Chemiluminescence Based Sensors for Turbine Engines

Abstract

This work focuses on the use of naturally occurring optical emissions, specifically chemiluminescence, for sensing applications in active control and health monitoring of combustors. First, monitoring local equivalence ratio (φ), at the reaction zone, has been demonstrated using the ratio of CH to OH chemiluminescence. This ratio (CH*/OH*) increases monotonically with equivalence ratio, and the dependence on equivalence ratio has been shown to be a universal function for combustor configurations ranging from unconfined jet flames to swirl and dump stabilized combustors. There is essentially no difference between the CH*/OH* ratio for methane and natural (city) gas, but the ratio has a lower sensitivity to φ for n-heptane compared to methane or natural gas. The ratio was found to increase almost linearly with pressure for natural gas/methane combustion above 3 atm. Second, chemiluminescence emission from the combustor was used to detect precursor events to blowout, using a robust thresholding method. This method was shown to be successful in jet flames and swirl/dump stabilized combustors using premixed methane/air and nonpremixed Jet-A/air. This method gives the kind of information on proximity to blowout that can be used by an active control system to prevent lean blowout in low NO x turbine engine combustors.

Internal entrainment effects on high intensity distributed combustion using non-intrusive diagnostics

“…Several researchers have focused their efforts on developing this method for equivalence ratio measurements in a swirl combustor relating to gas turbine applications with focus on lean combustion. Muruganandam et al [26] have shown that the CH ⁄ /OH ⁄ signal ratio for turbulent jet flame, swirl dump combustor, and gas turbine simulator exhibit the same trend and similar value for equivalence ratios between 0.65 and 0.95. Other researches have reached similar conclusions on the trend of CH ⁄ /OH ⁄ ratio (or OH ⁄ /CH ⁄ ) in swirl burners [27][28][29].…”

Basic aspects of OH(A), CH(A), and C2(d) chemiluminescence in the reaction zone of laminar methane–air premixed flames

“…Chemiluminescence-based fuel-air ratio measurements are becoming a standard approach in industrial applications as several researchers have employed this technique in internal combustion engines and model gas turbine combustors [9][10][11][12][13]. A principle idea for the chemiluminescence-based F/A sensing is to use the ratio of the chemiluminescence intensity of one species to another such as OH(A) to CH(A) [11,14,15].…”

Flame chemiluminescence in premixed combustion of hydrogen-enriched fuels

“…The most common method of using chemiluminescence consists in calculating the intensity ratios between different zones of the spectrum, typically, those associated with OH*, CH*, C * 2 (at 309, 431 and 517 nm, respectively) or CO * 2 (responsible for the broadband background radiation). Working with intensity ratios displays some advantages such as, avoiding interferences due to geometrical or optical parameters of the measurement setup and being independent of the strain rate [13,16,17], aerodynamics or turbulence intensities [18,19]. However, although chemiluminescence emission, especially from OH*, has been recorded and analyzed as an indicator of flame behavior for different fuels (syngas, longer hydrocarbons, such as n-heptane, or liquid fuels) in previous works [8,18e24], most of the results have been obtained in methane flames and only a few of them, such as those from Nori et al [18e20], are focused on analyzing the feasibility of chemiluminescence as a monitoring technique in syngas flames and on how the fuel composition may change the relations between chemiluminescence and equivalence ratio by modifying the flame spectra [8].…”