Experimental Investigation of a Swirler Burner

CHAPTER 1CHAPTER 1: INTRODUCTION

Continuous combustion processes are encountered in many applications related to power generation, heating, as well as domestic and industrial burners. The need for high thermal efficiency and low levels of pollutant emissions requires continuous research and development in the field of power generation. To comply with today’s stringent regulations, the concept of lean premixed combustion has been adopted as it offers a certain number of advantages in controlling the emissions level. The reliability and flexibility of the modern cycle power gas turbine has imposed this technology as standard energy supply source in the present and in the foreseeable future.

Industrial practice has proven this technology to be sensitive to the development of self sustained thermo-acoustic combustion instabilities resulting in high levels of pressure pulsations in the combustion chamber. These disturb the normal operation and can produce extensive hardware damage to the system. The driving mechanism for this undesired phenomenon is mainly the feedback loop with a positive growth rate linking the unsteady heat release of the turbulent premixed flame and the acoustic field of the combustion system. These processes exhibit a wide range of dynamics, thereby promoting the resonant coupling between the unsteady parts of the heat release and the acoustic field, leading to sustained large amplitude pressure oscillations, known as Thermo acoustic Instabilities (Rayleigh criteria). These instabilities are more likely to occur in combustion systems near the extinction limit (increased flame receptivity).

Modern, ultra-low NOx gas turbines running in a lean, premixed mode meet all these conditions and avoiding instability remains a challenging task for the design of power plants.

Active control to suppress thermo acoustic instabilities and consequently to enhance stable heat release close to the lean extinction limit offers the advantage to increase the...