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Title:
JET ENGINE EXHAUST AUGMENTATION UNIT
United States Patent 3684054
Abstract:
A turbojet engine exhaust augmentation unit comprising an elongated nozzle for receiving the turbojet engine exhaust, a water injection system for injecting water into the engine exhaust for cooling the exhaust, an enlarged rear discharge conduit for discharging the cooled engine exhaust from the augmentation unit and an elongated shroud having a forward collar for close coupling the augmentation unit to the turbojet engine tail pipe and operable for returning a portion of the nozzle exhaust from the nozzle outlet to the nozzle inlet for augmentation of the jet exhaust.


Application Number:
05/118905
Publication Date:
08/15/1972
Filing Date:
02/25/1971
Primary Class:
Other Classes:
60/39.5
International Classes:
F01D25/30; F02K1/34; (IPC1-7): B64D33/06
Field of Search:
60/264,39.5,310 181
View Patent Images:
US Patent References:
Primary Examiner:
Hart, Douglas
Claims:
I claim

1. A jet engine exhaust augmentation unit comprising a longitudinally extending augmentation tube having an inlet for receiving the exhaust from a jet engine and an outlet, recycling means for returning a portion of the exhaust from the augmentation tube outlet for reintroduction into the inlet thereof for combination with the jet engine exhaust, and a water injection system for injecting water into the jet engine exhaust for lowering the temperature of the exhaust out of the augmentation tube outlet.

2. A jet engine exhaust augmentation unit according to claim 1 wherein the recycling means comprises a return shroud having a forward coupling for close coupling a jet engine thereto in alignment with the augmentation tube.

3. A jet engine exhaust augmentation unit according to claim 2 wherein the forward coupling provides for introducing secondary augmentation air around the jet engine into the inlet of the augmentation tube.

4. A jet engine exhaust augmentation unit according to claim 1 further comprising secondary air inlet means for introducing secondary air into the inlet of the augmentation tube for combination with the jet engine exhaust.

5. A jet engine exhaust augmentation unit according to claim 4 wherein the total mass flow rate of the additional fluid introduced into the augmentation tube inlet is no less than the mass flow rate of the jet engine exhaust.

6. A jet engine exhaust augmentation unit according to claim 1 further comprising a rear discharge conduit having a forward inlet opening in alignment with the augmentation tube for discharging from the augmentation unit the remainder of the exhaust from the augmentation tube outlet.

7. A jet engine exhaust augmentation unit according to claim 6 wherein the augmentation tube comprises a rear divergent nozzle section with a rear outlet opening in alignment with the discharge conduit inlet opening.

8. A jet engine exhaust augmentation unit according to claim 7 wherein the rear outlet opening of the divergent nozzle section is larger than and is spaced forwardly of the forward inlet opening of the discharge conduit.

9. A jet engine exhaust augmentation unit according to claim 8 wherein the recycling means comprises an annular concave deflector for substantially reversing the flow of said returned portion of the exhaust from the augmentation tube outlet.

10. A jet engine exhaust augmentation unit according to claim 1 wherein the water injection system provides for injecting sufficient water to reduce the temperature of the jet engine exhaust out the augmentation tube outlet to approximately 212° F.

11. A jet engine exhaust augmentation unit according to claim 1 wherein the water injection system provides for injecting water into the augmentation tube for lowering the temperature of the jet engine exhaust.

12. A jet engine exhaust augmentation unit according to claim 1 wherein the water injection system provides for injecting water into said returned portion of the exhaust as it is returned for reintroduction to the tube inlet.

13. A jet engine exhaust augmentation unit according to claim 1 wherein the augmentation tube outlet comprises a plurality of generally radial openings in a rear portion of the augmentation tube.

14. A turbojet engine exhaust augmentation unit for a turbojet engine test cell comprising a housing with an elongated shroud having a forward opening for receiving a turbojet engine and a rear discharge conduit with a forward inlet opening substantially larger than and in alignment with the rear exhaust opening of the turbojet engine, an elongated augmentation nozzle mounted within the shroud intermediate of and in alignment with the turbojet engine and discharge conduit and having a forward inlet opening for receiving the turbojet engine exhaust and a rear divergent nozzle section with a rear outlet opening in alignment with and forwardly of the discharge conduit inlet opening, the augmentation nozzle forming with the elongated shroud a substantially annular recirculating passage around the nozzle for returning a portion of the exhaust from the rear outlet opening of the nozzle to its forward inlet opening, and water injection means for injecting water into the engine exhaust for lowering the temperature of the exhaust out the rear nozzle outlet opening, the augmentation nozzle being dimensioned so that the engine exhaust flow through the nozzle provides for drawing said returned exhaust portion into the nozzle inlet opening for augmentation of the engine exhaust.

