GB2039614A

GB2039614A - Two-stroke fuel injection engine with piston controlled ports

Info

Publication number: GB2039614A
Application number: GB8001588A
Authority: GB
Original assignee: ZSCHOPAU MOTORRAD VEB
Current assignee: ZSCHOPAU MOTORRAD VEB
Priority date: 1979-01-18
Filing date: 1980-01-17
Publication date: 1980-08-13
Also published as: DE2945593A1; DD140269A1; GB2039614B; CS223569B1

Abstract

The relatively offset similar piston and cylinder head recesses 3 and 4 promote rotation in the combustion chamber, about an axis perpendicular to the cylinder axis, of the scavenging air flow 16. Turbulence produced by squish between the piston and cylinder head and the sharp edges 8 and 9 assists mixing of fuel injected into the recess 3 for ignition by the plug 2. The nozzle fuel jet may have a penetration varying between 30% of the piston stroke at high load and 10% at low load. <IMAGE>

Description

SPECIFICATION Piston-controlled two-stroke fuel injection-type internal combustion engine This invention relates to a piston-controlled twostroke fuel injection type internal combustion engine of the kind having inlet and exhaust ports, scavenging flows rising and falling along the cylinder axis, and an injection nozzle and ignition source disposed in the cylinder head, the fuel jet being directed towards the piston in known manner.

German Patent Specification No. 720 728 discloses an internal combustion engine in which the fuel is injected against the rising scavenging flow with the exhaust ports closed.

German Patent Specification No. 923 753 also discloses an internal combustion engine in which the fuel is injected at an inclination into the rising scavenging flow against its direction of flow; when the scavenging flow is reversed, the axis of the injection nozzle is at tangent thereto.

One characteristic of these prior art internal combustion engines with fuel injection was that the kinetic energy of the fuel jet was used to produce a homogeneous mixture. It is true that scavenging losses could be avoided to a very considerable extent, since as a rule injection was effected only when the outlet port was closed, but an ignitable mixture could not always be supplied to the sparking plug, more particularly with small loads.

Internal combustion engines are also known which have combustion chambers disposed in the cylinder and piston and operate as layer-charging engines. German Auslegeschrift No. 1 900 404 discloses an Otto two-stroke layer-charging engine with Schnurle scavenging reversal, in which the fuel is injected directly against the air flow. Injection is effected into the marginal layer of the air flow deflected by the cylinder head projection. The fuel accumulating in the depression in the cylinder head is removed as a layer by the air flowing behind. A disadvantage is that to produce a homogeneous mixture on the opposite side a multi-aperture injection nozzle is used, since the intensity of flow adjacent the wall is inadequate for the removal of relatively large fuel layers.

German Auslegeschrift No. 2233962 also discloses a mixture-densifying internal combustion engine which has two semi-spherical offset shells, the crushing flow being rendered more intense by the application of additional sickle-shaped "stumbling edges" or deflecting lugs. This specification does not deal with the particular scavenging requirements in relation to the position of the half-shells in the piston and cylinder head of a two-stroke engine.

It is an object of the invention to obviate the afore-mentioned disadvantages of the prior art twostroke injection-type internal combustion engines and to widen their field of application, and also to reduce the emission of harmful substances, more particularly unburnt hydrocarbons.

It is another object of the invention to find for an internal combustion engine of the kind specified a suitable form of combustion chamber and nozzle arrangement, so as to allow controlled combustion with a turbulent flow in the combustion chamber.

Another object is to supply an ignitable mixture to the sparking plug even with a thin mixture, more particularly under partial load. More particularly the fuel is to be so injected that only small fuel losses occur due to the scavenging branch flowing to the exhaust.

