scholarly journals Explosion-Suppression Characteristics of Nonmetallic Spherical Spacers on Propane-Air Mixtures in Confined Space

2021 ◽  
Vol 11 (19) ◽  
pp. 9238
Author(s):  
Yangyang Yu ◽  
Lehai Liu ◽  
Junhong Zhang ◽  
Jun Wang ◽  
Xiangde Meng ◽  
...  
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Confined Space ◽  
Effective Prevention ◽  
Jet Flame ◽  
Explosion Suppression ◽  
Explosion Overpressure ◽  
Suppression Effects

The explosion-suppression effects of NSSs on overpressures, flame propagation and flame tip velocities were explored under the initial pressures of 0.2 MPa, 0.3 MPa and 0.4 MPa. All experiments tested in a constant volume combustion bomb (CVCB). Explosion reaction of premixed propane–air gas in a new designed CVCB filled with nonmetallic spherical spacers (NSSs) was analyzed. The results showed that overpressures decreased under the different initial pressures. With the increase of filling density, the overpressure decreased, the time to reach explosion overpressure decreased, and the decay rate of explosion overpressure increased. It was also found that the explosion-suppression effects of NSSs on pressures. Flame front could be captured by high-speed schlieren photography. Combustion phenomena were captured including flame propagation, corrugated laminar flame, jet flame, corrugated turbulent flame as well as tulip flame under different initial pressures. Flame tip velocities also were captured. The results demonstrate that flame tip velocities decreased with the increase of filling densities. However, compared with unfilled CVCB, flame tip velocities increased after filling NSSs in CVCB under different initial pressures. NSSs suppressed the explosion overpressure in the cylinder, and promoted the flame propagation. In both cases, NSSs played a dual role. The suppression effect of NSSs was affected by both its suppression and promotion effect on the explosion. This work provides a scientific basis for the effective prevention of explosion accidents with propane–air premixtures and the development of explosion-suppression products.

High Speed OH PLIF Measurements of Combustor Effusion Films in a High Pressure, Liquid Fueled Combustor

2021 ◽  
Author(s):  
Aravind Chandh ◽  
Shivam Patel ◽  
Oleksandr Bibik ◽  
Subodh Adhikari ◽  
David Wu ◽  
...  
Keyword(s):  
High Speed ◽  
Laser Sheet ◽  
Turbulent Flame ◽  
Combustion Products ◽  
Elevated Pressure ◽  
Inlet Temperature ◽  
Lean Burn ◽  
Jet Flame ◽  
Reduction Techniques ◽  
Planar Laser

Abstract This paper presents measurements of 10 kHz OH planar laser induced fluorescence (PLIF) with an objective to study the interaction of effusion cooling with the flame and hot combustion products in the liquid fueled combustor. The combustor rig is a single sector representation a rich-burn/quick-quench/lean-burn (RQL) configuration. It consists of a swirl nozzle, dilution, and effusion jets. The rig is operated under realistic aircraft conditions, including elevated combustor inlet temperature, and elevated pressure. The PLIF laser sheet was arranged perpendicular and parallel to the liner at distinct liner locations. Parametric variations of important parameters, namely equivalence ratio, and effusion cooling air blowing ratio are conducted to investigate their effect on flame-effusion jet interactions. The PLIF images were analyzed using several data reduction techniques to de-noise the images and identify patterns in the effusion jet-flame interactions. Results show that the effusion jets are highly unsteady, interacting strongly with the turbulent flame from the swirl nozzle and the dilution jets. This work is an extension of recent effusion film mixing studies that were performed with acetone PLIF under non-reacting conditions.

High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions

2019 ◽  
Author(s):  
Pradeep Parajuli ◽  
Tyler Paschal ◽  
Mattias A. Turner ◽  
Eric L. Petersen ◽  
Waruna D. Kulatilaka
Keyword(s):  
Natural Gas ◽  
Flame Front ◽  
Gas Turbines ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Initial Pressure ◽  
Flame Speed ◽  
Operating Conditions ◽  
Important Species

Abstract Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.

Fuel Variation Effects in Propagation and Stabilization of Turbulent Counter-Flow Premixed Flames

2018 ◽  
Author(s):  
Ehsan Abbasi-Atibeh ◽  
Sandeep Jella ◽  
Jeffrey M. Bergthorson
Keyword(s):  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Mass Diffusion ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Flame Surface ◽  
Differential Diffusion ◽  
Turbulent Flame Speed

Sensitivity to stretch and differential diffusion of chemical species are known to influence premixed flame propagation, even in the turbulent environment where mass diffusion can be greatly enhanced. In this context, it is convenient to characterize flames by their Lewis number (Le), a ratio of thermal-to-mass diffusion. The work reported in this paper describes a study of flame stabilization characteristics when the Le is varied. The test data is comprised of Le ≪ 1 (Hydrogen), Le ≈ 1 (Methane), and Le > 1 (Propane) flames stabilized at various turbulence levels. The experiments were carried out in a Hot exhaust Opposed-flow Turbulent Flame Rig (HOTFR), which consists of two axially-opposed, symmetric turbulent round jets. The stagnation plane between the two jets allows the aerodynamic stabilization of a flame, and clearly identifies fuel influences on turbulent flames. Furthermore, high-speed Particle Image Velocimetry (PIV), using oil droplet seeding, allowed simultaneous recordings of velocity (mean and rms) and flame surface position. These experiments, along with data processing tools developed through this study, illustrated that in the mixtures with Le ≪ 1, turbulent flame speed increases considerably compared to the laminar flame speed due to differential diffusion effects, where higher burning rates compensate for the steepening average velocity gradient, and keeps these flames almost stationary as bulk flow velocity increases. These experiments are suitable for validating the ability of turbulent combustion models to predict lifted, aerodynamically-stabilized flames. In the final part of this paper, we model the three fuels at two turbulence intensities using the FGM model in a RANS context. Computations reveal that the qualitative flame stabilization trends reproduce the effects of turbulence intensity, however, more accurate predictions are required to capture the influences of fuel variations and differential diffusion.

