US2975773A

US2975773A - Combustion chambers for pistons

Info

Publication number: US2975773A
Application number: US740908A
Authority: US
Inventors: Meurer Siegfried
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1957-07-06
Filing date: 1958-06-09
Publication date: 1961-03-21
Anticipated expiration: 1978-03-21

Description

March 21, 1961 s. MEURER COMBUSTION CHAMBERS FOR PISTONS Filed June 9. 1958 zzyz 4 Sheets-Sheet 1 INVENTOR ATTORN 6' March 21, 1961 4 Sheets-Sheet 2 Filed June 9, 1958 INVENTOR March 21, 1961 Filed June 9, 1958 s. MEURER 2,

COMBUSTION CHAMBERS FOR PISTONS 4 Sheets-Sheet 3 f u I INVENTOR March 21, 1961 s. MEURER 2,975,773

COMBUSTION CHAMBERS FOR PISTONS Filed June 9, 1958 4 Sheets-Sheet 4 INVENTOR ATT RNEY 7 an area of the chamber wall.

r tes United COMBUSTION CHAMBERS FOR PISTONS Siegfried Meurer, Numberg, Germany, assignor to Maschinenfabrik Augsburg-Numberg A.G., Nurnberg, Germany This invention relates to combustion chambers for pistons. In particular, the invention is directed to combustion chambers for self-ignition engines.

The piston of this invention is designed to operate in self-ignition engines such as disclosed in US. patent to Meurer et al. No. 2,907,308. In such engine, the liquid fuel is injected into a hollowcombustion chamber in the piston. the major portion of the fuel travels over a short free path and is applied immediately to the wall of the combustion chamber. After striking the chamber wall, the fuel spreads out as a film over a part of the wall. The remaining minor portion of the fuel is atomized directly in the air in the chamber and is self-ignited for igniting the fuel vaporized from the film of fuel. Combustion air is swirled over the film of fuel to vaporize the same.

In these engines, it is desirable to have the fuel cover as much as possible of the chamber wall. If the chamber, as in former pistons, is spherical or ellipsoidal and the fuel' strikes the wall at a sharp angle, the fuel is spread as a film in a satisfactory manner. Because of the kinetic energy of the fuel, it has a tendency to spread peripherally about the wall of the combustion chamber. However, in these chambers, the spreading of the fuel is handicapped by the concave curve of the spherical or ellipsoidal chamber. Such chamber forms act in the nature of a groove with the fuel tending to flow along the bottom thereof and not completely spread out.

The object of this invention is to produce a combustion chamber formed as a body of rotation and having a shape such that the fuel will spread out evenly in all directions on the wall of the chamber.

'One way of accomplishing the object of the invention is to form the combustion chamber wall at least in the area adjacent the places where the fuel jet strikes the wall as a flat or convexly curved surface extending inthe direction of the longitudinal axis of the piston and chamber. 'In other words, the chamber wall is fiat or con ,vexly curved perpendicularly to the circumferential direction of the body of rotation, at least in the areas where the fuel strikes the chamber wall.

By so constructing the combustion chamber, the undesirable grooved effect described above is avoided, and the fuel is spread as a film over as large as possible Because of the kinetic energy of the fuel, it still tends to spread circumferentially about the wall of the chamber, but simultaneously also has the tendency to spread in other directions.

In another form of the invention, the flat or convexly curved surface extending in the direction of the longitudinal axis of the piston can be continued into a concave portion adjacent the opening of the combustion chamber through the head of the piston. In such construction, a constricted opening is formed which enhances the air swirl produced in the chamber.

In another form of the invention, the combustion chamber is in the form of a hollow cone. This form is used especially when the combustion chamber is to have a The injection is made in such a way that atent Patented Mar. 21, 1961 hollow conical section forming the side wall of the charm her and the bottom is shaped as a torus. A further form of chamber is in having two oppositely directed conical chamber portions, with the two portions connected at their bases. A chamber so constructed has been found to improve the cold stanting of an engine. This is because of the sudden change given the direction of the spreading fuel over the joint between the two conical sections.

