US2131957A - Charging and scavenging of the cylinders of two-stroke internal combustion engines - Google Patents

Description

Oct. 4, 1938. M. KADENACY CHARGING AND SCAVENGING OF THE CYLINDERS OF TWO-STROKE INTERNAL COMBUSTION ENGINES Filed Oct. 25, 1955 Patented Oct. 4, 1938 UNITED STATES CHARGING AND SCAVENGING 0F CYL- INDERS OF TWO-STROKE INTERNAL COM- BUSTION ENGINES Michel Kadenacy, Paris, France Application October 25, 1935, Serial No. 46,804 In Great Britain November 3, 1934 10 Claims.

This invention relates to two-stroke cycle internal combustion engines wherein the burnt gases leave the cylinder at a speed higher than that obtaining when adiabatic action only is involved and in such a short time interval that they are discharged wholly or substantially wholly from the cylinder into the exhaust system as a mass leading behind them a high depression which may reach a complete vacuum.

In such an internal combustion engine when the exhaust port opens there is first a period of delay during which no appreciable movement takes place in the gaseous medium external to the exhaust orifice and after this delay has elapsed the burnt gases issue from the cylinder as a mass at high velocity and leave a profound depression behind them in the cylinder and also in the exhaust pipe close to the cylinder. A reversal in direction of motion of the burnt gases then. follows, whereupon the depression is first destroyed and then the pressure rises above atmospheric pressure in the exhaust duct adjacent the cylinder and in the cylinder itself, if the exhaust orifice is then open.

The occurrence of the above mentioned depression, its duration and its cessation can be determined by known means, and if an inlet orifice is opened in the cylinder after the exhaust orifice opens, but with only the required delay to ensure that the mass of burnt gases is then moving outwardly through the exhaust orifice or duct and causes a suction to be exerted at the inlet orifice as a consequence of said mass exit from the cylinder, a fresh charge may be admitted through the said inlet orifice by atmospheric pressure only.

Now the interval elapsing between the commencement of opening of exhaust and the reversal in direction of motion 'of the burnt gases subsequent to their mass exit from the cylinder is a duration of time which is largely independent of the engine speed; consequently this interval will extend over a larger crank angle at high engine speeds than at low engine speeds.

If the reversal in direction of motion of the burnt gases occurs too soon and while the exhaust orifice is still open, burnt gases may re-enter the cylinder, and if the inlet orifice is then also open some of the fresh charge may be forced out of the cylinder. On the other hand, if the inlet orifice closes while a depression still exists in the exhaust duct and the exhaust port is then still open, this may cause some of the fresh charge to be drawn out of the cylinder into the exhaust system.

The former of these objectionable actions is most likely to be exerted at low speeds and the latter at high speeds. According to the present invention a quantity of fresh gases is admitted or introduced into the exhaust system during the exhaust period. These fresh gases may serve for delaying the return of the burnt gases and obstructing their re-entry into the cylinder, or for combatting any loss of charge due to a prolonged suction in the exhaust duct, and in this way the charging of the cylinder will be improved.

In order to satisfy the requirement of the invention the fresh gases must be introduced or admitted into the exhaust system while the exhaust orifice is still open and at a point in the exhaust duct situated nearer the cylinder than the point in this duct from which the return of the burnt gases occurs, andv the introduction or admission must occur after the mass exit of the burnt gases from the cylinder and before their return into the latter. 1

If the fresh gases are admitted by atmospheric pressure, then this admission can only be made while there is still a depressionin the exhaust duct, and the means employed for this purpose must be such that they establish communication between the interior of the exhaust duct and the source of fresh gases only when this depression exists in the exhaust pipe.

If the introduction is effected under a pressure higher than atmospheric, there will normally be no advantage in commencing this introduction before the mass exit of the burnt gases occurs as this will simply increase the pressure required for effecting the introduction; and there will be no advantage in continuing it after the closure of the exhaust orifice as it will then cease to be of use.

In order to obtain an advantage from this introduction under pressure an economy must be combatting or delaying the return of the burnt.

gases, it will thus not be advantageous to effect the injection of fresh gases into the exhaust duct at moments when this high depression exists in the working chamber and inthe exhaust duct.

The most advantageous moment for effecting this injection will then be, immediately before the said return wave occurs, so as to oppose and even prevent the returning burnt gases from reentering the engine cylinder and pushing out the new charge admitted to the latter.

The quantity and volume of these injected gases, in order to avoid any waste of energy must, in general, be introduced not sooner than the moment when the return wave occurs and must not continue later than the closure of the exhaust orifice.

