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Influence of new fuel flexible premix combustors on thermo-acoustic behaviour of annular combustion chambers


Supervisor: Subject:
    network modeling, thermo acoustic instability, transfer matrix and transfer function, annular combustor
Editor: Cooperation/Funding:

Motivation

Reliability and flexibility of modern lean premixed gas turbine combustion technology have become more and more important. Because of the susceptibility to thermo-acoustic instabilities which result in strong pressure pulsations, increased heat transfer and higher levels of emissions it is desirable to include thermo-acoustic behaviour of new premix combustors in the design process and to reduce costs.

Strategy and goals

The goal of this project is the prediction of thermo-acoustic stability of new fuel flexible premix combustors in annular combustion chambers. Therefore, a Design for Stability - procedure will be developed, basing on experimental investigations in the single combustor test rig. This procedure consists of three steps:

  • Measurement and modeling of burner transfer matrices and flame transfer functions of several burner types
  • Stability analysis with the network model of the annular combustion chamber
  • Burner geometry restrictions
The measured transfer matrices of several burner types are compared to parametrical transfer matrices derived from an analytical network model of the burners. The network models mainly consist of straight or curved ducts and area changes with or without losses. The parameters of the network model are pressure loss coefficients and effective lengths, depending on the burner geometry. A parameter analysis of the modeled burner transfer matrices of the different burner types gives information about parameters which have a great impact on thermo-acoustic stability. Then, a stability analysis of the important parameters with the network model of the annular combustion chamber identifies optimal parameters. Finally, the optimal parameters are applicated to geometry restrictions of the burner. The result of the Design for Stability - procedure is a burner design which allows stable combustion in annular combustion chambers as used in real gas turbine combustion.

The in such a way predicted thermo-acoustic stability of one burner type will be verified with investigations in the annular combustor test rig.

Figure: Annular combustor test rig

Experimental work

One of the first steps of the Design for Stability procedure is to measure burner transfer matrices und flame transfer functions of several burner types. Therefore, a burner tool kit is developed which includes characteristics of new fuel flexible combustors. Types of this burner tool kit are investigated in the single combustor test rig.

Figure: Sketch of the single combustor test rig

Transfer matrices couple pressure and velocity fluctuations upstream and downstream of the burner. The multi-microphone method is used to determine such transfer matrices by measuring pressure fluctuations at three positions each.

Figure: Transfer matrix

These measured transfer matrices are used to develop the parametric network model of the burner. To analyze the stability of the burner the model is implemented in the network model of the annular combustion chamber. To guarantee a good prediction of the system stability an existing burner is investigated with the network model and in the test rig first. When the results show a good agreement the parametric model of the new designed burner is implemented in the network model of the annular combustor and stability analyses are performed. By varying the parameters of the burner model the optimal configuration will be derived. Finally the developed burner is investigated in the test rig to validate the predicted system behavior.

Acknowledgment

This project is part of the research initiative "Power plants for the 21st century", KW21 with the overall goal of more efficient, economic and eviromental friendly power plants. Partners for this project are ALSTOM Power Systems GmbH and Bavarian Research Alliance.