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

TL;DR

This paper investigates how micro-particles absorbing radiation influence flame propagation and ignition, revealing that radiative preheating can significantly accelerate flames or trigger ignition, affecting combustion regimes.

Contribution

It demonstrates the impact of radiation absorption by particles on flame speed and ignition, highlighting the potential for radiation to dominate heat transfer and induce different combustion regimes.

Findings

Radiative preheating increases flame velocity, especially in slow reactive mixtures.

Radiation can trigger ignition in particle clouds if temperature thresholds are met.

Different combustion regimes can be initiated depending on radiation absorption length.

Abstract

Thermal radiation of the hot combustion products usually does not influence noticeably the flame propagating through gaseous mixture. the situation is changed drastically in the presence even small concentration of particles, which absorb radiation, transfer the heat to the surrounding unburned gaseous mixture by means of heat conduction, so that the gas phase temperature in front of the advancing flame lags that of the particles. It is shown that radiative preheating of unreacted mixture ahead of the flame results in a modest increase of the advancing flame velocity for a highly reactive gaseous fuel, or to considerable increase of the flame velocity in the case of a slow reactive mixture. The effects of radiation preheating as stronger as smaller the normal flame velocity. The radiation heat transfer can become a dominant mechanism compared with molecular heat conduction, determining the structure and the speed of combustion wave in the case of a small enough velocity of the advancing flame. It is shown that in the case of non-uniform distribution of the particles, such that time of the radiation heating is longer so that the maximum temperature in the region of denser particles cloud ahead of the advancing flame is sufficient for ignition, the thermal radiation may trigger additional independent source of ignition. Depending on the steepness of the temperature gradient formed in the unburned mixture, either deflagration or detonation can be initiated via the Zeldovich's gradient mechanism. Ignition of different combustion regimes, depending on the radiation absorption length, is illustrated for the particle-laden hydrogen-oxygen flame.