. The influence of turbulence on flame structure in both configurations is studied using experimental and numerical data.…”

“…Mikofski et al [8] experimentally investigated the flame length in relation to the jet velocity. Zhang et al [9] identified differences between IDFs and NDFs based on OH* chemiluminescence in a CH 4 -O 2 mixture.…”

Three-dimensional flame measurements with large field angle

“…Using just the emitted photons of combustion reaction, chemiluminescence measurements of combustion provide an important indicator of heat release rates [1][2][3][4], equivalence ratios [2,5], excited species concentrations [6,7], without the need for lasers to be subjected to harsh conditions. This advantage of chemiluminescence enables researchers to use multiple 2D projections from various views of the target flame, combined with reconstruction algorithms, to obtain multidimensional measurements.…”