US3380246A

US3380246A - Exhaust manifold system for internal combustion engines

Info

Publication number: US3380246A
Application number: US518308A
Authority: US
Inventors: Millard F Dowell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-01-03
Filing date: 1966-01-03
Publication date: 1968-04-30
Anticipated expiration: 1985-04-30

Description

April 30, 196 M. F. ooweu.

EXHAUST MANIFOLD SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Jan. 5. 1966 2 Sheets-Sheet 1 INVENTOR.

("HLLA D F. DOWELL HIS ATORNEY April 30, 1968 M. F. DOWELL EXHAUST MANIFOLD SYSTEM FOR INTERNAL COMBUSTION ENGINES 2 sheets-she t 2 Filed Jan. 5. 1966 FIGA-I FIG-.5

. INVENTOR. NILLARD E DOM/ELL BY a ms ATTORNEY United States Patent 3,380,246 EXHAUST MANIFOLD SYSTEM FOR INTERNAL COMBUSTION ENGINES Millard F. Dowell, Erie, Pa., assignor to General Electric Company, a corporation of New York Filed Jan. 3, 1966, Ser. No. 518,308 13 Claims. (Cl. 6013) ABSTRACT OF THE DISCLOSURE An exhaust manifold, for a turbo-supercharged internal combustion engine, having a single central conduit and a plurality of branch pipes for the various cylinders, which pipes have sections of progressively decreasing cross-section in the direction of flow and curve to meet the conduit at a relatively small angle to the direction of gas flow in the conduit.

This invention relates to exhaust manifold systems for internal combustion engines and more particularly to a new and improved system of the single duct type wherein exhaust gases from each cylinder of the engine are con ducted to a single main conduit, which may or may not deliver such gases to a turbocharger.

In some commonly used manifold arrangements for the large diesel engines, a number of separate pipes are employed to conduct the exhaust gases from the engine cylinders to the turbo-supercharger. For example, in a particular manifold arrangement of such type for a 16 cylinder, V-type diesel engine, eight separate pipes were employed each of which included one or more bends. In such arrangement, tests indicated throttling losses in going from the cylinders to the supercharger of about several hundred horsepower. Since this throttling loss introduces large vibration forces, the multiple duct system has certain extremely undesirable characteristics.

Since a single duct manifold promised improved engine performance, as well as other advantages, and inherently requires less installation space, such systems have long been attractive as a replacement for the still commonly used multiple duct systems. A number of different single duct manifold arrangements are known in the prior art, but such arrangements have not proven to be entirely satisfactory.

Although, in theory at least, a single duct manifold system should provide improvements in acceleration characteristics of the engine as well as in the overall performance thereof, the performance and operating life of such systems has, heretofore, been disappointing since entirely satisfactory solutions to the many physical and mechanical problems presented in developing an actual practical single duct manifold system have not been provided. For example, ejection of the exhaust gases from the individual cylinders into the single main conduit may so disturb scavenging, introduce high frictional losses, or both, that the use of such a single duct manifold system may hinder rather than improve the overall performance of the engine. Also, the intense heat of the exhaust gases causes distortion and misalignment problems which are particularly severe with manifolds for the large engines, which manifolds may be, for example, from to 12 feet in length. Prior art attempts to solve one or more of these problems have usually resulted in manifolds which were not only too expensive for competitive use but often introduce serious practical probiems as well. For example, some single duct manifold systems require balfies or divider means within the main conduit which, in addition to a tendency to increase costs and frictional losses, are objectional also since if such baffle breaks and enters the turbocharger, damage to the turbocharger and the engine could result. Thus, prior art attempts to minimize one problem often exaggerate some 3,380,246 Patented Apr. 30, 1968 other problems so that none of such prior art single duct manifold systems have been entirely saitsfactory. Accordingly, there has remained a continuing need to develop a more satisfactory single duct manifold arrangement, especially for the large V-type engines, which could achieve at least some of the hoped for engine performance improvement, provide long operating life and reliable operation.

It is an object of this invention, therefore, to provide a single duct manifold system which achieves the foregoing dcsiderata.

It is another object of this invention to provide a single duct manifold system which exhibits low overall losses while still requiring a minimum installation space.

It is a further object of this invention to provide an improved single duct manifold system which exhibits extremely low stress levels and which is essentially free of end thrust loading.

