The project consists of 6 academic partners (University of Twente, Netherlands – BRNO University of Technology, Czech Republic – Keele University, UK – Imperial College London, UK – University of Zaragoza, Spain – Boston University, USA), two research institutions (CERFACS, France – DLR, Germany) and five industrial partners (Ansys, UK – IfTA, Germany – (GDF Suez) Electrabel, Netherlands & Laborelec, Belgium – Sulzer Turbo Services, Netherlands – Siemens Power Generation, Germany).
- Can Altunlu (A.C.) MSc
- Prof.dr.ir. André de Boer
- Dr.ir. Peter van der Hoogt (P.J.M.)
- Dr.ir. Jim Kok (J.B.W.)
- Juan Roman Casado (J.C.) MSc.
- Mehmet Kapucu (M.) MSc.
- Mina Shahi (M.) MSc.
- Santosh Tarband Veraraghavan (S.K.) MSc.
In order to investigate the thermo-acoustic instabilities in combustion systems, and resulting unstable pressure oscillations, which leads to elevated mechanical vibrations at high temperatures, European Commission supported LIMOUSINE project under Marie Curie Initial Training Network (ITN) program was initiated.
Figure 1. Illustration of a typical gas turbine engine
Reducing pollutant emissions and preserving our environment, as well as maintaining efficiency and performance of gas turbines, are the key directions of engine manufacturers towards sustainable economic future. The stringent regulations for NOx emissions have led the development of lean, premixed (LPM) combustion systems in gas turbine engines. Premixing large amount of air with fuel prior to its injection into the combustion zone to avoid the formation of stoichiometric regions, and thus local high temperatures can be prevented. Hence, burning a leaner mixture can reduce the peak temperature.
LPM combustion systems are prone to combustion instabilities . These combustion systems generally operates near the lean blowout limit, thus a perturbation in the equivalence ratio is susceptible to produce heat release oscillations. Hence, if these oscillations match with one of the chamber acoustic resonance frequencies, high amplitude oscillations of pressure are generated. These pressure oscillations elevate mechanical load in the chamber, which results in high amplitude vibrations. Furthermore, the unsteady flow enhances heat transfer, thus higher temperature exposure to the components. High amplitude vibrations together with elevated temperatures can lead to failure of the system. Figure 6 illustrates a comparison between an intact burner assembly and a damaged burner assembly due to combustion instabilities.
Figure 2. Burner assembly – intact (left) and damaged (right) 
Combustion instabilities in LPM combustion systems reveal substantial challenges to maintain reliability and safety. Therefore, the instabilities must be predicted and recognised in the design stage, and precautions must be taken in advance to prevent unexpected failures of in-service components. However, avoiding or controlling of instabilities remains a challenge within the entire range of operating settings depending on power transition (idle to nominal), or climate conditions. Thus, developments of mechanical integrity tools are essential to ensure and maintain the reliability and safety, as well as the efficiency, of the new and existing engine components.
The main focus in this research is devoted to improve the understanding of two-way interaction between combustion instabilities and structure, and the development and application of design and operation tools used for mechanical integrity analysis of the combustor. The thermo-acoustic instability is a multiphysical phenomenon, thus it was investigated in an interdisciplinary framework. It is composed of Structural Health Monitoring (structural dynamics), Safe-life Approach (fluid-structure interaction, fatigue and creep), Damage-Tolerant Life Approach (fracture mechanics) and Condition Monitoring (statistical and probabilistic analysis).
Lieuwen, T., Torres, H., Johnson, C., and Zinn, B. T., 2001, "A Mechanism of Combustion Instability in Lean Premixed Gas Turbine Combustors," Journal of Engineering for Gas Turbines and Power, 123(1), pp. 182-189.
Goy, C. J., James, S. R., and Rea, S., 2005, "Monitoring combustion instabilities: E.ON UK’s experience," Combustion Instabilities in Gas Turbine Engines: Operational Experience, Fundamental Mechanisms, and Modeling, T. C. Lieuwen, and V. Yang, eds., American Institute of Aeronautics and Astronautics, pp. 163-175.