US2795215A

US2795215A - Internal combustion engines of the compression ignition liquid fuel injection type

Info

Publication number: US2795215A
Application number: US604210A
Authority: US
Inventors: Holt George Allen
Original assignee: Ricardo and Co Engineers 1927 Ltd
Current assignee: Ricardo PLC
Priority date: 1955-08-22
Filing date: 1956-08-15
Publication date: 1957-06-11
Anticipated expiration: 1974-06-11
Also published as: DE1017409B

Description

G. A. HOLT INTERNAL COMBUSTION ENGINES OF THE COMPRESSION IGNITION LIQUID FUEL INJECTION TYPE June 11, 1957 2,795,215

Filed Aug. 15, 1956 2 Sheets-Sheet 1 \NVENTOR (520202 A. Hour BY 3 M.

m ATTORNEY-Y June 11, 1957 c; A. HOLT 2,795,215

INTERNAL COMBUSTIUN ENGINEIS OF THE COMPRESSION IGNITION LIQUID FUEL INJECTION TYPE Filed Aug. 15, 1956 2 Sheets-Sheet 2 INVENTOR GEORGE. A. Hot-'1' BY 694 M v WM ATTORNEY-r United States PatentO INTERNAL COMBUSTION ENGINES OF THE COMPRESSION IGNITION LIQUID FUEL IN JECTION TYPE George Allen Holt, Shoreham-by-Sea, England, assignor to Ricardo & Co., Engineers (1927) Limited, Pall Mall, London, England Application August 15, 1956, Serial No. 604,210

Claims priority, application Great Britain August 22, 1955 14 Claims. (Cl. 123-32) This invention relates to internal combustion engines of the compression ignition liquid fuel injection type and of the kind including a combustion pocket, into which the fuel is injected, associated with the cylinder bore or each cylinder bore and communicating with its associated cylinder bore by way of a mouth in which is disposed a plug (hereinafter referred to as a hot plug) usually having limited heat conducting contact with the cooled adjacent walls and containing at least one transfer passage through which combustion air is forced into the pocket during each compression stroke and through which products of combustion and fuel and air in process of combustion flow from the pocket into the cylinder bore dur ing each working stroke.

In internal combustion engines of the kind referred to the form of the pocket and the disposition of the transferpassage or passages are generally such that the air forced into the pocket through the transfer passage is caused to have an organised rotation within the pocket about an axis, the fuel being injected into the rotating air charge, the rotation of which tends to cause distribution of the fuel in the body of air, and the invention is particularly applicable to internal combustion engines of the kind in question in which the pocket is of approximately spherical or similar generally globular form as described and shown for example in the specifications of United States Patents Nos. 2,003,311, 2,113,711 and United States patent application No. 539,212, filed Oct. 7, 1955 or is of flattened oval cross section in planes containing the axis about which the organised rotation takes place as described and shown for example in the specification of United States Patent No. 2,058,827.

In internal combustion engines of the kind referred to the hot plug is subject to high temperatures and thermal stresses which vary as a function of the load and, in order to resist failure, the qualities required in the material of which the plug is formed are, a high resistance to burning, a low modulus of elasticity, a low co-efficient of expansion, high thermal conductivity and high tensile strength and resistance to creep. While steel and cast iron having these qualities to a reasonably high degree are available it is found that under high load operation hot plugs made of both these materials are liable to cracking. Nimonic materials are also available which have the required qualities to as satisfactory degree and are less subject both to burning and cracking but such materials are expensive and difficult to work.

In most engines of the kind referred to the transfer passage or each such passage is so disposed in order to cause the desired organised rotation of the charge in the pocket. The necessary tangential disposition of the passage creates an acute angle formation in the hot plug at each end of the passage and experience indicates that in the case of engines of the kind referred to having combustion pockets of approximately spherical or similar globular form and a single transfer passage cracks are particularly liable to be initiated at either of these acute Patented June 11, 1957 angle edges of the passage while in the case of engines having combustion pockets of the flattened oval cross section mentioned above and two transfer passages, cracks extending between the passages are particularly apt to occur. It is not thought that the cracking is due to combustion pressures or to high static thermal stresses under high load running conditions but to fatigue produced by thermal stress changes resulting from repeated engine load changes. Thus, during operation, considerable temperature gradients exist between the high temperature part of the plug immediately surrounding the transfer passage or passages and, where two passages are provided, lying between these passages due to the burning gases passing at high velocity through such passage or passages, and the cooler outer circumferential parts of the plug, these temperature gradients depending on and vary with variations in the'engine load. The stresses resulting from these temperature gradients have a complicated pattern due to the shape of the hot plug, the interference fit usually provided between an external circumferential flange on the plug and the surrounding ice ' 1 cooled wall in order to support and locate the plug, the

