M.Sc Thesis


M.Sc StudentJoseph Shamenzon
SubjectPerformance of a Combustion Chamber that Implements
Flameless Oxidation, Using a Heat Exchanger of
Recirculated Exhaust Gases
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Levy Yeshayahou
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

One of the pollutants that are formed in gas turbines and jet engines is Nitric Oxides (NO, NO2, and N2O). The formation of these pollutants depends on various factors, of which the dominant is the presence of hot spots in the flame.

There are various techniques of reducing nitric acids pollutant: Air Staging, Fuel Staging, Staged Combustion, LPP, RQL, and more. The strategy on which the present thesis focuses is Flameless Oxidation.

The flameless oxidation process is successfully implemented in industrial furnaces, using a recirculation of hot burnt products into the reaction zone. It is impossible to implement this technique “as is” in gas turbines and jet engines because of the adiabatic nature of their combustor and the high air pressure in it.

This thesis refers to a new technique which uses heat exchanger in burning chamber, which will extract heat from recirculated burnt products, and transfer it to the excess dilution air (air that doesn’t take part in oxidation process). This technique lowers flame temperature, while maintaining the conditions needed for flameless oxidation to occur (low oxygen concentration). This thesis performs preliminary design analysis of such a technique. The analysis is performed using a computer simulation.  

The discussed burning chamber consists of two main areas:

?         Cylindrical burning area, where the flameless oxidation and the recirculation of the burnt products occur.

?         Surrounding air area, which surrounds the burning area, and where the excess dilution air flows.

Recirculation of burnt products is achieved by presence of a toroid vortex, which causes the recirculated burnt products to flow in opposite direction, back to reaction zone. In order to amplify heat exchange between recirculated burnt products and the surrounding air, longitudinal fins are placed in both places: surrounding air area and the area where the recirculated burnt products flow.

The focus of current work is heat exchange and pressure loss calculations. Optimization of fins geometry, and their quantity, that will lead to maximal flame temperature reduction was carried out. Influence of compressor pressure ratio and allowed pressure loss in the chamber was also investigated.

This thesis shows that use of heat exchanger between recirculated burnt products and the surrounding air, with the implementation of flameless oxidation, has the potential to reduce nitric acid pollutants in gas turbine engines. Further promotion of such a technique requires additional elaborate scientific efforts, such as CFD simulations and laboratory experiments.