The relative effectiveness of gaseous and powdered agents in inhibiting real fires is approached by coflow diffusion flame. The effect of addition of $CO_2$ gas to the air side of propane-air flame is shown. A comparision of two commercial powdered agents added to the air stream of a propane-air flame is shown. Two kinds of powder have to be distinguished: ‘thermal’ and ‘chemical’ inhibitors, the former acting mainly by a cooling effect and the latter by a more specific surface destruction of the free radicals which propagate the chain reaction. In this experiment, chemical inhibition effectiveness of powder is very small.
Incident total and radiative heat transfer rates have been measured experimentally in a steady state. Adding small amount of $Al_2O_3$ particle to the flame, the radiative heat flux is increased. But high density of $Al_2O_3$ particle in the oxidizer resulted in decrease of radiation from the flame to the sensor. It has something to do with optical thickness theory in radiation part. $CO_2$ absorbed rays participated in radiation from the flame.
