GB2041079A - Internal combustion engines - Google Patents

Abstract

Primary combustion air is pumped by a rotary pump 12 into a precombustion chamber 5 through a valved port 9, fuel being added either by a carburettor 13 or injector. Secondary combustion and scavenge air is induced through port 8 by the suction effect of outgoing exhaust gases, or forced by a turbocharger, into the main combustion chamber 4. The pumped primary combustion air allows engine starting without the need for crankcase pumping so that the disadvantages of conventional two- stroke crankshaft and crankcase design can be eliminated to produce a clean two-stroke engine. Retention of the primary charge in the precombustion chamber during scavenging eliminates charge loss to exhaust and uneven running at low loads. <IMAGE>

Description

SPECIFICATION Improvements in or relating to internal combustion engines This invention relates to internal combustion engines.

Internal combustion engines having a precombustion chamber or zone are well known and are used as diesel (or compression ignition) engines and as petrol (or spark ignition) engines. It is also known to equip such an engine with two separate inlets, one for fuel or a richer than stoichiometric mixture and the other for air or a leaner than stoichiometric mixture. In such an engine, the rich mixture is induced, or the fuel is injected, into the precombustion chamber or zone and the lean mixture is induced into the main combustion chamber. Ignition of the rich mixture either by compression or a spark causes the rich mixture to expand out of the precombustion chamber or zone into the main combustion chamber where combustion is completed.

Whilst such engines have been used with some success in a four-stroke form to achieve reduced exhaust emissions, this has been at the expense of economy and power output.

The present invention aims to provide a new and improved internal combustion engine based on the two-stroke cycle, but adaptable to four-stroke and rotary cycles, in both spark and compression ignition forms.

According to the present invention there is provided an internal combustion engine including: one or more combustion cylinders, each of which cylinders comprises a main combustion chamber and a precombustion chamber or zone; a first inlet provided in the main combustion chamber for scavenge and secondary combustion air or a leaner than stoichiometric mixture; a second inlet provided in the precombustion chamber or zone for primary combustion air or a richer than stoichiometric mixture of primary combustion air and fuel; means for pumping the primary combustion air or richer than stoichiometric mixture of primary combustion air and fuel into the precombustion chamber or zone; means for injecting fuel into the precombustion chamber or zone when the primary combustion mixture is not richer than stoichiometric;; an outlet provided in the main combustion chamber for the outlet of exhaust gas.

When constructed as a four-stroke engine the inlets and outlet are fitted with valves in the conventional way and the primary mixture or air is pumped into the precombustion chamber or zone whereas the secondary mixture or air is induced into the main combustion chamber.

The most advantageous construction, however, is in the form of a two-stroke engine in which the second inlet is fitted with a valve whereas the first inlet and the outlet are opened and closed due to the movement of the piston in the cylinder, although either the first inlet or the outlet may be fitted with a valve.

In this new type of two-stroke engine the primary mixture or air is pumped into the precombustion chamber or zone whereas the secondary mixture or air is induced into the main combustion chamber by the suction effect of outgoing exhaust gas or forced into the main combustion chamber by a turbocharger.

Since neither the suction effect of outgoing exhaust gas or the output of a turbocharger is adequate at low engine speeds, the pumped primary mixture or air is provided sufficient for engine starting and low speed running.

It is thus no longer necessary to utilise the crankcase as a pump for incoming fuel-air mixture as has hitherto been the case with two-stroke engines. A cheaper conventional four-stroke type of bearing, crankshaft and lubrication system can be used to replace the complex and costly conventional two-stroke design incorporating inter-cylinder seals. The elimination of these inter-cylinder seals enables the development of compact vee-from two-stroke engines using a single crankshaft.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawing which shows, schematically and in vertical cross-section, one embodiment of an internal combustion engine in accordance with the present invention.

