US3474622A - Backflow guide for turbine starter - Google Patents

Description

9 as. SIEGLER ET 3,474,622

BACKFLOW GUIDE FOR TURBINE STARTER Filed Sept. 18, 1967 INVENTORS 3085197 4. E/A/SA 5w ,eoaser s. 5/561 52 United States Patent O 3,474,622 BACKFLOW GUIDE FOR TURBINE STARTER Robert S. Siegler, Calabasas, and Robert L. Binsley, Sepulveda, Calif., assignors to North American Rockwell Corporation, a corporation of Delaware Filed Sept. 18, 1967, Ser. No. 668,549 Int. Cl. F02g 3/00; F02c 3/00; F02k 1/00 U.S. Cl. 6039.77 6 Claims ABSTRACT OF THE DISCLOSURE A pulse jet-type combustor for discharging combustion product through a plurality of tubes to start a turbine. Adjacent the exit side of the turbine is a backfiow guide that promotes superior flow characteristics of the backflowing air being inducted through the turbine rotor into the combustor between successive combustion strokes. The guide allows enhanced precompression to be achieved to increase combustion efliciency.

BACKGROUND OF THE INVENTION The instant invention relates to a power system Ior starting self-sustaining engines and more specifically concerns a pulse jet combustor whose hot gases are discharged into the inlet side of a starter turbine. The output motion of the turbine is coupled to the self-sustaining engine being started.

The broad concept of positioning the exhaust portion of a pulse jet-type combustor in operative driving relationship with a turbine is known in the art. Such a power generating arrangement used as a supercharger for a vehicle internal combustion engine is disclosed in U.S. Patent No. 2,963,863 to Middlebrooks.

It is also known in the art to use the hot gases generated in a combustor, not of the pulse jet-type, for operating a turbine designed to start, i.e., initiate motion of, an engine system (e.g., U.S. Patent No. 3,004,387 to Woodward).

As disclosed in co-pending U.S. applications, Ser. No. 576,726, filed Sept. 1, 1966, now Patent No. 3,411,292, and Ser. No. 583,624, filed Oct. 3, 1966, now abandoned (which applications are assigned to the assignee of this invention) the combustion product of a resonating or pulse jet-type combustor may be discharged through a plurality of exhaust tubes to the inlet side of a starter turbine designed to start a self-sustaining engine. This invention is an improvement over the combustors disclosed in these applications and is primarly aimed at increasing the combustion efiiciency by a backfiow guide that promotes superior flow characteristics of the charge of ambient air that is automatically inducted through turbine rotor and the combustor tubes and into the combustion chamber between successive combustion strokes.

SUMMARY OF THE INVENTION Briefly described, the instant invention contemplates an accessory incorporated in a power system characterized by a pulse jet or resonating type combustor which discharges gases to the inlet side of an adjacent starter turbine. The accessory is a backflow guide positioned adjacent the exit side of the turbine. It is well-known that between successive pulses of combustion in the pulse jet-type combustor the internal pressure of the combustor diminishes to a value below the ambient pressure with the result that a new charge of ambient air is inducted through the turbine and into the combustor. The occurrence is commonly referred to as the backflow stroke or phase of the overall power cycle.

The backfiow guide has a guideplate that encircles the turbine and diverges rearwardly, i.e., in the direction in which the hot gases are to be ejected, from the exit side of the turbine. In addition its interior periphery may be slightly convex. Between successive combustion strokes, the backfiowing air attaches to or flows along the surface of the guideplate and is smoothly guided through the passageways defined by the turbine blades and introduced into the combustor. By eliminating turbulent, erratic flow characteristics of the backflowing air, a greater mass of backflow air traveling at a greater velocity arrives in the chamber for accomplishing enhanced precompression of the air. The backfiowing air and the charge of air being inducted through the conventional one-way flapper valves rarn together with an increased force to produce the greater precompression. This in turn accomplishes superior combustion efliciency. In another aspect, the backflow guide has a second guideplate concentric with the turbine and which converges rearwardly from the exit side of the turbine. The second guide plate functions to further augment the desired smooth flow characteristics of the backflowing air. The two guideplates define an annular passage with a funnel-shaped opening exposing the turbine blades. The plates may be rigidly interconnected by a plurality of stiffening ribs.

The advantages and operation of the invention will be fully understood upon studying the following detailed description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view partially schematic and sectional, showing a pulse jet combustor adjacent a starter turbine with the backflow guide of this invention positioned adjacent the exit side of the turbine.

