Dynamics of Lean Blowout in Premixed Combustion With Hydrogen Addition

2012 ◽  
Author(s):  
Shengrong Zhu ◽  
Sumanta Acharya
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Flame Structure ◽  
Fuel Mixture ◽  
Premixed Combustion ◽  
Fluorescence Measurement ◽  
Extinction Time ◽  
High Speed Imaging ◽  
Lean Premixed Combustion ◽  
Hydrogen Addition

An experimental study of lean premixed combustion in a swirl-stabilized combustor is undertaken to characterize the dynamics and time scales close to Lean Blow Out (LBO) conditions. Due to the recent interest in syngas fuels, the effect of hydrogen addition on LBO is studied. In present study, both confined and unconfined turbulent methane air premixed flames have been examined with different hydrogen levels during the extinction transition with high speed imaging of OH* chemiluminescence at 2 KHz. Planar laser induced fluorescence measurement of OH is also performed for studying the flame structure. The blowout conditions are approached by reducing the flow rate of fuel mixture or the equivalence ratio with constant air flow rate. The estimated extinction times from high speed imaging and corresponding flame structures are analyzed and compared between confined and unconfined flames with different hydrogen blends. The extinction time scale and the heat release fluctuations show inverse trends with hydrogen addition for the confined and unconfined flames, and are indicative of different stabilization and blow out mechanisms for the two configurations. These mechanisms which involve heat losses from the flame, inner- and corner recirculation zones and unsteady flame dynamics are described in the paper.

Characterisation of Waves and Ligaments in Films Close to an Aeroengine Ball Bearing

2019 ◽  
Author(s):  
Jee Loong Hee ◽  
Kathy Simmons ◽  
David Hann ◽  
Michael Walsh
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Ball Bearing ◽  
Capillary Waves ◽  
Operating Conditions ◽  
Research Centre ◽  
Shaft Speed ◽  
High Speed Imaging ◽  
Liquid Phases ◽  
Mass Transfers

Abstract Surface waves are observed in many situations including natural and engineering applications. Experiments conducted at the Gas Turbine and Transmissions Research Centre (G2TRC) used high speed imaging to observe multiscale wave structures close to an aeroengine ball bearing in a test rig. The dynamic behavior and scale of the waves indicate that these are shear-driven although highly influenced by gravity at low shaft speed. To understand the interactions between gas and liquid phases including momentum and mass transfers, characterization of the observed waves and ligaments was undertaken. Waves were studied at surfaces close to the ball bearing and ligaments were assessed near the cage. Characterization was in terms of frequency and wavelength as functions of speed, flow-rate, bearing axial load and gravity. The assessments confirmed the existence of gravity-capillary waves and capillary waves. Gravity-capillary waves were measured to have a longer mean wavelength on the co-current side of the bearing (gravity and shear acting together) compared to the counter-current side (gravity and shear opposing). Using a published definition of critical wavelength (λcrit), measured wavelengths at 3,000 rpm were 2.56λcrit on the co-current side compared to 1.86λcrit at the countercurrent location. As shaft speed increases, wavelength reduces with transition to capillary waves occurring at around 0.83λcrit. At shaft speeds beyond 5000 rpm, capillary waves were fully visible and the wavelength was obtained as 0.435λcrit. Flow-rate and load did not significantly influence wavelength. Wave frequency was found to be proportional to shaft speed. The gravity-capillary waves had frequencies within the range 13–25 Hz while capillary waves exhibited a frequency well beyond 100 Hz. The frequencies are highly fluctuating with no effect of load and flow rate observed. Ligaments were characterized using Weber number and Stability number. The number of ligaments increased with shaft speed. A correlation for ligament number based on operating conditions is proposed.

scholarly journals High Speed Imaging of Flame Structure and Dynamic Processes in Swirl Stabilized Prevaporized Liquid Fuel Flames

2019 ◽  
Author(s):  
Christoph M. Arndt ◽  
Adam M. Steinberg ◽  
Jan Böhnke ◽  
Redjem Hadef ◽  
Wolfgang Meier
Keyword(s):  
High Speed ◽  
Liquid Fuel ◽  
Flame Structure ◽  
Dynamic Processes ◽  
High Speed Imaging