usually asymmetrical disposition of the transfer passage or passages in the plug, and the interference of various parts of the plug with the expansion and contraction of other parts. Moreover the presence of fluctuating thermal stresses in the surface layers of the material exposed to the combustion process, although confined to such surface layers can produce high local thermal stress concentrations at the acute angle edges referred to above and may thus be a contributory factor in initiating the cracks mentioned. In this connection it can be assumed that the greatest heat flow occurs at and adjacentto the surface of the transfer passage or passages, the resultantexpansion being resisted by the comparatively rigid cooler surrounding part of the plug, with the result that the material immediately surrounding the transfer passage,

and between the passages when two such passages are.

provided, is subject to high compressive stresses and plastic deformation of this material will occur if the compression yield point of the material at the temperature attained is exceeded. This plastic flow will allow relaxation of the stresses setup under load running conditions, but it causes corresponding tensile stresses to be set up when the plug cools down. These tensile stresses are limited to the value of the hot yield strength of the material in compression and therefore may not be suflicient in themselves to initiate the cracks referred to, but their repetition, due to load changes during operation and stopping and re-starting of the engine is thought to lead ultimately to fatigue failures represented by the cracks.

Experience shows that the tendency for the cracks at the acute angle edges to occur can be reduced, as would be expected, by providing each of these with a radius but this tends to depreciate engine performance if the radius is substantial and moreover, does not provide a solution of the problem for very high output conditions.

In an internal combustion engine of the kind referred to according to the present invention there is provided in the hot plug at least one slit extending from the circumferential portion thereof into the body of the plug and serving to reduce thermal stresses in the plug due to thermal expansions and/ or contractions. Usually a single slit only will be provided and in the case of a plug having a single transfer passage this slit preferably extends from the circumferential portion of the plug into the transfer passage so that its inner end extends longitudinally of the latter. Thus in this arrangement, which is particularly applicable to engines of the kind having an approximately spherical or like globular combustion pocket mentioned above the inner end of the slit opens in to the transfer 3 passage to form therewith a slot resembling in general form a keyhole slot; Moreover in such an arrangement the slit preferably lies in a plane containing also the longitudinal axis of the transfer passage, that is to say; the imaginary line extending along the centre of the transfer passage. Since in many cases the longitudinal axis of the transfer passage lies in a plane which also contains the axis of the plug, that is to say the axis about which the outer surface of the plug is a figure of. revolution,'the slit will thus in many cases lie in the plane which is coramon to the axis of the plug and the longitudinal axis of the transfer passage. Where two transfer passages are provided a similar slit might extend into each of them.

With such an arrangement where, due to the inclinations of the transfer passage or each transfer passagethe sides thereof terminate at the mouth of the passage in acute angled edges as above mentioned, the inner endof the slit preferably opens through one of these edges, thus tending torelieve to a high degree-the thermalstresses,

which hitherto have caused cracks to be initiated in these edges.

Alternatively where the invention is applied to an en-; gine of the kind having a combustion pocket of thefiat tened oval cross section mentioned, the slit may extend approximately radially from the circumference of the plugto a point which may be adjacent to the centre of the plug, or in the case of a plug having two transfer passages, may be in the neighbourhood of the bar of metal between the transfer passages. With an internalcombustion according to the present invention during the initial running under full or heavy load conditions, the slit will tend to become narrower due to the circumferential thermal expansion of the plug flange in the restraining bore of the. recess in the cylinder head. It may become permanently strained in this running position as the result of the thermal expansion stresses exceeding the reduced yield strength of the high temperature zones of the plug material. On cooling and contracting, however, .the flange of the plug may be 'a slack thin the recess and the slit may become appreciably and permauentlynarrower under cold conditions, especially at its outer end where it opens through the outer circumferential part of the plug, but also to a lesser degree at its inner end where, as mentioned, in many cases it opens into the transfer passage. During subsequent running of the, engine the slit will open and close with varying runningconditions while the fit of the circumferential flange or other circumferential locating part of the plug in the cooledsurround:

ing wall will vary, thus relieving to a considerable degree the thermal stresses which would otherwise be set up.