FIG. 2 is a perspective view of the backfiow guide showing its inner and outer guideplates and the annular passage defined therebetween that exposes the turbine blades.

FIG. 3 is a schematic view showing the backflow guide with a single guideplate integrally formed with a mounting plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in conjunction with a combustor 10 of the resonating or pulse-jet type, shown in FIG. 1, that generates power for starting a turbine 14 suitably keyed to a power shaft (not shown). The specific details and mode of operation of combustor 10 are fully explained in the two previously referred to U.S. applications that are incorporated by reference. As disclosed in these applications, air is intermittently admitted through a bank 20 of one-Way flapper valves and through a fuel injector 24. Initially a predetermined suitable mixture of fuel and air prepared for combustion is introduced into combustion chamber 30 where it is ignited by spark plug 32 to produce combustion product. The combustion product is propelled into and against dome 34 and eventually is discharged outwardly through a plurality of exhaust tubes 40, 42, 44, and 46. Exhaust tube 40 extends rearwardly from dome 34, is bent in a spiral configuration around the exterior of combustion chamber 30 and terminates in an exit opening 41 adjacent turbine 14. The other exhaust tubes 42, 44, and 46 that are depicted schematically are arranged similarly to exhaust tube 40. Combustion product being ejected through the exit openings of the exhaust tubes impinges against turbine blades 16 to thereby, in the customary manner, impart rotation to turbine 14. Thus, the combustion product enters the turbine through inlet side 18 and egresses through exit side 19.

The power output capacity and overall efiiciency of combustor 10 can be markedly improved by facilitating and increasing the back-flow of ambient air through turbine blades 16 and the exhaust tubes into the combustion chamber. One of the prime functions of the backfiowing air is to ram and mix with the fresh charge of air being admitted through the bank 20 of flapper valves to achieve precompression of the air. By intensifying the precompression value of the air prior to its combustion with the fuel, a greater energy release and hence power capacity can be achieved.

The precompression that can be achieved is a function of the mass of the backflowing air and to the lesser extent its velocity. The sharp edges of the individual turbine blades which define the passageway through which the combustion product and backflowing air intermittently pass, naturally inhibit the mass and volume of air that can be inducted between combustion strokes. The sharp edges tend to cause turbulence which significantly reduced the mass and velocity of the backi'lowing air causing a power loss. In addition the edges promote separation of the backfiowing air thereby failing to take ad vantage of the maximum space of the flow passageways. These conditions that have heretofore inhibited and impaired attaining maximum precompression are eliminated by the instant invention.

Referring to FIGS. 1 and 2, there is shown a backflow guide 50 designed to greatly augment precompression. Backflow guide 50 includes an outer annular-shaped guideplate 52 which encircles turbine 14 and is positioned a radial distance in the order of 0.030 inch from the outer tips of turbine blades 16. The spacing is standard to assure minimal energy loss with respect to the hot gases being exhausted. Plate 52 diverges outwardly and rearwardly from turbine 14 in the direction in which the hot gases are to be ejected. Its inner periphery 53 is convex in the axial direction. The optimum convexity, to assure the desired flow characteristics of the backflow air, is primarily dictated by the turbine diameter. By way of example, when the turbine diameter is approximately 9 inches, the minimum optimum diameter for the curvature of plate 52 has been found to be approximately 2% inches. Below the minimum optimum radius, the entering stream of backfiowing air tends to separate from convex inner periphery 53. Other secondary factors influencing the optimum curvature are: (l) The ratio of blade height to pitch diameter, and (2) The exhaust gas temperature and velocity. The axial length of plate 52 terminates at a point beyond that zone of plate 52 where the stream of backfiowing air first attaches to periphery 53. The curvature of plate 52 will always be described by an arc less than 90. The desired arc, as best determined by experiment action, will generally be in range of between 50 and 75 The inner end of plate 52 terminates in a radially outwardly extending flange 54 that is welded or otherwise suitably attached to mounting plate 55 which also serves to fix the relative positions of the exit openings of the exhaust tubes. Backflow guide 50 also includes an inner guideplate 60 whose inner end 62 terminates adjacent and slightly downstream of the exit side 19 of turbine 14. Guideplate 60 converges inwardly in a downstream direction and preferably terminates in the same plane in which the downstream end of plate 52 terminates. The inner periphery 63 is slightly convex in the axial direction. A plurality of narrow stiffening ribs 68 interconnect plates 52 and 60 to fix their relative spatial relationship and support the overall backflow guide 50. Plates 52 and 60 define an annular passage 65 which exposes blades 16 and allows communication between the amibent air and combustion chamber 30.

