Flameless combustion is a novel combustion mode in which the flame has no visible nor audible signature. It is based on recirculating a substantial portion of hot product gases (300%) to be mixed with inlet fresh reactants prior to combustion. Computational Fluid Dynamics (CFD) is an efficient tool to evaluate the performance of flameless combustors. Our work in this paper was based on non-reacting species-transport CFD models with RANS turbulence closures.
Numerical non-reacting computations aimed to study the effect of
both combustor geometry and inlet air velocity on recirculation ratio
and mixing were performed. Criteria for the preliminary design and
optimization of the non-premixed flameless combustors with central air
jet arrangement was then developed.
The following conclusions were reached:
- Reducing the air jet diameter to half its original value results in a
100% increase in the recirculation ratio. This increase in recirculation
ratio significantly promotes combustor operation in the flameless
- Scaling down the combustor to half its original size results in 66%
reduction of recirculation ratio, which might cause abortion from
the flameless mode.
- As the level of excess air increases inside the combustor, the minimum necessary value of recirculation ratio, Kcritical, to achieve flameless combustion increases as well.
- Several expressions are developed to help guiding a preliminary
combustor design and/or optimization for flameless combustion.
- 1.Khalil HM, Eldrainy YA, Saqr KM, Abdelghaffar WA. Evaluation criteria for a flameless combustor based on recirculation and mixing – A CFD approach. Acta Astronautica [Internet]. 2018 Nov;127–36. Available from: http://dx.doi.org/10.1016/j.actaastro.2018.07.054