US3075353A - Supersonic combustion - Google Patents

Description

Jan. 29, 1963 G. J. MULLANEY ETAI. 3,075,353

SUPERSONIC COMBUSTION Filed Aug. l9, 1959 3 Sheets-Sheet 3 2.02- zaom- 8724 rum/2 inventors.-

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George J. Mufld he United States Patent Ofiice 3,075,353 Patented Jan. 29, 1963 3,075,353 SUPERSONIC COMBUSTION George J. Muilaney, Burnt Hills, and Paul H. Kydd, Scotia, N.Y., assignors to General Electric Company, a corporation of New York Filed Aug. 19, 1959, 'Ser. No. 834,706 6Claims. (til. 60-3934) This invention relates to supersonic combustion and more particularly to a method and apparatus to provide for the combustion of fuels in a supersonic gas or air flow stream.

Together with the increasing technological advancement of propulsion devices capable of providing speeds well into the supersonic region, there has also been the problem of effectively initiating and thereafter maintaining combustion of fuel in these propulsion devices where the air flow through the engine or combustion chamber moves at a supersonic rate of speed. Heretofore, one solution to this ever-present problem has been reducing the air flow to the subsonic range and permitting the combustion to take place at subsonic velocities. One important disadvantage of this process is that the air stream must be diffused from a high to a low velocity, a diffusion process which involves not only a substantial pressure loss but also an excessively high static temperature and pressure. Furthermore, such diffusers are generally of excessive length. It is therefore desirable in high speed vehicles that combustion take place at supersonic velocities to minimize or eliminate these problems. However, further problems appear at the higher speeds, in that for example, (1) the air flow velocities are in excess of the burning velocities of generally known fuel air mixtures, (2) the various mechanisms for improving the mixing of fuel and air and providing large scale low velocity regions for the stabilization of a flame entail severe penalties in pressure losses and drag because of the propensity for non-isentropic shock wave formation in supersonic flow, and (3) the static pressure levels are generally low, particularly for high altitude flight, which reduces the possible space heat release rate because of the positive" pressure dependence of the combustion reaction.

, It is therefore an object of this invention to-provide for the combustion of fuels in supersonic gas flow.

It is a further object of this invention to provide an apparatus for effective introduction and mixing of the fuel in a supersonic gas flow stream.

It is another object of this invention to provide an apparatus to effectively inject fuel into a supersonic gas stream in combination With a particular class of fuels.

It is yet another object of this invention to provide supersonic fuel injection apparatus with low drag.

It is still another object of this invention to provide small wake regions behind supersonic fuel injectors in supersonic gas flow where the flow is sufficiently turbulent and subsonic to maintain combustion.

It is another object of this invention to provide a pilot flame-main flame combination in supersonic flow combustion systems.

Briefly described, this invention in one form relates to the combustion of a particular class of fuels, for example, hydrogen, acetylene, and preheated and pyrolysed propane, by introducing the fuel into a supersonic flow .stream parallel to the flow of the stream by means of a fuel injecting apparatus injecting fuel in the downstream direction.

This invention will be better understood when taken in connection with the following description and the drawings in which:

FIG. 1 is a cross-sectional view of one form of this invention.

each other.

FIG. 2 is an end view of FIG. 1 taken at the larger end.

FIG. 3 is a modification of the invention illustrated in FIG. 1.

FIG. 4 is a Mach No. plot of a flow pattern of a fuel injector in accordance with this invention where the main fuel system is operating on C H FIG. 5 is a pressure curve illustrating the static pressures of the injector of FIG. 4 at a distance of 9 inches from the injector.

FIG. 6 is a curve illustrating the Mach No. in the flow past the injector of FIG. 4 at a distance of 9 inches from the injector.

FIG. 7 is a series of curves showing composition products of combustion at the 9 and 12 inch stations together with combustion efliciency.

FIG. 8 is an illustration of one method of mounting fuel injectors of this invention.

-FIG. 9 is an illustration of a plurality of fuel injectors of this invention positioned in a combustion cham her in downstream relationship to each other.