The engine shown in the drawing comprises an engine block 1 having secured to the upper surface thereof a cylinder head 2. Sli- dably mounted within a cylinder formed in the engine block 1 is a piston 3 defining with the engine block 1 and the cylinder head 2 a main combustion chamber 4. Formed within the cylinder head 2 and communicating with the main combustion chamber 4 is a precombustion chamber 5 formed with an opening containing a spark plug 6. As is usual in a two-stroke engine, the cylinder has an outlet port 7 for the outlet of exhaust gases from the combustion chamber 4 with the piston 3 acting as a valve for the outlet port 7. In addition, there are provided two inlet ports 8 and 9.Inlet port 8 opens directly into the main combustion chamber 4 and again utilises the piston 3 as a valve, but inlet port 9 opens into the precombustion chamber 5 through the cylinder head 2. A cam 10 operates a valve 11 located in the inlet port 9 and upstream of the valve 11 is a rotary pump 1 2 which delivers a richer than stoichiometric primary mixture into the precombustion chamber 5 when the valve 11 is opened by the cam 10. A carburettor 1 3 is provided for metering the addition of fuel to the primary air to produce the primary mixture induced by the pump 12.

In operation of the engine, the primary mixture is delivered by the pump 1 2 into the precombustion chamber 5 and secondary air is drawn into the main combustion chamber 4 by the suction effect of outgoing exhaust gas from the previous cycle. The primary mixture is confined to the precombustion chamber 5 by the action of the piston 3 rising in the cylinder to close the ports 7 and 8 and compress the secondary air. As the piston 3 continues to rise the secondary air and primary mixture are further compressed to give charge stratification. Combustion is initiated by the spark plug 6 and the ignited primary mixture expands out of the precombustion chamber 5 into the main combustion chamber 4 where mixing with the secondary air occurs and combustion continues to completion.

The engine described above has several advantages over existing designs in addition to the advantages already stated. The problem of fuel loss to the exhaust is greatly reduced since the primary mixture is confined to the precombustion chamber 5 during scavenging, and this also leads to the elimination of uneven running at low loads. The secondary air supplied through inlet port 8 can be in excess of combustion requirements, particularly if inlet port 8 is unthrottled, thus enabling more complete scavenging to be achieved and allowing a higher compression ratio to be used without the danger of detonation. The excess secondary air will also allow more complete combustion to be achieved leading to reduced exhaust emissions. The problem of heat transfer to the incoming charge as it passes through the crankcase of a conventional twostroke engine is eliminated.

From the foregoing, it will be appreciated that the invention can be applied with advantage to any form of internal combustion engine incorporating a precombustion chamber or zone, whether it be powered by petrol, diesel or other fuel and whether it be a twostroke, four-stroke or rotary engine. Indeed, it is possible to use more than one fuel simultaneously, the primary mixture, for example, incorporating a first fuel and the secondary mixture incorporating a second fuel.

Claims (11)

1. An internal combustion engine operating on the two-stroke cycle, having one or more combustion cylinders, each of which cylinders comprises a precombustion chamber or zone containing a spark plug, a valve and a primary inlet port through which primary combustion air is pumped into said precombustion chamber or zone, fuel being added by a carburettor fitted to said primary inlet port, and a main combustion chamber containing piston controlled outlet port or ports, and piston controlled secondary inlet port or ports through which secondary combustion and scavenge air is drawn by the suction effect of exhaust gases leaving the main combustion chamber through said outlet port or ports.

2. An internal combustion engine in accordance with Claim 1, wherein said outlet port or ports are fitted with an exhaust driven turbocharger which delivers secondary combustion and scavenge air to said secondary inlet port or ports.

3. An internal combustion engine in accordance with Claim 1 or 2, wherein said fuel is injected into said primary inlet port.

4. An internal combustion engine in accordance with Claim 1 or 2, wherein said fuel is injected into said precombustion chamber or zone.

5. An internal combustion engine in accordance with any one of Claims 1 to 4, wherein said secondary combustion and scavenge air is induced and transferred to the main combustion chamber by piston movement.

6. An internal combustion engine in accordance with any one of Claims 1 to 5, wherein said secondary inlet port or ports and/or outlet port or ports are fitted with valves.

7. An internal combustion engine in accordance with any one of Claims 1 to 6, wherein said internal combustion engine operates on the four-stroke cycle.

8. An internal combustion engine in accordance with any one of Claims 1 to 7, wherein said fuel is ignited by compression.

9. An internal combustion engine in accordance with any one of Claims 1 to 8, wherein fuel is added to said secondary combustion air.

10. An internal combustion engine in accordance with any one of Claims 1 to 9, wherein said internal combustion engine is of a rotary type.

11. An internal combustion engine substantially as herein described and as illustrated in the accompanying drawings.