Optical Sensing of Lean Blowout Precursors in a Premixed Swirl Stabilized Dump Combustor

Abstract

The work described here is part of an effort to detect and prevent lean blowout in turbine engine combustors. The approach uses optical emission, primarily chemiluminescence, to identify blowout precursor events, and is demonstrated in a premixed, swirl-stabilized dump combustor. The results show that the transient behavior of the flame as lean blowout is approached is characterized by short duration, localized extinction and reignition events. These events increase in frequency and duration, and spatial extent, as LBO is approached. Several methods can be used to detect these events in the raw sensor output, including signal thresholding and frequency analysis. The paper describes examples of how these analysis techniques can be used to calculate a simple LBO proximity measure that would be ideally suited for use in an active (closed-loop) control system. The LBO proximity sensing is also demonstrated using sensor technology that is close to what would be required in a realistic turbine engine environment, specifically, optical fibers to collect the chemiluminescence and miniature, metal package PMTs for detection. Possible detection locations within the combustor are discussed and various locations are compared, based on their practicality and sensitivity to LBO precursor detection. It was found that the best detection was from fiber that was mounted on the head end and viewed downstream.