US2688843A - Apparatus for augmenting mass and velocity of exhaust streams - Google Patents

Description

Sept. 14, 1954 P PITT APPARATUS FOR AUGMENTING MASS AND VELOCITY OF EXHAUST STREAMS Flled Nov 13, 1945 INVENTOR. PAUL A. PITT ATTORNEY Patented Sept. 14, 1954 APPARATUS FOR AUGMENTIN G MASS AND VELOCITY OF EXHAUST STREAMS Paul A. Pitt, San Diego, Calif., assignor to Solar Aircraft Company, San Diego, Calif., a corporation of California Application November 13, 1945, Serial No. 628,108

8 Claims.

This invention relates to the treatment and disposal of exhaust gases from combustion devices generally, and has particular application to the internal combustion engines of aircraft.

An object of the invention is to increase the reaction force of the exhaust stream from a combustion device.

Another object is to increase the mass and temperature of the gas stream discharged from the exhaust pipe of a combustion device.

Another object is to complete combustion of unburned components of the exhaust gas of a combustion device.

Other more specific objects and features of the invention will appear from the description to follow of certain specific embodiments of the invention.

It is well known that the stream of gas issuing from the exhaust pipe of an internal combustion engine has a thrust effect, which, if the exhaust pipe is directed rearwardly, in the case of aircraft, helps to propel the craft. In the case of a jet engine, the entire propulsive force is produced in this way. In the case of an ordinary engine, most of the thrust is obtained from the propeller which is rotated by the engine, and the thrust resulting from the reaction of the gas stream issuing from the exhaust pipe is relatively small. The reaction force depends upon the volume of the gas being discharged, which in turn depends in part upon the temperature. In the case of an aircraft having a propeller driven by an internal combustion engine, a substantial portion of the heat of combustion is abstracted in the engine, with a corresponding reduction in the temperature and pressure of the exhaust gas. However, the exhaust gas usually contains unburned constituents representing energy that is wasted.

In accordance with the present invention, the temperature and volume of the gas discharged from the exhaust pipe is substantially increased by secondary combustion within the exhaust duct, with the addition of outside air. The addition of the outside air not only supplies oxygen for the complete combustion of unburned fuel components appearing in the gas discharged from the engine, but adds to the total volume of gas discharged. It is not broadly new to attempt to produce secondary combustion in the exhaust pipe by the addition of air thereto, but to the best of my knowledge previous attempts to produce secondary combustion in this way have been unsuccessful, for all practical purposes, because of the difflculty of initiating and maintaining the (Cl. Gil-35.6)

secondary combustion. This difficulty is overcome in accordance with the invention by introducing into the exhaust pipe, in addition to auxiliary air, additional fuel which facilitates the ignition and burning of the unburned constituents of the exhaust gas.

I find it desirable to introduce the auxiliary air and mix it with the exhaust gas before the resultant mixture is mixed with the fuel. It is also desirable to introduce the fuel in the form of a combustible air-fuel mixture which may be supplied under pressure from the supercharger of the engine. The stream of fuel and air from the supercharger is preferably ignited by a spark plug, hot wire, or other igniting device prior to its mixture with the exhaust gas, as this promotes thorough combustion of all unburned components in the exhaust gas.

A full understanding of the invention may be had. from the following detailed description of certain specific embodiments thereof as illustrated in the drawing, in which Fig. 1 is a side elevation view of an aircraft en ine assembly to which the invention is applied, the conventional parts of the assembly being shown in broken lines and the added structures in accordance with the present invention being shown in full lines;

Fig. 2 is a 1ongitudina1 section on a larger scale of the structure shown in full lines in Fig. 1, the plane of the section being indicated by the line 11-11 of Fig. 3;

Fig. 3 is a front end view of the structure shown in Fig. 2; I

Fig. 4 is a detail horizontal section taken in the plane IVIV of Fig. 2;

Fig. 5 is a longitudinal section showing a design alternativeto that of Fig. 2, the plane of the section being indicated by the line V-V of Fig. 6; and.

Fig. 6 is a cross-section taken in the plane VI VI of Fig. 5.

Referring first to Fig. 1, there isshown in broken lines the main elements of an aircraft engine unit. These elements include a nacelle ID in which the engine is mounted, an engine II to which is attached a propeller I2, an enginedriven supercharger 13 through which fuel-air mixture is supplied to the engine, and an exhaust manifold M through which exhaust gas from the engine is discharged.

The intake of the supercharger I3 is shown connected to a carburetor [5, which, as shown, receives air from a scoop IS the inlet end of which extends exterior of the nacelle l0 and faces forwardly so that the slip stream past the nacelle it, when the airplane is in flight, builds up air pressure in the scoop l6.

