Proceedings of ASME Turbo Expo 2003 June 16–19, 2003, Atlanta, USA 2003-GT-38393 COMBUSTION PROCESS OPTIMIZATION USING EVOLUTIONARY ALGORITHM Christian Oliver Paschereit ¤ , Bruno Schuermans, Dirk B ¨ uche y ALSTOM (Switzerland) Ltd. CH-5405 Baden Switzerland ABSTRACT Flame stabilization in a swirl-stabilized combustor oc- curs in an aerodynamically generated recirculation region which is a result of vortex breakdown. The characteristics of the recirculating °ow 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 °ow and mixing properties. The mixing properties of the investigated burner can be in°uenced by the position and the amount of fuel injection into the burner. The fuel injection is controlled by two di®erent setups using (a) 8 proportional valves to adjust the mass °ow 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 °ame. These two objectives are con°icting, a®ecting the environment and the lifetime of the combustion chamber, respectively. A multi-objective evolutionary algorithm is applied to opti- mize 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 di®erent compromise between the con°icting objectives. One compromise solu- tion 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 ∗ Address all correspondence to this author (email: oliver.paschereit@power.alstom.com.) † Also at: Institute of Computational Science, Swiss Federal Insti- tute of Technology (ETH), CH-8001 Z¨ urich, Switzerland that a more uniform distribution of heat release in the re- circulation zone was achieved. The results were con¯rmed in high pressure single burner tests. The suggested fuel injection pattern has been successfully implemented in en- gines with su±cient stability margins and good operational °exibility. This paper shows the careful development process from lab scale tests to full scale pressurized tests. 1 INTRODUCTION Modern design of low emission combustors is character- ized by swirling air in the combustor's dome coupled with distributed fuel injection to maximize mixing. This design results in e±cient combustion with extremely low emissions. The fuel distribution and mixing with the air stream play a critical role in the combustion process and in the per- formance of the system. Various °ow dynamics processes control the mixing between fuel and air in di®usion °ame con¯gurations and the mixing between the fresh fuel/air mixture and hot combustion products and fresh air in pre- mixed combustors. They include large-scale vortices that evolve in a separating shear layer downstream of a sudden expansion or blu® body °ame holders, and swirling vortices that undergo vortex breakdown in swirl-stabilized combus- tors. Interaction between these vortices which are related to °ow instabilities, acoustic resonant modes in the com- bustion chamber and the heat release process was shown to cause undesired thermoacoustic instabilities in combustors (Paschereit et. al, 1999). The ALSTOM EV burner has the unique property of °ame stabilization in free space near the burner outlet uti- 1 Copyright c ° 2003 by ASME