. The fuel at this point is momentarily detached from the wall. Consequently, the air swirling across this separated fuel atomizes the fuel which is of special advantage for high boiling point fuels. A similar effect can be obtained if the chamber wall and bottom are of spherical shapes with diflerent curvatures. In the latter construction, as compared to the two conical portion construction, the momentary separation of the fuel from the film can be accomplished closer to the opening into the combustion chamber so that the atomization is more effective in the starting of the engine.

When the combustion chamber is in the form of two conical portions, these conical portions can be symmetrical and axially aligned. However, in a modified construction, the conical portions can be either nonaxially aligned, or can be axially out of line, or can be non-symmetricalfor purposes of forming fuel films desirable for certain combustion processes. a

A still further form of the invention has the combus tion chamber opening connected to the combustion chamber by a short cylindrical neck. A variation of this is to form the neck as a polygon, and especially as a triangle. The fuel can be injected from one corner of the triangle. Also,-when the neck is triangular and two valves are provided for the cylinder, the fuel injection can be through one corner while the other two corners of the triangle are positioned beneath the valves. In a still further modified form, the neck can be elliptical, and then the fuel nozzle is positioned so that its longitudinal axis is aligned with the major axis of the el liptical neck.

A periodical momentary separation of the fuel from the film on the combustion chamber wall, which in connection with the forming of secondary swirls to atomize the fuel, can also be obtained by other ways of joining the conical combustion chamber portions. As already mentioned, Spherical portions of different curvature can be used. Basically, the atomizing effect can be obtained if the combustion chamber wall has an irregularity. For producing such an irregularity, another form of the invention has a stepped wall surface, with the steps extending transversely to the direction of both the injected fuel and the air swirl in the chamber.

The means by which the objects of the invention are obtained are described more fully with reference to the. accompanying drawings, in which:

Figure 1 is a longitudinal cross-sectional view through a piston in a'cylinder with the piston having a combustion chamber according to one form of the invention;

Figures 2, 3 and 4, respectively, are modified forms of the combustion chamber;

Figure ,5 is a top plan view of a piston having an elliptical opening in the combustion chamber;

Figure 6 is a transverse sectional view through a piston 7 having a stepped combustion chamber wall;

Figure 7 is a longitudinal view through a piston constructed according to Figure 6;

Figures 8, 9 and 10 are cross-sectional views similar to Figure 1 but showing, respectively, further modified forms of the combustion chamber;

Figure 11 is a plan view of a piston having a cylindrical neck forming the opening into the combustion chamber;

Figures 12 and 13 are modifications of the neck opening and show, respectively, a triangular and a hexagonal opening; and

Figure 14 is a cross-sectional view showing a still further modification of the invention shown in Figure 1.

As Shown in Figure 1, the combustion chamber 1 having the shape of a body of rotation is positioned in the piston head of piston 2, the chamber being coaxial with the axis of piston 2 and cylinder 3. A nozzle 4 is inclined in the cylinder head 4a above the combustion chamber. The major portion of the injected fuel is applied to the combustion chamber wall by several fuel jets 4b which are directed at a sharp angle toward the wall and form a film thereon. This film is vaporized from the wall and mixed with the air swirling in the chamber to produce a combustible fuel air mixture. The minor portion of the fuel is atomized immediately in the air swirling in the chamber. This atomizing is accomplished by either deflecting a part of the injected fuel into the air or by a special ignition jet, not shown. As the fuel leaves the nozzle, it has a kinetic energy which moves the fuel circumferentially around and upon the combustion chamber wall. In a vertical direction, as shown in Figure 1, and in the direction of the longitudinal axis of the piston, the spreading of the fuel is enhanced by a convexly curved portion of the chamber wall, this curved portion extending between the planes 55 and 6-6. A concave portion forms the bottom 7 of the combustion chamber, which bottom is joined to the convexly curved portion. At the top of the chamher is a concave portion 8 which extends from the convexly curved portion to the cylindrical neck 9 through which the combustion chamber communicates with the piston cylinder through the piston head, and through which the fuel is injected into the cylinder. Concave portion and neck 9 form a kind of a restriction of the upper end of the combustion chamber which produces a better swirling of the air Within the chamber. As shown in Figure 8, if neck 9 is omitted, the combustion chamber wall is extended by the continued outwardly curved portion 10. In horizontal cross-section, the combustion chamber can be in the shape of a circle or an ellipse.

