Jozef Jarosinski

Flame quenching by turbulence

Abstract Quenching of laminar flames entering a region of intense turbulence without mean flow was studied by instantaneous temperature, global and local chemiluminescence measurements, and fast Schlieren photography. The experiments were performed in a constant-pressure, square 50 × 50 mm tube for flammability limit studies for two integral scales of turbulence, namely, 2.14 and 6 mm over the rms turbulent velocity range of 0.1-1.2 and 0.5-3.4 m/s, respectively. Lean and rich methane and propane air mixtures and ammonia-air mixtures in the entire burning range were studied. It was shown that premixed flames are quenched by turbulence for a critical value of Karlovitz-Kovasznay criterion K = ( u′ L )( δ l ν l ) of the order of 10–20, where u′ denotes the rms turbulent velocity, L the integral scale of turbulence, δl the laminar flame thickness, and νl the laminar burning velocity.

Combustion phenomena : selected mechanisms of flame formation, propagation, and extinction

Challenges in Combustion, Jozef Jarosinski and Bernard Veyssiere Measurements to Unravel Combustion Chemistry, Katharina Kohse-Hoinghaus Flammability Limits, Ignition of a Flammable Mixture, and Limit Flame Extinction Flammability Limits: History and Mechanism of Limit Flame Extinction, Jozef Jarosinski Ignition by Electric Sparks and Mechanism of Flame Formation, Michikata Kono and Mitsuhiro Tsue Influence of Boundary Conditions on Flame Propagation Propagation of Counterflow Premixed Flames, Chih-Jen Sung Flame Propagation in Vortices: Propagation Velocity along a Vortex Core, Satoru Ishizuka Edge Flames, Suk Ho Chung Instability Phenomena during Flame Propagation Instabilities of Flame Propagation, Geoff Searby Perturbed Flame Dynamics and Thermo-Acoustic Instability, Sebastien Candel, Daniel Durox, and Thierry Schuller Tulip Flames: The Shape of Deflagrations in Closed Tubes, Derek Dunn-Rankin Different Methods of Flame Quenching Flame Propagation in Narrow Channels and Mechanism of Its Quenching, Artur Gutkowski and Jozef Jarosinski Flame Quenching by Turbulence: Criteria of Flame Quenching, Shenqyang S. Shy Extinction of Counterflow Premixed Flames, Chih-Jen Sung Flame Propagation in a Rotating Cylindrical Vessel: Mechanism of Flame Quenching, Jerzy Chomiak and Jozef Jarosinski Turbulent Flames Turbulent Premixed Flames, Roland Borghi, Arnaud Mura, and Alexey A. Burluka Non-Premixed Turbulent Combustion, Jonathan H. Frank and Robert S. Barlow Fine Resolution Modeling of Turbulent Combustion, Laurent Selle and Thierry Poinsot Other Interesting Cases of Combustion and Flame Formation Candle and Jet Diffusion Flames: Mechanism of Combustion under Gravity and Microgravity Conditions, Fumiaki Takahashi Combustion in Spark-Ignition Engines, James D. Smith and Volker Sick Combustion in Compression-Ignition Engines, Zoran Filipi and Volker Sick Deflagration to Detonation Transition, Andrzej Teodorczyk Detonations, Bernard Veyssiere Index

Properties of flames propagating in propane-air mixtures near flammability and quenching limits

Flammability limits and flame quenching in a narrow channel were studied during flame propagation in propane/air mixtures. Most of the experiments were carried out in a vertical, square (50 mm×50 mm) flammability tube 1.8 m long and in a wedge-shaped quenching channel. Some new details of the extinction mechanism of lean limit upward and downward propagating flames (Le>1) in a vertical tube were deduced using schlieren and direct light photography, temperature measurements, and transient phenomena observations. Behavior and properties of the upward propagating rich flames (Le<1) were also studied. Additionally, flame quenching in a narrow channel for upward and downward propagating flames was examined over the entire range of mixture composition. Reliable data related to flammability limits and quenching distance were obtained. The quenching distance appeared to be twice as wide as the flame thickness. The Peclet number, expressed by the quenching distance and laminar burning velocity, is constant and equal to Pe D ≅42. Flames propagating upward in very rich mixtures are characterized by substantial flame thickness and small laminar burning velocity. The flame front of such flames contains several luminous zones (cool flames). In the hottest part of the flame soot is produced.

