Measurement of the local flamefront structure of turbulent premixed flames by local chemiluminescence

Abstract

Local chemiluminescence measurements of OH * , CH * , and C 2 * were made at the flamefront of premixed turbulent propane flames to study details of the reaction zone and flamefront structure. The relationship between excited OH, CH, and C 2 concentrations and the intensity of chemiluminescence emissions was investigated by PREMIX (GRI-Mech), and a strong correlation was proven. Cassegrain optics were developed to detect the intensity of these chemiluminescent emissions simultaneously at a single point to obtain flame spectroscopic data for a local point. The relationship between the scale of turbulence and the thickness of the flamefront was investigated using simultaneous measurement of the three chemiluminescences and laser Doppler velocimetry. Particle velocimetry was also used to demonstrate combustion flow characteristics of interest. It was found that local chemiluminescence can provide very useful spectroscopic data on the flamefront region. Time-series chemiluminescence can describe the timescale of the reaction and the flows at the flame front. Furthermore, the structure of the flamefront can be characterized by the duration of the chemiluminescence and by the patterns of its occurrence, which were found to correspond to the thickness of the flamefront and the Damköhler number. A new technique for measuring the local flamefront structure using local chemiluminescence measurements is proposed, and its performance is proven.