US3485169A

US3485169A - Impingement and composition enhanced infrared flare

Info

Publication number: US3485169A
Application number: US704739A
Authority: US
Inventors: William Lai
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1968-02-12
Filing date: 1968-02-12
Publication date: 1969-12-23
Anticipated expiration: 1986-12-23

Description

W. LAI

IMPINGEMENT AND COMPOSITION ENHANCED INFRARED FLARE Filed Feb. 12, 1968 United States Patent O M 3,485,169 IMPINGEMENT AND COMPOSITION ENHANCED INFRARED FLARE William Lai, Los Altos, Calif., assignor to the United States of America as represented by the Secretary of the Air Force Filed Feb. 12, 1968, Ser. No. 704,739 Int. Cl. C06d 1/10 U.S. Cl. 102-37.8 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates generally to infrared flares and, more particularly to an impingement and composition enhanced infrared flare.

There has been a recent tendency to supplement radar detection and guidance systems with infrared or IR systems. Sources of radiation in the infrared spectrum are useful as target devices in testing equipment and training personnel in weapons having infrared sensitive homing mechanisms.

For the purpose of training personnel and development of new equipment, infrared flares, which can simulate the IR output from various thermal engines, are required. The infrared flares may be attached to the wings of target drones which are remotely controlled, or the flare may be propelled by rocket to high altitudes and suspended at the peak of its ascent by parachute. The flare may be balloon-dropped from aircraft or carried by a manned plane to trained detection equipment operators.

Initially, infrared flares were of pyrotechnic compositions which were towed in appropriate targets by high performance aircraft. This type of flare, however, left much to be desired, the two principal drawbacks being their inability to be stopped and restarted and their inflexibility to adjusting the characteristics of the flare. Therefore, the application of a hybrid combustor for the purpose of circumventing the two problems was introduced. Although the hybrid combustor flare appeared to satisfy past requirements, it has become desirable to produce greater enhancement in the radiation of present day infrared flares, While maintaining the restartability and throttleability characteristics of the hybrid combustor.

SUMMARY OF THE INVENTION The `present invention is an infrared flare which incorporates into a single compact package radiation enhancement by impingement and compositional effects, and also restart and throttling capabilities.

The present invention uses a hybrid combustor. Therefore, restartability, throttleability and other capabilities unique to hybrids apply, The high temperature combustion products generated in the mixer-nozzle section of the hybrid combustor flare flow out of an annular nozzle and stagnate at the axis of the abovementioned section. The rear side of the stagnated flame impinges on an impingement block located adjacent the nozzle At steady state, the heated impingement block will add to the continuum in the flame spectrum. In addition, the high temperature flame will also ablate the block, thus en- 3,485,169 Patented Dec. 23, 1969 hancing the flame by altering its composition. Thus, this new flare enhances the radiation of the flame by (l) impingement effects which may be separated into that due to stagnation of the flow and that due to heating of the impingement block, and (2) by compositional effect arising primarily from ablation of the impingement block. The chemical composition of the impingement block can be chosen to enhance various regions of the spectrum.

It is therefore an object of this invention to provide an infrared flare which has radiation enhancement by impingement.

It is a further object of this invention to provide an infrared flare which has radiation enhancement by composition.

It is another object of this invention to provide an infrared flare which has all the unique features of a hybrid combustor, such as restart and throttling capabilities.

It is still a further object of this invention to provide an infrared flare which has a large radiating area.

It is still another object of this invention to irovide an infrared flare which is made in removable sections so that most of the hardware is reusable.

It is yet another object of this invention to provide an infrared flare which is economical to produce and which utilizes conventional, currently available components that lend themselves to standard mass production manufacturing techniques.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWING The figure of the drawing represents a fragmentary side elevational view of the infrared flare of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figure, the infrared flare 10 is made up of a hybrid combustor 12, having the characteristics of restartability and throttleability. The combustor 12 is made up of an oXidizer section 14 and a mixernozzle section 16.

The mixer-nozzle section 16 has a cylindrical compartment therein which contains a solid fuel 20. Although only one compartment is shown in the drawing any suitable number may be used. The solid fuel 20 is composed of any suitable base such as castable rubber or methylmethacrylate or the like, The mixer-nozzle section 16 is further defined by a plurality of ports 22 located adjacent the solid fuel 20 and terminating in a nozzle 24.

Although only two such ports 22 are shown, any suitable number rnay be used, or the plurality of ports may be replaced by a single cylindrical port. The entire inner portion of the mixer-nozzle section 16 is lined with a suitable insulatory material, such as ceramic-coated material 25.

Adjacent the solid fuel 20 and proximate the nozzle 24 is an impingement block 26. The impingement block 26 in adjustably mounted by any suitable means, such as mounts 28 on an insulated support member 27 in the rear portion of the mixer-nozzle section 16. The block 26 is composed of any suitable material, such as polymethylmethacrylate and potassium nitrate. In order to further enhance the emissivity the following additives may be used in the block 26: aluminum, magnesium, silicon, carbon, camphor, polyethylene, Teflon or polystyrene, depending upon the desired IR spectrum of the flame emanating from the nozzle 24. The ports 22 continue past the sides of the impingement block 26 before exiting through nozzle 24.

