US2972231A - Rod-igniters for ramjet burners - Google Patents

Description

Feb. 21, 1961 J. w. MULLEN, 1|

ROD-IGNITERS FOR RAMJET BURNERS Filed Sept. 25; 1954 FIG. 7.

MAIN FUEL SUPPLY PILOT FUEL SUPPLY PILOT AIR SUPPLY AIR FOR MAIN I BURNER MAIN FUEL SUPPLY m A N m mu mm AB FIG. 2.

7 JAMES M MULLEN I INVENTOR ATTORNEYS United States Patent f ROD-IGNI'I'ERS FOR RAMJET BURNERS James W. Mullen II, Richmond, Va., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Sept. 23, 1954, Ser. No. 458,034

2 Claims. (Cl. Gil-39.82)

The present invention relates to a combustion chamber flame igniter. More specifically, it relates to an improved flame igniter, of simple and lightweight construction, for use in the combustion chamber of a ramjet engine.

This application is a continuation-in-part of application Serial Number 121,101, for Rod Igniters for Ramjet Burners, filed October 13, 1949, now abandoned.

The flame igniter is an extremely important component of a ramjet engine, since, as has been well established, proper ignition of the air-fuel mixture injected into the combustion chamber of the engine must take place in order to obtain smooth burning and therefore a high combustion efliciency along with a large developed output thrust.

In order to achieve proper ignition of a combustible fuel in a combustion chamber, it is esential that an igniting flame be spread over substantially the full cross-sectional area of the chamber in a manner that will allow symmetrical burning of a homogeneous air-fuel mixture. Prior art methods of achieving symmetrical burning include the use of flame holders constituted by arrayed radial gutters, grids, etc. which, though comparatively successful, are nevertheless large and complex. As a result, badly needed space is occupied and unnecessary weight is added to the vehicle in which the engine is mounted.

It is therefore one object of the present invention to provide a means for improving burning in the combustion chamber of a ramjet engine.

Another object of this invention is to provide a flame igniter for effectively igniting a combustible mixture contained in a combustion chamber, over the entire crosssectional area of the chamber.

A further object of the present invention is to provide an igniter of simple and lightweight construction which will permit simplification of the structure of a ramjet engine combustion chamber.

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

Fig. 1 is a perspective view, partly in axial section, of the combustion chamber of a ramjet engine showing the rod igniter which is the subject of the present invention, and illustrating a pilot burner having portions thereof broken away to reveal fuel injection and ignition means; and

Fig. 2 is a View similar to Fig. 1, but showing a modification of the invention and in which the pilot burner comprises a pyrotechnic flare.

Reference is first made to Fig. 1, where a combustion chamber 2 of a ramjet engine is shown, together with a pilot burner and rod igniters constructed in accordance with the present invention. The ramjet engine conventionally comprises a duct having a diffuser inlet at its forward 2,972,231 Patented Feb. 21, 1961 end and an exhaust nozzle at its downstream end. The intermediate portion of the duct serves as the combustion chamber where fuel and air are intermixed and ignited to produce a mass of hot gases which are expelled through the exhaust nozzle thereby delivering thrust. Only the intermediate portion of the duct which comprises the combustion chamber is illustrated, at 2, in the drawing, since the showing of that portion alone is sufficient for an understanding of the present invention.

The pilot burner shown generally at 3 comprises a cylindrical housing 4 flaring downstream into a frusto conical skirt 5. The pilot burner 3 is suspended within the combustion chamber 2 by pipes 6, 7 which may conveniently serve as conduits from air or fuel sources (not shown) to the housing 4, terminating therewithin in suitable nozzles 8, and 9. If so desired, an aperture as at 11 may be provided at the upstream end of the housing 4 to admit air to said housing for pilot flame combustion. The necessity for providing a separate pilot air supply can thereby be eliminated.

