US2863512A - Flame-trap means for limiting the effects of explosions - Google Patents

Description

Dec. 59,1958 w. P. MANSFIELD 2,853,512

FLAME-TRAP MEANS FOR LIMITING THE EFFECTS OF EXPLOSIONYS Filed April 17, 1956 3 Sheets-Sheet 1 FLAME-TRAP MEANS FOR LIMITING THE EFFECTS OF EXPLOSIONS Filed April 17, 1956 Dec. 9, 1958 w. P. MANSFIELD 5 Sheets-Sheet 2 Dec. 9, 1958 w. P. MANSFIELD 2,863,512

FLAME-TRAP MEANS FOR LIMITING THE EFFECTS OF EXPLOSIONS Filed April 17, 1956 3 SheetsSheet 31 P Pateii ted Dec. 9, 1958 FLAME-TRAP MEANS FOR LIMITING THE EFFECTS OF EXPLOSIONS Wilfred Percival Mansfield, Slough, England, assignor to The British Internal Combustion Engine Research Association, Slough, England Application April 17, 1956, Serial No. 578,692 Claims priority, application Great Britain April 18, 1955 12 Claims. (Cl. 169-1) This invention relates to flame-traps. A well known method of preventing the passage of aflame of limited duration is to arrange a barrier comprising an open structure which, while allowing the passage of gases, otters a large surface for the reception of heat, so that a rapid cooling of the gases is produced and no flame appears downstream of the barrier. Thus one or more layers of copper wire gauze are commonly used, while in another well known construction alternate layers of corrugated and flat sheet metal are coiled to form a series. of passages of small cross sectional area bounded by heat receptive surfaces.

The object of the present invention is to provide flame-traps of improved efliciency and reduced size and cost.

The invention consists in a method of preventing the passage of flame across a barrier which will allow the passage of gas comprising causing the flame to give up heat at the barrier by vaporising a substance.

The invention further consists in a flame-trap of the kind comprising a structure permitting the passage of gas but which acts as.a barrier to the passage of flame characterised in that the structure is or includes a vaporisable substance.

The invention still further consists in a flame-trap as set forth in the preceding paragraph in which the vaporisable substance is a fuel and the vaporisation of said substance extracts heat from the gases and raises the mixture strength of the gases passing beyond the said barrier above the inflammable limit.

It has been found that the provision of a vaporisable substance greatly increases the effectiveness of flametraps, particularly where they are required to prevent ignition of fuel/air mixtures on the side of the trap remote from theflame source. If the circumstances are such that the vapour produced may, after mixing with air, encounter a flame, spark or other igniter, then, as a further precaution, the coating may be of a material which produces a vapour which is non-ignitable when mixed with air in any proportion. It is believed that at least two distinct actions are present. Firstly, the substance absorbs not only the amount of heat necessary to bring it to boiling point, but also a much larger amount corresponding to its latent heat of vaporisation. Secondly, as the substance evaporates it forms a non-ignitable belt of vapour and condensed droplets in the path of the explosion gases. Also, when the substance is a fuel it may be arranged that the strength of the mixture formed upon vaporisation rises above the inflammable limit thereby quenching the flame.

, The vaporising substance may be solid or liquid. As an example of the use of a solid, good results have been obtained by using a gauze-type flame-trap with the gauzes coated with a petroleum grease (i. e. a petrolatum). When several layers of gauze are employed, it has been found sufficient to coat only the layers nearer to the flame, which are usually of coarser gauze. As an example of the use of a liquid, engine lubricating oil has been found very effective.

The following description is directed particularly to the provision of flame-traps in the crank cases of engines, compressors and the like, but it is to be understood that flame-traps constructed in accordance with the invention have many other applications and that, broadly speaking, they may be provided in those constructions where an explosive mixture of gases may be produced in a confined space and where there is a risk of ignition and resultant explosion of the gases taking place.

An important application of the invention is to the flame-traps used in conjunction with the explosion relief valves fitted to the crankcases of engines, compressors and the like. The trap may be placed either externally so that the explosion gases pass through it after they have passed the relief valve or internally so that the flame is quenched before the gases reach the relief valve.. If the external arrangement is used, solid substances such as the grease referred to above are suitable as coatings for the flame-trap surfaces since they remain unaifected by exposure to the atmosphere for long periods. By coating only the inner portions of the flame-trap, e. g. the coarse inner gauzes in the case of a gauze-type trap, clogging of the passages by collection of dust is avoided.