Flame Dynamics With Hydrogen Addition at Lean Blowout Limits

2013 ◽  
Author(s):  
Shengrong Zhu ◽  
Sumanta Acharya
Keyword(s):  
High Speed ◽  
Combustion Process ◽  
Minimum Ignition Energy ◽  
Lean Premixed Combustion ◽  
Lean Blowout ◽  
Hydrogen Addition ◽  
Extinction Process ◽  
Flame Dynamics ◽  
Nitric Oxide Emissions ◽  
Proper Orthogonal

Lean premixed combustion is widely used in power generation due to the low nitric oxide emissions. Recent interest in syngas requires a better understanding of the role of hydrogen addition on the combustion process. In the present study, the extinction process of hydrogen enriched premixed flames near Lean Blow Out (LBO) in a swirl-stabilized combustor has been examined in both unconfined and confined configurations. High speed images of the flame chemiluminescence are recorded and a proper orthogonal decomposition (POD) procedure is used to extract the dominant flame dynamics during the LBO process. By examining the POD modes, the spectral information and the statistical properties of POD coefficients, the effect of hydrogen addition on the LBO processes are analyzed and described in the paper. Results show that in unconfined flames, the shear layer mode along with flame rotation with local quenching and re-ignition is dominant in the methane-only case. For the open hydrogen enriched flames, the extinction times are longer and are linked to the lower minimum ignition energy for hydrogen that facilitates re-ignition events. In confined methane flames, a conical flame is observed and the POD mode representing the burning in the central recirculation zone appears to be dominant. For the 60% hydrogen enriched flame, a columnar burning pattern is observed and the fluctuation energies are evenly spread across several POD modes making this structure more prone to external disturbances and shorter extinction times.

Numerical Simulation to Characterize Homogeneity of Air-Fuel Mixture for Premixed Combustion in Gas Turbine Combustor

2012 ◽  
Author(s):  
Kamalika Chatterjee ◽  
Arkadeep Kumar ◽  
Souvick Chatterjee ◽  
Achintya Mukhopadhyay ◽  
Swarnendu Sen
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Flow Rate ◽  
Combustion Zone ◽  
Equivalence Ratio ◽  
Fuel Mixture ◽  
Premixed Combustion ◽  
Internal Diameter ◽  
Gas Turbine Combustor ◽  
Ansys Fluent

Homogeneity in mixing of air and fuel in premixed combustion for a gas turbine combustor is a critical criterion to ensure efficient combustion and less environmental hazards. The current work deals with determining this homogenous characteristic of air-fuel mixture through computational simulation to specify homogeneity for a particular premixing length and equivalence ratio required for gas turbine combustion. A 3-D geometry of combustion chamber with combustion zone of internal diameter 6 cm is constructed. A premixing tube is augmented with the combustion chamber which has one air inlet port at the bottom and 3 fuel inlet ports. Air-fuel mixture is considered to enter the combustion zone with inlet swirl. The homogeneity of the mixture is found out at the dump plane and other important planes from simulation done with ANSYS FLUENT® for the meshed geometry. The results show whether mixing of air and fuel is full or partial and the extent of partial premixing. The parameters varied in the ANSYS FLUENT®. based simulation are the premixing length i.e. port of entry of fuel, the fuel flow rate i.e. the equivalence ratio and the air flow rate.

scholarly journals On the Ejection of Filaments of Polymer Solutions Triggered by a Micrometer-Scale Mixing Mechanism

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3399
Author(s):  
Fernando Marín-Brenes ◽  
Jesús Olmedo-Pradas ◽  
Alfonso M. Gañán-Calvo ◽  
Luis Modesto-López
Keyword(s):  
Flow Rate ◽  
Liquid Flow ◽  
High Speed ◽  
Large Scale ◽  
Liquid Flow Rate ◽  
Scaling Law ◽  
Feeding Tube ◽  
Scale Production ◽  
High Speed Imaging ◽  
Poly Ethylene

Polymer filaments constitute precursor materials of so-called fiber mats, ubiquitous structures across cutting-edge technological fields. Thus, approaches that contribute to large-scale production of fibers are desired from an industrial perspective. Here, we use a robust liquid atomization device operated at relatively high flow rates, ~20 mL/min, as facilitating technology for production of multiple polymer filaments. The method relies on a turbulent, energetically efficient micro-mixing mechanism taking place in the interior of the device. The micro-mixing is triggered by radial implosion of a gas current into a liquid feeding tube, thus resulting in breakup of the liquid surface. We used poly(ethylene oxide) solutions of varying concentrations as test liquids to study their fragmentation and ejection dynamics employing ultra-high speed imaging equipment. Taking an energy cascade approach, a scaling law for filament diameter was proposed based on gas pressure, liquid flow rate and viscosity. We find that a filament dimensionless diameter, Df*, scales as a non-dimensional liquid flow rate Q* to the 1/5. The study aims to elucidate the underlying physics of liquid ejection for further applications in material production.

