Influence of the radiation absorbed by micro particles on the flame propagation and combustion regimes

摘要

Thermal radiation of the hot combustion products usually does not influencenoticeably the flame propagating through gaseous mixture. the situation ischanged drastically in the presence even small concentration of particles,which absorb radiation, transfer the heat to the surrounding unburned gaseousmixture by means of heat conduction, so that the gas phase temperature in frontof the advancing flame lags that of the particles. It is shown that radiativepreheating of unreacted mixture ahead of the flame results in a modest increaseof the advancing flame velocity for a highly reactive gaseous fuel, or toconsiderable increase of the flame velocity in the case of a slow reactivemixture. The effects of radiation preheating as stronger as smaller the normalflame velocity. The radiation heat transfer can become a dominant mechanismcompared with molecular heat conduction, determining the structure and thespeed of combustion wave in the case of a small enough velocity of theadvancing flame. It is shown that in the case of non-uniform distribution ofthe particles, such that time of the radiation heating is longer so that themaximum temperature in the region of denser particles cloud ahead of theadvancing flame is sufficient for ignition, the thermal radiation may triggeradditional independent source of ignition. Depending on the steepness of thetemperature gradient formed in the unburned mixture, either deflagration ordetonation can be initiated via the Zeldovich's gradient mechanism. Ignition ofdifferent combustion regimes, depending on the radiation absorption length, isillustrated for the particle-laden hydrogen-oxygen flame.