Correlations between light emission, acoustic emission and ion density in premixed turbulent flames

Mehta, Gopal; Ramachandra, M. K.; Strahle, Warren C.

doi:10.1016/s0082-0784(81)80109-9

Cited by 21 publications

(6 citation statements)

References 5 publications

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“…2 This work focuses on using optical methods, observing the chemiluminescence, due to its direct relationship with the local chemical reaction rates. [25][26][27][28] Chemiluminescence is appropriate for understanding the dynamics of the blowout process since it can provide information on the presence and strength of the combustion process in a specific region of the combustor. The primary sources of chemiluminescence in lean hydrocarbon flames are OH (ultraviolet emission around 308 nm), CH (visible emission around 430 nm) and CO 2 (broadband ultraviolet and visible emission).…”

Section: Introductionmentioning

confidence: 99%

Characterization of Extinction Events Near Blowout in Swirl Dump Combustors

Muruganandam¹,

Seitzman²

2005

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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This work examines the evolution of the lean blowout (LBO) process in a swirl-dumpstabilized combustor with center body. Previous studies identified extinction-reignition events as precursors to LBO. These events are investigated in greater detail using simultaneous fiber optic-based chemiluminescence sensors and high speed imaging in an atmospheric pressure, premixed methane-air combustor. It is found that the flame, which is stabilized above the center body, at first partially detaches due to turbulent fluctuations. This detached region moves around the center body due to the swirl and the feedback mechanism of the inner recirculation zone. As the LBO limit is approached, the weaker flame detaches more often and over a larger extent of the center body. When the flame is detached beyond a certain extent, enough cold packets of unburned gases move around the inner recirculation zone to reduce the feedback needed for stabilization and the flame detaches completely from the center body. This is the source of the extinction events previously noted in the sensor data. The flow field responds to the decreased heat release with a larger recirculation zone and stronger swirl. The flame shape and flame stabilization change to a tornado mode. In this mode, the flame is stabilized much farther downstream of the combustor inlet, but an occasional packet of burning gases is convected back to the inlet. If this flame packet is sufficiently strong, the original flow field and flame shape are restored. This return of the original stable flame mode is the onset of the reignition events found in the sensor data. Several occurrences of these events in time gradually weaken the combustion process and eventually the convected flame packets are not strong enough to restabilize the combustor, i.e., the combustor blows out. This understanding of the process of flame stabilization loss provides the necessary insight for improved design and analysis of LBO sensors systems.

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Section: Introductionmentioning

confidence: 99%

Characterization of Extinction Events Near Blowout in Swirl Dump Combustors

Muruganandam¹,

Seitzman²

2005

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…1 For this reason, chemiluminescence has been used previously as a rough measure of reaction rate and heat release rate. [2][3][4][5][6][7][8] Thus chemiluminescence can provide information on the presence and strength of the combustion process in a specific region of the combustor, making it well-suited for health monitoring and diagnostics.…”

Section: Introductionmentioning

confidence: 99%

Chemiluminescence Based Sensors for Turbine Engines

Muruganandam¹,

Kim²,

Olsen³

et al. 2003

39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

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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.

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“…Chemiluminescence provides information on the presence of the combustion process and its energy, as its measurements are linked to reaction rate and heat release rate. Therefore, chemiluminescence is commonly employed for monitoring the flame stability and blowout detection (Keller & Saito, 1987), (Lawn, 2000), (Roby, Hamer, Johnsson, Tilstra, & Burt, 1995), (Mehta, Ramachandra, & Strahle, 1981) and (Khanna, Vandsburger, Saunders, & Baumann, 2002). In this case, the primary chemiluminescent species of interest in a hydrocarbon flame are electronically excited OH.…”

Section: Lbo Sensing: State Of the Artmentioning

confidence: 99%

Lean Blowout Sensing and Processing via Optical Interferometry and Wavelet Analysis of Dynamic Pressure Data