15. A method of augmenting jet engine exhaust in a jet engine test cell for reducing the exhaust temperature and noise, comprising the steps of returning a portion of the jet exhaust from a relative downstream point for aspiration into the jet engine exhaust at a relative upstream point for augmentation of the exhaust, and injecting water into the jet exhaust to form an exhaust and water mixture for cooling the exhaust and vaporizing the water at least in part and such that a jet exhaust and water mixture is aspirated into the jet exhaust at said relative upstream point.

16. A method of augmenting jet engine exhaust in a jet engine test cell according to claim 15 further comprising the step of aspirating secondary air into the jet engine exhaust at a mass flow rate substantially less than the mass flow rate of the exhaust and water mixture aspirated into the jet engine exhaust.

Description:
BRIEF SUMMARY OF THE INVENTION

The present invention relates to a new and improved jet engine exhaust augmentation unit having notable utility in turbojet engine test cells for attenuating the engine exhaust temperature and noise.

Heretofore it has been the practice in the operation of turbojet engine test cells to provide for the aspiration of a large amount of secondary or augmentation air into the jet engine exhaust to reduce the engine exhaust temperature (from for example in excess of 1,250° F during normal military engine operation and in excess of 3,400° F during afterburner operation) to approximately 500° F to prevent damage to the engine test cell and the exhaust silencing system. In such prior augmentation systems it was customary to employ a mass flow rate of secondary air substantially greater than and in any event not less than the mass flow rate of the jet engine exhaust to avoid unstable engine operation and engine overheating. In accordance with the present invention the mass flow rate of secondary air is substantially reduced without causing unstable engine operation or engine overheating and the present invention therefore provides for substantially reducing the total mass flow rate through the engine test cell.

It is a primary aim of the present invention to provide a new and improved turbojet engine exhaust augmentation unit for substantially reducing the secondary air conventionally used for augmenting the engine exhaust and for thereby reducing the required capacity of the jet engine exhaust and intake air handling equipment.

It is another aim of the present invention to provide a new and improved jet engine exhaust augmentation unit which provides for assisting in abating the jet engine exhaust noise.

It is a further aim of the present invention to provide a new and improved jet engine exhaust augmentation unit which facilitates converting jet engine test cells for testing higher thrust jet engines.

It is another aim of the present invention to provide a new and improved jet engine exhaust augmentation unit which facilitates removing pollutants from the jet engine exhaust.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawings of illustrative applications of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a generally diagrammatic side elevation view, partly broken away and partly in section, of a turbojet engine test cell employing an embodiment of an exhaust augmentation unit incorporating the present invention;

FIG. 2 is an enlarged generally diagrammatic longitudinal section view, partly broken away and partly in section, showing the exhaust augmentation unit in more detail; and

FIGS. 3-5 are generally diagrammatic longitudinal section views, partly broken away and partly in section, similar to FIG. 2 and showing three additional embodiments of an exhaust augmentation unit incorporating the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail wherein like numerals designate like parts throughout the several figures, and referring particularly to FIGS. 1 and 2, an embodiment 10 of an exhaust augmentation unit incorporating the present invention is shown employed in a turbojet engine test cell 12 for augmentation of the jet engine exhaust of a turbojet engine 14. In a conventional manner the test cell 12 comprises an elongated generally rectangular housing 20 for the turbojet engine 14 to be tested, a vertical air inlet stack 22, and a vertical exhaust stack 24 having vanes 26 for directing the exhaust upwardly through a suitable scrubbing and sound treatment unit 28 provided for reducing noise and removing pollutants from the exhaust.

The exhaust augmentation unit 10 is shown comprising a housing with a generally bullet-shaped shroud 30 having a forward inwardly tapered generally conical collar or coupling 32 for receiving a turbojet engine tail pipe 16 and a rear cylindrical discharge conduit 34 secured to a rear flange 35 of the shroud 30 in alignment with the tail pipe outlet opening 36. As seen in FIG. 2, the forward inlet opening 37 of the discharge conduit 34 is substantially larger than the tail pipe outlet opening 36 (e.g., having a diameter more than twice the diameter of the tail pipe outlet opening 36) and the collar 32 provides for close coupling the jet engine tail pipe 16 to the augmentation unit 10 with, however, suitable spacing between the tail pipe 16 and collar 32 to permit air flow between the collar 32 and tail pipe 16 to cool the tail pipe and provide a small amount of secondary air for augmenting the jet engine exhaust.

An elongated generally cylindrical tube or nozzle 38 is mounted within the housing 30 by vanes 39 intermediate of and coaxially with the jet engine 16 and discharge conduit 34. The nozzle 38 has a forward throat 40 substantially larger than the tail pipe outlet opening 36, a forward relatively short convergent nozzle section 41 and a rear relatively long divergent nozzle section 42 with a rear outlet opening 43 slightly larger than the forward inlet opening 37 of the discharge conduit 34.

