Comparison of OH radical species in n-butanol and methane diffusion flames

This paper compares the structure of n-butanol flames with the well understood and studied structure of methane flames. The fuels were studied in a coutnerflow diffusion flame configuration under different equivalence ratios and different strain rates. Laser induced fluorescence (LIF) was used to probe the structure of the flames and image major species and radical concentrations. Simulations were performed for the same conditions, and the resulting flame structures are compared with the experimental results. In order to measure OH LIF, the second harmonic of a Nd:YAG was used to pump a dye laser which produces a 284nm wavelength used to create a population inversion for OH, which then fluoresces at 308nm. The OH fluorescence is captured by an ICCD camera using a bandpass filter with a 310 nm center wavelength. Methane flames were computed using the well-established GRI30 reaction mechanism while n-butanol flames were computed using a mechanism developed by the Lawrence Livermore National Laboratory. Experimental results show that OH appears to be closer to the fuel side of the reaction sheet for both fuels. A strong chemiluminescence was observed, which at times interfered with the OH LIF signal.