CFD Study Exploring Jet Configurations and Jet Pulsing for an Aeroengine Scoop-Based Oil Delivery System

2018 ◽  
Author(s):  
Kathy Simmons ◽  
Luke Harrison ◽  
Evgenia Korsukova ◽  
Paloma Paleo Cageao
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Operating Conditions ◽  
Capture Efficiency ◽  
Direct Access ◽  
High Speed Imaging ◽  
Ansys Fluent ◽  
Practical Applications ◽  
Single Jet ◽  
Oil Jet

With reduction of gas turbine core size, clearances between internal components are reduced and directing oil jets for bearing lubrication becomes more difficult. If direct access to the bearings or scallops is impeded, the inclusion of oil scoops becomes highly desirable for lubricant supply. With a scoop-based system oil is targeted at a scooped rotor, collected and fed along axial passages and delivered at a different axial location thus enhancing design opportunities. The proportion of oil from the supply jet retained by the scoop system is an important design parameter that can be characterised by the concept of capture efficiency. Previous investigations have focussed on a proposed scoop device’s operating conditions and oil jet configurations; this study proposes new methods of utilising the jets to improve scoop capture efficiency. A parametric study of a 2D scoop geometry was conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The simulation utilised the Volume of Fluids (VOF) approach for multiphase modelling and the k-ω SST model to account for turbulence. In the configuration studied the oil was supplied via two nozzles separated by 10 degrees circumferentially. An uneven flow rate between two oil jets in tandem allowed for the identification of jet interaction effects. A transition in capture efficiency responses was also highlighted between shallow and steep jet angles. The knowledge of individual jet behaviour may immediately improve existing tandem jet configurations. Further, the concept of pulsing the jets was investigated, the idea being initiated following observation of high speed imaging of a scoop system tested experimentally. The imaging shows that most of the uncaptured oil is deflected or splashed following interaction with the scoop. Turning the oil off for part of the cycle potentially reduces or eliminates this. By defining and implementing an optimised time scheme for the pulsation of a single jet, the capture efficiency was improved by 10%. Compensating for the associated flow rate reduction by increasing the jet velocity resulted in a further 5% increase in capture efficiency. The development of pulsed jets for practical applications has the potential to significantly improve oil scoop capture efficiency.

Application of Proper Orthogonal Decomposition to High Speed Imaging for the Study of Combustion Oscillations

2017 ◽  
Author(s):  
Siddhartha Gadiraju ◽  
Suhyeon Park ◽  
David Gomez-Ramirez ◽  
Srinath V. Ekkad ◽  
K. Todd Lowe ◽  
...  
Keyword(s):  
Proper Orthogonal Decomposition ◽  
High Speed ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Low Frequency ◽  
Orthogonal Decomposition ◽  
Pressure Measurements ◽  
High Speed Imaging ◽  
Flame Structures ◽  
Proper Orthogonal

The flame structure and characteristics generated by an industrial low emission, lean premixed, fuel swirl nozzle were analyzed for understanding combustion oscillations. The experimental facility is located at the Advanced Propulsion and Power Laboratory (APPL) at Virginia Tech. The experiments were carried out in a model optical can combustor operating at atmospheric pressures. Low-frequency oscillations (<100 Hz) were observed during the reaction as opposed to no reaction, cold flow test cases. The objective of this paper is to understand the frequency and magnitude of oscillations due to combustion using high-speed imaging and associate them with corresponding structure or feature of the flame. Flame images were obtained using a Photron Fastcam SA4 high-speed camera at 500 frames per second. The experiments were conducted at equivalence ratios of 0.65, 0.75; different Reynolds numbers of 50K, 75K; and three pilot fuel to main fuel ratios of 0%, 3%, 6%. In this study, Reynolds number was based on the throat diameter of the fuel nozzle. Since the time averaged flame images are not adequate representation of the flame structures, proper orthogonal decomposition (POD) was applied to the flame images to extract the dominant features. The spatiotemporal dynamics of the images can be decomposed into their constituent modes of maximum spatial variance using POD so that the dominant features of the flame can be observed. The frequency of the dominant flame structures, as captured by the POD modes of the flame acquisitions, were consistent with pressure measurements taken at the exit of the combustor. Thus, the oscillations due to combustion can be visualized using POD. POD was further applied to high-speed images taken during instabilities. Specifically, the instabilities discussed in this paper are those encountered when the equivalence ratio is reduced to the levels approaching lean blowout (LBO). As the equivalence ratio is reduced to near blowout regime, it triggers low-frequency high amplitude instabilities. These low-frequency instabilities are visible as the flapping of the flame. The frequencies of the dominant POD modes are consistent with pressure measurements recorded during these studies.

