Combustion rate and ignition delay time of boron particles in flat-flame burner experiments

Abstract

The main part of available data on boron particles combustion was obtained in flat-flame burner experiments. Boron particles were injected into flat-flame burner post-flame zone with a transporting jet of cold nitrogen; the combustion process of boron particles was registered with a number of optical methods. Systematization of ignition delay and combustion times of boron particles obtained in that type of experiment was done. Combustion times are represented in the form of particles linear combustion speeds. Combustion speed shows classic dependence on temperature, at low temperatures the reaction is temperature dependent and seems to be kinetically controlled, at high temperatures the reaction is diffusion controlled one. Most of the combustion data was obtained in wet environment. Kinetically controlled combustion depends on surrounding gas temperature, so the heat generation doesn't significantly heat the particle above the ambient temperature, such an effect is possible if heat release of the reaction on the surface of the particle is reduced. Ignition delay time shows smooth decay with flame temperature growth in each of the individual experiment but random values between independent measurements. The particles of the same size at the same flame temperature can show 1 or 5 ms ignition delay in independent experiments, and are several orders higher than in shock tube experiments. Supposition of inner hidden influencing factor specific for flat-flame burner experiments is done.