Two examples of the invention 'are shown in the accompanying drawings, in which Figure 1 is a cross section through the upper part of the cylinder and the cylinder head of one form of engine according to the invention, the cross section being taken in the plane containing the axis of the combustion pocket, the longitudinal axis of the transfer passage 'anclthe axis of the cylinder,

Figure 2 is a cross section on a large scale of a form of hot plug hitherto used in such engines showing where cracks have tended to occur,

Figure 3 is an underneath plan view of the form of plug shown in Figure 2,

Figure 4 is an underneath plan view on an enlarged scale of the hot plug according to the invention embodied in the construction shown in Figure 1 prior to operation of the engine,

Figure 5 is a similar view to Figure 4, showing the form which such hot plug tendsto take when cold after the engine has been inoperation for some appreciable period,

Figure6 is a similar view to Figure .1 of another form of the invention but taken in the broken plane indicated by the line 6-6 in Figure 9,

Figures 7 and 8 are similar views to Figures 2 and 3 of one form of hot plug as hitherto used in such engines and Figures 9 and 10 are similar views to Figures 4 and 5 of the hot plug embodied in the form of the invention shown in Figure 6.

in the construction shown in Figure 1 the assembly comprises a cylinder block 1 containing a number of sleeves, one of which is shown at 2,. constituting the cylinders, and a cylinder head 3 provided with the usual inlet and exhaust ports controlled by poppet valves in known manner, the ports and valves not appearing in the cross section shown but being of well known form constituting no part of the present invention.

Formed in the cylinder head is a combustion pocket 4 also of known form, having a generally cylindrical mouth which overlaps the bore of the cylinder 2 so as to communicate therewith. The pocket 4 has an approximately hemispherical upper end 5 with which communicates a bore 6 constituting a housing for a fuel injection nozzle 7.

Disposed, in amanner known in itself,in the cylindrical mouth of the pocket 4 is a hot plug 8 according to the invention the outer surface of which is of generally cylindricalform and spaced from the wall of the month except for a flange 9 at its lower end which is located within and makes contact with the surface of an annular recess or enlargement at the extreme lower end of the mouth as is usual in engines of the kind in question.

The hot plug has an approximately hemispherical inner surface 10 providing with the end 5 of the pocket a sub stantially spherical combustion pocket which communicates with the cylinder bore by way of a transfer passage 11 formed in the plug and so disposed that the air charge forced therethrough during each compression stroke of the engine will be caused to rotate within the combustion pocket about an approximately horizontal axis normal to the plane in which lie both the axis of the pocket (that is to say the vertical axis about which its surface is a surface of revolution) and the axis of the transfer passage (that is to say the line which may be regarded as lying in the centre of the stream of gas flowing through the transfer passage).

As so far described the parts of the assembly are of normal known form. If the assembly were entirely of such normal known form the plug 8 would be constructed as shown for example in Figures 2 and 3 and experience has shown that when an engine embodying such a hot plug has been in use for some time cracks are apt to do vclope where indicated at 12 and 13.

In the example. of the present invention shown, however, the hot plug is of the form shown in Figures 1 and 4, that is to say includes a slit 14 extending through the plug from the side of the tnansfcr passage 11 remote from the cylinder bore to and through the periphery of the plug so that its inner endextends through the inner acute angled edge 15 while its lower edge lies almost completely over part of the usual gasket between the cylinder block and cylinder head.

The initial width of the slit 14 if the plug be assumed to have an external diameter of about 1.25 inches or 1.5 inches might be about 0.04 inch.

The hot plug may, as stated, initially have such dimensions that the external circumferential flange 9 makes an interference fit with the .recess in which it lies, as is the present common practice, sothat in effect the flange 9 would be sprung into the recess after the manner of a spring ring. After heavy load running, however, it has been found that the slit 14 may become appreciably and permanently narrower and take the form indicated in Figure 5.

In the second example of the invention, shown in Figures 6, 9 and 10, the assembly comprises a cylinder block 16 :and head 17, the block having sleeves therein, one of which is shown at 18, and the head having inlet and. exhaust ports and passages all generally as in the construe tion shown in Figure 1. In the construction shown in Figures 6, 9 and 10 however, the cylinder head is formed with a pocket of different from from the pocket in the construction shown in Figure 1. The pocket 20 has a general-1y cylindrical mouth portion 21 and an upper end portion 22 of circular cross section about the axis of the cylindrical mouth portion (hereinafter referred to as the axis of the pocket) and of the cross section shown in planes containing such axis. The mouth of the pocket overlaps the cylinder bore and has disposed therein a hot plug 22 which, as with the plug in the construction shown in Figure 1 is spaced from the surface of the mouth of the pocket except for circumferential flange 23 at the lower end of the plug which makes contact with a circumferential recess or enlargement in the lower end of the mouth of the pocket.

