Passage Of Flame Research Articles

Nanosecond pulsed discharge dynamics during passage of a transient laminar flame

This work presents an experimental study of a nanosecond repetitively pulsed dielectric barrier discharge interacting with a transient laminar flame propagating in a channel of height near the quenching distance of the flame. The discharge and the flame are of comparable size, and the discharge is favoured at a location where it is coupled with the reaction zone and burnt gas. The primary goal is to determine how the discharge evolves on the time scale of the flame passage, with the evolution driven by the changing gas state produced by the moving flame front. This work complements the large body of work investigating the effect of plasma to modify flame dynamics, by considering the other side of the interaction (how the discharge is modified by the flame). The hot gas produced by the combustion had a strong effect on the discharge, with the discharge preferentially forming in the region of hot combustion products. The per-pulse energy deposited by the discharge was measured and found to increase with the size of the discharge region and applied voltage. The pulse repetition frequency did not have a direct impact on the per-pulse energy, but did have an effect on the morphology and size of the discharge region. Two distinct discharge regimes were observed: uniform and filamentary (microdischarges). Higher pulse repetition frequencies and faster-cooling combustion products were more likely to transition to the filamentary regime, while lower frequencies and slower-cooling combustion products maintained a uniform regime for the entirety of the time the discharge was active. This regime transition was influenced by the ratio of the time scale of fluid motion to the pulse repetition rate (with no noticeable impact caused by the reduced electric field), with the filamentary regime preferentially observed in situations where this ratio was small. This work demonstrates the importance of considering how the discharge properties will change due to combustion processes in applications utilizing plasma assistance for transient combustion systems.

Downward flame spread along a single pine needle: Numerical modelling

In this work downward flame spread over single pine needle of Pinus Sibirica is studied. Pine needles are thin cellulosic charring combustible forest fuel elements. Idealising pine needles to thin cylinders, a 2D axisymmetric numerical model is developed accounting for char formation and char oxidation to investigate the important mechanisms which control the downward spread of flame over a pine needle in normal gravity, atmospheric condition and at various opposed flow conditions. Simultaneous formation of char and pyrolysate during the pyrolysis process was found to significantly reduce the flame spread rate over thin fuel. Presence of char resulted in change in distribution of fuel vapour mass flux above the fuel surface which led to decrease in forward heat feedback to the fuel and hence the flame spread rate. This mechanism is different from char acting as a thermal barrier to heat transfer from the flame in case of thick fuel. Char oxidation had no influence on flame spread rate as char oxidation was found to occur only after passage of flame with the availability of surrounding oxygen diffusing through the hot plume of combustion products. Char oxidation was primarily controlled by oxygen diffusion rate to the charred fuel surface. The flame spread data for quiescent flame spread, and the blow off opposed flow velocity was used to calibrate gas phase kinetics and pyrolysis kinetics. The model predicted flame spread rate variation with opposed flow velocity quite well. The predicted spatial distribution of temperature and species concentration also compared very well with the experimentally determined flame structure.

N-Class Fire Resistant Divisions in U.S. Naval Ships

Abstract The U.S. Navy has now developed an N-Class division system to classify fire resistant boundaries in accordance with MIL-STD-3020, fire resistance on U.S. naval surface ships. The N-Class division is analogous to the commercial International Maritime Organization (IMO) system (e.g., A-Class) division. The key difference is that N-Class divisions are designed to have satisfactory fire resistance when exposed to hydrocarbon pool fire (UL 1709 fire exposure) following a shock event. In addition, N-Class is applicable to fire resistant divisions constructed from polymer composites structures when they meet the requirements of DDS-078-1. MIL-STD-3020 requires a hydrocarbon pool fire exposure (UL-1709 fire exposure) which provides a minimum average total heat flux of 188 kW per square meter (kW/m2) (60,000 British thermal unit per square foot/hour (Btu/ft2∣h)) within the first 5 min of the test exposure. At all times after 5 min, the average temperature within the furnace shall be maintained at a minimum of 1038 °C (1900 °F) and a maximum of 1149 °C (2100 °F) for the duration of the test. These fire conditions simulate a post-flashover fire scenario for shipboard applications. Performance is defined as the time period during which assemblies will continue to perform their intended function when subjected to fire exposure. The minimum duration of fire exposure is 30 min. Shock testing prior to fire resistance test is performed to ensure that fire resistance of divisions, with fire insulation, penetrations, and associated attachment methods, is not degraded in a combat environment. Shock test specimen size of 1219 by 3048 mm (4 by 10 ft) was selected to reduce the cost of shipping a full size fire test specimen of 3048 by 3048 mm (10 by 10 ft) or greater to the fire test laboratory. A full scale fire resistance test is still required for qualification purposes after successful completion of the shock test prior to fire resistance test. MIL-STD-3020 also permits AN-Class fire resistant divisions when fire threat is from common combustibles (Class A) and where liquid flammable (Class B) fire threat is non-existent. AN-Class divisions are those divisions formed by bulkheads and decks that are designed to protect against structural failure and prevent the passage of flame or hot gases when exposed to IMO Resolution A.754(18) fire exposure after shock testing. For all AN-Class divisions, including those with penetrations, the fire test duration is a minimum of 60 min. This paper will discuss fire resistance test results conducted using steel, aluminum, and composite substrates.