When the flame-traps are arranged internally, it is convenient to use engine lubricating oil as the coating. The flame-traps may be so positioned that oil flung off the moving parts falls'directly or via deflectors onto the flame-trap surfaces. Alternatively or additionally, an oil supply pipe provided with a series of holes may be arranged to discharge oil onto the surfaces continuously so that the oil keeps the whole of the surfaces coated. The use of the oil feed pipe is preferred because by this means it can be arranged that the supply of oil to the flame-trap commeces before the engine is started and is maintained for some time after the engine is stopped.

A known method of avoiding the ill effects of explosions occurring in the crankcases of engines consists in the provision of a number of relief valves through which the explosion gases are vented to the atmosphere and the pressure attained inside the crankcase is thereby limited to a safe value. The relief valves may be provided with some form of flame-trap to prevent injury of personnel or the starting of fires by issuing flame.

These provisions are practicable in the case of engines of medium size, but in the case of larger engines suitable provisions of this kind are difiicult or impossible for two reasons. Firstly, the area of crankcase wall available for the accommodation of relief valves is smaller in relation to the quantity of fuel-air mixture which the crankcase may hold, and secondly, the larger crankcase is less able to withstand internal pressure.

The crankcases of larger engines are usually divided by partitions midwaybetween the cylinder centres and these partitions contain certain apertures, and in accordance with the present invention these apertures may be furnished with flame-traps.

In an engine thus equipped not only is the explosion confined to a single compartment, thus avoiding the accumulative effect of the passage of flame through communicating compartments, but this compartment is provided with a large additional relief area.

Although any effective form of flame-trap may be employed for this purpose, flame-traps as proposed above are particularly well suited. By way of example, experiments have shown that the following simple arrangement is completely effective. Two sheets of wire gauze are placed on each side of the apertures in the dividing partitions and secured by suitable frames surrounding the aperture and bolted together. The sheets of gauge further away from the partition are of heavy Wire and coarse mesh, and the sheets nearer to the partition are of lighter wire and finer mesh. An oil supply pipe is arranged across the top of the aperture between the two pairs of gauzes, and is provided with a series of holes from which engine lubricating oil is sprayed continuously onto the gauzes. As in the case of the internal flame-traps for the crankcase relief valves, the oil supply to these flame-traps is preferably commenced before the engine is started and continued for some time after the engine is stopped.

The accompanying drawings show, by way of example only, a number of embodiments of the invention in which:

Figure 1 is a vertical section of a combined flame-trap and pressure relief valve,

Figure 2 is a vertical section of a further combined flame-trap and pressure relief valve,

Figures 3, 4 and 5 are an elevation, vertical section and horizontal section respectively of a flame-trap employing a sprayed liquid,

Figures 6, 7 and 8 are an elevation, vertical section and detail of the upper portion respectively of a further flame-trap,

Figures 9, 10 and 11 are a longitudinal section, a section showing a detail and a cross section respectively showing the application of a partition flame-trap to a three cylinder engine, while Figure 12 is a vertical section through a factory ventilating system.

Figures 1 and 2 show two ways in which the invention may be used to prevent the emission of flame from explosion relief valves fitted to engine crankcases.

In the external arrangement of the flame-trap shown in Figure 1, strips of wire gauze 1 are arranged circumferentially in known manner inside a cylindrical container 2, the sides 3 of which are perforated. The container is attached by bolts 4 to the outside of a crankcase wall or crankcase door 5, in which is mounted a housing 6, carrying an explosion relief valve 7. In accordance with the invention, one or more of the layers of gauze are coated with grease.

It is preferable to coat the inner gauzes only, since this has been found fully effective and coating the outer gauzes accelerates the accumulation of dust. The grease should have a high melting. point and should be sufficiently viscous that it remains in place at any temperature to which it may be subject prior to the arrival of the flame. When the flame-trap operates, the grease is rapidly heated by the first part of the flame and part of it is blown into the outer layers of gauze so that all or most of the gauzes become coated at an early stage of the process. In the internal arrangement of the flame-trap shown In Figure 2, flat sheets of wire gauze 8 are fastened to a frame 9 mounted on the inside of a crankcase door 1.0 provided with a relief valve 11. The gauze assembly may be so placed that oil from the lubricated moving parts in the crankcase reaches it directly or indirectly, but a more certain means of oiling the whole of the gauze is preferred.

In Figure 2, a trough 12, arranged at the top of the assembly, has a row of holes 13 just above the gauzes, through whichlubricating oil supplied to the trough pours continuously over the gauze. The trough is fed with oil by a pipe 14 which may be connected to an adjacent point in. the engine lubricating oil feed system. It is preferable however to arrange a separate oil supply system for the flame-traps so that the supply of oil to the gauzes may be continued for some time after the engine has been stopped, and before re-starting while the engine is still hot.

