Characteriation of spherical hydrocarbon fuel flames: Laser diagnosis of the chemical structure through the oh radical

For the first time, spherical diffusion flames of n -decane, n -heptane, and methanol established around fuel-drenched porous spheres were investigated by applying the two-dimensional laser-induced predissociation fluorescence method to measure the OH radical under microgravity conditions. Focus of this work was laid on the development of a UV-laser diagnostic system attached to the Bremen drop tower for the characterization of combustion under buoyant-free conditions and on its applicability to the diffusion zone of hydrocarbon droplet flames. The experiments carried out on the previously mentioned fuels showed capabilities and limitations of this method applied on liquid fuels. While it is relatively straightforward to investigate the chemical structure of methanol droplet flames because of the absence of Mie scattering soot particles and of nonresonant fluorescing species, it is difficult for larger hydrocarbons such as n -hepatane and n -decane. It is considered that with the development of a luminous zone, strong broadband absorption by fuel vapor and intermediates larger than methane in connection with high laser pulserepetion rates may cause interactions of the input energy with the chemical kinetics of the combustion process.