Investigation of Flame Structure and Soot Formation in a Single Sector Model Combustor Using Experiments and Numerical Simulations Based on the Large Eddy Simulation/Conditional Moment Closure Approach
2018
In this work, a single sector lean burn model combustor operating in pilot only mode has
been investigated using both experiments and computations with the main objective of
analyzing the flame structure and soot formation at conditions relevant to aero-engine
applications. Numerical simulations were performed using the large eddy simulation
(LES) approach and the conditional moment closure (CMC) combustion model with
detailed chemistry and a two-equation model for soot. The CMC model is based on the
time-resolved solution of the local flame structure and allows to directly take into account
the phenomena associated to molecular mixing and turbulent transport, which are of
great importance for the prediction of emissions. The rig investigated in this work, called
big optical single sector rig, allows to test real scale lean burn injectors. Experiments,
performed at elevated pressure and temperature, corresponding to engine conditions at
part load, include planar laser-induced fluorescence of OH (OH-PLIF) and phase Doppler
anemometry (PDA) and have been complemented with new laser-induced incandescence
(LII) measurements for soot location. The wide range of measurements available
allows a comprehensive analysis of the primary combustion region and can be exploited
to further assess and validate the LES/CMC approach to capture the flame behavior at
engine conditions. It is shown that the LES/CMC approach is able to predict the main
characteristics of the flame with a good agreement with the experiment in terms of flame
shape, spray characteristics and soot location. Finite-rate chemistry effects appear to be
very important in the region close to the injection location leading to the lift-off of the
flame. Low levels of soot are observed immediately downstream of the injector exit, where
a high amount of vaporized fuel is still present. Further downstream, the fuel vapor disappears
quite quickly and an extended region characterized by the presence of pyrolysis
products and soot precursors is observed. The strong production of soot precursors
together with high soot surface growth rates lead to high values of soot volume fraction
in locations consistent with the experiment. Soot oxidation is also very important in the
downstream region resulting in a decrease of the soot level at the combustor exit. The
results show a very promising capability of the LES/CMC approach to capture the main
characteristics of the flame, soot formation, and location at engine relevant conditions.
More advanced soot models will be considered in future work in order to improve the
quantitative prediction of the soot level.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
31
References
10
Citations
NaN
KQI