US2168528A - Exhaust passage of two-stroke internal combustion engines - Google Patents

Description

Aug. 8, 1939. KADENACY 2,168,528

EXHAUST PASSAGE OF TWO-STROKE INTERNAL COMBUSTION ENGINES Filed Oct. 25, 1935 ,fivenioz' 772. Kaela/v 30y M66 I "#14 f Patented Aug. 8, 1939 EXHAUST PASSAGE F TWO-STROKE IN- TERNAL COMBUSTION ENGINES Michel Kadenacy, Paris, France Application October 25, 1935, Serial No. 46,805 In Great Britain November 8, 1934 3 Claims.

This invention relates to two-stroke cycle internal' combustion engines wherein at least a substantial portion of the burnt gases leaves the cylinder at a speed much higher than that ob- 5 taining when a flow resulting from an adiabatic expansion only is involved, and in such a short interval of time that it is discharged as a mass leaving a depression behind it which is utilised in introducing a fresh charge into the cylinder by opening the inlet orifice with the required delay after the opening of the exhaust orifice to ensure that the burnt gases are then moving outwardly through the exhaust orifice or duct and that a suction effect is exerted at the inlet orifice as a consequence of the exit of the said mass.

The applicant has explained, for example in Patents numbered 2,102,559 issued December 14, 1937; 2,110,986 issued March 15, 1938 and 2,113,480 issued April 5, 1938, that he has found that in an internal combustion engine, the gases in the cylinder when exhaust opens behave as though they formed a resilient body, possessing ballistic energy.

When the exhaust orifice first commences to open there is a period of delay during which no appreciable movement of the static gases external to the exhaust orifice can be observed, and after this delay has elapsed the burnt gases issue as a mass at high velocity, and by passing through the exhaust orifice form a column moving rapidly in the direction of exhaust.

Thereafter this outward movement is reversed in direction, and a return of the gases towards the cylinder takes place.

When the burnt gases leave the cylinder as a mass in the manner stated above, they leave a depression behind them in the cylinder and in the exhaust duct close to the cylinder, the volume of which will depend upon the distance to which the mass of burnt gases travels away from the cylinder. Consequently, if the inlet is opened while the exhaust orifice is open and the burnt gases are moving outwardly through the exhaust orifice or duct, the charge will enter into a substantially void space and may, therefore, if desired be introduced by atmospheric pressure alone.

In this connection it should be noted that the mass exit may be considered to have commenced when the exhaust gases have acquired such a momentum in the direction of exhaust that if the inlet orifice is then opened they will continue to move in the direction of exhaust and will not leave the cylinder through the open inlet. This may, for example, be determined by means of records of pressures obtained at the inlet and exhaust ducts.

As, owing to mechanical limitations, the inlet orifice can be opened only progressively, and not instantaneously, it will be understood that it is 5 of advantage to commence the opening of the inlet orifice at an earlier instant of time than that at which the suction efiect is exerted thereat, so that when the suction effect is exerted, a sufficient area of inlet orifice is opened to .permit 10 optimum utilisation thereof.

But the return of the burnt gases, if it occurs too soon and while inlet and exhaust are still open, materially affects the charging. If at a certain speed, in a variable speed engine, the re- 15 turn coincides with the closure of inlet, which is a satisfactory condition, then at all lower speeds, the return will occur at an earlier crank angle.

This will tend to foul the charge and will also reduce the period of depression and the effect on 20 the torque will be to cause it to fall rapidly away from its optimum value.

Further in a fixed speed engine, if the exhaust pipe is changed for one having characteristics such that an earlier return of the burnt gases 00- 25 curs, this will have the same effect.

The object of the invention is to provide means in the exhaust passages of such engines whereby the effect of such an early return of the burnt gases before the closure of inlet is minimised, 3o always assuming exhaust to be open when this return occurs.

With this object in view the invention consists in providing means in the exhaust duct preferably close to the engine cylinder whereby a free out- 35 flow of the exhaust gases in the direction of exhaust is permitted and any return of the said gases tends to be by-passed into a chamber other than the engine cylinder.

In this way the torque of the engine is rendered 40 more stable under the varying conditions described above.

In establishing the position of such means relative to the engine cylinder it should be borne in mind that the burnt gases return from some zone along the exhaust pipe which may be determined by taking records at intervals along the exhaust pipe, by apparatus capable of revealing the directlon of motion, velocity and pressure of the gases during the exhaust period. It will be obvious that if the means according to the invention are situated further from the engine cylinder than the point from which this return occurs, they will be inoperative.

Preferably such means should be situated close to the cylinder, but a certain amount of latitude may be allowed within the limits defined above.

In a practical embodiment of such an arrangement the exhaust pipe terminates at its end connected "to the cylinder in an enlarged chamber preferably of bulbous form and the exhaust gases are fed past this chamber through a relatively short neck or nozzle, the outlet cross-section of which is small relative to the cross-section of the chamber at this point.

In a modification of such an embodiment a deflector body is mounted in the exhaust duct in such a way that it allows the passage of the explosition gases issuing from the neck or nozzle but opposes the return of gases into the cylinder through this nozzle, as described in Patent No. 2,110,986 and deflects any return of the explosion. gases into the said chamber.

As stated above, the device according to the invention is provided in order to counteract any objectionable effect of an early return of the burnt gases on the charging.

Further, an increase in speed of the engine, or a change in exhaust pipe may cause the return of the burnt gases to occur after exhaust closes, so that exhaust closes when the depression still exists in the exhaust duct. If in such an engine inlet is arranged to close before exhaust closes, this will cause a loss of charge from the cylinder by suction through the exhaust port during the period elapsing between inlet closure and exhaust closure. This again will be represented by a rapid drop in torque beyond the optimum point.

This objection may be avoided by closing exhaust at the same time as or before the closure of inlet.

An engine having such timing and provided with means according to the invention will be protected against the objectionable actions of an early return of the burnt gases at low speeds and a prolonged suction in the exhaust duct at high speeds, and it will also be protected against the disturbing effect of changes in the exhaust pipe.

The invention will now be described simply by way of example, and with reference to the accompanying drawing, in which:

Figure l is a cross sectional view through the cylinder of an opposed piston engine, the exhaust passage of which is provided with an example of a device according to the invention.

Figure 2 illustrates a modification of the device applied to the exhaust pipe in Figure 1.

In Figure 1 the invention is illustrated as applied to an opposed piston engine comprising a cylinder I, in which move two opposed pistons 2 and 3. The piston 2 controls the inlet ports 5 communicating through ducts 4 with a source of fresh air or gas, for example the external atmosphere, and the piston 3 controls the exhaust port 1 which discharges the burnt gases from the cylinder through the duct 6, the end of which situated adjacent the cylinder is provided with means in accordance with the invention.

With an engine of the kind illustrated it is well known that while retaining the piston control of the ports, inlet may be arranged to close before or after exhaust closes by suitably off-setting the cranks of the two pistons when assembling the gears.

According to the invention, the exhaust pipe 6 is enlarged at its end connected to or closely adjacent the cylinder to form a chamber 8 of bulbous shape, having on its side facing the exhaust pipe an annular wall 9 which in the example is shown as being curved inwards at its centre oriflce so as to give the chamber a toroidal shape, but which may be fiat as shown in Figure 2.

A short neck or nozzle I 0 is mounted or formed upon the exhaust port and extends coaxially into this charmber 8, while carrying the wall 9 of the latter, and the diameters of the chamber and nozzle on a plane including the outlet end of the nozzle are so proportioned that the cross sectional area of the chamber 8 at this point is great compared with that of the nozzle.

With the arrangement shown in Figure 1, when the burnt gases leave the cylinder and issue from the nozzle they leave behind them a depression which causes the chamber 8 to be evacuated. Upon the opening of inlet, the charge admitted into the cylinder reduces the depression existing therein, and this charge tends to follow the path of the burnt gases through the exhaust port and through the nozzle. On account of the suitable arrangement of the outlet end of the nozzle in the throat of the chamber, any portion of the charge which issues through the nozzle will have the minimum tendency to enter the chamber, so that the depression in the latter will tend to be maintained at a higher level than that in the cylinder. Consequently when the burnt gases return they will not only find an easier path of entry into the chamber on account of the larger area of the annular space surrounding the nozzle, but they will also tend to enter the chamber 8 in preference to the cylinder on account of the fact that a higher depression exists at this moment in the chamber.

The requirement to be borne in mind in selecting suitable proportions for the outlet area of the nozzle and the area of the annular space surrounding this outlet is that when the burnt gases return they should find a less restricted path through the annular space than through the nozzle.

In practice it has been found that a suitable relationship is obtained if the area of the annular space is twice that of the nozzle outlet.

In co-operation with the relative areas, the nozzle outlet should be so positioned that the issuing gases upon leaving the nozzle exert the maximum influence in evacuating the chamber 8. It will therefore be seen that the annular space should not be excessively great in proportion to the nozzle outlet area, and that the nozzle outlet should be suitably situated with respect to the outlet end of the chamber.

In establishing the position of the nozzle outlet relative to the chamber, it should also be noted that if the nozzle is extremely short then the chamber will become a simple expansion chamber while if the nozzle extends too far into the exhaust pipe it may prevent the entry of the returning burnt gases into the chamber.

A suitable arrangement is obtained when the outlet end of the nozzle is situated at or about the throat of the chamber 8, as indicated in the figure. In practice it is found that a little movement from this position does not reduce to any considerable extent the output of the engine, but that as the nozzle outlet is moved further from the throat of the chamber and nearer the cylinder, a point of instability is reached after which the torque drops suddenly to a lower value: thereafter further movement of the nozzle outlet in the same direction produces a further and progressive decrease in output.

If records are taken on the exhaust pipe of an engine in the manner indicated above, both with Gil and without the device according to the invention, it will be found that when the device is fitted the return of the gases is delayed and also that the peak of pressure accompanying such return is considerably reduced. It will also be found that the moment of outflow of the burnt gases remains substantially unafiected, so that the timing of inlet remains satisfactory and the duration of the suction into the cylinder is extended.

The device according to the invention may advantageously be combined with means which oppose the re-entry of the burnt gases through the neck or nozzle into the cylinder while permitting them to enter the chamber, as illustrated in Figure 2.

The arrangement illustrated in Figure 2 is similar to that illustrated in Figure 1 as regards the general form and arrangement of a nozzle I I delivering into a chamber l2, but in this embodiment the device described above is combined with deflecting means situated in the exhaust duct and adapted to permit the outflow of the burnt gases and to prevent their re-entry through the neck or nozzle into the cylinder by deflecting the returning gases into the chamber l2.

A deflector body l3 having the shape of two cones with their bases in contact is mounted in theexhaust pipe in alignment with the nozzle II and preferably close to the outlet end of the latter. This deflector body is advantageously so arranged that its surface l4 allows the passage of the explosion gases in the outflowing direction, while its surface [5 guides any return wave of the gases into the chamber, the wall of the chamber I2 around the deflector being suitably shaped for this purpose as indicated at It.

This deflector body is only illustrated by way of example and it will be understood that any other suitable deflecting means may be employed.

By the addition of the deflector body or the like a highly eflicient obstacle is presented to any return into the cylinder of explosion gases.

It should be noted that the action which creates the suction efi'ect occurring in engines according to the present invention originates in the cylinder and is propagated from the cylinder into the exhaust duct, in that this suction effect is caused by the exit of at least a substantial portion of the burnt gases from the cylinder at a speed greatly in excess of the speed obtaining when a flow resulting from an adiabatic expansion only is involved and in such a short interval of time that it is discharged as a mass. In carrying out the present invention the natural tendency of the burnt gases to project themselves from the cylinder as a mass should be facilitated and not opposed, that is to say the area of the exhaust oriflce available for the discharge of the burnt gases should be as large as possible and the interval of time in which the area required for this discharge of the burnt gases is made available should be as short as possible in order to obtain the most satisfactory results.

I claim: I

1. A two-stroke cycle internal combustion engine, wherein the burnt gases are discharged from thecylinder into an exhaust conduit subexhaust system for modifying the action of the said mass on the gases in the exhaust pipe, and the action of the return of the burnt gases upon the cylinder contents, the said means comprising a chamber other than the engine cylinder in open communication with the exhaust conduit at a point situated nearer the cylinder than the limit of outward travel of the burnt gases upon their mass exit from the cylinder, whereby upon the opening of the exhaust orifice for the discharge of the mass of burnt gases, the said mass is directed past the said communication during its outward motion, so that there is first an increase in pressure in the exhaust pipe adjacent the cylinder, which is transmitted through the gases contained in the exhaust pipe to the gases contained in said chamber, and thereafter a depression is formed in the cylinder and in the exhaust pipe adjacent the cylinder followed by a depression in the said chamber, and returnfng gases enter the said chamber, which is then at a lower pressure than the engine cylinder and the exhaust pipe adjacent'the engine cylinder.

2. A two-stroke cycle internal combustion engine wherein the burnt gases are discharged from the cylinder into an exhaust conduit substantially as a mass whereby the said mass moves outward and thereafter returns towards the cylinder from a point which may be within the said exhaust conduit, the said conduit providing a free passage for the burnt gases to the limit of outward travel of said mass, and wherein an inlet is opened for the introduction of fresh charge while the exhaust port is still open and when the said issuance of the burnt gases is in full progress and causes a suction effect to be exerted in the cylinder, having a chamber other than the engine cylinder in open communication with the exhaust conduit at a point situated nearer the cylinder than the limit of outward travel of the'burnt gases upon their mass exit from the cylinder and means forming a part of the said conduit whereby the said mass is directed past the said communication MICHEL KADENACY.

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