Materials and constructions used in devices to prevent the spread of flames in pipelines and vessels

This paper surveys a selection of materials and constructions that are in current use and a selection that could potentially be used as the elements of flame arrester devices fitted to pipelines or vessels. Each material and construction type is discussed with reference to key performance criteria for successful flame arrester element application. The essential feature in any flame arrester element is a matrix of very small holes, apertures or cells. These cells allow the flow of flammable gases or vapours under conventional process conditions but are too small to allow the passage of flames, in the unfortunate situation of the gas or vapour igniting. For a practical flame arrester, the element's cell structure has to achieve an optimum combination of low gas flow resistance and adequate flame quenching at reasonable cost.

Vorticity generation and attenuation as vortices convect through a premixed flame

A sequence of PIV images shows the time history of both the vorticity field and the velocity field as vortices of different strength convect through a premixed flame. The vortices represent individual eddies in turbulent flow; the goal is to understand how each eddy wrinkles the flame and how the flame also may alter the eddy. It is found that weak vortices are completely attenuated primarily due to volume expansion. Strong vortices do survive flame passage, but only if they can weaken the flame due to stretch effects. Intense flame-generated vorticity is measured which has a magnitude that exceeds that of the incident vortex in some cases. The flame-generated vorticity in the products induces a velocity field that tends to reduce the amplitude of flame wrinkling; thus it acts as an additional flame-stabilizing mechanism. This mechanism affects the wrinkling process and should be included in models. A new nondimensional vorticity enhancement parameter ( E) is suggested as a way to estimate the effect of vortex size, strength, Reynolds number, and Froude number on vorticity attenuation and production. Measurements are made for E approximately equal to 0, −1, and −2, corresponding to no change in vorticity, total attenuation of the vortex, and flame-generated vorticity, respectively. Buoyancy forces are important in one case that is considered, but not in other cases. The results can be used to quantify the size of the small eddies that can be neglected in large eddy simulations; the role of small eddies is estimated in one example.

Dust explosions in interconnected vented vessels

Explosion venting is used often to protect industrial dust-handling plant from pressures generated by accidental dust explosions. Many calculation methods are available to estimate a safe vent area, but these are without exception applicable to single vessels. In industry, vessels are usually linked and flames can travel through connecting pipework from one vessel to another. The behaviour of flames in such configurations is not well understood and the pressures that can be developed are not well known. As a result, the venting requirements are difficult to estimate. This report describes a project in which the behaviour of dust explosions in linked vented vessel systems was studied. Vessels ranging in size from 2 to 20 m3 were used, linked via pipes up to 15 m long with diameters of 0.15, 0.25 and 0.5 m. Tests were carried out using coal dust, toner dust and anthraquinone dust. The work has shown that the passage of flame from the primary ignition vessel can result in a secondary explosion which produces a much higher pressure than expected from a vented single vessel. Secondary explosion pressures up to 6.2 bar were recorded. The pressure in the first vessel was also enhanced but to a lesser degree. These effects were dependent on the pipe diameter, the pipe length, the vessel volumes and volume ratio, the vessel in which the explosion was initiated, the explosibility of the dust, and the vent area. Effectively, the Kst nomograph approach for sizing the vent area was found to be adequate for vessels linked via the 0.15 m diameter pipe using coal or toner dust. However, explosions in vessels linked by pipes having larger diameters (0.5 and 0.25 m) and a short length generated enhanced reduced explosion pressures. The pressure enhancement was greatest when the primary ignition occurred in the larger of the two vessels. The vessel volume ratio tended to increase the pressure enhancement. Also, the larger the vessel volume for a volume ratio of 1:1, the greater was the pressure enhancement. The more reactive dusts, toner and anthraquinone, generally produced significantly higher reduced explosion pressures in equivalent vessel/pipe configurations when compared with coal. Larger vent areas generated lower absolute pressure than the smaller vent areas.