The oxidizer section 14 contains therein any suitable oxidizer, such as gaseous oxygen which is -underconstant pressure. The oxidizer section 14 further includes a plurality of valves 30, equal to the number of ports 22, or a single valve in the case of a single cylindrical port. Alternatively, a plurality of valves may be spaced around the cylindrical port.

The mixer-nozzle section 16 and the oxidizer section 14 are removably mounted to each other by any suitable fastening means, such as clamps 32 and sealing means 34. In this manner, either the oxidizer section 14 or the mixernozzle section 16 may be readily interchanged with another such section. The oxidizer, such as gaseous oxygen, flows under pressure through valves 30 and into the ports 22 in the mixer-nozzle section 16. The high temperature combustion products generated in the mixer-nozzle section 16 flow out of the annular nozzle 24 and stagnate at the axis of the mixer-nozzle section 16. The upstream side of a stagnated llame 36 impinges upon the downstream side of the impingement block 26.

At steady state the heated impingement block 26 Will add to the continuum in the flame spectrum. ln addition, the high temperature flame 36 will also ablate the block 26, thus enhancing the flame -by altering its composition. Thus, the flare of the instant invention enhances the radiation of the flame by (1) impingement effects, and (2) compositional effect arising from ablation of the irnpingement block.

MODE OF OPERATION Referring again to the figure, the infrared flare 10 of this invention utilizes the restartability and throttleability of the hybrid combustor 12 which is designed to supply an oxidizer, such as gaseous oxygen to a solid fuel. The gaseous oxygen is under constant pressure whereby it iS injected into ports 22 of the mixer-nozzle section 16.

Operation of the infrared flare 10 is initiated in an injector section (not shown) wherein an oxidizer rich mixture of the oxidizer and a gaseous fuel, such as propane, is ignited by a spark to generate a hot gas which produces the initial vaporization of the fuel 20. The starting device 1 is then terminated after which time combustion of the solid fuel is sustained by the gaseous oxidizer. Additional oxidizer may be introduced into the hot combustion gases in the mixer-nozzle section 16 by regulating valves 30, accordingly, thus further controlling the applicable burning parameters. A coolant, such as water, (not shown) is continuously circulated in a conventional manner through the mixer-nozzle section 16 to provide cooling protection for the systems hardware.

In accordance with the instant invention the radiant intensity of the exhaust flame 36 of the infrared flare 10 is enhanced by the judicious adjustment of the motor parameters, which include propellant composition and jet impingernent.

The infrared flare exhaust flame 36 will thermally degrade and mechanically erode, that is ablate the impingement block 26 of the instant invention which is mounted in the path of the exhaust. T he block-26 further obstructs the flow of the flame 36 and hence gives rise to pressure or shock waves in the exhaust. Thus, depending upon the composition, configuration and orientation of the impingement block 26 in the exhaust, radiation may be enhanced by (1) an increase in effective emissivity as a result of particles introduced by ablation, (2) an increase in effective emissivity as a result of local density increase due to presence of pressure or shockwave, (3) an increase in local temperature due to the presence of pressure and shockwaves, and (4) additional after-burning of ablative products.

I claim:

1. An infrared .flare having the characteristics of restartability and throttleability comprising a combustor, said combustor including an oxidizer section and a mixernozzle section, said mixer-nozzle section having a compartment therein containing a solid fuel, a port located in said compartment and adjacent said solid fuel and terminating in a nozzle, said oxidizer section having therein a suitable oxidizer under constant pressure and a valve means, whereby the oxidizer flows through said valve into said port in said mixer-nozzle section generating high temperature combustion products which flow out the nozzle in the form of an exhaust flame, and an impingement block of suitable composition which includes an additive means for enhancing the emissivity of said flame is mounted in the rear portion of said mixer-nozzle section adjacent said solid fuel and proximate said nozzle, whereby the upstream side of said flame impinging upon the downstream side of said impingement block thereby enhances the emissivity of said flame.

2. An infrared flare as defined in claim 1 wherein said composition comprises polymethylmethacrylate and potassium nitrate.

3. An infrared flare as defined in claim 2 wherein said additive means includes aluminum for,v enhancing the emissivity of said flame.

4. An infrared flare as defined in claim 2 wherein said additive means composition further includes a magnesium additive for enhancing the emissivity of said flame.

5. An infrared flare as defined in claim 1 wherein said oxidizer section and said mixer-nozzle section are removably mounted to one another.

References Cited UNITED STATES PATENTS 3,068,641 12/1962 Fox 60-207 3,141,294 7/1964 Lawrence et al 60--216 3,144,751 S/l964 Blackman et al. '-251 BENJAMIN A. BORCHELT, Primary Examiner JAMES FOX, Assistant Examiner