Referring now to FIG. 1, there is illustrated in crosssection a fuel injector apparatus 10 utilized to inject fuel into a supersonic flow stream. When fuel is introduced into a supersonic gas stream normal to the direction of flow, combustion is generally accompanied by a strong shock Wave at the point of fuel injection. Shock waves should be avoided in supersonic gas streams as they indicate drag and pressure losses. In this type of apparatus, fuel injection in a downstream direction is employed at a high fuel velocity to minimize drag and other losses and to recover the momentum of the fuel stream as thrust. A plurality of injectors are used to distribute fuel in the air stream to compensate for the inherently poor mixing of parallel fuel injection. Additionally, the use of a reactive fuel is preferred so that the mixing of the fuel and air and the combustion thereof occurs simultaneously rather than consecutively. The latter principle is particularly important inasmuch as it has been shown that it is relatively easy to burn a reactive fuel, such as hydrogen and acetylene, but it becomes more difiicult to burn less reactive fuels, such as ethylene and propane.

A highly reactive fuel as employed in'this invention not only includes the aforementioned fuels of, forexample, acetylene, hydrogen and propane, etc., but also various mixtures of these and other fuels. Additives may also be added to a fuel to increase its reactivity.- One such additive and fuel is disclosed and-claimed in US. Patent No. 2,894,830, Nerad et al., assigned to the same assignee as the present invention. In Patent No. 2,894,830 there is disclosed a gaseous fuel such as, for example, illuminating gas, alcohol vapor, and hexane, together with a boron hydride additive. To be highly reactive, a fuel, in accordance with this invention, mutt ign'te and burn under the conditions set forth and maintain combustion near or adjacent the injector. i

Fuel injector 10 comprises a body 11 and a supporting strut 12. This apparatus is mounted or positioned in a fast moving gas stream 13, such as found in ramjet engines, for example, in combustion chamber 14. One or more fuel injectors may be mounted in combustor'chamber 14, for example, in a downstream relationship from While various forms of struts 12 may be empToyed in this invention, a preferred form is a simple shape generally with a sharp leading edge 15 and a blunt trailing edge 16, such as for example, as found on cones and Wedges, etc., with the sharp edge 15 facing into the moving gas stream. Injector body 11 in one embodiment of this invention comprises a hollow cone-shaped metal body, for example,stainless steel of a 7 half angle. This cone body is approximately 4 inches in length with a /2 b inch smaller opening 17 facing the oncoming gas stream.

Fuel injection into the cone body 11 consists of a main fuel system and a pilot fuel system. The pilot fuel system is an auxiliary source of fuel and it is understood that the injector apparatus would operate on the main fuel system alone. Pilot fuel is introduced in the cone body 11 by means of a suitable conduit 13 connected to a source of fuel, not shown, and is injec ed directly into the interior of body 11. A further conduit 1% is connected to the main fuel system, not shown, and introduces fuel into a particular nozzle 20. Nozzle 20 in one form cf the invention as disclosed, comprises a threaded member 21 having a series of passages 22 parallel to its longitudinal axes and ending in an annular manifold type passage 23 which is connected to the main fuel conduit 19. As illustrated in FIG. 1, nozzle 20 provides a restricted flow from the hollow member 11 and represenls an obstruction to the supersonic flow therethrough. it is also to be noted that fuel issuing from passages 22 issues within the radial dimension of the largest portion of the member 11, or alternatively so that no supersonic gas flow is between the injecting main fuel and the pilot fuel. Pilot fuel is employed to provide a pilot flame for preheating and igniting the main fuel stream. it is understood from the description as given that a portionof the fast moving gas stream enters the smaller opening 17 of body if and is diffused therein to subsonic velocities. Thereafter, of the stoichiometricamount of fuel is introduced through the pilot fuel conduit 18 and the mixture ignited. Ignition of the fuel may be provided by various means well known in the art including spark ignition illustrated gen erally as 24. The products of combustion emerge from nozzle opening 25 at the rear of body If in a pilot flame jet. Main fuel is introduced into the conduit 19 to enter manifold 23 and issue from hcles or passages 22. This method of introducing fuel also provides cooling of body 11.

