DOI: 10.1615/ICHMT.2015.IntSympAdvComputHeatTransf
ISBN Print: 978-1-56700-429-8
ISSN: 2578-5486
A Study of Radiative Flameless Combustion in a Furnace
SINOPSIS
In this work radiative flameless combustion (RFC) was investigated experimentally, by Chemkin
calculations, and an analytical model with radiation was developed to determine the dimensionless
parameter space where RFC is possible.
The experimental results show ultra-low NO, CO and THC and also show that UV emission
corresponding to OH is considerably reduced in flameless combustion. This is confirmed by Chemkin
calculations. Both the experimental and Chemkin results show that increasing the preheat temperature
for the same recirculation rate changes flameless to flaming combustion, indicating more complex
requirements for flameless combustion.
This led to the development of the analytical model where both steady-state and transient solutions
were obtained in the optically thin limit by noting that: (i) nearly isothermal environment is associated
with flameless combustion, and (ii) the chemical reaction must be spread out over the largest possible length
scale, i.e. (D8734;/α0)1/2. These hypotheses are consistent with Chemkin calculations. The steady state
solutions established the boundaries in the parameter space within which RFC is possible.
Three important non-dimensional parameters were found: (i) The Boltzmann number 'B' (ii) The
Damkohler number 'A', and (iii) The dimensionless Arrhenius factor 'β'. These, in addition to the equivalence ratio 'Ø', define the parameter space for RFC. It was also found that the Damkohler number must be small for flameless combustion to be possible and that the Boltzmann number expands the
flameless combustion domain. Available experimental data agrees with this analysis.