Autoignition Limits of Hydrogen at Relevant Reheat Combustor Operating Conditions

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
J. Fleck ◽  
P. Griebel ◽  
A.M. Steinberg ◽  
M. Stöhr ◽  
M. Aigner ◽  
...  
Keyword(s):  
Flue Gas ◽  
Gas Turbines ◽  
High Speed ◽  
Initial Position ◽  
Operating Conditions ◽  
Dominant Factor ◽  
High Speed Imaging ◽  
Lean Premixed Combustion ◽  
Fuel Jet ◽  
Image Velocimetry

The use of highly reactive fuels in the lean premixed combustion systems employed in stationary gas turbines can lead to many practical problems, such as unwanted autoignition in regions not designed for combustion. In the present study, autoignition characteristics for hydrogen, diluted with up to 30 vol. % nitrogen, were investigated at conditions relevant to reheat combustor operation (p = 15 bar, T >1000 K, hot flue gas, relevant residence times). The experiments were performed in a generic, optically accessible reheat combustor, by applying high-speed imaging and particle image velocimetry. Autoignition limits for different mixing section (temperature, velocity) and fuel jet (N2 dilution) parameters are described. The dominant factor influencing autoignition was the temperature, with an increase of around 2% leading to a reduction of the highest possible H2 concentration without “flame-stabilizing autoignition kernels” of approximately 16 vol. %. Furthermore, the onset and propagation of the ignition kernels were elucidated using the high-speed measurements. It was found that the ability of individual autoignition kernels to develop into stable flames depends on the initial position of the kernel and the corresponding axial velocity at that position. While unwanted autoignition occurred prior to reaching the desired operating point for most investigated conditions, for certain conditions the reheat combustor could be operated stably with up to 80 vol. % H2 in the fuel.

Simulation of the Ignition Process in an Annular Multiple-Injector Combustor and Comparison With Experiments

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Maxime Philip ◽  
Matthieu Boileau ◽  
Ronan Vicquelin ◽  
Thomas Schmitt ◽  
Daniel Durox ◽  
...  
Keyword(s):  
High Speed ◽  
Burning Velocity ◽  
Flame Structure ◽  
Combustion Model ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Flamelet Model ◽  
Swirl Injectors ◽  
Eddy Simulation ◽  
Annular Combustor

Ignition is a problem of fundamental interest with critical practical implications. While there are many studies of ignition of single injector configurations, the transient ignition of a full annular combustor has not been extensively investigated, mainly because of the added geometrical complexity. The present investigation combines simulations and experiments on a complete annular combustor. The setup, developed at EMC2 (Energétique Moléculaire et Macroscopique Combustion) Laboratory (Mesa, AZ), features sixteen swirl injectors and quartz walls allowing direct visualization of the flame. High speed imaging is used to record the space time flame structure and study the dynamics of the light-round process. On the numerical side, massively parallel computations are carried out in the large eddy simulation (LES) framework using the filtered tabulated (F-TACLES) flamelet model. Comparisons are carried out at different instants during the light-round process between experimental data and results of calculations. It is found that the simulation results are in remarkable agreement with experiments provided that the thermal effects at the walls are considered. Further analysis indicate that the flame burning velocity and flame front geometry are close to those found in the experiment. This investigation confirms that the LES framework used for these calculations and the selected combustion model are adequate for such calculations but that further work is needed to show that ignition prediction can be used reliably over a range of operating parameters.

Sign in / Sign up

Export Citation Format

Share Document