In this way the duration of the suction exerted proving the charging of the engine.

If the injection or admission of fresh gases into the exhaust duct is eflected at bottom dead centre, this will generally be found satisfactory for the purposes above stated. Most usually it will commence shortly after bottom dead centre and it is obvious that it is useless to continue this injection or admission after the closure of the exhaust orifice.

The introduction or admission of fresh gases may be so disposed relative to the closure of exhaust and the occurrence of the return of the burnt gases that the latter may overcome the inertia of the fresh gases and may even force them into the cylinder. The effect of this will be to force fresh gases into the cylinder and not burnt gases.

In the case when the exhaust orifice remains open longer than the inlet orifice, this effect may cause the final charge contained in the working charge of the engine, in which case separate inlet orifices on the cylinder may be dispensed with.

One embodiment of the invention in which a charge is introduced into the exhaust pipe of an engine under pressure is illustrated in the accompanying drawing, in which Figure l is a cross section through an engine provided with means for carrying the inventon into effect.

Figure 2 is a timing diagram applicable to such an engine.

The drawing shows an engine comprising a cylinder block I mounted on a crank case 2, and in which moves a piston 3 driven by the connecting rod 4 from the crank shaft 5.

The cylinder is provided with piston operated inlet and exhaust ports 6 and 1 and in the example chosen, the inlet ports 6 communicate with the atmosphere and open very shortly after the exhaust ports open; the interval between exhaust opening and inlet opening being established so as to ensure that inlet opens with the required delay to ensure that the burnt gases are then moving outwardly through the exhaust port or duct and cause a suction to be exerted at the said inlet.

The skirt of the piston comprises a further port 8 co-operating with the ports 6 when the piston rises in order to permit a charge of air to be drawn into the crank case.

The crank case also communicates through a duct 9 in the cylinder block with an injector nozzle l extending within the exhaust duct in the direction of outlet and situated close to the exhaust port. This duct 9 is controlled by suitable means such as the rotary valve H suitably actuated so as to open and close at required moments during the cycle of operations of the engine.

On the firing stroke the piston 3 opens the exhaust port I and then the inlet port 6 for the admission of the working charge, while compressing the air which has been drawn into the crank case 2 during the preceding upward stroke of the piston 3.

Shortly after bottom dead center, the rotary valve I l opens and puts the crank case into communication with the nozzle 10 so that a compressed charge of air from the crank case is injected through this nozzle into the exhaust duct.

The period during which the crank case charge is transferred through the nozzle l0 into the exhaust duct is shown in Figure 2, in which EO and EC represent exhaust opening and closure, A0 and AC represent the opening and closing of the inlet on the cylinder through which the fresh charge is introduced into the latter and C0 and CC represent the commencement and termination of the injection into the exhaust duct. It will be seen thatthis injection commences shortly after bottom dead centre and terminates at or about the closure of the exhaust port.

As already mentioned the injection or admission of fresh gases into the exhaust duct may be so applied that these gases serve to charge the cylinder through the exhaust duct. Y

For example, the exhaust duct may comprise orifices situated close to the cylinder and controlled by automatic one way valves adapted to open into the exhaust duct when a high depression exists therein as a consequence of the mass exit of the burnt gases from the cylinder, and to close when this depression is destroyed. I

Such valves may, for example, be formed of very light blade springs controlling orifices opening to the atmosphere. v

If these valves or the like and the orifices they control are suitably designed, the high depression left in the exhaust duct when the burnt gases are discharged as a mass from the cylinder, will cause the valves to open and admit air into the exhaust duct. When the return occurs, these valves will automatically re-close and the fresh air enclosed in the exhaust duct will be driven into the cylinder by the return wave and thereby charge the latter through the exhaust port. In this case a separate admission port may become unnecessary,

It should be clearly understood that the fresh gases admitted or introduced into the exhaust duct may be utilized a simply for improving the charging of the engine by opposing the re-entry of the burnt gases into the working chamber or additionally for providing all 01' apart of the fresh charge supplied to the cylinder, whether the charge is admitted by atmospheric pressure or injected under compression.

