scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor

2021 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit Singh Pathania ◽  
Patton Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
Bluff Body ◽  
Ignition Probability ◽  
Annular Combustor

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit S. Pathania ◽  
Patton M. Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Annular Combustor ◽  
Initial Flame ◽  
Limiting Condition

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff-Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit Pathania ◽  
Patton Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Design And Optimization ◽  
Annular Combustor ◽  
Favorable Conditions

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess ignition probability and provide insights into the mechanisms of failure and of successful flame propagation. Two configurations were employed, with 12 and 18 burners, mixture velocity was varied between 10 and 30 m/s, and equivalence ratio between 0.58 and 0.68. Ignition was initiated by a sequence of sparks and "ignition" is defined as successful ignition of the whole annular combustor. Mechanism of success and failure of the ignition process was investigated via high-speed imaging of OH*chemiluminescence. Lean ignition limits were evaluated and compared to the lean blow-off limits. It was found that failure is linked to the trapping of the flame kernel inside the inner recirculation zone (IRZ) of a single burner, followed by localised quenching on the bluff body due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner. Finally, the ignition probability(Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign~0 for most conditions, while Pign increased moving the spark away from the bluff body or placing it between two burners and peaked to Pign~1 when the spark was located downstream in the combustion chamber. The results provide information on the most favorable conditions for achieving ignition and could help design and optimization of realistic gas turbine combustors.

Lean Blowout Phenomena and Prior Detection of Lean Blowout in a Premixed Model Annular Combustor

2019 ◽  
Author(s):  
Arijit Bhattacharya ◽  
Bikash Gupta ◽  
Satyajit Hansda ◽  
Zohadul Haque ◽  
Ashish Kumar ◽  
...  
Keyword(s):  
Bluff Body ◽  
Nox Reduction ◽  
Marked Change ◽  
Nox Emission ◽  
Thermoacoustic Instability ◽  
Lean Blowout ◽  
Lean Combustion ◽  
Annular Combustor ◽  
Lean Limit ◽  
Lift Off

Abstract Strict emission norms in the last few decades have paved the path for adaptation of new low NoX emission alternatives to power generation and aircraft propulsion. Lean combustion is a very promising and practicable technology for reducing NOX reduction and also have very high fuel efficiency. However, lean combustion technology suffers from inherent combustion instabilities that are manifested under different conditions, most importantly, thermoacoustic instability and lean blowout. Lean blowout occurs when a gas turbine combustor operating close to lean limit, for lowest NoX emission, faces abrupt changes in fuel homogeneity, quality or flow rate. While many work have been done in thermo-acoustic instability and flame propagation in annular combustors, studies in lean blowout in annular combustors are very limited. The lean limit of combustors are not fixed and is dependent on fuel characteristics and operating condition including environmental effects. So accurate online prediction of lean limit is very important to keep the combustors operating safely near lean limit. Recent works have demonstrated that single burner combustors leave out a significant amounts of physics including interaction of flames from different burners prior to blowout. In this work, a stepped down swirl and bluff body stabilized annular combustor in CB configuration (having chamber and burner), is used as experimental test rig having 4 number of identical burners. Video and heat release data are taken at different conditions as lean blowout is approached. Frequent attachment and reattachment of the flames prior to lift off was seen. As lean blowout is approached, inherent subtle differences in the different burners get amplified when flame becomes sufficiently weak and flame symmetry is broken. As air fuel mixture is made gradually leaner, one by one the flames from different burners elongates although remains partially attached to burner. Further lowering the equivalence ratio results in lift off and merging of the flame fronts of different burners. Three pixel averaged color ratios are extracted from still camera RGB images as flame stability indicators which are, red by blue, red by green and blue by green. The parameters show marked change at the point of lift off as well as at the lean blowout point.

scholarly journals Simulations and experiments on the ignition probability in turbulent premixed bluff-body flames

2016 ◽  
Vol 20 (3) ◽  
pp. 548-565 ◽  
Author(s):  
Michael Philip Sitte ◽  
Ellen Bach ◽  
James Kariuki ◽  
Hans-Jörg Bauer ◽  
Epaminondas Mastorakos
Keyword(s):  
Bluff Body ◽  
Ignition Probability ◽  
Turbulent Premixed

scholarly journals Characteristics of self-excited spinning azimuthal modes in an annular combustor with turbulent premixed bluff-body flames

2019 ◽  
Vol 37 (4) ◽  
pp. 5129-5136 ◽  
Author(s):  
Marek Mazur ◽  
Håkon T. Nygård ◽  
James R. Dawson ◽  
Nicholas A. Worth
Keyword(s):  
Bluff Body ◽  
Annular Combustor ◽  
Turbulent Premixed

Experimental Study of Damper Position on Instabilities in an Annular Combustor

2018 ◽  
Author(s):  
Marek Mazur ◽  
Håkon T. Nygård ◽  
James Dawson ◽  
Nicholas Worth
Keyword(s):  
Bluff Body ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Mode Switching ◽  
Periodic Mode ◽  
Pressure Oscillations ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor

The present study experimentally investigates the effects of different circumferential damper configurations on the instabilities in an annular combustor. The combustor consists of multiple bluff body swirl stabilized flames. It is operated with an ethylene-air premixture at a power of 66 kW. Combinations of Helmholtz resonators are used as dampers circumferentially arranged around the combustion chamber. The tests are performed at operating conditions where the combustor is self-excited and characterized by a strong standing mode and periodic mode switching. For each test, the dynamic pressure is measured at different locations and overhead imaging of OH* of the entire combustor is conducted simultaneously at a high sampling frequency. The measurements are then used to compare the pressure fluctuations of the different cases in order to find the best positioning of the dampers. The azimuthal modes in the chamber are determined and the phase shift between OH* and pressure is analysed. Based on the Rayleigh criterion, these investigations allow us to find out if the dampers only remove energy from the pressure oscillations, or if they also influence the instability margins of the combustor and the flame dynamics. Finally, the results are compared with the theoretical findings in literature and observed discrepancies are discussed.

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