EXPERIMENTAL AND COMPUTATIONAL STUDY OF LEAN LIMIT METHANE-AIR FLAME PROPAGATING UPWARD IN A 24 MM DIAMETER TUBE

Lean limit methane-air flame propagating upward in a 24 mm diameter tube was studied experimentally and by numerical simulations. Gas velocity field was measured using Particle Image Velocimetry (PIV) method. The experimental measurements are compared with the results of numerical simulations and with previous similar measurements performed for a standard flammability tube. The experimentally determined lean flammability limit in 24 mm diameter tube was 4.9±0.03% CH4 by volume, against determined earlier flammability limit 5.1–5.2% CH4 in a standard tube. Maximum stretch rate value was found to be at flame leading point and was higher in a 24 mm diameter tube than in a standard flammability tube. The observed extension of the lean flammability limit is attributed to the strengthening effect of positive flame stretch on lean methane-air flames, characterized by Lewis number, Le < 1. Numerical simulations of limit methane/air flame in a 24 mm diameter tube demonstrated presence of negative flame speed at the flame leading edge.

Combustion mechanism of flame propagation and extinction in a rotating cylindrical vessel

Abstract The effect of radial acceleration in a rotating vessel on flame propagation has been investigated experimentally. Methane–air mixture compositions between the lean flammability limit and stoichiometric were studied. The behavior of flame propagation and the extinction mechanism were examined in detail. The flame propagating in a rotating vessel is axisymmetric. Initially it propagates axially from the ignition point at one end of the cylindrical vessel to the opposite end. After touching the side wall of the cylindrical vessel the flame starts to propagate radially and is locally quenched at the contact surface with the walls. The axial propagation velocity of the flame under all conditions increases with the rotation rate. When local quenching occurs, the radial flame propagation velocity decreases and the extinction rate increases with increasing rotation rate. The extinction mechanism is a multistep process. The most probable stages in that mechanism are as follows. First, heat loss causes the cylindrical flame to extinguish locally near the walls. Once this happens, the combustion gases, which are in contact with the walls, are cooled and displaced radially under the action of centrifugal forces. They flow towards the region of the fresh mixture, which remains in contact with the previously extinguished flame. Differential buoyancy forces the cool gases to move ahead of the flame, which is then extinguished because it is now propagating into a partially diluted nonflammable mixture. The extinction wave propagates along the cylindrical surface of the flame to complete extinction.

Comparative study of the influence of obstacles on the propagation of dust and gas flames

The well known technique to accelerate gas flames by introducing obstacles has been used for studying the properties of dust flames. To study in detail the mechanism of flame acceleration by means of obstacles some tests were carried out in an open 5 cm×5 cm square tube 1 meter long modified for visualization of the combustion process. The propagation of both dust and gas flame was studied. Analysis of the results show that flame acceleration in obstacle environments is due mainly to the effects of nonuniformity of the mean velocity across the tube. The explosion characteristics of gas and dust flames have been investigated in a closed tube 0.19 meters in diameter and 1.86 meters long, filled with obstacles. A comparative study of flame propagation velocity and, the maximum rate of pressure rise shows the similarity between flame propagation in a premixed cornstarch-air mixture and in a lean limit methane-air mixture. This similarity agrees with some conclusions obtained from the previous research, which indicated that the fundamental characteristics (such as the minimum quenching distance and the minimum ignition energy) between the above flames are comparable. It is inferred that there is some similarity in the processes controlling flame propagation in these flames.