It has been found that the internal arrangement of the gauzes is more efiicient than the external because there is a more uniform distribution of gas flow through the gauzes.

As an alternative to the use of a perforated oil trough to distribute the oil across the surface of the gauze assembly, the spraying system shown in Figures 3, 4 and 5 may be employed. Rows of nozzles 15 fitted to pipes 16 at the side of (or in front of) the gauze surface 17 may be arranged so that oil is continuously projected onto the whole area. This arrangement, of the oil over the whole surface, is recommended where a prolonged discharge of hot gases through the gauze is likely to occur, as when the total discharge area of the flame-traps provided is small in relation to the volume of the crankcase.

When it is not convenient to arrange a separate supply of oil which will continue for some time after the engine has stopped, the construction illustrated in Figures 6, 7 and 8 may be used to ensure an immediate supply of oil to the gauzes in the event of an explosion occuring some time after an engine has been stopped or on restarting after a brief stop and before the engine has cooled down. The grid 18 is formed of strip metal elements 19 (Figs. 7 and 8) or arcuates of other section forming a series of receptacles for oil. These are filled, either by oil splash or by more positive means such as the trough 20 and cascade arrangement shown in Figure 8, which assembly can conveniently be attached to a sloping crankcase wall or door. In the event of an explosion, the oil retained by the grid is flung into the gauzes 21 by the explosion gases. The grid itself acts as a flame-trap, sothat fewer layers of gauzes are needed. If the spacing of the grid elements is sufficiently close, and the area of the grid is great enough in relation to the quantity of gases to be discharged, the oil retaining grid alone is sufficient. to trap the flame.

A further application of the invention to engines is in the provision of flame-traps in apertures in the partitions separating the several crank chambers of large multi-cylinder engines. Figures 9, 10 and 11 show the invention applied in this way to a three-cylinder engine.

Gauze assemblies 22 supported by frame 23 (Figure 10) are wetted by oil fromtroughs 24' supplied by pipes 25. It has been found that when an exposion occurs, the oilwetted flame-traps limit combustion to a single compartment, and reduce the maximum explosion pressure reached to a fraction of the value attained without the partition flame-trap. This is because in addition to confining the explosion to the compartment in which ignition occurs, the flame-traps also provide a large area for pressure relief of that compartment. This form of pressure relief is far less expensive than that provided by relief valves, since it requires no moving parts, and hence large relief areas can be provided. When this arrangement is employed, the relief area necessary from the crankcase to the atmosphere is reduced to one-tenth or less of that which is otherwise necessary. Tests have shown that a system, comprising oil-wetted flame traps in the crankcase partitions together with relief valves of limited size provided with oil-wetted internal flame-traps, has a further advantage over the use of relief valves alone for pressure relief, in that discharge of combustion gases to the atmosphere occurs comparatively slowly and is not followed by a large depression in the crankcase such as occurs when relief valves alone of adequate area are provided. The danger of inward collapse of crankcase doors or walls is thus avoided.

The invention may be applied not only to engines, compressors and the like but also in other situations where it is desirable to prevent the passage of flame without preventing the passage of gases. By the way of example, Figure 12 shows three rooms in a factory servedby a ventilating fan 26, and duct 27 joining three branch ducts 28. When work involving the use of explosive materials is being conducted in the rooms, an explosion in one room can result, when no safeguard is provided, in the passage of flame to the other rooms where further explosions may occur. To prevent this, coated flametraps 29 are arranged as shown in the duct to prevent the passage pf flame while allowing the removal of vitiated air. In such applications a flame-trap coating which is solid at atmospheric temperature is conveniently used, but in some cases, according to the nature of the contaminant, it may be more satisfactory to wet the flame-traps by a liquid circulating system which includes filters to remove the contaminant.

In certain cases the gauzes may be omitted, a curtam of liquid only being provided, and the flow of the liquid, for example by means of sprays, being related to the flow of the gases in such a manner that the liquid supply at the desired barrier is continuous under the highest gas flow conditions.

It will be apparent from the above description that the forms of flame-traps constructed in accordance with the invention are not restricted to the limiting of the effects of explosions in crankcases of engines, compressors and the like, but have a wide field of applications and therefore it is to be understood that the above description is by way of example only and also that details for carrying the invention into effect may be varied without departing from the scope of the invention.