One example of the operation of this combustion apparatus is as follows. Fuel injector 10 was placed in an air stream moving with a static pressure of one atmosphere and a static temperature of about 550 R. at a Mach No. of about 2.7. The smaller opening 17 of the conical body 11 faces the upstream direction and permits a diffusion of air from Mach No. 2.7 to almost at rest at about 6 atmospheres pressure. Thereafter /a of the stoichiometric amount of hydrogen with respect to air entering opening 17, is introduced into the pilot system and the mixture ignited. Hot gases flowing through nozzle 20 serve to preheat, ignite and disperse the main fuel. The main fuel in this operation was acetylene stored at 15 lbs/sq. inch pressure. Pressure at nozzle 20 was about -10 psi. The use of a reactive fuel, such as, for example, acetylene, is important because this fuel burns immediately upon contact with the air stream so that the fuel injector itself functions as a fiameholder, and the expansion of hot products of combustion serves to spread the fuel more fully into the passing air stream.

It has been found that togetherwith the use of various fuels as heretofore mentioned under various operating conditions, the pilot burner operates satisfactorily using hydrogen as a fuel and that less favorable pilot flame operations were encountered when using ethylene or mixtures of hydrogen with more than 30% ethylene. Both acetylene and hydrogen burn effectively when ignited by the pilot flame and continue to burn with the pilot flame extinguished.

To determine combustion efliciency and the effect of combustion on a supersonic jet, a flame of 7.5% of the stoichiometric amount of acetylene burning from the main fuel injector was chosen as a standard. A Mach No. profile plot with combustion is illustrated in PEG. 4. Measurments were made in a horizontal plane normal to the supporting strut of the injector, and are plotted in FIG. 4 as a function of distance, behind the injector and from the centerline of the jet. When combustion takes place behind the injector the air stream is expanded and the central core of the jet is heated sufficiently to render it subsonic. Measurements of static pressure at the 9 inch station show, as illustrated in FIG. 5, that it is approximately unifo:m across the jet. FIG. 6 is a curve illustrating the Mach Nos. at the 9 inch station below and above the centerline of the injector.

Some difficulty was encountered with the gas sampling measurements as a result of the very high temperatures and flow rates involved. Measurements could not be made closer than 9 inches behind the injector because the probe was rapidly destroyed. The absolute concentratious of combustion products near the centerline are somewhat in doubt, but it is believed that the ratio of CO to CO and the extent of mixing of the products with the air stream have been reliably established. No hydrocarbon products were found within the limits of the gas analysis (approx. 0.05%). No hydrogen was found either, although the sensitivity for hydrogen is considerably less (approx. 2%). Consequently, the combustion efficiency Tfwas computed on the basis of the CO/ (CO.+CO

ratio measured as a function of distance from the centerline at stations 9 inches and 12 inches downstream from the injector. These ratios were multiplied by 0.433 (the fraction of the heat of combustion of acetylene due to oxidation of CO), and the result Was subtracted from one to give the combustion efficiencies These are plotted in FIG. 7 along with the distribution of the products in the jet at the two stations.

Average values of combustion efliciency were arrived at by assuming cylindrical symmetry. The efficiencies measured at various points could then be related to the fraction of the whole fuel stream burning with that efliciency, and from these the over-all efficiency for the whole fuel stream was found. Comparing the results at 9 inches and 12 inches, it appears that combustion is about 91% complete at the former station. This corresponds to a reaction time of approximately 0.25 millisecond. Fragmentary results at 7 inches gave CO/CO ratios similar to those observed farther on, so that the actual reaction time with acetylene under these conditions may be somewhat less.

The fact that the combustion efficiency is not a sensitive function of transverse position in the flame indicates that there is good mixing in the combustion zone. The products have spread into the air stream to a considerable extent from the point at which the fuel was injected in a ring of inch radius. This process appears to be still going on between 9 inches and 12inches, and the radius of the product distribution is about 1 inch atthe latter station.