Accordingly, the present invention consists in a piston-controlled two-stroke fuel injection-type internal combustion engine, having a cylinder with inlet and exhaust ports, scavenging flows rising and falling along the cylinder axis, a fuel injection nozzle and an ignition source disposed in the cylinder head, the fuel jet being directed towards the piston in the cylinder, characterised in that the engine has a combustion chamber disposed in the cylinder head and piston crown which chamber includes offset spherical or semi-spherical, shell or lens-shaped, ellipsoidal or barrel-shaped fuel chamber shells, and in piston positions around the top dead-centre there is in the combustion chamber a crushing flow which produces a turbulent flow rotating transversely of the cylinder axis and in the same direction as the crushing flow, the fuel jet emerging from the fuel injection nozzle being directed, substantially parallel with or partially inclined to the rising scavenging flow, at the combustion chamber shell in the piston crown. Advantageously, the tear-off edges produced by the offsetting of the fuel chamber shells are constructed with an obtuse, right or acute angle.

This particular design of the combustion chamber edges produces microturbulence, so that the fuel is very quickly and intimately mixed with the air and fed to the combustion process via tear-off edges.

Preferably, the position of the combustion chamber shell in the piston crown is in the zone of the intersecting rising scavenging flows. This arrangement ensures a satisfactory scavenging of the combustion chamber shell in the piston crown by the carburetted gases entering. The combustion chamber is conveniently so designed that the swirl of the inflowing scavenging flow air present particularly in two-stroke internal combustion engines is maintained in the combustion chamber and further boosted by a crushing flow. The result is a charging stratification, the course of combustion being accelerated by the turbulence.

The fuel is injected substantially parallel with or at a slight inclination to the rising scavenging flow.

This direction of the injected jet is very advantageous, since injection is not effected in the direction of the exhaust port, thereby avoiding scavenging losses.

The combustion chamber may be designed in such away that the quantity of fuel injected under partial load is introduced essentially with a relatively late start of injection - i.e., shortly before the instant of ignition. The fuel component most of which is applied to the combustion chamber wall during injection is removed by the swirl and the effect of inertia on piston deceleration and mixed with the air.

It was found to be advantageous if in order to obtain high performance injection is effected relatively early, i.e. adjacent the bottom dead-centre.

Also advantageously the ignition source is disposed behind the tear-off edges to ensure stable ignition. The arrangement of the sparking plug at the transition from the crushing gap to the combustion chamber also ensures that the flame also burns into the crushing gap and thereby ensures that the exhaust gases have a low content of harmful materials and reduces fuel consumption.

To the extent that a small two-stroke diesel engine is operated with a pre-defined ignition point, a heater plug can be used as the ignition source.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which Figure 'shows a cylinder unit of the pistoncontrolled two-stroke injection-type internal combustion engine, with inlet and exhaust ports and injection nozzle and ignition source in the cylinder head, with the piston in the bottom dead-centre position, Figure 2 is a cross-section on the line A-B of Figure 1, showing the preferable position of the piston combustion chamber shell, Figure 3 is a view similar to that of Figure 1, showing the piston position with the outlet and overflow ports closed, and Figure 4 is a view similar to that of Figure 1, showing the piston in the top dead-centre position.

In a piston-controlled two-stroke injection-type internal combustion engine (Figures 1 to 4) having air inlet ports 5,6 and a combustion gases exhaust port 7, a fuel injection nozzle 1 disposed in a cylinder 18 and an ignition source, for example a sparking plug 2, the combustion chamber is subdivided into two combustion chamber shells 3,4 disposed in piston crown 19 and cylinder head 18 respectively.

The combustion chamber made up of combined combustion chamber shells 3, 4 can be spherical, lens or shell-shaped, ellipsoidal or barrel-shaped.

Scavenging flows 14, 15 entering the cylinder through the inlet ports 5,6 combine to form a rising scavenging flow 16. The swirl 12 of the scavenging flow remains preserved during the scavenging operation in the cylinder and is subsequently boosted by the crushing flow set up in the same direction.