I claim:

1. Flame-trap comprising a non-inflammable structure forming a portion of the boundary of an enclosed space, said structure being perforated for the passage of hot gases produced by the combustion of air/fuel mixtures within said space, the combined area of the passageway provided by said perforations being that necessary to relieve rising pressure of the gases in said space at a rate which prevents them reaching a pressure which will damage the boundaries of said space, the said perforated structure being coated with a vapourisable substance which, when vapourised by a flame, quenches the latter and thus prevents its passage by way of said perforations.

2. Flame-trap as claimed in claim 1 in which the structure forms a portion of the boundary wall common to two enclosed spaces.

3. Flame-trap comprising a non-inflammable structure forming a portion of the boundary of an enclosed space, said structure being provided with at leasts one layer of gauze for the passage of hot gases produced by the combustion of air/fuel mixtures within said space, and means for coating the gauze with a liquid which, when vapourised by a flame, quenches the latter and thus prevents its passage by way of said gauze.

4. Flame-trap as claimed in claim 3 in which the means for coating the gauze is spray means.

5. Flame-trap as claimed in claim 1 in which the vapourisable substance is a fuel of sufficiently high viscosity that upon arrival of the burning gases under pres sure it will remain adjacent the structure for the time necessary for its vapourisation and for the quenching of the flame, and will raise the mixture strength of part at least of the gases, locally, above the inflammable limit.

6. Flame-trap comprising a non-inflammable structure forming a portion of the boundary of an enclosed space,

said structure being provided with at least one layer of gauze and a series of vertically spaced weir-like troughs, so shaped as to act as reservoirs to contain a liquid, and into which the liquid is fed and from which it cascades from trough to trough and which form apertures for the passage of hot gases produced by the combustion of air/fuel mixtures within said space, the said gauze being coated with liquid from said troughs by the passage of said gases, which liquid, when vapourised by a flame, quenches the latter and prevents its passage by way of said gauze.

7. Flame-trap in accordance with claim 1 in which the non-inflammable structure comprises a. series of horizontal weir-like troughs at close vertical spacing, so shaped as to act as reservoirs to contain liquid, and into which the liquid is fed and from which it cascades from trough to trough, the spaces between the troughs forming apertures for the passage of hot gases produced by combustion of air/fuel mixtures within said space, the said cascading liquid, when vapourised by a flame, quenches the latter and thus prevents the passage of the flame by way of said apertures.

8. Flame-trap as claimed in claim 1 in which the enclosed space is within the crankcase of an internal combustion engine.

9. Flame-trap as claimed in claim 1 in which the enclosed space is within the casing of a compressor.

10. Flame-trap as claimed in claim 1 in which the enclosed space is within a gear casing.

11. Flame-trap as claimed in claim 1 in which a gaspressure relief valve is provided in series with the said structure.

12. In an internal combustion engine of the kind having a multi-compartment crankcase the improvement comprising a flame-trap including an non-inflammable perforated structure having a large area for the passage of hot gases produced by combustion of air/fuel mixtures in any one of said compartments provided in each wall between adjacent compartments, and a further flame-trap as above defined but having a smaller area for the passage of said gases and having a gas-pressure relief valve in series therewith provided .in an external wall of at least one compartment, the perforated structures of the fiame-traps being coated with a vapourizable substance, which when vapourised by a flame, quenches the latter and prevents its passage by way of said perforations.

References Cited in the file of this patent UNITED STATES PATENTS 844,677 Johnston Feb. 19, 1907 855,448 Doherty June 4, 1907 1,061,775 Newton et a1. May 13, 1913 1,895,597 Williams Jan. 31, 1933 2,586,797 Dunlop et a1, Feb. 26, 1952

Claims (1)

1. FLAME-TRAP COMPRISING A NON-INFLAMMABLE STRUCTURE FORMING A PORTION OF THE BOUNDARY OF AN ENCLOSED SPACE, SAID STRUCTURE BEING PERFORATED FOR THE PASSAGE OF HOT GASES PRODUCED BY THE COMBUSTION OF AIR/FUEL MIXTURES WITHIN SAID SPACE, THE COMBINED AREA OF THE PASSAGEWAY PROVIDED BY SAID PERFORATIONS BEING THAT NECESSARY TO RELIEVE RISING PRESSURE OF THE GASES IN SAID SPACE AT A RATE WHICH PREVENTS THEM REACHING A PRESSURE WHICH WILL DAMAGE THE BOUNDARIES OF SAID SPACE, THE SAID PERFORATED STRUCTURE BEING COATED WITH A VAPOURISABLE SUBSTANCE WHICH, WHEN VAPORISED BY A FLAME, QUENCHES THE LATTER AND THUS PREVENTS ITS PASSAGE BY WAY OF SAID PERFORATIONS.

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