Radiation-affected laminar flame quenching

Abstract

Under the influence of radiation, the increase in Peclet number characterizing the flame quench distance A, p.cpSu Tb ° adiabatic flame enthalpy flow Pe-hTb°/A conduction and the decrease in flame temperature are shown in terms of an original radiation number T/T(I-6./2)Bb 0 total radiation I + 3~'2(2/¢.-1)/(1-o~) adiabatic flame ethalphy flow where p is the density, cp the specific heat at constant pressure, Su the laminar flame speed, Tb the flame temperature, subscript u the unburned gas and superscript 0 the adiabatic gas,), the thermal conductivity, 7/= (rp/rR)"2 the weighted nongrayness, rp and rR being the Planck mean and the Rosseland mean of the absorption coefficient, ¢. the wall emissitivity, r= rMI the optical thickness, XM = (rpxR)~/2 being the mean absorption coefficient and I a characteric length (related to geometry or quench distance), o~ the albedo of single scattering, and Bb ° the adiabatic flame Boltzmann number. 4Eb ° emission Bb0=-p,cpS. °T b° adiabatic flame enthaipy flow where Eb is the blackbody emissive power. It is qualitatively shown that the contribution of radiation to the heat transfer and the laminar flame quenching in small diesel engines can be as much as 35%. I. INTRODUCTION A recent study by Arpaci and Tabaczynski [1], hereafter called P1, introduces a radiative heat flux which includes the emission, absorption,

Buoyancy-driven turbulent diffusion flames

“…As is well known, the primary effect of thermal radiation on high-temperature problems is on the heat flux. Studies by Arpaci and coworkers [58,59,61,62,[64][65][66], and Selamet and Arpaci [63,67] show the emission, absorption, and scattering (hotness, optical thickness, and refractive) effects on this flux. However, there is no experimental literature on pool fires separating these effects.…”

“…On intuitive grounds, the emission effect of radiation (hotness of flame) has been already incorporated into the heat of combusion and the latent heat of evaporation by fractional lowering (say 3' and ~b) of these properties (see Kanury [19]). Following the studies of Arpaci and coworkers [58][59][60][61][62] and Selamet and Arpaci [63], the optical thickness and scattering effects of radiation can be incorporated into 3' and ~b. However, because of the lack of experimental data, no attempt is made here to demonstrate their influence on 3' and ~b.…”

Entropy production in flames

“…Rearrange Eq. 25 [14], and McIntosh and Clarke [15] for the case excluding radiation, and Arpaci and Tabaczynski [16,17] for the case including radiation; also, see Kooker [18] and Sohrab and Law [19] for the importance of radiation on quenching processes, and Lee and Tien [20] for the effect of condensed fuels on this process). References [12,13,16,17] follow the usual practice and evaluate the minimum quench distance from the tangency condition,…”