The normal form of plug as at present used in engines of the kind shown in Figure 6 is as shown in Figures 7 and 8 with two

transfer passages

24 and 25 passing therethrough and it has been found that with such construction a crack tends to develope between the two passages as indicated at 26.

'In the construction according to the invention shown in Figures 6, 9 and 10 a modified form of plug is employed which is similar in general form to the plug shown in Figures 7 and 8 but has formed therein a radial slit 27 extending from a small diameter cylindrical hole 28 at its centre to a point on its circumference remote from the cylinder bore, as shown in Figure 6.

In this construction also the flange 23 may be a press fit in the recess in which it lies when the plug is first assembled in the cylinder head and it is found that after load running the slit may have been appreciably and permanently reduced in width in the manner indicated in Figure 10.

The initial width of the slit 27 in a plug having an external diameter of about 1.25 to 1.5 inches might be about 0.04 inch.

A fuel injector 29 is disposed in the usual position for engines of the kind to which the invention is shown applied in Figure 6.

What I claim as my invention and desire to secure by Letters Patent is:

1. An internal combustion engine of the compression ignition type including in combination a cylinder, a cylinder head together providing a combustion pocket communicating with the bore of the cylinder by way of a mouth, means for injecting fuel into the combustion pocket, and a plug disposed in the said mouth and containing at least one transfer passage through which combustion air is forced into the pocket during each compression stroke in the said cylinder and through which products of combustion and fuel and air in process of combustion flow from the pocket into the cylinder bore during each working stroke, the plug being provided with at least one slit extending from its circumferential portion into the body of the plug and serving to reduce thermal stresses in the plug due to thermal expansion and construction.

2. An internal combustion engine as claimed in claim 1, in which the plug has a single transfer passage and in which the slit extends from the circumferential portion of the plug into the transfer passage with the inner end of the slit extending longitudinally of said transfer pas- 8883a 3. An internal combustion engine as claimed in claim 2, in which the mean plane in which the slit lies contains or lies approximately parallel and adjacent to the longitudinal axis of the transfer passage.

4. An internal combustion engine as claimed in claim 3, in which the longitudinal axis of the transfer passage lies in a plane containing also the axis of the plug and the slit also lies in said plane.

5. An internal combustion engine as claimed in claim 4, in which the slit extends along the side of the transfer passage which terminates at the mouth of such passage in a lip formed where such side of the transfer passage meets the adjacent end surface of the ping at an acute angle.

6. An internal combustion engine as claimed in claim 3, in which the slit extends along the side of the transfer passage which terminates at the mouth of such passage in a lip formed where such side of the transfer passage meets the adjacent end surface of the plug at an acute angle.

7. An internal combustion engine as claimed in claim 1, in which the plug has two transfer passages both displaced radially from the axis of the plug and the slit extends from approximately the axis of the plug to and through the circumferential portion thereof at a point circumferentially displaced from the transfer passages.

8. A hot plug for an internal combustion engine of the compression ignition type including a cylinder, a cylinder head, together providing a combustion pocket the mouth of which communicates with the cylinder bore and contains a plug, said hot plug having at least one transfer passage therein and at least one slit extending from the circumferential surface of the plug into the body thereof.

9. A hot plug as claimed in claim 8 having a single transfer passage and in which the slit extends into the transfer passage with its inner end extending longitudinally of such transfer passage.

10. A hot plug as claimed in claim 9, in which the slit lies in a plane which lies approximately parallel and adja cent to the longitudinal axis of the transfer passage.

11. A hot plug as claimed in claim 10, in which the longitudinal axis of the transfer passage in the plug and the slit both lie in a plane which also contains the axis of the plug.

12. A hot plug as claimed in claim 11, in which the inner end of the slit extends along that side of the transfer passage which terminates at the mouth of the passage in a lip formed where said side of the transfer passage meets the inner surface of the plug at an acute angle.

13. A hot plug as claimed in claim 10, in which the inner end of the slit extends along that side of the transfer passage which terminates at the mouth of the passage in a lip formed where said side of the transfer passage meets the inner surface of the plug at an acute angle.

14. A hot plug as claimed in claim 8, in which the plug has two transfer passages displaced radially from the axis of the plug and the slit extends from approximately the axis of the plug to and through its circumference at a point angularly displaced from the passages about the plug axis.

No references cited.