The fuel for the pilot flame may consist of hydrogen gas or other suitable fuel which has the satisfactory burning characteristics of rapid flame propagation and sustained combustion over a wide range of air-fuel mixture ratios. The pilot fuel is injected into the housing 4 where a combustible air-fuel mixture is created. A spark plug 12 ignites the combustible mixture injected into the housing, while the flared skirt 5 serves to stabilize the flame against extinguishment by pressure surges in the combustion chamber 2.

The rod igniters, which constitute the present invention, comprise a plurality of radially extending, preferably cylindrical rods 14. The rods are firmly secured at their outer ends to the wall of the combustion chamber and extend transversely thereto substantially in the plane of the open end of the skirt 5.

In Fig. 2, there is illustrated a modification of the apparatus shown in Fig. 1. The rod igniters 114 shown in Fig. 2 are similar in construction except that said rods are arranged to extend inwardly of the skirt 5 toward the axis of the combustion chamber 2. Also, in the Fig. 2 structure the pilot burner including the fuel supply and ignition means of Fig. 1 are shown as having been replaced by a pyrotechnic flare 15. It will be understood, however, that since both the pilot burner 3 and pilot flare 15 interchangeably serve the same purpose, it is not intended to limit either form of the invention to the specific pilot shown. Of course, when a flare is used, pipes 6 and 7 may be replaced by supporting rods 17.

It will now be understood that fuel for main burner consumption is conveyed from the main fuel supply (not shown) to the combustion chamber 2 by a pipe 18 terminating in a circular perforated conduit serving as the main fuel injector 19. The fuel, generally a liquid hydrocarbon, is conveyed from the supply to the combustion chamber under high pressure so that the injector 19 efliciently atomizes the fuel. Following injection the atomized fuel rapidly combines with air moving through the chamber 2 at high velocity to form a homogeneous air-fuel mixture for combustion. The combustible mixture is swept downstream from the injector past the pilot burner and rod igniter by the force of the inrushing air. In the immediate region of the pilot burner and rod igniter, the mixture is ignited by the combined effect of the pilot flame and said rod igniter.

Though the exact mode of operation of rods 14 in the system is not certain, it is believed that they serve to initiate or hold flame fronts, which have angles of spread that are substantially larger than any heretofore attainable, and that bring about complete combustion in a much'wshorteretime' than has. been. previously. possible. By use of the present rod igniters it is therefore possible, not only to simplify greatly the construction of the combustion chamber itself, but also to utilize "a much shorter-tailpipe; thereby effecting a further saving in weight and size ofithevehicle'in TVvhlCh the igniter is mounted.

Obviously many modificationsand variations; of the present invention are possible'inthe light of the above teachings. It is therefore'to beunderstood that within thescope of the appended claims the invention may be practiced otherwise than'as specifically described.

What is claimed is:

LA-burner, assembly comprising a duct, means to supply'fuel'to said' duct, ahousing within said duct downstream-from said means, said housing-being outwardly:flared to'an opening atits downstream end and beinig substantially closed at its usptream end, :means producing a pilot flame within said housing, and a pin-r rality of substantially radially extending rods connecting the'said downstream end of the housing to the inner wall of said duct, and located substantially in the plane of said downstream end out of the path of the pilot flame and in the pathtof a combustible stream moving downstream in theduct for producing expanded flame fronts and smooth, even burning of thecombustible' prising a plurality of: substantially radially Y extending rods" connecting the flared downstreamendof-"the'housingto the wall of the duct, whereby substantially the entire combustible. stream flows between. said"rods,:said rods producing eddies resultingtin expanded flame fronts so that smooth, even coinbustion'of the combustible stream occurs. 7

References Cited in the file of this patent UNITED STATES PATENTS 2,385;833 Nahigyan Oct.---2, 1945 2,622,396 Clarke et a1. Dem 23, 1952 1 2,625,795 Brzozowski Jan. 20, 1953" 2,632,300 Brzozowski Mar-.= 24, 1953 2,640,321 Po-uchot' June 2,4953 2,780,916 Collins Feb: 12, 1957

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