With the structural characteristics of backflow guide 50 now understood, its advantages and operation can be fully explained. Admission of the fuel-air mixture in combustion chamber 30 accompanied by ignition from spark plug 32, produces an explosion that instantaneously generates compression waves and a concomitant pressure increase. The increased pressure in chamber 30 serves to close the flapper valves as the combustion product is propagated through exhaust tubes 40 through 46 to be eventually impinged against turbine blades 16. The combustion product in imparting rotation to turbine 14 is exhausted through exit side 19 and annular passage 65. It should be noted that guideplates 52 and 60 neither promote nor restrict the ejection of the combustion product, i.e., they do not function to influence the movement of the exhaust product either positively or negatively. After a predetermined lapse of time the pressure within combustion chamber 30 decreases to a value less than ambient pressure at which time the flapper valves reopen to admit a fresh charge of air. Simultaneously a charge of air is drawn into combustion chamber 30 over backflow guide 50.

Backflow guide 50 promotes a smooth flow of ambient air through annular opening into the passageway defined by blades 16. Rather than experiencing irregular and turbulent flow, the charge of backflowing air attaches to the peripheries 53 and 63 of guideplates 52 and 60 respectively and becomes relatively laminar. The air occupies the maximum volume of the passageways defined between blades 16 and hence the overall charge of air being admitted into chamber 30 through the individual exhaust tubes 40 through 46 is maximized. The charge of backflow air passing through the exhaust tubes 40 through 46 eventually enters combustion chamber 30, hammers into, and becomes mixed with the fresh charge of air admitted through the flapper valves. The two charges of air approaching each other from opposite directions serve to precompress the air and prepare it for the next combustion cycle. At this juncture the sparkplug 32 or other igniting source is no longer required and has been terminated. Reignition of the fuel-air mixture is accomplished by the residual hot gas trapped between the two new charges of air. Hence the power cycle of combustor 10 is self sustaining much like the operation of a conventional pulsejet.

It can now be seen that overall combustion efficiency is greatly enhanced clue to the fact that backflow guide 50 greatly minimizes the turbulence and obstruction to the charge of backflowing air so that a smooth flow of air characterized by maximum mass can be drawn into the combustion chamber to achieve a much enhanced precompression.

FIG. 3 depicts a backflow deflector 70 having only a single guideplate 80, analogous to guideplate 52, shown in FIG. 2, integrally formed with a mounting plate 82. Formed through the center of guideplate 80 is a circular opening 84 having a diameter slightly larger than the diameter of the turbine. Guideplate 80 and outer guideplate 52 of the backflow guide 50, shown in FIG. 2, operate identically.

What is claimed is:

1. In a turbine starter device characterized by a pulsejet type combustion chamber which alternately generates combustion products and inducts backflow air through a turbine positioned adjacent the exhaust portion of the combustion chamber, and means for conducting gas between the combustion chamber and turbine, the improvement comprising:

a backflow guide extending rearwardly from the exit side of the turbine and having an end exposed to atmospheric air and diverging from the outer periphery of said turbine for improving the flow characteristics of backflowing air to enhance precompression of air in the combustion chamber, said guide having an inner periphery over which backflow air passes which is convex in axial direction.

2. The structure according to claim 1 wherein the backflow guide is a cantilevered annular plate encircling the turbine that diverges away from the exit side of the turbine.

3. The structure according to claim 2 wherein the interior periphery of the plate over which backflow air passes extends from 50 to of arc.

4. The structure according to claim 2 wherein the backfiow guide has a second annular cantilevered plate spaced radially inwardly from said first mentioned plate and being concentrically aligned with the turbine, said second plate converging away from the exit side of the turbine, the two plates defining an annular funnel-like passageway exposing the turbine blades to atmospheric air.

5. The structure according to claim 4 wherein the outer periphrey of the second plate over which backfiow air passes is convex in an axial direction.

6. The structure according to claim 4 wherein the backflow guide further comprises a plurality of stiifening ribs interconnecting the two plates to fix their relative spatial relationship.

References Cited UNITED STATES PATENTS 6/1965 Melenric. 8/1966 Keen.

' CARLTON R. CROYLE, Primary Examiner US. Cl. X.R.

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