Ordinarily, the exhaust manifold [4 would be directly connected to the atmosphere through a tail pipe H, which, in this instance, is shown discharging through the' tail end of the nacelle H]. In accordance with the present invention, however, a special structure is interposed between the exhaust manifold M and the tail pipe I! for producing secondary combustion of the exhaust gas and increasing its heat content or enthalpy.

Referring now to Figs. 2 and 3, the special structure for producing the secondary combustion comprises a tubular coupling element 23 which is connected at its forward end 2| to the exhaust manifold l4 (Fig. 1) and is connected at its rear end 22 to the forward end of the tail pipe IT. This coupling member may be formed in three parts for convenience in manufacture and assembly, and as shown, it consists of a front section 23, an intermediate section 34, and a rear section 24. The two sections 34 and 24 are secured together by a clamp 25. The intermediate section 34 telescopes into the rear end of the front section 23 and may be welded thereto.

Exhaust gas entering the forward end 2| of the section 23 from the exhaust manifold M is directed through an inner tubular member 26,

which tapers to a smaller diameter at its rearward end and is traversed near its rear end by a hollow mixing duct 21, the opposite ends of which extend through the wall of the member 26 and are open. As best shown in Fig. 4, the member 21 is of airfoil shape and is provided with discharge apertures 28 in its rear inwardly tapering side walls.

Air is supplied into the annular space between the tubular members 23 and 26, respectively, through an intake duct 29 the forward end of which is positioned at the leading edge of the nacelle l0 (Fig. l) and the rear end of which opens through the wall of the member 23. The air entering the annular space 30 flows rear wardly through a second inner tubular deflector member 3| which, like the inner tubular member 26,- is tapered inwardly and rearwardly, the space substantially enclosed by deflector 3| in which the air supplied through the intake 29 is mixed with the combustion products supplied through the member 26 may be termed a mixing zone. The front large end 32 of the member 3| is of somewhat smaller diameter than the intermediate outer section 34, and the annular space between the two members is filled by a channelshaped member 33 which defines with the section 34 an annular space 35 for a purpose to be described later. The front half of the channelshaped member 33 is imperforate and forces all of the air entering the annular space 33 to flow into the front end 32 of the inner tubular member 3|. Due to the constriction of the rear end of the member 3| and the cross-sectional shape of the member 21, some of the air entering the member 3| flows into the opposite ends of the cross member 2! and is discharged through the apertures 28 therein into the exhaust stream flowing through the member 26. The remaining air is mixed with the exhaust gas and air issuing from the outlet end of the member 26 and the resultant mixture is discharged at substantial velocity through the member 3| into the rear casing section 24 where it is mixed with fuel and ignited. The portion of the casing 24 rearwardly of the deflector 3| together with the forward portion of the tail pipe I! thus forms a main combustion zone.

The structure for supplying the fuel includes the annular channel member 33 which, together with the mid casing section 34, defines the annular passage 35. Thus, the rear portion of the front casing section 23 is provided. with an annular corrugation 31 near its rear end, which, with the mid casing section 34, defines an annular space 38, and this space 38 is supplied with a mixture of fuel and air through a pipe 39 (Fig. 1) leading from the supercharger l3 of the engine.

That portion of the mid section 34 of the casing that is interposed between the annular spaces 35 and 38, respectively, is perforated at intervals as indicated at 40 to permit passage of the fuel-air mixture from the annular passage 38 to the an.- nular passage 35, and it is discharged from the annular space 35 through circumferentially spaced holes 4| in the rear wall of the channel member 33.

The fuel-air mixture leaving the apertures 4| enters an ignition chamber or sheltered combustion zone including the annular space 42 between the inner tubular member 3| and the outer member 24, where it is ignited by any suitable means, such as a spark plug 43 to form a continuously burning primary or ignition flame as long as fuel is supplied via pipe 39. The burning mixture flows rearwardly around the inner tapered tubular member 3| and mixes with the mixture of exhaust gas and air discharged through the member 3|.

The annular channel member 33 is exposed on its front and inner sides to the cool air that flows through the annular space 30. This is desirable because it cools the combustible fuel-air mixture in the channel 35, thereby preventing starting of combustion within the channel.

Because of the velocity of the air and exhaust gas mixture turbulence is created in the mixture as it leaves the tapered tubular member 3 i. It is, accordingly, thoroughly mixed with the burning air-fuel mixture leaving the ignition chamber 42, so that substantially all of the fuel components in the exhaust are completely burned and their energy used to raise the temperature of the exhaust gas and air.

