US2925716A - Flame holder - Google Patents

Description

Feb. 23, 1960 J. F. REGAN ETAL FLAME HOLDER Original Filed Sept. 29, 1955 INYENTORS JOSEPH F. REGAN SEYMOUR BELLAK X3 iinited States Patent O FLAME HOLDER Joseph F. Regan, Manchester, and Seymour Bellak, East Meadow, N.Y., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Original application September 29, 1955, Serial No. 537,612. Divided and this application June 29, 1956, Serial No. 601,097

2 Claims. (Cl. 60--39.72}

This invention relates to means for stabilizing or holding a flame and is particularly directed to flame holding or stabilizing means suitable for combustors in ram jet engines.

This application is a division of copending application Serial No. 537,612, filed September 29, 1955, now abandoned.

Combustion gases pass through the combustion chamber of a jet engine at relatively high velocities. This is particularly true in the ram jet engine. Accordingly, this high velocity presents problems in igniting the gases and maintaining a stable combustion flame in a desired location in the engine. Not only must the combustion flame be stabilized but for efficient combustion the flame must be so located and maintained that substantially all of the gases are ignited.

The flame holder structure of the present invention provides for unusually high combustion efficiency through the enlargement of the ignition and flame zones, the establishment of a low velocity preheat zone, and the additional feature of continuous augmentation of the pilot flame by a reverse flow action of the gases downstream of the flame holder.

Accordingly, it is an object of the present invention to provide an improved flame holder for jet engines.

It is a further object to present a flame holder structure which increases the preheat and flame zones for more efficient combustion.

Still another object is to obtain a flame holder structure which provides for low velocity of the gases in the ignition and flame zones such that the combustion of fuel is complete within a short distance from the flame holder.

It is also an aim of the present invention to provide flame holder means which retards the velocity of the gases allowing for preheating of portions of and thorough combustion of the gases due to a large turbulence and reverse flow action of the gases which in turn forms enlarged ignition and flame zones downstream of the holder structure.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a side view of a ram jet engine with portions broken away to illustrate one embodiment of the invention;

Fig. 2 is a view of the device of Fig. 1 taken along line 2-2 looking upstream;

Fig. 3 is a side view of a ram jet engine with portions broken away showing another embodiment of the invention; and

Fig. 4 is a view of Fig. 3 taken along line 44 looking upstream.

Referring first to Figs. 1 and 2 of the drawings, there is illustrated a ram jet duct comprising a forwardly 2,9253% Patented Feb. 23, 1960 directed air entrance opening 11 and a rearwardly directed discharge opening 12. Fuel is introduced into the incoming air by means of conventional fuel injection devices such as the fuel nozzles 13 to form a combustible mixture within mixing chamber 14. The combustible mixture is subsequently burned in the aft combustion chamber 15.

A flame holder structure is disposed a suificient distance downstream from the fuel nozzles 13 to permit thorough mixing of the air and fuel prior to the ignition and combustion of same. The flame holder structure may comprise a turbulence creating spoiler 16 which may be shaped in the form of a truncated cone or frustum of a cone and which may be secured to the inner wall of duct 10 to extend inwardly and forwardly in the upstream direction. The spoiler 16 has a centrally disposed opening 17 therethrough comprising an orifice for passage of the gases within the duct 10. The cross-sec tional area of the orifice 17 is not particularly critical, however, the opening should be as large as possible so as not to unnecessarily restrict the flow of gases through the duct 10. If the opening is made too large the sheltered zone or ignition zone 18 will diminish to a point where flame holding will become diflicult. A blockage of approximately 60% has proved satisfactory during test operations.

Circumferentially spaced around the peripheral surface of the spoiler 16 are a plurality of perforations 19 which provide for the passage of a portion of the gases from the preheat zone 20 through the spoiler 16 into the sheltered or ignition zone 18. Means are provided for initially igniting the combustible mixture in the sheltered zone 18. As shown, a plurality of pilot burners 21 are positioned adjacent and directly downstream of the spoiler 16. The pilot burners 21 may be supplied with their own fuel and ignition means such as spark plugs (not shown). If desired spark plugs may be used for directly igniting the combustible mixture in the sheltered zone 18.

In operation air enters the air entrance opening 11 and is mixed with fuel to form a combustible mixture in the mixing chamber 14. Subsequently, the combustible mixture passes through the orifice 17 and the perforations 19. Due to the non-streamlined converging peripheral surface configuration of the truncated cone shaped spoiler 16 in relation to the oncoming gases, a high pressure drop is developed thereacross resulting in a considerable flow of gas into the preheat zone 20 and through the perforations 19. Also, as a result of the spoiler configuration there is formed a large zone 9 of turbulent gases substantially immediately downstream from the flame holder with additional reverse flow or eddy currents in the ignition zone 18. It will thus be seen that as the combustible mixture passes through the orifice 17 portions thereof will swirl to create eddy currents downstream of the spoiler 16 in the ignition zone 18 whereupon with the aid of diminishing velocities the gases may be easily ignited by pilot burner 21. These gases once ignited will move forwardly upstream against the spoiler 16 heating it and then flow downstream igniting the gases in the turbulent zone 9. Those gases trapped between the forwardly directed converging peripheral surface of the spoiler 16 and inner surface of the duct 10 also move with a relatively low velocity and will be preheated by the heated spoiler 16 as they approach and pass through the perforations '19. The large preheat zone 20 and the extensive ignition zone 18, together with the additional factor of the low velocity of the gases therein, provide for stable flame holding and ready propagation of the ignited gases throughout the flowing combustible mixture. Moreover, as previously pointed out the unstreamlined design of the flame holder causes a large turbulent zone immediately to the rear of the flame holder. Since it has been found that combustion takes place in the turbulent wake of a flame holder, ignition will therefore be more universal in this large turbulent zone since less flame travel is required to complete the combustion process.