For heat addition at constant pressure, the velocity of the stream does'not change. The calculation of temperature change from Mach No. change is therefore straight forward for portions of the jet in which the velocity gradient is small. A temperature profile computed on this basis is shown in FIG. 7 for comparison with the composition profiles at 9 inches.

The space heat release rate of this flame has beencalculated from its physical dimensions, fuel flow rate, and the combustion efiiciency at the 9-inch point. This has been found to be equal to about 2.7 10 B.t.u./hr./ cubic ft./ atmosphere, a high value compared to the usual range of about 1X10 for generally well known turbo jet combustors operating on kerosene type fuels.

Because a combustion system may utilize a large number of injectors as described, such a system is adaptable to a large variety of overall engine designs including those which utilize outside surfaces of the aircraft as a diffuser or nozzle or both. Combustion need not extend to the walls of a combustion chamber or other surface, but may be maintained in the free stream so that cooling requirements are minimized.

One exemplary illustration of the use of the injector of this invention together with an air foil surface is shown in FIG. 8. In FIG. 8, 28 represents a high speed surface of a vehicle, for example, a fuselage, cowling or Wing section. One or more of the fuel injectors of this invention is positioned generally adjacent the surface where the surface slope, for example at 29, is changing to that illustrated at 30. At high Mach No. flow the passing air stream acts as an assumed surface cooperating with surface 29 as a supersonic diffuser to diffuse the air stream and cooperating with surface 30 to provide a divergent nozzle for the expansion of the products of combustion. In this manner effective combustion and thrust are obtained with, in effect free stream combustion. FIG. 8 is exemplary of various mountings, for example, a plurality of injectors along a wing span or a ring of such injectors around the fuselage or 'body of a missile. In a combustion system within an engine, by staggering the injectors in the direction of the air flow, the rate of heating of the air stream may be controlled independently of the flame reaction rate which may be important in achieving proper aerodynamic and thermodynamic cycles.

Some of the more prominent features indicated by the use of such an injector are that, (l) downstream injection may be utilized from a number of injectors, (2) ignition and stabilization by a pilot flame may be obtained by decelerating a small part of the air stream injecting fuel therein, and then burning and reaccelerating this air stream through a nozzle surrounded by the main fuel flow, (3) the use of highly reactive fuels achieves stable and rapid burning, (4) stabilization of flame is obtained by the wake of the fuel injectors and (5) the flame may be dispersed either in the wake of the mounting struts or in the free stream between parallel fuel jets.

The advantages of such a fuel combustion system and/ or injector are the achievement of the maximum aerol dynamic efficiency in introducing fuel into a highvelocity air stream, and after the fuel is effectively injected, combustion is completed in a short distance generally less than one foot. Extreme flexibility may be achieved by the generally unrestricted arrangement of fuel injectors together with control of the overall burning process. When the flame is carefully controlled, it may be maintained in a free stream out of contact with all surfaces, thus minimizing cooling requirements.

FIG. 3 illustrates a modification of the apparatus of FIGS. 1 and 2 to include an additional or auxiliary strut 26 positioned at about a 90 angle from strut 16. A main fuel conduit 27 provides fuel from the main fuel source, not shown, to an opening 28 which in one form of the invention measured about A; inch by 1 inch. With acetylene burning in nozzle 20, the flame spreads immediately into the wake of auxiliary strut 26 and when acetylene is injected from opening 28, it is ignited by the burning of fuel from nozzle 20. This combustion is also complete in a short distance and a quantity of acetylene was injected to consume about 10% of the available air.

It is thus evident that the objects of this invention are achieved through the use of a fuel injector which effective ly injects fuel in the downstream direction of a supersonic gas stream together with a reactive fuel. Among the important features are that the flow stream is disturbed as little as possible, fuel is effectively introduced and ignited and that combustion is sufficiently rapid to the effect that the injector also acts as a flameholder. It is to be understood that optimum conditions or results are obtained when fuel injection takes place parallel to the gas flow and in the downstream direction, and that optimum results become increasingly less as injection takes place at a greater angle to the flow stream.