As a result of the additional air introduced into the exhaust system through the duct 29 and the volume increase resulting from the increased temperature produced by the combustion, the volume and velocity of the gases issuing from the tail pipe I! are greatly increased so that a material thrust effect urging the aircraft forwardly is obtained.

Flow of air through the air intake duct 29 is produced in part by pressure developed at the forward end of the duct (resulting either from the motion of the airplane or the thrust of the propeller |2) and in part by the suction resulting from the flow of exhaust gases through and out of the inner tubular member 26. Thus, as a result of the streamlined cross-sectional shape of the cross member 21, the flow of exhaust gas therepast produces a reduced pressure adjacent the apertures 28 that tends to draw air therethrough. Likewise, the relatively high velocity of the exhaust gases issuing from the reduced rear end of the tubular member 26, reduces their pressure at that point, which tends to draw air into the member 3| from the annular space 30.

The tail pipe I! should be of relatively large diameter and only long enough to allow the gases to burn completely. However, a compromise must sometimes be resorted to because of the size and shape of the nacelle. If the tail pipe is longer than necessary it results in additional frictional loss, whereas if it is too short the burning may not be completed within the pipe, and flame will be discharged. In either event the thrust obtained will be somewhat reduced.

The structure described has been very successful in practice, operating smoothly and positively, despite the fact that it is usually very difficult to initiate and maintain smooth combustion in a high velocity gas stream. Tests indicate that the chief reason for the success of the structure is that only the marginal portion of the stream leaving the member. 3| is mixed sufficiently to support combustion, and the flame resulting from the burning of this marginal portion ignites remaining portions of the stream progressively as they become sufficiently mixed to burn. Because of the fact that there is no instantaneous ignition of a large body of combustible mixture, explosions and rough burning and popping are prevented. The burning of the gas stream leaving the member 3| commences at the downstream edge of member 3|, but extends downstream as it moves into the center of the stream. The gas passing through the member 3! is moving at much higher velocity than the gas in the ignition chamber 42, and this produces swirling and eddy currents which promotes combustion at the edge of member 3|.

It has been found in tests made on apparatus of the dimensions stated, that by the introduction of only 600,000 B. t. u. per hour from the fuel taken from the supercharger, the heat of the exhaust gas is boosted from 6,000,000 to approximately 18,000,000 B. t. u. per hour. In other words, the heat of the fuel added to the exhaust pipe by my apparatus sets free about twenty times as much heat from unburned constituents in the exhaust gas that would otherwise be wasted.

In the modified structure of Figs. 5 and 6, the positions of the exhaust gas and air passages are reversed. Thus, in Fig. 5, the air enters through an inner tubular member 50, the forward end 5| of which is open so that air is rammed into it by the forward motion of the airplane. The rear end of the member 50 extends into the inturned end 52 of a middle tubular member 53, the latter being bulged outwardly exterior of its inturned end 52, to form a manifold space 54 which may be directly connected by a short coupling conduit 55 directly to the exhaust manifold M of the engine (Fig. 1).

The exhaust gas flowing through the annular passage 54 flows rearwardly through an annular passage 56 defined between the inturned end 52 and the juxtaposed side wall portion of the mid section 53 and is mixed with the air entering through the front section 59. The mid section 53 is tapered to a reduced diameter at its rear end and projects into the. enlarged forward end 5'! of the rear section 58 which may connect to the tail pipe I I (Fig. 1) or may discharge directly into the atmosphere.

The forward end 51 of the rear section 58 is connected to the mid section 53 by an annular channel-shaped member 59 which is welded to the exterior surface of the section 53. The forward end of the rear section 51 may in turn be welded to the outer wall of the channel member 59. The channel member 59 functions together with the wall of the mid section 53 to define an annular manifold 60 which receives combustible mixture from the pipe 39 and discharges it through openings 62 in the rear wall of the channel member 59 into the rear tubular section 58 where it is ignited by a spark plug 64 and thereafter mixed with the mixture of exhaust gas and air issuing from the rear end of the mid section 53.

Although for the purpose of explaining the invention two specific embodiments thereof have been disclosed in detail, various departures from the exact structure shown will be apparent to those skilled in the art, and the invention is limited only to the extent set forth in the appended claims.