In Figure 2, the combustion chamber is in the form of a cone. Again, chamber 1 is coaxial with piston 2 and cylinder 3, and opens through the piston head. The side wall 11 of chamber 1 is connected by a curved portion with the fiat bottom 13. The inclination of wall 11 can be reversed, and it has been found that the diameter 14 should preferably be from about 0.8 to 1.4 times the diameter 15 of the opening through the piston head. To enhance the spreading of the fuel in the direction of the longitudinal axis of the chamber, side wall 11 is so formed as to appear as a straight line in the cross-sectional view of Figure 2. However, side wall 11 can be convexly curved as shown in Figure l to enhance further the spreading of the fuel over a large surface of the chamber wall. In horizontal cross-section, the combustion chamber can appear as circular, elliptical or polygonal.

In Figure 3, the chamber 1 differs from that shown in Figure 2 by the shape of the chamber bottom. While in Figure 2, bottom 13 is flat, in Figure 3 the bottom 13a between curved portions 12 is in the shape of a cone with the apex thereof pointing to the interior of chamher 1. Thus the combustion chamber has a conical side wall 11 and a bottom in the form of a toms.

Figure 4 has a chamber 1 composed of two oppositely directed conical portions with their bases joined on the line 16. Here also the chamber 1 is coaxial with the longitudinal axis of the piston. Along the line 16, the Wall of the chamber is interrupted to form an irregular surface which causes the fuel film being applied to be momentarily separated from the chamber wall. This separated fuel mixes with the air swirl in the chamber and thus causes an atomizingof at least a part of this separated fuel.

When it is desired to apply the fuel to particular wall areas, such can be accomplished by the arrangement of the portions of the chamber wall. For example, the conical sections, instead of being coaxial, can be displaced with respect to one another as by having the two axes at an angle to each other, as in Figure 9, or by making the conical sections unsymmetrical with respect to each other, as in Figure 10. Combinations of the above are also possible.

The momentary separation of the film being applied to the wall, as disclosed in Figures 4, 9 and 10, can be further increased if step-like projections 17 are formed in the wall, as shown in Figures 6 and 7. These steps form an irregular wall surface with the separation of the fuel film occurring at the interruptions. The fuel spreading along the chamber wall is intercepted by the air swirl during the time it passes step 17 and then contacts the chamber wall. The secondary air swirls formed at these steps mixes with the fuel separated from the wall to atomize the fuel, which is very desirable with fuels having a high boiling point. Nozzle 4, through which the fuel is injected into chamber 1, is preferably mounted close to one of the steps 17. Fuel jets 4a have the direction of nozzle 4. Steps 17 are directed either parallel to or at an angle to the axis of chamber 1 and trans versely of the direction of the fuel jets and the direction of the air swirl.

The opening of the combustion chamber 1 through the piston head can be as heretofore stated by means of a neck 9. As shown in Figure 1, this can be a cylindrical neck. In Figures 5, ll, 12 and 13, the cylindrical opening is replaced by either a polygon 9a, Figure 13, or a circle 9d, Figure 11. If the opening is an equilateral triangle 9b, as in Figure 12, the fuel is injected from a nozzle 4 located in one corner of the triangle. When two valves 19 and 20, Figure 12, are provided for the cylinder, each of these valves is positioned over one of the other two corners of the triangle 9b. As shown in Figure 5, the opening 9c is elliptical with the major axis of the ellipse being aligned with the longitudinal axis of the nozzle 4.