A modification of the invention is illustrated in Figs. 3 and 4 wherein the flame holder structure is secured onto the centrally disposed inner body member 22 of the ram jet duct 23. The flame holder of the modified form comprises a generally conical shaped spoiler or gas flow disturber 24- positioned on the inner body 22 such that its peripheral surface diverges in an upstream direction. The annular space between the forward outer or leading edge of the peripheral surface of the spoiler 24 and the adjacent inner wall of the rain jet duct 23 forms an annular orifice 25 for passage of the combustible gases-from the mixing zone 26 to the combustion chamber 27. The cone shaped spoiler 24 has a plurality bf openings or perforations 28 which allow for passage of those gases which are trapped between the spoiler 24 and the inner body 22. Conventional fuel injection means 29 and igniter means 30 are provided in a manner similar to that previously described.

The function of the modified flame holder is substantially the same as that of the device of Figs. 1 and 2.

Ram air enters through the forward opening 31 of the duct 23 and fuel is subsequently introduced therein by the fuel injection means 29. The combustible mixture thus formed then passes rearwardly between the inner body 22 and the duct 23 until it reaches the flame holder structure. At this point the flame holder operates on the flowing gases in substantially the same manner as that afore-mentioned. That is, eddy currents are created to the rear of the spoiler 24 in the ignition zone 32 where the gases are ignited under reduced velocity. A large turbulence zone 33 is also formed substantially immediately downstream of or behind the ignition zone 32 which provides for a closely positioned combustion area whereby the distance for flame travel from the ignition zone to said area is diminished. The eddying burning gases heat the baflde or spoiler 24 such that the gases trapped in the preheat zone 34 are preheated as they approach and pass downstream through the openings or perforations 28. As in the device of Figs. 1 and 2 there is a high pressure drop across the flame holder due to its unstreamlined configuration in relation to the flowing gases. This characteristic will result in a large quantity of the mixture being drawn through the perforations 28 in the heated spoiler 24, which in turn provides for a preheated mixture augmenting the pilot flame and hence supplemented flame holding at the perforations. Moreover, in addition to these characteristics other factors assure stable flame holding and effective spreading of the flame to the combustion zone, for example, the enlargement of 'the ignition zone 32 together with the closely associated combustion area provides for ample flame, and a minimum of necessary flame travel for complete burning action.

Oviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a jet engine having combustion apparatus includmg a tubular duct for flow of gases therethrough from an upstream end to a downstream end, an angular elongated inner body member coaxially positioned within the duct and fuel injection means located adjacent the upstream end of the duct for injecting fuel into the flowing gases to form a combustible mixture; at flame holder structure comprising a gas flow disturbing baflie member, said baflle member having a peripheral surface in the general shape of a truncated cone, the peripheral surface of the baflle member having a plurality of openings therethrough, said baffle member being attached to the rear portion of the inner body member transversely of the duct in a position such that said peripheral surface diverges in the upstream direction, the forward outer edge of said peripheral surface being in spaced angular relationship with the inner wall of the duct to form an angular opening for passage of the combustible gases, and ignition means disposed on said inner body downstream and adjacent the baflle member, whereby upon the passage of the gases through the angular opening eddy currents are formed in the area immediately downstream of the baffle member and adjacent the rear portion of the inner body and a large area of turbulence is formed further downstream thereof, the eddying gases upon ignition heating said baflle member and subsequently flowing downstream to provide ignition for the gases within the turbulent area, portions of the combustible gases trapped between the diverging peripheral surface of the bafl le member and said inner body being preheated by the baflle member upon passing through perforations thus augmenting flame holding in the eddy current area.

2. In a jet engine having combustion apparatus includ ing a tubular duct for flow of gases therethrough from an upstream end to a downstream end, a gradually tapered elongated body centrally and coaxially disposed within said duct and having one end pointed and in proximate relation with respect to one end of the duct and a straight cylindrical portion at the other end thereof and spaced a substantial amount from the other end of the duct, fuel injection means located adjacent the upstream end of the duct for injecting fuel into the flowing gases to form a combustible mixture, a flame holder structure centrally mounted on said cylindrical portion and includ ing a gas flow disturbing baflle member having a pcripheral surface in the general shape of a truncated cone, the peripheral surface of the baflie member having a plurality of openings therethrough, said baffle member being attached to said'cylindrical portion of the body transversely of the duct in a position such that said peripheral surface diverges in the upstream direction and the forward outer edge of said peripheral surface is maintained in spaced angular relationship with the inner surface of the duct to form an angular opening for passage of the combustible gases, and ignition means disposed on said cylindrical portion downstream and adjacent the baflie member thereby to allow the passage of the gases through the angular opening whereupon eddy currents are formed in the area immediately downstream of the baflie member and adjacent the cylindrical portion of the body and a large area of turbulence is formed in advance thereof, the eddying gases upon ignition heating said baffle member and subsequently flowing downstream to provide ignition for the gases within the turbulent area, portions of the combustible gases trapped between the diverging peripheral surface of the baffle member and said cylindrical portion being preheated by the baflie member upon passing through said perforations thus augmenting flame holding in the eddy current area.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,396 Clarke et a1. Dec. 23, 1952 2,751,844 Bixby June 26, 1956 2,780,916 Collins Feb. 12,

Images