Combustion Process Optimization Using Evolutionary Algorithm

Flame stabilization in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown. The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling to downstream pressure pulsations is also possible. Flame stability and emission formation depend on flow and mixing properties. The mixing properties of the investigated burner can be influenced by the position and the amount of fuel injection into the burner. The fuel injection is controlled by two different setups using (a) 8 proportional valves to adjust the mass flow for each fuel injector individually or using (b) 16 digital valves to include or exclude fuel injectors along the distribution holes. The objectives are the minimization of NO_x emissions and the reduction of pressure pulsations of the flame. These two objectives are conflicting, affecting the environment and the lifetime of the combustion chamber, respectively. A multi-objective evolutionary algorithm is applied to optimize the combustion process. Each optimization run results in an approximation of the Pareto front by a set of solutions of equal quality, each representing a different compromise between the conflicting objectives. One compromise solution is selected with NO_x emissions reduced by 30%, while mainaining the pulsation level of the given standard burner design. Chemiluminescence pictures of this solution showed that a more uniform distribution of heat release in the recirculation zone was achieved. The results were confirmed in high pressure single burner tests. The suggested fuel injection pattern has been successfully implemented in engines with sufficient stability margins and good operational flexibility. This paper shows the careful development process from lab scale tests to full scale pressurized tests.