In Figure 14, nozzle 4, instead of extending through a neck, is positioned to inject fuel through an auxiliary bore 21. This bore 21 as well as the neck 9' are inclined with respect to the longitudinal axis of the chamber.

Having now described the means by which the objects of the invention are obtained, I claim:

1. In a piston having a combustion chamber for receiving a film of fuel injected upon the wall of the chamber, said fuel being then vaporized and burned, the improvement comprising a downwardly directed generally conically shaped combustion chamber extending from the top surface of the piston into the piston body, said chamber having a convexly curved wall portion extending entirely around the longitudinal axis of said chamber for receiving and spreading said film of fuel.

2. In a piston as in claim 1,- further comprising a cylindrical neck portion forming an opening from said chamber to the surface of the piston head.

3. In a piston as in claim 1, further comprising a polygonal neck portion forming an opening from said chamber to the surface of the piston head.

4. In a piston as in claim 3, said neck portion being triangular and adapted to have fuel injected through one corner thereof,

5. In a piston as in claim 4, said triangular neckportion having its second and third corners positioned at the valve openings into a piston cylinder.

- 6. In a piston as in claim 1, further comprising an elliptical neck portion forming an opening from said chamberto the surface of the piston head.

7. In a piston as in claim 6, said elliptical neck portion having its major axis adapted to be aligned with the axis of a fuel nozzle.

8. In a piston as in claim 1, said combustion chamber having a concave wall portion and lying between the surface of said piston and said concave portion.

9. In a piston as in claim 1, said convexly curved wall portion being inclined downwardly from the upper edge of the chamber opening in the piston surface and joined to a concave bottom wall.

10. In a piston as in claim 1, further comprising a neck between said top surface of said piston and said convexly curved wall portion, said neck being parallel to the longitudinal axis of said piston.

11. In a piston as in claim 10, said neck forming a triangular opening in the top surface of said piston.

12. In an internal combustion engine having a cylinder and a piston, means for introducing air into said cylinder and simultaneously imparting to such air a swirling mo tion about the cylinder axis, said piston having a combustion chamber of smaller diameter than the cylinder and communicating therewith through a generally centrally located opening whereby the swirling air, when compressed, will be introduced into the combustion chhmber with an accelerated velocity of swirl, and means including an injection nozzle for injecting liquid fuel into said combustion chamber with said nozzle being oriented to atomize a minor portion of the fuel in said combustion chamber and to direct the major portion of the fuel in the direction of the air swirled through said opening and onto said wall portion, the improvement comprising a generally conically shaped combustion chamber having a convex wall portion extending entirely around the longitudinal axis of said chamber for receiving said major portion of said fuel.

13. In an. internal combustion engine as in claim 12, said opening being triangularly shaped.

14. In an internal combustion engine as in claim 13, said nozzle being oriented through a first corner of the triangular opening.

15. In an internal combustion engine as in claim 14, further comprising an intake and an exhaust valve for said cylinder with each valve being located, respectively, at a second and a third corner of said opening.

16. In an internal combustion engine as in claim 12, said opening being elliptically shaped.

l7.' In an internal combustion engine as in claim 16, said nozzle being aligned with the major axis of said elliptically shaped opening.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,570 Nallinger Dec. 23, 1952 2,718,882 Gerecke Sept. 27, 1955 2,803,229 Schwaiger Aug. 20, 1957 2,887,995 Stump May 26, 1959 FOREIGN PATENTS 643,351 Great Britain Sept. 20, 1950 789,423 Great Britain Jan. 22, 1958 1,067,634 France Jan. 27, 1954 1,078,961 France May 19, 1954