Computer Modeling of Intumescent Penetration Seals

Penetrations in rated barriers require protection, or sealing, to prevent the passage of flame and smoke during a fire. In terms of the properties desirable for a penetration seal (high heat absorbing ability and strength after fire exposure), intumescent materials offer an excellent choice. This paper describes a simple three-dimensional heat transfer model for an intumescent penetrating seal exposed to a fire in accordance with that specified in the ASTM E814, Standard Test Method for Fire Tests of Through Penetration Fire Stops. The model is limited to estimating the temperature on the unexposed side as a result of heat transfer through the assembly. It makes no attempt at modeling flame passage or ability of the seal to withstand hose stream exposure. The model also assumes a very simplified hot gas emissivity model for heat transfer from the furnace to the assembly. Radiant view factors and emissivities are not calculated, but must be entered by the user. This model was validated by comparing predicted results with actual test data. Obtaining necessary physical property data for intumescent materials was found to be very difficult. Language: en

Flame propagation through periodic vortices

The discovery of a new class of Navier-Stokes solutions representing steady periodic stretched vortices [1] offers a useful test-bed for examining interactions between flames and complex flow-fields. After briefly describing these vortex solutions and their wide-ranging parameterisation in terms of wavelength and amplitude, this article examines their effect on flames of constant normal propagation speed as observed through numerical solutions of an eikonal equation. Over certain ranges of vortex amplitude and flame-speed, a corridor of enhanced flame passage is seen to be created as a leading flame-tip manages to leap-frog between successive vortices. However, for large enough amplitudes of vorticity or small enough flame-speeds, the flame fails to be able to benefit from the advection due to the vortices. It is shown that the leading tips of such flames are effectively trapped by the stretched vortices.

An Improved Method for Measuring Temperatures during Range Fires

A technique for recording time-temperature curves within field-scale range fires was accomplished using a commercially available data logger capable of rapidly reading large numbers of thermocouples. A specially designed fireproof box was utilized to house and protect the data logger within the center of the burned area. Programming features allowed temperatures to be measured and recorded rapidly (each second) during the passage of the fire front and recorded as 1-minute means before and after the combustion interval. Strategic placement of thermocouples provided time-temperature profiles for various heights above ground, rate of spread, and duration of heat above specific temperatures. Additionally, measurement of preheating prior to the actual flame passage was obtained by placement of the recorder and thermocouples well within the burned area. This technique may provide better quantification of fire effects on vegetation, especially woody weeds targeted for control with fire, by documenting temperature extremes and their duration at critical growing points on plants.

Ceeprce: Unique Fire Barrier from a Versatile Filler

ICI have launched a new versatile additive for plastics, coatings, adhesives and sealants. Ceepree* fire barrier filler, unlike conventional flame retardants, increases the fire resistance of materials by virtue of its unique composition of powdered specially-designed glasses. Ceepree melts over a wide temperature range (350–900°C) to encapsulate and fuse with combustible material, char, reinforcing fibres and other fillers. In this way Ceepree confers in situ integrity, crystallinity and high temperature strength up to 1100°C which protects against the thermal degradation of plastics and other materials and prevents the passage of flames, smoke and toxic fumes. Ceepree uprates the fire resistance and high temperature strength of adhesives, sealants and protective surface coatings thereby making it possible to use plastics for greater design flexibility in new applications in building and construction, mass transit, aerospace, military and offshore industries where compartmentation of fire is essential.