While specific embodiments of this invention have been shown and described, it is not desired that the invention be thus limited and it is intended by the appended claims to cover all modifications within the spirit and scope of this invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A unitary supersonic fuel injection device for supersonic combustion in a supersonic air stream consisting essentially of:

(a) a hollow open ended supersonic diffuser body tapering from a small open inlet end to a larger open exit end,

(11) a support for positioning said body in a supersonic stream with the small inlet end in the upstream direction to diffuse the flow of said stream entering said body,

(a) fuel injection means to inject pilot fuel into said hollow body,

(d) means to ignite said pilot fuel as a pilot flame for the products of combustion to issue from said body,

(e) fiow restriction nozzle means in said body radially within the larger open exit end and adjacent said exit to increase the velocity of the products of combustion of said pilot flame, and

(7) separate fuel injection means in said flow restriction nozzle and within the radial dimension of said exit end to inject fuel into said supersonic gas stream in the downstream direction'parallel with the axis of said body.

2. A unitary supersonic fuel injection device for a supersonic flow gas stream consisting essentially of:

(a) a hollow open conical injector body having a small inlet opening and a larger exit opening therein respectively,

(b). a wedge shaped support for said body,

(0) said support and said body positioned in the said supersonic flow stream with the smaller end thereof facing the upstream direction to diffuse a portion of saidgas stream flowing therethrough, I

(d) nozzle means within and adjacent the open exit end of said injector body,

(e) said nozzle means having flow restricting opening therethrough positioned in axial alignment with the inlet opening of said injector body, said flow restricting member characterized by accelerating gas flow therethrough,

(7) fuel injection means leading through said wedge to inject a pilot fuel into said hollow injector body adjacent the downstream end,

(8) means to ignite said pilot fuel to provide a pilot flame issuing from said nozzle opening with said opening accelerating the products of combustion, and

(h) separate fuel injection means in said nozzle surrounding said nozzle opening and facing the downstream direction and parallel therewith to inject a highly reactive fuel into said supersonic flow stream for ignition by said pilot flame.

3. A method of burning fuel by means of a fuel injector in a supersonic gas stream comprising, diffusing a small proportion of said gas stream in said inector to subsonic velocity, injecting a highly reactive fuel into said diffused portion, igniting and burning said highly reactive fuel with the products of combustion moving out of said injector and parallel to and in downstream relationship to said gas flow, restricting the flow of said products of combustion of said diffused portion to increase the velocity thereof to supersonic, separately injecting a highly reactive main fuel from said injector and from Within the radial confines of said injector and into the supersonic gas stream in a plurality of streams parallel to and next adjacent said products of combustion of the pilot fuel in the downstream direction for ignition thereof by said pilot fuel, said fuels being taken from the group consisting of hydrogen, acetylene and pyrolysed propane.

4. A method of burning fuel by means of a fuel injector device in a supersonic gas stream which comprises, in axial relationship diffusing a small portion of said gas stream to subsonic velocity in said injector, injecting hydrogen into said diffused portion, igniting and burning said hydrogen with the products of combustion moving out of said injector parallel to and in downstream relationship to said gas stream, restricting the flow of said products of combustion to increase the velocity thereof, separately injecting a plurality of streams of acetylene from within the radial confines of said injector surrounding and parallel and next adjacent said products of combustion and in the downstream direction for ignition thereof by said products of combustion, extinguishing said pilot flame, and continuing the combustion process with acetylene alone.