It is a still further object of this invention to provide a compact, mechanically rugged single duct manifold system which allows for ease of assembly and repair.

Briefly stated, in accordance with one aspect of the invention, the new and improved manifold system comprises a main conduit including a plurality of longitudinally arranged sections interconnected by flexible bellows means in sealing relationship therewith. The system also includes a number of branch pipes, one for each of the cylinders of the engine, which are adapted to conduct the exhaust gases from the exhaust passages of the cylinders to the main conduit. Each of the branch pipes connects with the main conduit in such manner that the axial velocity of the gas in the main conduit and the incoming velocity of the gas from the cylinder is in approximately the same direction thereby providing momentum transfer-ejector action.

In a preferred embodiment of the invention each of the branch pipes has a cross-sectional area which continually decreases throughout the curved portion thereof in the direction from the end which connects with the engine toward the end which connects with the main conduit. Further the radii of curvature of such curved portion and the inside surfaces of the pipe are proportioned to prevent separation of the boundary layer and minimize secondary flow losses to provide a compact manifold arrangement having low overall losses.

The novel features believed characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, together with its organization and method of operation, as well as further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which like or corresponding elements are designated by similar reference numerals and wherein FIGURE 1 is a side elevation view of the single duct manifold system of this invention;

FIGURE 2 is a top elevation view of the right hand portion of FIGURE 1;

FIGURE 3 are enlarged cross sectional views of the curved portion of the branch pipe shown in FIGURE 2 and taken along the lines a-a, b-b, cc and dd respectively;

FIGURE 4 is a top elevation view of the left hand portion of the manifold of FIGURE 1;

FIGURE 5 is a plan view taken in elevation substantially on the line 5-5 of FIGURE 1; and

FIGURE 6 is a perspective view of a turning elbow in accordance with another embodiment of this invention.

The illustrative embodiments of the invention are shown for application to a turbo-supercharged, multiple cylinder, V-type engine; however, it will be understood that the manifold system of this invention may be employed with internal combustion engines generally, either V-type or inline, and whether or not equipped with a turbo-supercharger. The manifold system of this invention is especially suited for use with the large, V-type, turbo supercharged diesel engines, such as those used on locomotives and the like and will be described in detail in that connection.

Referring now to the drawings, there is shown in FIG- URE 1 a single duct manifold system, generally designated at 10, including a main conduit 12 and a number of branch pipes 14 adapted to conduct the exhaust gases from the individual cylinders of the engine into the main conduit. As shown, one end of the main conduit is connected through a transition member 15 to a turbo-supercharger 16, only a portion of which is illustrated; the other end of the main conduit being closed ofl and supported against axial pressure by a thrust support member 17. Although only a portion of the length of the main conduit is shown, it will be apparent that the length of the main conduit and the number of branch pipes required will be determined by the particular engine and the number of cylinclers thereof since a separate branch pipe is employed for each cylinder of the engine.

As shown, the main conduit 12 is made up of a number of main conduit sections 18 arranged longitudinally in the space between the two banks of engine cylinders (not shown). To prevent distortion and misalignment of the main conduit, due to expansion thereof as a result of the high temperature of the exhaust gases therein during engine operation, the main conduit sections 18 are interconnected by suitable bellows members 26. The bellows members 20 allow for expansion between adjacent main conduit sections.

The main conduit sections 18 and bellows members 20 may be interconnected in any suitable manner to provide the complete main conduit 12. Conveniently, as shown, the respective ends of the main conduit sections 18 and the bellows members 20 are provided with flanges which may be clamped or otherwise suitably connected together to provide a gas-tight joint between the bellows members and the main conduit sections adjacent thereto. In the arrangement illustrated, the main conduit sections 18 are provided with a flange 22 at each end thereof adapted for connection to similar flanges 24 provided on the ends of bellows members 20. To facilitate assembly and repair, the main conduit sections are assemblied so that any given section may be readily connected and disconnected without disturbing the remainder of the manifold. As shown, this is conveniently provided by permanently connecting one end of each of the bellows members 20 to a main conduit section 18, as by welding the

respective flanges

24 and 22 thereof together, with the remaining flanges of the bellows members and main conduit sections removably connected together by a suitable clamp 25. To this end also, the branch pipes 14 are arranged to enter at the top of the main conduit, although, as will be apparent, such branch pipes may enter the main conduit from the side or bottom thereof without affecting the operation of the manifold system of the invention. Further, although in the manifold system selected for illustration, the main conduit 12 is made up of sections of circular cross-section, it will be understood that sections of other cross-section, such as square, oval or rectangular, for example, may be employed if desired.