2021

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This paper introduces a novel approach to monitor combustion instabilities in turbomachinery. This innovation is motivated by the need to better analyze flame health in a continuous flow machine, and more precisely in its hot core expressed by machine OEMs and end-users. This improved monitoring system will support an optimization of the machine performance, leading to a safer, cleaner, more flexible and more cost-efficient operation for the end-user. There have been several numerical studies that simulate the nonlinear dynamics of flame instabilities limit in simple combustors, they predict the pressure oscillations frequency is very low 5-25 Hz. Nowadays, in gas turbine monitoring, dynamic pressure measurement sensors are based on electrical working principle technologies such as piezoelectric, piezo-resistive and capacitive measurement. While exposed to high temperatures, due to pyro-electric effects and noise spectral density of charge amplifiers, piezo sensors signal to noise ratio (SNR) decreases sharply at low frequencies (about a factor 10 every 100°). Optical sensing systems provide much better stability, in the low frequency range when exposed to high temperature and, moreover, are intrinsically insensitive to vibration or EMI perturbation. This feature allows analyzing more accurately low frequency flame dynamics. Within the frame of a joint study between Meggitt, Combustion Bay One e.U. and FH Joanneum GmbH, the behavior of an optical measurement system was tested under different combustion instability conditions. By acting on system parameters (equivalent ratio, air speed) several tests have been conducted where combustion has been driven to different instability conditions such as premixed to diffusion flame transition, lean blow out, flashback. Data have been recorded and analysed from both the optical and the piezo sensors installed within the combustion chamber. The objective of the test campaign is twofold: compare optical to piezo system performances under flame combustion instabilities and, taking advantage of improved low frequency SNR of pressure data coming from optical sensors, to develop and validate an algorithmic strategy to detect/prognose phenomena such as Lean Blow Out and Flashback. The paper initially describes the principia of the used optical sensing technology, including some relevant hardware and software aspects of the measurement chain. After that, the experimental set-up and tests conditions are presented. About piezo to optical data comparison, SNR analysis of test data confirms the expectations of a lower noise at low frequency and the improved visibility of flame instabilities provided by optical sensor. Based on this, in order to analyze the transient behavior at low frequencies associated to flame instabilities two algorithmic strategies have been developed: wavelet analysis and chaos dimension analysis. Based on these methodologies several Lean Blow Out indicators have been implemented and tested. Details of their behavior in response to the variation of the equivalence ratio close to the flame blow out are presented and discussed. Three of the proposed indicators, under the investigated test conditions, proved to possess the capability to detect the blow out event. Depending on how the approach to the blow out event occurs, some indicators also shown prognostics capability. Results show some indicators start reacting as the flame approaches to extinction or as the equivalence ratio reduces. These indicators can be considered flame health meters. The test campaign results shown in the paper allow to conclude that optical sensing technologies provide advantages over piezoelectric sensing technologies such as: insensitivity to pyro-electric effects and inherent insensitivity to external perturbations, i.e. electromagnetic interferences and radio frequency interferences, vibrations. Particularly the improved accuracy at low frequencies of the sensor coupled with new signal processing techniques, as the ones presented, may support a flame health monitoring capability and the ability to sense blowout precursors. The replacement of piezo-electric with fiber optic sensors will therefore be desirable for many combustion monitoring applications, especially the ones requiring monitoring of low frequencies. This can, provide significant payoffs in engine reliability and operability, in enabling optimal performance over extended time periods as an engine ages, in reducing maintenance costs, and in increasing engine life.

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Correlations between light emission, acoustic emission and ion density in premixed turbulent flames

Cited by 21 publications

References 5 publications

Characterization of Extinction Events Near Blowout in Swirl Dump Combustors

Characterization of Extinction Events Near Blowout in Swirl Dump Combustors

Chemiluminescence Based Sensors for Turbine Engines

Lean Blowout Sensing and Processing via Optical Interferometry and Wavelet Analysis of Dynamic Pressure Data

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