5. In a supersonic combustion system the combination comprising a chamber adapted for the flow of a supersonic gas stream therethrough, a plurality of fuel injectors in said chamber, one of said injectors being positioned in downstream relation to the other, each of said injectors consisting essentially of a hollow open conical body tapering axially from a small section to a larger section, said smaller section having an inlet aperture therein, said larger section having an exit aperture therein, said body positioned in said gas stream with the smaller section facing upstream, means including the hollow configuration of said body to diifuse incoming gas to subsonic velocity in the interior of said body, fuel injection means to introduce a highly reactive fuel into the interior of said body adjacent the downstream end thereof, means to ignite said fuel as a pilot flame issuing from said body, nozzle means restricting the outlet of said body, said nozzle means having a central aperture to accelerate the products of combustion of said pilot flame, separate fuel injection means in said nozzle at the downstream thereof, to inject fuel into said gas stream in a plurality of individual streams in a direction parallel to and in the downstream direction for ignition by said pilot flame.

6. In combination with a vehicle or object adapted for supersonic flights through the earths atmosphere, a tapered external surface on said vehicle exposed to a free supersonic air stream, at least one fuel injector positioned in said free supersonic air stream adjacent said surface, said injector and said surface cooperating to provide diffusing of part of the passing air stream to a lower velocity, said injector body being tapered from a smaller to a larger section with a flow passage therethrough, said injector body positioned in said air stream with the smaller section in the upstream direction so that a portion of the air stream entering said fiow passage is difiused to subsonic velocity means to introduce a highly reactive fuel into said body, means to ignite said fuel for combustion as a pilot flame, means restricting the exit end of said injector so that the products of combustion of said pilot flame are caused to issue from the larger section of said body into said air stream at a higher velocity, and means to introduce a plurality of streams of a highly reactive fuel into said passing air stream adjacent said pilot flame and parallel to and in the downstream direction with respect to said air stream for ignition by said pilot flame and within the larger dimension of the exit end of said injector.

References Cited in the file of this patent UNITED STATES PATENTS 2,520,388 Earl Aug. 29, 1950 2,651,178 Williams Sept. 3, 1953 2,663,142 W'ilson Dec. 22, 1953 2,679,137 Probert May 25, 1954 2,735,633 Manning Feb. 21, 1956 2,806,356 Bocchio Sept. 17, 1957 2,812,912 Stevens Nov. 12, 1957 2,832,402 Jurisich Apr. 29, 1958 2,867,979 Mullen Jan. 13, 1959 2,920,445 Bailey Jan. 12, 1960 2,944,399 McCardle Iuly 12, 1960 FOREIGN PATENTS 205,559 Australia Mar. 15, 1956 435,653 France Jan. 4, 1912

Claims (1)

1. A UNITARY SUPERSONIC FUEL INJECTION DEVICE FOR SUPERSONIC COMBUSTION IN A SUPERSONIC AIR STREAM CONSISTING ESSENTIALLY OF: (A) A HOLLOW OPEN ENDED SUPERSONIC DIFFUSER BODY TAPERING FROM A SMALL OPEN INLET END TO A LARGER OPEN EXIT END, (B) A SUPPORT FOR POSITIONING SAID BODY IN A SUPERSONIC STREAM WITH THE SMALL INLET END IN THE UPSTREAM DIRECTION TO DIFFUSE THE FLOW OF SAID STREAM ENTERING SAID BODY, (C) FUEL INJECTION MEANS TO INJECT PILOT FUEL INTO SAID HOLLOW BODY, (D) MEANS TO IGNITE SAID PILOT FUEL AS A PILOT FLAME FOR THE PRODUCTS OF COMBUSTION TO ISSUE FROM SAID BODY, (E) FLOW RESTRICTION NOZZLE MEANS IN SAID BODY RADIALLY WITHIN THE LARGER OPEN EXIT END AND ADJACENT SAID EXIT TO INCREASE THE VELOCITY OF THE PRODUCTS OF COMBUSTION OF SAID PILOT FLAME, AND (F) SEPARATE FUEL INJECTION MEANS IN SAID FLOW RESTRICTION NOZZLE AND WITHIN THE RADIAL DIMENSION OF SAID EXIT END TO INJECT FUEL INTO SAID SUPERSONIC GAS STREAM IN THE DOWNSTREAM DIRECTION PARALLEL WITH THE AXIS OF SAID BODY.

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