Associated with each main conduit section 18 are a pair of branch pipes 14 one for each of the engine cylinders, which cylinders are, of course, on opposite sides of the main conduit in a V-type engine. In order to conduct the exhaust gases from such cylinders into the centrally disposed main conduit, the gases must be turned. Moreover, to achieve the advantages provided by having the branch pipes enter the main conduit from the top, the exhaust gas flow must be turned in a corkscrew manner in three dimensions. That is, the flow must come out of the cylinder, turn upward, then straighten out and go downward again into the main conduit. The present in- 4- vention accomplishes these sharp turns with extremely low losses.

To this end, each branch pipe 14 includes a straight portion 35 and an arcuate or turning elbow portion 35. The branch pipes 14 may be made up as a single suitably curved pipe one end of which is provided with a flange 38 adapted to be secured to the engine exhaust port and the other end of which is adapted for connection to the main conduit section. The branch pipes 14 may then be connected individually, or through a common inlet adapter, to the main conduit section. Although only a limited amount of space is available in order to provide as compact an assembly as possible, the branch pipes are of sutiicient length to accommodate thermal growth from bank-to-bank. The branch pipes are also arranged to blend into the main conduit sections 18 so that the tensile stresses due to such bank-to-banl: thermal growth are spread over a large area.

Further, in accordance with this invention, the branch pipes are arranged to enter the main conduit section at an angle with respect to the longitudinal axis of the conduit which assures that the axial velocity of the exhaust gases in the main conduit and the incoming velocity of the exhaust gases from the cylinders are in approximately the same direction. In this way a momentum transfer-ejector action is provided. Satisfactory results in this respect ha as been obtained, for example, with the exhaust gases from the cylinders ejected into the main conduit at angles up to about degrees of the major axis of the main conduit. Thus, the pulse energy of the gases, which occurs in a very short time period, is nearly all conserved. For example, in a 16 cylinder engine 133 pulses per second occur in the main conduit so that the single duct manifold system of this invention effectively functions as a multiple pipe ejector system. This provides for a very advantageous arrangement for causing additional air flow through the engine since the pulses tend to entrain or suck additional flow through the engine cylinder. In a particular application on a 16 cylinder, V-type diesel engine, tests indicated an increase in inlet air volume over a multiple duct system of from 10% to 18%. Such increased air flow allows valves and cylinder walls to operate at a lower temperature for a given horsepower output. Tests have also shown a decrease in the manifold temperature of about F. to F. as a result of replacing the multiple duct system with the single duct manifold system of this invention.

In further accordance with this invention the turning elbow portion 36 of the branch pipes 14 are arranged and constructed so that the cross-sectional area thereof continually decreases along the length thereof in the direction from the flange 38, which is adapted to be connected to the exhaust ports of the engine, toward the end to be connected to the main conduit section as best illustrated in FIGURES 2 and 3; the cross sections shown in FTGURE 3 being taken along the lines a-a, bb, cc and dd respectively of the curved portion 36 of the branch pipe shown in FIGURE 2. For simplicity of description, the end of the branch pipe adapted to be connected to the engine will be referred to hereinafter as the entrance end while the end thereof which connects to the main conduit will be referred to as the exit end. In addition, the radius of curvature of the elbow portion 35 (or the radii of curvature thereof since more than one such radius may be required to provide the desired bend), as well as, the geometry of all inside surfaces of the turning elbow portion 36, are selected and constructed to prevent separation of the boundary layer and minimize secondary flow losses therein.

With regard to the selection of the radii of curvature and the geometry of the inside surfaces of the turning elbow it does not presently appear to be possible to set forth precise numerical limits which would govern for all of the different turning elbows which might be required tor the many different engine manifolds. One reason for this is that the available space in which the turn must be made will be dilferent for the different engines. Another reason is that the angle through which the exhaust gases must be turned from the engine exhaust ports to the main conduit will be different for different engines. However, one skilled in the art, given the teaching that the cross sectional area of the turning elbow should be made to decrease in the direction from the entrance end toward the exit end thereof and that the radii of curvature of the bend and the geometry of the inside surfaces would be controlled to prevent separation of the boundary layer and minimize secondary flow losses in the pipe, should have no difiiculty in constructing a suitable high efficiency turning elbow. By following the foregoing teachings, turning elbows having an energy elficiency of 90% to 95% and more can be provided. Such low loss turning elbows contribute significantly to the low overall losses of the manifold system of the present invention.

