Title: A stochastic model for aircraft gas turbine combustor emissions
Abstract:The emission of NOx from aero-gas turbine combustors, which in the present generation of
designs consists mainly of thermal NOx ' is of great concern due to its potential damage to the
stratospheric o...The emission of NOx from aero-gas turbine combustors, which in the present generation of
designs consists mainly of thermal NOx ' is of great concern due to its potential damage to the
stratospheric ozone layer. Soot production in gas turbine combustors is also undesirable since
it is both the major source of exhaust smoke and, more importantly, the principal agent in
thermal radiation to the combustor liner. Furthermore thermal radiation from the soot redistributes
energy in the combustor, modifying the temperature field. This consequently
affects the production of other pollutants, notably that of thermal NOx> since the production
rate is especially sensitive to temperature.
Mathematical models for predicting gas turbine combustor emissions can be divided, in
general terms, into two main groups, Methods based on zonal (or modular) approach and on
CFD modelling. CFD modelling allows the use of computation intensive multi-dimensional
Navier-Stokes codes but cannot account for detailed chemistry which is responsible for
emissions. On the other hand, although the modular approaches make significant assumptions
about the mean flowfield and mixing, they employ detailed chemical kinetics.
The work reported in this thesis seeks to develop a model for emission predictions in the gas
turbine combustor which combines the advantage of both the modular approach and CFD
modelling. The strategy was based on a pdf calculation using the Monte-Carlo simulation
technique because the chemical source term is in closed form for the approach and the
solution procedure requires a CFD based calculation. Averaging of the particle properties was
on an extended zonal or planar basis in order to reduce computational effort. The predictions
are evaluated against available experimental results and other predictions employing more
conventional approaches.
Since the pdf method allows the modelling of slow chemistry and simultaneous influence of
multiple scalars, the thermal NO x production rate was implemented considering the effect of
NO concentration itself. Predicted exit NOx concentration was higher than the measured exit
level. It has been thought that this discrepancy is mainly due to neglecting radioactive heat loss
for temperature calculations.
The modelling of soot formation and oxidation has proved more problematic since the
assumption that soot is simply perturbation to the gaseous field, analogous to the NO
concentration, and temperature may be accurately described by single adiabatic flamelet are
no longer valid at elevated pressure and temperature conditions. Soot bum-out is
under-predicted. The computed mean soot oxidation is less than 10% of the maximum
production levels, even when OH is considered to be oxidising species in addition to
O2 ••
Although high soot formation rate was predicted as a result of neglecting radioactive loss and
using single perturbed flamelet calculation, the main uncertainties come from instantaneous
soot oxidation rate and the particle size effect which influence the…Read More
Publication Year: 1995
Publication Date: 1995-04-01
Language: en
Type: dissertation
Access and Citation
Cited By Count: 1
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot