US2617400A

US2617400A - Combustion chamber of internal-combustion engines

Info

Publication number: US2617400A
Application number: US76588A
Authority: US
Inventors: John H Weaving
Original assignee: Austin Motor Co Ltd
Current assignee: Austin Motor Co Ltd
Priority date: 1948-02-20
Filing date: 1949-02-15
Publication date: 1952-11-11
Anticipated expiration: 1969-11-11

Description

NOV. 1 1, 1952 WEAVING 2,617.400

COMBUSTION CHAMBER OF INTERNAL-COMBUSTION ENGINES Filed Feb. 15, 1949 2 SHEET$SHEET 1 INVENTOR J. H. WEAVING AT TORNEY Nov. 11, 1952 J. H. WEAVING 7,

COMBUSTION CHAMBER OF INTERNAL-COMBUSTION ENGINES Filed Feb. 15, 1949 2 SHEETS-SHEET 2 v IN VEN TOR.

JOHN H; WEAVING Patented Nov. 11, 1952 COMBUSTION CHAMBER OF INTERNAL- COMBUSTION ENGINES John H. Weaving, Moseley, Birmingham, England, assignor to The Austin Motor Company Limited, Northfield, Birmingham, England Application February 15, 1949, Serial No. 76,588 In Great Britain February 20, 1948 1 Claim. 1

The. invention relates to the suppressing or minimizing of detonation, prevalent notably in O. H. V. engines of high specific output, and in particular to the type of combustion chamber which derives its necessary turbulence mainly by a directional influence on the influx of the mixture from the inlet valve.

In such a case, it has been found that this turbulence persists through the compression stroke. This directional turbulence, which we will term induced turbulence, has a great influence on the rate of flame travel, and experiments show that the flame travel against the stream of directional turbulence towards the inlet valve is considerably less than the rate of flame travel in the same direction as that of the turbulent flow, which, in the type of head considered, is usually in the direction of the exhaust valve.

It is appreciated that temperature gradient and the composition of the products of combustion also have an eflect on the flame velocity, but this is automatically taken into account by the fact that the velocity of flame propagation is measured experimentally in the manner to be described below.

It is generally recognised that detonation is caused by the last portion of the charge to be burned being compressed by the expansion of the already burnt gases to such a degree that the temperature rises to a point at which combustion is virtually spontaneous, thus causing the characteristic knock.

In this invention, detonation is suppressed by the avoiding of any pockets of unburnt gas being left for late burning in the combustion processes, and in the combustion chamber to be described, the ideal situation is for burning to be completed at the major part of the combustion chamber remote from the sparking plug simultaneously.

To accomplish this, the invention defines the major part of the periphery remote from the combustion chamber as the two most remote portions of the combustion chamber from the sparking plug as follows:

It has previously been assumed that the best method-of minimizing detonation is to move the sparking plug towards the exhaust, exhaust valve or hot portion of the combustion chamber.

The invention comprises a combustion chamber. for an overhead-valve engine with the sparking plug so placed that the flame front shall reach the two portions of the combustion chamber most remote from the sparking plug,

namely, in the vicinity of the exhaust and inlet 2 valves, at the same instance of time, or as near to this ideal as possible.

Thus, from the phenomenon discovered, the following relationship is given for the said combustion chamber:

Where turbulence takes place in a general direction from the inlet valve past the sparking plug toward the exhaust valve, and

V1:Ve1ocity of the flame front in direction of induced turbulence Vzzvelocity of the flame front against direction of induced turbulence DizDistance to farthest point from plug in the direction of the exhaust valve Dz Distance to farthest point from plug in the direction of the inlet valve This entails the measurement of flame velocity in at least two principal directions. This can be performed comparatively easily, by means of ionization gaps, which consist of two electrodes insulated from each other but in close proximity (one electrode can be the combustion chamber itself). The gap remains non-conducting until the arrival of the flame front initiated from the sparking plug. When the flame front arrives, the gas becomes conducting, and by connecting the electrodes of the gap into a simple electronic circuit, a pulse may be recorded on a cathode ray oscilloscope. A similar pulse is also recordedwhen the spark occurs in the sparking plug, also" by means of a simple electronic device of known construction.

The position in respect of time or crank angle cal considerations, such as valves, ports, water;

jackets, etc. The plug is then inserted in a trial position and ionization gap electrodes are placed at the two remote positions of the combustion chamber, and the procedure described above is applied.

In general, the condition as laid down in the above relationship will not be fulfilled, but it can be obtained (a) By changing the position of the plug to a more favorable position on the locus,

(b) By shortening or lengthening of any of the principal paths of flame propagation by modifying the combustion chamber.

Whereas the condition laid down will apply to a particular engine speed, very closely similar conditions will be obtained for other speeds within a wide normal operating range, and the average velocity ratio obtained from a number of trials at different normal engine speeds would determine the position of the plug according to the equation.

Figure 1 is a diagrammatic plan view showing of a combustion chamber showing the inlet and exhaust valves according to the present invention.

Figure 2 is a diagrammatic plan view showin the relation of the combustion chamber to the piston and cylinder.

Figure 3 is a sectional view taken on line 33 of Figure 2.

A combustion chamber having the above described characteristics is illustrated diagrammatically in the accompanying drawing, in which a represents the shape of the combustion chamher, in inverted plan, b is the inlet port, is the exhaust port and d is the opening in which the sparking plug is fitted. A point e on the outline a is the point which is farthest from the sparking plug opening (1 in the direction of the exhaust c, and f is the point on said outline which is farthest from d in the direction of the inlet port 12. The line 9, g, is the centre line of the engine cylinder at right angles to the common centre line of the ports I), c. The outline of the cylinder bore is represented by the dot-dash line It. The inlet passage to the inlet port b is designated by reference character 2' as shown in Figs. 2 and 3.

The induced turbulence which is derived mainly by a directional influence on the influx of the mixture entering the combustion chamber through the inlet port b, and which persists throughout the compression stroke, is in the general direction of the exhaust port 0.

V1 represents the velocity of the flame front toward the point e, that is in the same general direction as the induced turbulence or toward the exhaust c, and V2 represents the flame front velocity towards the point f against the induced turbulence.

D1 is the distance of the point e from the sparking plug and D2 is the distance of point from said plug.

The disposition of the sparking plug opening at is such that D1:V1: 2D22V2, or nearly so. Thus the bias of the sparking plug is towards the inlet port, this being the opposite to the generally adopted practice where the bias, if any, is towards the exhaust valve.

In a particular application of the invention, the induced swirl is obtained by a combination of port guidance and combustion chamber shape, such that the latter causes the inlet valve to discharge substantially on approximately half of its periphery only and in a direction tangential to an imaginary cylinder concentric with a cylinder bore but of smaller diameter. This offsetting of the induced stream of inlet charge from the center of the cylinder bore induces a rotational turbulence which persists throughout the combustion stroke and is forced by the piston into the combustion chamber, thus giving the required turbulence for rapid burning and orderly turbulence, in contra-distinction to random turbulence. This directional turbulence we have termed above induced turbulence.

This orderly turbulence has a stabilizing eifect on the velocity of flame propagation enabling the plug position to be placed in accordance with the invention after one or two experimental trials, as described above, so that the relationship nfi is obtained.

The invention thus defines a combustion chamber in which rotary turbulence is induced, such that it gives a directional turbulence relative to the sparking plug, this turbulence being induced by means of suitable port inclination and valve masking due to the proximity of the combustion chamber wall, or alternatively on the valve itself, and such that the sparking plug is placed in accordance with the equation an V1 V2 the V1 and V2 being found as the best experiment compromise over this speed range of the engine.

Having fully described my invention, what I claim and desire to secure by Letters Patent is:

A combustion chamber of an internal combustion engine, in which the relationship of the sparking plug to the inlet and exhaust valves is represented by:

and where turbulence takes place in a general direction from the inlet valve and past the sparking plug toward the exhaust valve.

JOHN H. WEAVING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,892,838 Horning Jan. 3, 1933 2,151,428 Janeway Mar. 21, 1939 2,202,246 Dake May 28, 1940 2,457,652 Fisher Dec. 28, 1948 2,481,890 Toews Sept. 13, 1949 OTHER REFERENCES Automotive Industries, Mar. 9, 1935, p. 354. Air Service Information Circular, vol. V, #401, Feb. 15, 1923, p. 1.