The arrangement of the injection nozzle 1 ensures that the fuel jet 11 is so directed that with small and medium loads, i.e. with small quantities of injected fuel, which are injected at the same time relatively late, namely shortly before the instant of ignition, the majority of the quantity of fuel passes directly into the combustion chamber formed by the combustion chamber shells. The offsetting of the combustion chamber shells 3,4 forms tear-off edges 8,9 which are constructed with an obtuse, right or acute angle.

Fuel sprayed on to the combustion chamber wall and accumulating adjacent such wall is swirled by the flow around the tear-off edges 8,9 and fed to the combustion process, so that combustion takes place economically with small proportions of unburnt hydrocarbons in the exhaust gases.

The fuel deflected by the tear-off edge 8 is fed directly to the ignition source 2, so that combustion can take place even with extremely thin partial load mixtures. At the same time this sparking plug position at the edge of the crushing gap 10 encourages combustion in this zone also. With full load the fuel jet 11 is injected relatively early, i.e. shortly after the bottom dead-centre. This enables the charge layering effect to be reduced in the direction of chamber charging. As a result a high full load performance is also guaranteed, in contrast with other processes.

The offsetting of the combustion chamber shells 3,4 in relation to one another amounts to 25% of the piston diameter, and the combustion chamber shell in the piston crown is disposed on the line between the centre of the exhaust port 7 and the centre of the cylinder bore 17. The centre of the combustion chamber shell 3 is preferably disposed substantially at the point 13 of intersection of the intersecting rising scavenging flows 14,15. With heavy loads, i.e.

large quantities of injected fuel, the path of the fuel jet bounded by the combustion chamber shell in the piston crown corresponds to at least 30% of the piston stroke, and with decreasing loading, i.e.

smaller quantities of injected fuel, such path corresponds to at least 10% of the piston stroke.

The sparking plug 2 is disposed at the transition between the crushing gap 10 and the combustion chamber shell 4. The ignition source may alternatively be consituted by a heater plug (not shown).

Claims

1. A piston-controlled two-stroke fuel injectiontype internal combustion engine, having a cylinder with inlet and exhaust ports, scavenging flows rising and falling along the cylinder axis, a fuel injection nozzle and an ignition source disposed in the cylinder head, the fuel jet being directed towards the piston in the cylinder, characterised in that the engine has a combustion chamber disposed in the cylinder head and piston crown which chamber includes offset spherical or semi-spherical, shell or lens-shaped, ellipsoidal or barrel-shaped fuel chamber shells, and in piston positions around the top dead-centre there is in the combustion chamber a crushing flow which produces a turbulent flow rotating transversely of the cylinder axis and in the same direction as the crushing flow, the fuel jet emerging from the fuel injection nozzle being directed, substantially parallel with or partially inclined to the rising scavenging flow, at the combustion chamber shell in the piston crown.

2. An internal combustion engine according to claim 1, wherein tear-off edges produced by the off-setting of the fuel chamber shells are constructed with an obtuse, right or acute angle.

3. An internal combustion engine according to claim 1,wherein the offsetting of the combustion chamber shells in relation to one another amounts to 25% of the piston diameter, and the combustion chamber shell in the piston crown is disposed on the line between the centre of the exhaust port and the centre of the cylinder bore.

4. An internal combustion engine according to claim 1, wherein the centre of the combusion chamber shell in the piston crown is disposed substantially at the point of intersection of the intersecting rising scavenging flows.

5. An internal combustion engine according to claim 1, wherein with heavy loads, i.e. large quantities of injected fuel, the path of the fuel jet bounded by the combustion chamber shell in the piston crown corresponds to at least 30% of the piston stroke, and with decreasing loading, i.e. smaller quantities of injected fuel, such path corresponds to at least 10% of the piston stroke.

6. An internal combustion engine according to claim 1, wherein the ignition source is a sparking plug disposed at the transition between the crushing gap and the combustion chamber shell in the cylinder head.

7. An internal combustion engine according to claim 1, wherein the ignition source is a heater plug.

8. A piston-controlled two-stroke fuel injectiontype internal combustion engine, substantially as herein described with reference to and as shown in the accompanying drawings.