After the elbow is suitably constructed in the foregoing described manner, the remainder of the length of the straight portion 35 of branch pipe 14 may be of a constant cross-sectional area, or the cross-sectional area thereof may be increased if diffusion is desired.

Alternatively, a similar high efiiciency turning elbow portion 36 may be provided by controlling the aspect ratio of the gas flow turning passage. To this end, at every point throughout the turn the aspect ratio should be controlled so that a maximum aspect ratio greater than unity is obtained at a desired location of the turn. Preferably, the maximum aspect ratio at the selected location of the turn should be greater than about 2. The term aspect ratio refers to the ratio of the height of the gas flow passage L to the width of the gas flow passage D at a given cross sectional position of the turn. The dimensions L and D are shown at one cross sectional position or" the turning elbow 36 in FIGURE 6. Thus, the aspect ratio is given by the ratio L/D and, as stated, has a maximum value greater than unity and preferably greater than about 2.

In a preferred embodiment, the cross sectional area of the gas flow passage would also be controlled. That is, in addition to controlling the aspect ratio, the cross sectional area of the turning elbow portion 36 would be made to decrease from the entrance end to at least the throat; that is, to the location of maximum aspect ratio.

Accordingly, the turning elbow portion 36 may be constructed by controlling the cross sectional area, radii of curvature and inside surface geometry as described, by controlling the aspect ratio or by controlling both the aspect ratio and the cross sectional area. By constructing the turning elbows 36 in accordance with the foregoing principles the secondary flow losses are minimized and the high velocity gas flow may be turned through the required large angle with very high efficiency.

Although, as described, branch pipes 14 may be made up as single suitably curved pipes, preferably such branch pipes are provided in two separate portions, a straight portion 35 and a turning elbow portion 36. These two separate portions are then connected together in any suitable manner, such as by the clamp 40, for example. In this preferred embodiment, therefore, each main conduit section 18 is provided with an exhaust inlet transition member 42, which is shown more clearly in FIGURES 2 and 4. Exhaust inlet transition member 42 includes diverging straight pipe portions 35 which converge into a common inlet portion 44 at the main conduit section 18. The diverging straight pipe portions 35 are adapted to be clamped to the ends of the respectively turning elbow portions 36 which connect to the cylinders on opposite sides of the main conduit.

As described, hereinbefore, the common inlet portion 44 is also arranged to blend into the main conduit section 18 so as to distribute the tensile stresses, resulting from the bank-to-bank thermal growth, over a large area. Also the common inlet portion 44 is connected to the main conduit section 18 at a suitable angle which assures that the axial velocity of the exhaust gases in the main conduit and the incoming velocity of the exhaust gases from the cylinders are in approximately the same direction.

Conveniently, since the exhaust ports of engines are often of rectangular cross section, the entire length of branch pipes 14, or as illustrated, the turning elbow portion 36 thereof, may be provided of a similar cross section. It will be understood, however, that branch pipes of any suitable cross section may be employed as long as such branch pipes are formed and constructed and arranged with respect to the main conduit in the foregoing described manner.

The use of branch pipes having two separate, removably connected sections allows for ease of removal of any given conduit section, such as from the middle of the manifold assembly, for example, without disturbing the rest of the assembly. In addition to the foregoing, the two portion branch pipe arrangement allows for unloading the manifold assembly statically. For example, the most stressed area is that where the curved and straight portions of the branch pipe come together. The removable connection thereat allows for both lateral and angular off-set which operates to unload the manifold assembly statically.

In order to reduce the stresses in the inside joint area 48 where the straight portions 35 first come together in the common inlet member 44, the distance from the engine exhaust port to this junction is kept to a minimum in the plane normal to the major axis of the main conduit 12. For example, since it has een found that this inside joint area 48 is loaded only in compression, keeping the distance from the exhaust port connection to this joint area 48 a minimum in the plane normal to the major axis of the main conduit, reduces the amount of deflection and hence the stresses at the joint area 48. As a result the stress levels of the overall manifold system are very low.