A Comparative Computational Fluid Dynamics Study on Flamelet-Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Pravin Nakod ◽  
Rakesh Yadav ◽  
Pravin Rajeshirke ◽  
Stefano Orsino
Keyword(s):  
Laminar Flame ◽  
Turbulent Flame ◽  
Molecular Transport ◽  
Turbulent Flames ◽  
Jet Flames ◽  
Jet Flame ◽  
Air Jet ◽  
Flamelet Generated Manifold ◽  
Vitiated Coflow ◽  
Laminar Flamelet

The laminar flamelet model (LFM) (Peters, 1986, “Laminar Diffusion Flamelet Models in Non-Premixed Combustion,” Prog. Energy Combust. Sci., 10, pp. 319–339; Peters, “Laminar Flamelet Concepts in Turbulent Combustion,” Proc. Combust. Inst., 21, pp. 1231–1250) represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical nonequilibrium effects considered in this model are due to local turbulent straining only. In contrast, the flamelet-generated manifold (FGM) (van Oijen and de Goey, 2000, “Modeling of Premixed Laminar Flames Using Flamelet-Generated Manifolds,” Combust. Sci. Technol., 161, pp. 113–137) model considers that the scalar evolution; the realized trajectories on the thermochemical manifold in a turbulent flame are approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry, and quenching effects far away from the equilibrium. In FGM, 1D premixed flamelets are solved in reaction-progress space rather than physical space. This helps better solution convergence for the flamelets over the entire mixture fraction range, especially with large kinetic mechanisms at the flammability limits (ANSYS FLUENT 14.5 Theory Guide Help Document, http://www.ansys.com). In the present work, a systematic comparative study of the FGM model with the LFM for four different turbulent diffusion/premixed flames is presented. The first flame considered in this work is methane-air flame with dilution air at the downstream. The second and third flames considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H2 and CH4 flames (Cabra, et al., 2002, “Simultaneous Laser Raman-Rayleigh-LIF Measurements and Numerical Modeling Results of a Lifted Turbulent H2/N2 Jet Flame in a Vitiated Coflow,” Proc. Combust. Inst., 29(2), pp. 1881–1888; Lifted CH4/Air Jet Flame in a Vitiated Coflow, http://www.me.berkeley.edu/cal/vcb/data/VCMAData.html) where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer, and molecular transport as recirculation burners without the complex recirculating fluid mechanics. The fourth flame considered is a Sandia flame D (Barlow et al., 2005, “Piloted Methane/Air Jet Flames: Scalar Structure and Transport Effects,” Combust. Flame, 143, pp. 433–449), a piloted methane-air jet flame. It is observed that the simulation results predicted by the FGM model are more physical and accurate compared to the LFM in all the flames presented in this work. The autoignition-controlled flame lift-off is also captured well in the cases of lifted flames using the FGM model.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen-Air Swirl Flames

2014 ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen-air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed PIV/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approx. 1/3 of the typical flow velocities in gas turbine burners. In that range the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approx. 0.45 and delivers NOx-emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2001 ◽  
Author(s):  
Jassin Fritz ◽  
Martin Kröner ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying High Speed Video recordings, the Laser Doppler Anemometry and the Laser Induced Fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechansim of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

Flashback in Lean Prevaporized Premixed Combustion: Nonswirling Turbulent Pipe Flow Study

2003 ◽  
Vol 125 (3) ◽  
pp. 670-676 ◽  
Author(s):  
O. Scha¨fer ◽  
R. Koch ◽  
S. Wittig
Keyword(s):  
Flame Propagation ◽  
Pipe Flow ◽  
Laminar Flame ◽  
Fluid Dynamic ◽  
Turbulent Flame ◽  
Side Wall ◽  
Turbulent Pipe Flow ◽  
Flame Velocity ◽  
Fundamental Study ◽  
Wall Boundary Layer

A fundamental study has been performed on the upstream flame propagation of a turbulent kerosene flame, stabilized in a confined stagnation flow at atmospheric pressure. Besides temperature and equivalence ratio, mixture properties and fluid dynamic parameters have been varied. The flashback phenomenon is discussed in terms of critical mean velocities and additionally based on detailed LDV data at the outlet of the premixing duct. The largest critical velocities uc for flashback are found for the “perfectly” premixed case and equivalence ratios close to stoichiometric, which is in accordance with the theory on laminar flame propagation. In the case of a homogeneous mixture, flashback is determined by the velocity distribution at the outlet of the premixing section. In the undisturbed pipe flow the flame propagates through the wall boundary layer. The data for this case are compared with the theory of side-wall quenching in terms of a critical Peclet number and critical velocity gradients at the wall. Both are deduced from the experimental data. Reducing the velocity on the axis forces the flame to propagate through the center at a velocity predicted by correlations on turbulent flame velocity.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

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