Constant Volume Combustion of Aluminum and Cornstarch Dust in Microgravity

The subject of the present work is to report an experimental comparative study of the effect of dispersion-induced turbulence on dust combustion in constant volume vessel, carried out both in normal gravity and in microgravity environment. Dispersion system with small scale of turbulence, creating uniform homogeneous mixture, was used in experiments. To improve reproducibility of the explosion data an ignitor of small energy, with local soft ignition was developed. Both factors contributed to acquisition of more reproducible experimental data. In experiments under microgravity conditions a dust suspension during combustion remains constant. This makes possible to study dust explosion under stationary dust suspension without influence of turbulence.

Some Features of Propane-Air Flames Under Quenching Conditions in Narrow Channels

Knowledge of flame–wall interaction helps in the understanding of flame phenomena near a wall and of flame extinction. In the present work different flame characteristics were measured in square, narrow quenching channels. A propane/air mixture was employed and direct visualization was used to observe flame behavior under quenching conditions. Flame propagation velocity was determined during downward propagation. As expected, close to quenching condition it was found to be lower than that under adiabatic conditions and close to the values predicted by the quenching theory. The dead space appeared to be larger for rich mixtures than that found with lean ones. Flame curvature reached its maximum value for stoichiometric mixtures decreased for both leaner and richer mixtures. Numerical simulation revealed the structure of limit flames during their propagation in quenching channels. It was confirmed that flame quenching depends on the relation between heat release rate and heat loss rate.

Experimental study of flame propagation in propane-air mixture near rich flammability limits in microgravity

The experiments were carried out in a cylindrical closed vessel of 8.5-L capacity, made of transparent organic glass. Propane-air mixture was used; pressure history was measured. A high-speed video camera recorded the history of flame propagation. During the experiments the vessel was located inside the cage of a drop-tower assembly. The microgravity experiments started with ignition of the flammable mixture at the bottom or central part of the vessel. The video camera registered changes in flame development while pressure records indicated corresponding changes in heat release rate. The microgravity experiments were compared with similar experiments conducted under normal gravity conditions. Behavior of flame propagation was investigated in detail for mixture concentrations between 6.4% and 9.5% C 3 H 8 . It was found that the flammability limit under microgravity conditions was close to the limit for upward-propagating flame at 1 g (9.0% C 3 H 8 versus 9.5% C 3 H 8 at 1 g ). However, the behavior of flame propagation and pressure history was completely different: Under microgravity the flame was not visible but combustion was indicated by pressure rise.

An Experimental Study on Flame Propagation in Cornstarch Dust Clouds

Following the quantitative determination of dust cloud parameters, this study investigates the flame propagation through cornstarch dust clouds in a vertical duct of 780 mm height and 160 × 160 mm square cross section, and gives particular attention to the effect of small scale turbulence and small turbulence intensity on flame characteristics. Dust suspensions in air were produced using an improved apparatus ensuring more uniform distribution and repeatable dust concentrations in the testing duct. The dispersion-induced turbulence was measured by means of a particle image velocimetry (PIV) system, and dust concentrations were estimated by direct weighing method. This quantitative assessment made it possible to correlate observed flame behaviors with the parameters of the dust cloud. Upward propagating dust flames, from both closed/open bottom end to open/closed top end of the duct, were visualized by direct light and shadow photography. From the observation of propagation regimes and the measurements of flame velocity, a critical value of the turbulence intensity can be specified below which laminar flame propagation would be established. This transition condition was determined to be 10 cm/s. Laminar flames propagated with oscillations from the closed bottom end to the open top end of the testing duct, while the turbulent flames accelerated continuously. Both laminar and turbulent flames propagated with steady velocity from the open bottom end to the closed top end of the duct. The measured propagation velocity of laminar flames appeared to be in the range of 0.45–0.56 m/s, and it was consistent with the measurements reported in the literature. In the present experimental study, the influence of dust concentration on flame propagation was also examined, and the flame propagation velocity was found weakly sensitive to the variations in dust concentration. Some information on the flame structure was revealed from the shadow records, showing the typical heterogeneous feature of the dust combustion process.