Vertical expansion of the manifold, and vibratory loading thereof as well, is prevented by supporting the main conduit from the engine (not shown) and statically loading the branch pipes 14. To this end, each of the main conduit sections 18 is slidably supported from the engine by a support member 50 which is positioned between the engine and the bottom of the conduit section. One end of each support member 50 is secured to a rail member 52 which in turn is secured to the engine as by the bolts 53. The other end of the support member 50 is adapted to slidably engage the bottom of the conduit section so as to provide vertical support therefor and accommodate axial movement of the main conduit as a result of the large temperature changes to which the manifold assembly is subjected. Conveniently, support member 50 may be provided with a saddle-like portion 55 into which a suitable wear-plate 56 is disposed. The foregoing support arrangement also obviates the need for an additional means, such as a bellows member, to accommodate angular misalignment in the turbo-supercharger 16 such as is often necessary in prior art single duct manifold systems.

It will be understood that any suitable support arrangement which will provide vertical support and allow for axial movement of the main conduit assembly may be employed.

As previously stated, the forward end of the main conduit 12 connects with the turbo-supercharger 16 and the rear end of the main conduit is closed off and supported against axial pressure on the rear by a thrust support member 17. Thrust support member 17 is shown in most detail in FIGURE 5 and includes a circular plate 60 for closing off the end of the main conduit 12 and a bracket 62 connected between the plate and the engine. As shown, one end of bracket 62 is secured to plate 60, as by welding, and the other end is secured to the engine. The end closure plate 60 is clamped to the end flange of a terminating bellows member 20 by a clamp 25. In this way the bellows member 20 separates the end closure from the last section of the main conduit and the bracket "2 of thrust support member 17 carries the pressure on the rear end of the manifold to assure that the last two branch pipes are unloaded to provide a manifold assem bly which is essentially free of end thrust loading.

Since in the particular embodiment illustrated the horizontal axis of the main conduit and the axis of the turbo-charger are different, a transition section 15 was provided between the last forward conduit-bellows section 134% and the inlet to the turbo-charger 16. In this particular embodiment, for example, the main conduit had a diameter of 8%. inches and was employed on a 16 cylinder, V-type turbo-supercharged diesel engine. The horizontal axis of the main conduit differed from the axis of the turbo-supercharger by about 4 inches and the transition section 15 was employed to correct for this misalignment so that the gases from the main conduit would be properly conducted to the turbo-supercharger. It will, of course, be understood that where the horizontal axis of the main conduit and that of the turbo-charger are in line then no such specially shaped transition section would be required.

The foregoing described manifold arrangement allows for the duplicate use of common pieces which is advantageous from a manufacturing cost as well as from the repair standpoint. For example, all main conduit sections 18, bellows members 2% and the elbow portions 36 of branch pipes 14 are the same. The only exception occurs in the particular arrangements which may require a transition section 15. In such arrangements the transition section differs from the other main conduit sections and the branch pipes from the number one cylinders which connect to this transition section also differ from the branch pipes which connect to the other main conduit sections 18.

For some applications it has been found to be advantageous to eject the exhaust gases from the number one cylinders directly into the intake of the turbo-supercharger rather than into a main conduit section, or a transition section if one is required. In this way acceleration of the turbo-supercharger is improved under cold starting conditions. This is often an important consideration.

From the foregoing description, it will be apparent that the single duct manifold arrangement. of this invention provides a novel combination of aerodynamic, thermodynamic and mechanical advantages thereby providing a single duct manifold system which achieves improvements in engine performance together with long operating life and reliable operation.