It should be noted that the action which creates the suction effect 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 adiabatic action 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 orifice 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:

1. In a two-stroke cycle internal combustion engine of the kind described the combination with a cylinder having an inlet port and an exhaust port, an exhaust duct leading from the exhaust port and means for opening inlet after exhaust opens but only with the required delay to ensure that the burnt gases are then moving outwardly through the exhaust port and cause a suction to be exerted at inlet as a consequence of their mass exit from the cylinder, of means for introducing a quantity of fresh gases, into the exhaust duct under pressure duringthe exhaust period of the engine, said introduction commencing immediately before a return wave of the exhaust gases occurs. I

2. In a two-stroke cycle internal combustion engine of the kind described, the combination .with a cylinder having an exhaust port and an exhaust duct leading from said exhaust port, of an orifice on said duct intermediate its length, a source of compressed gaseous fluid, distribution means connecting said source of fluid to said orifice and means for controlling said distribution, means for introducing a compressed charge of gaseous fluid into the exhaust duct commencing at or about bottom dead centre and terminating not later than the closure of the exhaust port of the engine.

3. In a two-stroke cycle internal combustion engine, a cylinder,a piston or pistons in said cylinder, inlet and exhaust ports on said cylinder, an exhaust duct leading from said exhaust port, means which may comprise the said piston or pistons, for controlling said ports, said inlet port being opened after the exhaust port opens but only with the required delay to ensure that the burnt gases are then moving outwardly through the exhaust port or duct as a conse quence of their mass exit from the cylinder, a source of compressed gaseous fluid, an orifice in the exhaust duct close to the engine cylinder and communicating with a nozzle or nozzles extending within the exhaust duct and with said sourceof fluid and means for controlling communication between the said source and the said nozzle or nozzles in such a manner that the said communication will be opened during the exhaust period of the engine after the exhaust gases have issued from the cylinder and before these gases return to the cylinder.

4. In a two-stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port, and an exhaust duct leading from said exhaust port, of an orifice on said duct intermediate its length, a tubular element within said exhaust duct communicating with said orifice and extending in the direction of exhaust, a source of compressed gaseous fluid, distribution means connecting said source of fluid to said orifice and tubular element, and means for controlling said distribution means for introducing a working charge of gaseous fluid into the exhaust duct in the direction of exhaust commencing at or about bottom dead centre and terminating not later than the closure of the exhaust port of the engine.

5. In a two stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port, an exhaust duct'leading from the exhaust port, of means for introducing a quantity of fresh gases into the exhaust system while the exhaust port is still open and at a point in the exhaust duct situated nearer the cylinder than the point in this duct from which the burnt gases return after their mass exit from the cylinder, the said introduction being effected after the mass exit of the burnt gases from the cylinder and before the return of these gases to the cylinder.

6. In a two stroke cycle internal combustion the exhaust duct through said orifice after the mass exit of the burnt gases from the cylinder and before the return of these gases to the cylinder.

7. In a two stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port and an exhaust duct leading from said exhaust port, and an orifice on said duct situated nearer the cylinder than the limit of outward travel of the burnt gases upon their mass exit from the cylinder, a a

tubular element within said exhaust duct communicating with said orifice and extending in the direction of exhaust, a source of compressed gaseous fluid, distribution means connecting I source of fluid to said orifice d tubular element, and means for controlling? said distribution means for introducing com ressed gaseous fluid into the exhaust duct through said tubular element after the mass exit of the burnt gases from the cylinder and before the return of these gases to the cylinder.

8. In a two stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port and an exhaust duct leading from said exhaust port and an orifice on said duct situated nearer the cylinder than the limit of outward travel of the burnt gases upon their mass exit from thecylinder, a nozzle within said exhaust duct communicating with said orifice and extending in the direction of exhaust, a source of compressed gaseous fluid, distribution means connecting said source of fluid to said orifice and nozzle,and means for controlling said distribution means for introducing compressed gaseous fluid into the exhaust duct through said nozzle after the mass exit 'of the burnt gases from the cylinder and before return of these gases to the cylinder.

9. In a two stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port, and an exhaust duct leading from the exhaust port of means for introducing the whole of the fresh gases required for the working charge, into the said duct at a point situated nearer the cylinder than the limit of outward travel of the burnt gases upon their mass exit from the cylinder, after the saidmass exit has occurred and before the return of the burnt gases to the cylinder.

10. In a two stroke cycle internal combustion engine of the kind described, the combination with a cylinder having an exhaust port and an exhaust duct leading from the exhaust port, of an orifice on said duct close to the cylinder, a

the

source of fluid, distributing means connecting said source of fluid to said orifice and means for controlling said distribution means to introduce a working charge of gaseous fluid into the exhaust duct after the mass exit of the burnt gases from the cylinder and before their return to the cylinder.

MICHEL KADENACY.

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