Simultaneous OH and HCHO Laser Induced Fluorescence on Premixed Flames of Various Hydrocarbons

Abstract During the past decades, an important amount of experimental works has been dedicated to the detection of the local Heat Release Rate (HRR) which is of great interest in understanding the behaviour of turbulent flames, in particular in IC engines. Previous studies have shown that convolution of Laser Induced Fluorescence signals of hydroxyl radical (OH) and formaldehyde (HCHO) under atmospheric conditions was a promising way to estimate the heat release rate Najm et al. (1998), Paul and Najm (1998), Fayoux et al. (2004), Böckle et al. (2000). In this study, we investigate the performance of simultaneous LIF measurements of OH and HCOH for laminar stoichiometric premixed methane, n-heptane and isooctane counter-flow flames from 1 to 5 bar. Experiments were carried out in an axi-symmetrical premixed counter-flow burner producing two planar flames stabilized around the stagnation plane, Rolon et al. (1991), Lacas et al. (1992). The flames are excited by two vertical coplanar laser sheets crossing the burner’s axis. The first laser sheet is generated by a frequency-doubled Nd:YAG laser at 532 nm pumping a Dye laser, which frequency is also doubled. This first laser sheet is used in order to excite the OH radical in the A2S – X2P (1-0) Q1(6) band at 282.93nm (25 mJ, 7 ns pulse duration). The second laser sheet is generated by a Nd:YAG laser frequency tripled at 355 nm (50mJ, 7ns pulse duration) in order to excite HCHO in the A1A2 – X1A1 410 band. The two laser beams ar