Stetsyuk, V. (2009) Preliminary Analysis of Flameless Oxidation Combustion. Masters thesis, Technion – Israel Institute of Technology.

The subject of this work concerns the development of an ultra-low NOx emission burner for aircraft and industrial gas turbine applications. Thesis includes the development of a model that incorporates the thermal, aerodynamic and kinetic model of a low-emission combustion system.

Flameless oxidation is based on the principle of fuel combustion in hot vitiated air and it appears that this topic is still relatively unknown. Analysis showed that to develop such combustion systems, it is necessary that studies of combustion chemistry of fuels diluted with large quantities of combustion products, stability limits of flameless oxidation, and development of numerical simulation tools should be performed. The investigation under PSR (perfect stirred reactor) conditions of the influence of the chemical models on the flame temperature and species concentration predictions has showed that in certain cases the detailed chemistry model can be replaced with the global chemistry model giving reasonable error. Current global chemistry combustion models have important shortcomings; nevertheless they can be used when dealing with thermodynamics.

The influence of combustion air temperature and oxygen content (dilution) was studied using global heat - mass balance equations with special emphasis on the optimum of the equivalence and recirculation ratios. It was demonstrated that an increase in air dilution (decrease in oxygen content) decreases the flame temperature. A decrease in the equivalence ratio below 0.3 is irrational because the oxygen content in diluted mixture remains above 15% (oxygen content in diluted mixture must be less than 15%) even for high recirculation ratios. It was also demonstrated that combustion was possible under high concentration (high recirculation ratio) of CO2 in diluted mixture (reactants).

The developed flameless combustion model was integrated into a newly developed computer program. This computer program can be used further in prediction of the main characteristics of flameless combustion in the preliminary design phase. An integrated heat transfer model can be used as initial approximation in more sophisticated CFD simulations. The wall temperatures of the combustor calculated by the heat transfer model are expected to be quite well-predicted.

In this study, the influence of compressor pressure ratio (temperature after compressor), recirculation ratio, and type of fuel on main flameless combustion was illustrated. It showed the importance of adequately choosing the recirculation ratio for a specific working point. It was concluded that special care should be taken to optimize the geometric parameters of the flameless combustor to obtain fully homogeneous flameless oxidation combustion.

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