Performance of concrete block and steel panel stoppings in a simulated mine fire

The U.S. Bureau of Mines constructed a facility in the multiple-entry section of its Bruceton Experimental Mine to evaluate the fire endurance of mine stoppings. The test stopping (up to 6 ft high by 18 ft wide) is subjected to a 70 min, 75,000 Btu/min liquid fuel tray fire. The stopping and adjacent areas are instrumented with thermocouples and heat flux gauges. Two 8 in. thick concrete block stoppings and a galvanized steel stopping were evaluated in four tests. A crack developed on the fire-exposed surface of both block stoppings where the flames were most intense. However, the unexposed surface of the stoppings was undamaged and its maximum temperature was about 80°C. The steel stopping retained its structural integrity during the test. The temperature of the unexposed steel surface reached 490°C, but combustible materials located 1 ft from the surface did not ignite. Heat energy transmitted across the steel stopping was approximately halved when a 3/4 in. thick coating of construction plaster was applied to its fire-exposed surface. All stoppings prevented the passage of flame and smoke.

An Experimental Evaluation of the BLM Model of the Scalar Field in Turbulent Premixed Flames

An experimental evaluation of the BLM model of the scalar field in premixed turbulent flames is presented. Experimental measurements of probability density functions (pdfs) of the flame passage times, autocorrelations and spectra were made in open V-shaped and stagnation point flames by monitoring the Mie scattering of the laser beam by a dense oil aerosol which evaporates on passage through a flame front. These results are compared with predictions derived from the model using two a priori pdfs: the exponential and gamma two distributions. The product pdfs are self-similar and well described by the gamma two distribution. The reactant pdfs are also self-similar but are better represented by the exponential distribution except at small passage times. Comparisons between experimental and theoretical autocorrelations show the gamma two predictions to be more successful. The modeling of the low fequency region of the scalar spectra is also improved. Calculations of the integral time scale based on measured c...

Explosion pressures in enclosures compartmented by porous barriers

It has been found possible to substantially reduce the peak pressures observed when a gaseous mixture is exploded within a closed vessel; this can be accomplished by dividing the internal volume into several smaller volumes separated by suitable porous barriers. A suitable barrier is one which (a) provides little resistance to gas flow through it, and (b) prevents passage of flame (by cooling it) from one compartment to the next; plates of sintered bronze shot have been found to be effective barriers. A single stainless-steel screen (50*50 mesh) was not an effective barrier for stoichiometric ethylene/air flames; but it did quench for equivalence ratios below 0.7. For a simple geometry it has been found possible to predict the instantaneous pressure as a function of the fraction of the total volume filled by flame products. 2 refs.

Non-luminous Flame Gases

PROF. W. T. DAVID and his co-workers have published a moving-film record of passage of flame gases along a glass tube1. Such records have frequently appeared elsewhere2, but explanation given by writers of letter, namely, that the flame gases, although luminous after early stages of flame-front travel from igniting spark, suddenly become non-luminous after further travel (due apparently to a sudden change in mode of combustion in flame-front) is a mis-reading of photograph.

Gaseous Combustion

IT was shown by Mallard and Le Chatelier more than fifty years ago that, during the passage of flame through an inflammable gaseous mixture, two types of flame movement were clearly distinguishable, namely, the initial uniform slow movement and the very rapid movement known as detonation which is set up—if the mixture is strong enough—after the flame has travelled some distance.

Editorial Notes

Editorial NotesPublished Online:29 May 2014https://doi.org/10.1259/0007-1285-2-19-323SectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail AboutAbstractWith further reference to the question of fire risks with X-ray films we notice an article by Mr. R. B. Holbs in the November, 1928, issue of The Modern Hospital, dealing with a recent fire in a film store in the Memorial Hospital, New York. The article suggests that unexposed films should be stored in containers constructed of lead, or lead-lined, on shelves 2 ft. above the floor, or in double wall cabinets, vented to the outside air. The amount of unexposed films in standard containers kept outside the fireproof vaults should not exceed 50 lb., and all films should be transferred to storage as quickly as conditions permit. In discussing the use of the so-called non-inflammable films—which, in fact, are inflammable, though they burn slowly and without the production of poisonous gases—it is remarked that their disadvantages are an increased cost and a tendency to roll and curl, and it is concluded that property and lives may be endangered to facilitate handling and filing. The floor and walls of storage vaults should, it is suggested, be of brick at least 8 in. thick, or of reinforced concrete at least 6 in. thick; and double fireproof doors should be provided, one at each face of the wall. The inner door should be made to close automatically; the outer, self-closing, should be of a swinging type and made to close into a jamb so as to prevent the passage of flame around the edges. Next article FiguresReferencesRelatedDetails Volume 2, Issue 19July 1929Pages: 323-370 © The British Institute of Radiology History Published onlineMay 29,2014 Metrics Download PDF