The nozzle 38 is provided with a plurality of axially spaced water injection rings or manifolds 44-47 along the divergent nozzle section 42. Each water injection manifold has a plurality of equiangularly spaced nozzles (which may be formed by apertures in the manifolds) for injecting water into the gas stream passing through the nozzle. The water injection nozzles may be positioned to direct the water radially into the exhaust gas or rearwardly or forwardly thereof as found desirable in accordance with the requirements of each test cell installation. A suitable water conduit 49 (shown extending through one of the nozzle supporting vanes 39) is provided for supplying water under pressure to the ring manifolds. The mass injection rate of water is preferably controlled to reduce the temperature of the engine exhaust and water mixture in the discharge conduit 34 to approximately 212° F and such that the water constituent in the discharged mixture may be formed in part by water droplets and/or be readily condensed into water droplets for reducing the total volumetric flow rate and for assisting in removing pollutants from the discharged mixture. Accordingly, suitable flow controls (not shown) are preferably provided for automatically controlling the water injection rate in accordance with the power setting of the jet engine.

The injected water provides for assisting in decreasing the velocity and abating the noise of the jet engine exhaust and the divergent nozzle section 42 is preferably designed for expanding the combined jet exhaust and water vapor (formed by the vaporization of the injected water) with minimum turbulence for assisting in attenuating the exhaust velocity and noise.

The augmentation unit 10 provides for augmentation of the jet engine exhaust by providing for drawing a large volume of secondary fluid into the nozzle inlet opening 48. The secondary fluid consists of a relatively high percentage (e.g., 95 percent) of the fluid mixture from the rear nozzle outlet opening 43 and a relatively small percentage (e.g., 5percent) of secondary air drawn through the forward coupling 32. For this purpose the rear nozzle outlet opening 43 is made slightly larger than the discharge conduit inlet opening 37 and the rear end of the shroud 30 is formed to provide a concave annular section or baffle 50 surrounding the discharge conduit 34 for returning a portion of the mixed jet exhaust and water constituents from the rear nozzle outlet opening 43 to the forward nozzle inlet opening. Also the shroud 30 is preferably formed to provide a forward annular baffle 51 forward of the tail pipe outlet opening 36 and contoured to direct the returned jet exhaust and water mixture rearwardly and inwardly for facilitating aspiration of the mixture into the jet exhaust. It is preferred that a sufficient portion of the jet exhaust and water mixture is returned to the nozzle inlet to provide that the total mass flow rate of secondary fluid (including the secondary air) approximately equals and in any event is no less than the mass flow rate of the jet engine exhaust.

An additional or substitute water injection system 52 (shown in broken lines in FIG. 2) may be provided in the shroud for injecting water into the annular return passage surrounding the nozzle 38 and for thereby adding water to the fluid being recycled to the forward nozzle inlet opening, in which case the recycled fluid would preferably be cooled by the injected water to a temperature at or below 212° F and with a major portion of the injected water remaining in the liquid state (in the form of water droplets) for subsequent rapid cooling of the jet engine exhaust within the nozzle.

The augmentation unit 10 therefore provides for attenuating the jet engine exhaust temperature and noise without the addition of a substantial amount of secondary air as heretofore believed essential. Accordingly, the mass flow rate through the discharge conduit 34, exclusive of the injected water which is or may be readily condensed, is substantially less than and no more than approximately half the mass flow rate previously believed to be necessary. The required capacity of the exhaust handling equipment may therefore be substantially less than what was previously required.

Three alternative embodiments 60, 70, and 80 of an augmentation unit incorporating the present invention are shown in FIGS. 3-5 respectively. In each of these embodiments a portion of the jet engine exhaust and water mixture is returned from the rear nozzle outlet to the forward nozzle inlet in generally the same manner as the embodiment of FIG. 2, and the embodiments of FIGS. 3-5 are shown to illustrate alternative shroud and nozzle configurations. In each of these embodiments the nozzle is shown provided with an enlarged forward throat, a relatively long rear divergent nozzle section and a relatively short forward convergent nozzle section and the water injection system is shown provided for injecting water into the divergent section of the nozzle. In FIG. 5 the outlet of the nozzle 82 is provided by a rear outlet opening 84 having the same diameter as the inlet opening 37 of the discharge conduit 34 and a plurality of radial outlet openings 86 provided for returning a portion of the exhaust and water mixture to the forward nozzle inlet opening. Also, a deflector 88 is coaxially mounted within the discharge conduit 34 for assisting in diverting a portion of the exhaust and water mixture out through the nozzle outlet openings 86.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.