Jph. Sanders et al., FLAMELET-BASED MODELING OF NO FORMATION IN TURBULENT HYDROGEN JET DIFFUSION FLAMES, Combustion and flame, 111(1-2), 1997, pp. 1-15
The potential of using the laminar flamelet model for predictions of N
Ox emissions from turbulent hydrogen jet diffusion flames with various
amounts of helium dilution is explored in this study. The flamelet ap
proach treats turbulent flames as an ensemble of laminar flames subjec
t to local fluid dynamic stretch which causes chemical kinetics to dev
iate from equilibrium. This flame stretch rate can be described as the
scalar dissipation rate or as the strain rate. Numerical modeling is
performed to assess the merits of these two choices by comparing predi
cted scaling behavior of NOx emission index with the experimental data
of Driscoll and co-workers [1,2]. The present study reveals that only
with the scalar dissipation rate as the nonequilibrium parameter will
the predicted NOx emission indices exhibit a clear scaling relation v
s the Damkohler number. The flamelet predictions are found to improve
when the Damkohler number increases. However, the absolute NOx levels
are overpredicted, which is attributed to differential diffusion effec
ts. (C) 1997 by The Combustion Institute.