I claim:

1. An afterburner comprising an outer duct having a first inlet adapted to be connected to an engine exhaust pipe; a mixing duct within said outer duct and connected to said outer duct to receive all of the exhaust gases entering said first inlet to mix them and direct them axially of said outer duct; a transversely disposed element within said mixing duct for mixing and more evenly distributing the flow of gases therethrough; an annular chamber between said first and second ducts; an air intake connected to said annular chamber; a tubular member within said outer duct and disposed in alignment with said mixing duct to receive the exhaust gases therefrom and the air from said annular chamber, said tubular member forming a protected annular primary combustion zone surrounding the mixture of gases and air within said member; a wall between said tubular member and said outer duct at the upstream end of said member to prevent the passage of gases into said primary combustion zone; a distributor for supplying fuel evenly Y to said annular primary combustion zone; and

an igniter for initiating combustion in said primary combustion zone to establish a continuously burning primary flame in a zone surrounding and communicating with the blast of mixed exhaust gases and air issuing from said tubular member and which ignites matured and burnable portions of the mixture in a peripheral zone downstream of said tubular member with result that the remainder of the mixture burns downstream of said tubular member.

2. Propulsive thrust generating apparatus comprising a duct structurally formed to present netforward propulsive reacting surfaces; a mixing zone in said duct through which gases containing combustion components pass; means for supplying a component to form a combustible mixture with said gases in said mixing zone; a main combustion zone in said duct downstream of said mixing zone; means for causing said combustible mixture to flow through said main combustion zone at a velocity higher than the normal rate of flame propagation through said mixture; an annular structure forming a sheltered combustion zone adjacent said main mixing zone and causing turbulent flow of gases from said main combustion zone into said sheltered zone; ignition means for said sheltered zone; and means to deliver combustible fuel mixture to said sheltered zone operative to maintain anchored igniting and combustion supporting flame which mixes with said turbulent flow of gases to propagate flame across said combustible mixture in said combustion zone causing the generation of a thrust producing gaseous mass reacting against said surfaces.

3. For use in combination with the exhaust outlet of an internal combustion engine; propulsive thrust generating apparatus operative in any position comprising 9. mixing Z0116 through which gases containing combustion components pass and a main combustion zone downstream of said mixing zone, structurally formed to present forward propulsive thrust reacting surfaces; means for supplying a component to form a combustible mixture with said gases in said mix ing zone; a mixture deflector along a substantial portion of the periphery of said mixing zone forming both a sheltered combustion zone and a turbulent ignition zone adjacent the upstream end of said main combustion zone; ignition means for said sheltered zone; and means to deliver combustible fuel mixture to said sheltered zone operative to maintain anchored igniting and combustion supporting flame which mixes with and ignites said mixture in said turbulent zone and causes continuous flame propagation across mixture in said main combustion zone with said mixture traveling at a velocity higher than the rate of normal flame propagation in the mixture and with the generation of a thrust producing gaseous mass reacting against said surfaces.

4. Propulsive thrust generating apparatus having forward propulsivethrust reacting surfaces comprising: a duct; means for introducing into said duct a plurality of fluids which, When mixed, form a combustible mixture; means including a deflector forming a mixing zone in which said fluids are formed into said combustible mixture, said deflector extending along at least a substantial portion of a periphery of said mixing zone and forming a Wall of a sheltered combustion zone, and creating turbulence downstream of said sheltered combustion zone; means forming a main combustion zone downstream of said mixing zone; and means eifective to establish and maintain an ignition flame in said sheltered combustion zone which ignites said combustible mixture in said main combustion zone and causes continuous flame propagation across said combustible mixture in said main combustion zone with zone with said mixture travelling at a velocity higher than the rate of normal flame propagation in the mixture to cause thrust producing acceleration of said gases reacting against said surfaces.

5. The combination defined in claim 4 wherein said deflector peripherally bounds said sheltered combustion zone.

6'. The combination defined in claim 4 wherein said deflector peripherally bounds said sheltered combustion zone and said mixing zone.-

7. The combination defined in claim 4 wherein said deflector has surfaces inclined with respect to the axis of said duct which intercept and deflect said fluid away from said sheltered combustion zone.

8. The combination defined in claim 4 wherein said deflector has surfaces inclined with respect to the axis of said duct whereby the sectional area of said sheltered combustion zone increases in a downstream direction.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 791,002 Busey May 30, 1905 1,315,931 Poppink Sept. 9, 1919 1,824,820 Hynes Sept. 29, 1931 1,830,658 Hynes Nov. 3, 1931 1,839,880 Hyatt Jan. 5, 1932 1,938,851 McKee Dec. 12, 1933 2,047,471 Hepburn et al July 14, 1936 2,184,967 Winter Dec. 26, 1939 2,304,008 Muller Dec. 1, 1942 2,395,919 Sundell Mar. 5, 1946 FOREIGN PATENTS Number Country Date 309,273 Italy July 1, 1933

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