Local chemiluminescence spectra measurements in a high-pressure laminar methane/air premixed flame

Abstract

The spatially resolved chemiluminescence in the reaction zone of a laminar premised methane/air flamewas measured. The pressure dependence of the flame front structure and chemiluminescence spectra were examined up to 1.5 MPa. Local point measurements of chemiluminescence were obtained using the Cassegrain optics system that we have developed, which has a high spatial resolution of d=0.1 mm and L=0.8 mm. Two types of measurements were performed: a local point chemiluminescence measurement with an ICCD camera with monochromator and selected chemiluminescence intensity measurements to obtain its profile and the flame front thickness at the flame front. The chemiluminescence at different pressures was examined to identify the main OH*, CH*, and C2* spectra. Background spectra related to CO-O* were observed at pressures greater than 0.5 MPa. Detailed OH* and CH* spectra were measured at different pressures, and the results indicate that each vibrational and rotational peak is in the same location, regardless of the pressure. The chemiluminescence intensity ratio of OH*/CH* at different pressures was examined. Less dependence on pressure was observed, although the individual chemiluminescence intensities changed with increasing pressure. The CO-O* broadband spectrum was significant at 0.5 MPa: its intensity remained at the same level at pressures greater than 0.5 MPa. This background spectrum was not observed at 0.1 MPa. In order to examine these chemiluminescence intensity profiles with the reaction zone and their dependence on pressure, the peak locations of OH*, CH*, and C2* were measured. The OH* peak was located inside the CH* and C2* curves for all measured pressures.