Regulations for Handling and Storing X-Ray Films

HomeRadiologyVol. 3, No. 3 PreviousNext EditorialRegulations for Handling and Storing X-Ray FilmsPublished Online:Sep 1 1924https://doi.org/10.1148/3.3.265MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In AbstractRegulations for storing and handling of photographic and X-ray nitro-cellulose films presented by the committee on hazardous chemicals and explosives of the National Fire Protection Association were tentatively adopted by that association at its meeting May 13, 14 and 15, 1924.The article pertaining to the general storage of unexposed films in hospitals and similar institutions reads as follows: Storage of unexposed films shall be in metal boxes or cans on shelves two feet above the floor, or in approved double walled cabinets vented to the outside air. In regard to the storage of exposed films in hospitals and similar institutions the regulations read as follows: All films shall be kept in vented cabinets or in a vented. storage room.The specifications for vented cabinets are (1) no cabinet shall exceed thirty cubic feet capacity; (2) cabinets shall be of approved insulated construction; (3) cabinets having a capacity in excess of 250 pounds of film shall be divided into at least two distinct compartments; each compartment provided with an independent door and vent. The separating partitions should be practically air tight and of substantial construction equivalent to the sides; (4) cabinets holding over 100 pounds of film shall be equipped with at least one automatic sprinkler. If divided into two or more compartments, they shall have at least one automatic sprinkler in each compartment; (5) each compartment shall be provided with a vent to the outside air. The vent shall have a cross-sectional area of at least one square inch per cubic foot of capacity of the cabinet.Rules for vented storage rooms read as follows: (1) Walls or partitions, floors and ceilings shall be of a type affording one hour protection. Walls shall be continuous from floor to ceiling and shall be securely anchored. Construction of vented storage rooms affording one hour protection indudes the following: (<italic>a</italic>) reinforced concrete; (<italic>b</italic>) metal lath with solid cement plaster not less than two and one-half inches thick; (<italic>c</italic>) three-quarters of an inch of cement or gypsum plaster on metal lath on each side of studs; (<italic>d</italic>) brick, tile, or hollow concrete blocks plastered on each side to a thickness of one–fourth inch.(2) Openings from the storage room to other parts of the building shall be protected by a fire door on each side of the wall. Doors shall conform as to construction and installation to Class B of the regulations for the protection of openings in walls and partitions against fire. The interior door shall be automatic. The outer door shall be of the swinging type and close <italic>into</italic> a rabbet, or otherwise be made tight to prevent passage of flame around edges; it shall be self-closing, and if fastened open shall be arranged to close automatically in case of fire originating inside or outside of the storage room. (3) No skylights shall be permitted.Article HistoryPublished in print: Sept 1924 FiguresReferencesRelatedDetailsRecommended Articles RSNA Education Exhibits RSNA Case Collection Vol. 3, No. 3 Metrics Altmetric Score PDF download

Miners' Lamps1

OF late years there has been a tendency on the part of makers of miners' safety lamps to employ thin sheet-metal, perforated with holes of small diameter, to serve the same purpose as wire gauze—that is to say, with holes large enough to admit of the passage of the necessary volume of air through them, but small enough to arrest the passage of flame. It will be recalled that the lamp invented by George Stephenson depended upon perforated sheet-copper for its impermeability to flame. A further innovation that has recently been gaining ground is the addition of a short glass cylinder, known as the “combustion tube,” to the lower end of a metal chimney suspended directly above the flame of the lamp. This contrivance promotes a better circulation of air in the lamp, keeps the products of combustion separate from the incoming air, and, as a consequence;, produces a brighter flame and enhances the lighting power of the lamp.

XCIII. On safety-lamps, and the barrier formed by wiregauze against the passage of flame

(1816). XCIII. On safety-lamps, and the barrier formed by wiregauze against the passage of flame. The Philosophical Magazine: Vol. 48, No. 224, pp. 451-455.