Reduction of combustion noise and instabilities using porous inert material with a swirl-stabilized burner

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
University of Alabama Libraries

Combustion instabilities represent a major problem during operation of power generation systems that can lead to costly shutdown. Combustion instabilities are self excited large amplitude pressure oscillations caused by the coupling of unsteady heat release and acoustic modes of the combustor. These oscillations cause fluctuating mechanical loads and fluctuating heat transfer that can result in catastrophic premature failure of components. Combustion noise, a significant source of noise in gas turbines, can lead to combustion instabilities. Combustion noise and instabilities are different phenomena; however, they both occur due to unsteady heat release of turbulent flames that excites acoustic modes of the combustor. The instabilities self excite when flame adds energy to the acoustic field at a faster rate than it can dissipate it. Swirl-stabilized combustion and porous inert medium (PIM) combustion are two methods that have extensively been used, although independently, for flame stabilization. In this study, the two concepts are combined so that PIM serves as a passive device to mitigate combustion noise and instabilities. A PIM insert is placed within the lean premixed, swirl-stabilized combustor to affect the turbulent flow field reducing combustion noise. This study is the first step for eventual implementation in liquid fuel systems. After presenting the concept, a numerical investigation of the changes in the mean flow field caused by the PIM is presented. Changes in the flow field can be beneficial for noise reduction by optimizing the geometric parameters of the PIM. Next, atmospheric pressure experiments were conducted at low reactant inlet velocity (<10 m/s) and low reactant inlet temperature (<120 °C) to investigate effect of PIM parameters on sound pressure level (SPL), and CO and NOx emissions. Surface and interior combustion modes were identified and PIM geometric parameters were optimized. Next, a laboratory facility to conduct experiments at high reactant inlet velocity, high inlet air temperature, and high pressure was designed and developed. Results show that the porous insert substantially reduces combustion noise for a range of operating conditions. Moreover, experiments show that the porous insert can mitigate combustion instabilities without adversely affecting CO and NOx emissions.

Electronic Thesis or Dissertation
Mechanical engineering, Acoustics