While only preferred embodiments of the invention have been described in detail herein by way of illustration, many changes and modifications will occur to those skilled in the art. Thus, although the branch pipes are illustrated as entering at the top of the main conduit sections, it will be understood that all the operating advantages of the single duct manifold system may be achieved with such branch pipes arranged to enter from the sides or bottom of the main conduit sections. Also, branch pipes of various cross-sectional configurations may be employed consistent with the aerodynamic, thermodynamic and mechanical criteria set forth herein. It is, therefore, to be understood that the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

1. An exhaust manifold system for an internal combustion engine having an exhaust port associated with each cylinder thereof comprising:

(a) a main conduit including a plurality of longitudinally arranged sections interconnected by fiexible bellows members in sealing connection therewith;

(b) a plurality of normally rigid branch pipes one for each of the engine cylinders and each branch pipe arranged and adapted to conduct exhaust gases from said cylinders and eject said gases into said main conduit at an angle such that the axial velocity of the gas in said main conduit and the incoming velocity of gas from each cylinder is in approximately the same direction, said pipes each having at least one portion thereof with a progressively decreasing cross-sectional area in the direction of exhaust gas flow; and

(c) means for connecting one end of each branch pipe to the exhaust port of an engine cylinder and the other end thereof to a main conduit section.

2. The exhaust manifold system of claim 1 wherein the exhaust gases are ejected into the main conduit at an angle no greater than about 45 degrees of the major axis of the main conduit.

3. The exhaust manifold system of claim 1 wherein the said other end of said branch pipes are connected at the top portion of the main conduit sections.

4. The exhaust manifold system of claim 1 wherein each of said branch pipes has top and bottom walls and spaced-apart side walls connected thereto arranged to provide a gas flow passage including a curved portion and a straight portion, said top, bottom and side walls being further arranged throughout said curved portion to provide a gas flow turning passage whose aspect ratio is controlled to provide at a selected location of said turn an aspect ratio greater than unity.

5. The exhaust manifold system of claim 4 wherein the aspect ratio at the selected location of said turn is greater than about 2.

6. The exhaust manifold system of claim 4 wherein the cross sectional area of the curved portion decreases in the direction from the end connected to said exhaust port to at least the region of maximum aspect ratio.

7. The exhaust manifold system of claim 1 wherein said branch pipes include a straight portion and a curved portion, said curved portion having a cross-sectional area which continually decreases along the length of such curved portion in the direction from the entrance toward the exit ends thereof.

8. The exhaust manifold system of claim 4 wherein the radii of curvature of said curved portion and the geometry of all inside surfaces thereof are provided to prevent separation of the boundary layer and minimize secondary flow losses.

9. The exhaust manifold system of claim 8 wherein said straight and curved portions of said branch pipes are removably connected together to form the complete branch pipe, and straight portions blending into the main conduit section to distribute tensile stresses over a large area.

lit. The exhaust manifold system of claim 7 wherein the aspect ratio throughout the curved portion is controlled to provide at a selected location of said curved portion an aspect ratio greater than unity.

11. An exhaust manifold system for a turbo-supercharged internal combustion engine having an exhaust port associated with each cylinder thereof comprising:

(a) a main conduit assembly including a plurality of longitudinally arranged conduit sections intercom nected by flexible bellows members in sealing relationship therewith;

(b) means for connecting one open end of said main conduit to said turbo-supercharger;

(c) a thrust support member at the other open end of said main conduit assembly, said thrust support member being operative to close off and support said other open end of said main conduit from said engine;

(d) support members disposed between said main conduit and said engine for slidably supporting said main conduit and allowing longitudinal movement thereof 13. The exhaust manifold system of claim 11 whereil due to thermal cycling; and the aspect ratio throughout the curved portion is con (e) a plurality of branch pipes one for each of the trolled to provide foramaximum aspect ratio greater thar cylinders of said engine, each of said branch pipes unity at a selected location thereof.

being arranged to conduct the exhaust gases from its 5 particular cylinder to said main conduit and being References Cited connected to said main conduit so that said exhaust gases are ejected into said main conduit at an angle UNITED STATES PATENTS such that the axial velocity of the gas in said main 1,319100 10/1919 McElrath conduit and the incoming velocity of the gas from 10 2 113 077 4/1938 Buchi said cylinders is in approximately the same direction, 2321943 6/1943 Sam 'g Z each of said branch pipes including a curved portion 3043094 7/1962 l having a cross-sectional area which continually de- 3051147 8/1962 Jackson g creases along the length thereof in the direction from 3177649 4/1965 Tromel E the wward the ends- 15 312211492 12/1965 Carletti 60-15 12. The exhaust manifold system of claim 11 wherein the radii of curvature and internal surface geometry are selected and proportioned to prevent separation of the boundary layer and minimize secondary flow losses.

WENDELL E. BURNS, Primary Examiner.