GB2205900A

GB2205900A - Compound I.C. engine

Info

Publication number: GB2205900A
Application number: GB08814610A
Authority: GB
Inventors: Alan Francis Daniell
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-06-18
Filing date: 1988-06-20
Publication date: 1988-12-21
Also published as: GB8814610D0; GB8714312D0

Abstract

The cylinders A and C which may be of equal diameter operate on the four stroke cycle. The cylinder B has a larger diameter than the cylinders A and C and is out of phase with them by 180 DEG . The cylinders A and C are each fitted with inlet and exhaust valves, the latter communicating through ports to the cylinder B which in turn is fitted with an exhaust valve. In operation exhaust gases from each of the cylinders A and C are transferred to the larger cylinder B where they continue to expand and do useful work. Those products of combustion are exhausted from the larger cylinder B during its subsequent exhaust stroke. Water may be added to exhaust gases entering the cylinder B. <IMAGE>

Description

INTERNAL COMBUSTION ENGINES This invention relates to internal combustion engines.

In a four cycle compression - ignition engine of conventional design, air is drawn into the cylinder during the induction cycle, and compressed during the compression cycle. As a result of this compression, the air becomes heated. At the top of the compression stroke, fuel is injected into the heated air and ignites. The fuel-air mixture burns, and so leads to increased pressure, during the subsequent expansion cycle. Finally, during the exhaust cycle, the products of combustion are released to the atmosphere.

An engine of spark-ignition type operates in a similar manner except that the fuel is added to the air before entering the engine on the induction cycle, and is ignite by a spark plug at the end of the compression cycle. This Invention applies to both types of engine.

Power is wasted in the exhaust during operation of conventional four stroke engines. An object of this invention is to improve the efficiency of internal combustion engines, especially heavy duty engines such as are used for long distance haulage vehicles or in maringe installations, and at least when they are operating under load.

GB-A-454805 discloses a compound internal combustion engine having at least two high pressure cylinders operating on the four stroke cycle and each in communication with a common low pressure cylinder operating on the two stroke cycle. The low pressure cylinder is a form of supercharger. It also receives the products of combustion that are exhausted from the high pressure cylinders and allows them to expand further for part of its expansion/exhaust stroke, until the exhaust valve in it is opened towards the end of that stroke. As the intake valves also open into the same part of the low pressure cylinder, there is a risk that the subsequent charge formed by the next compression stoke of the low pressure cylinder will be a mixture of fresh air and products of combustion.

According to this invention there is provided an internal combustion engine having at least one group of cylinders, there being at least three cylinders in each such group and the diameter of one of the cylinders of each such group being greater than that of each of the other cylinders of that group, said other cylinders of each such group having an exhaust port and a four stroke engine operating cycle so that products of combustion are exhausted from one of them whilst another of them is in its compression stroke, the exhaust ports of each of said other cylinders of each such group being in communication with an inlet of said one cylinder of the respective group, said one cylinder of each such group being arranged to operate alternate induction/expansion and exhaust strokes out of phase with the other cylinders of that group so that products of combustion exhausted from each of said other cylinders of that group are transferred to said one cylinder of that group during one of its induction/expansion strokes whereby those products of combustion continue to expand and do useful work to the end of that induction/expansion stroke, those products of combustion being exhausted from that said one cylinder during its subsequent exhaust stroke.

The arrangement of this invention allows the exhausted products of combustion to be expanded for a greater amount of the expansion stroke of said one cylinder than is possible in the low pressure cylinder of the engine shown in GB-A-454805 and also keeps the intake air separate from the exhausted products of combustion.

In an embodiment, the present invention comprises an internal combustion engine having three cylinders, as indicated in Figure 1. The two outer "active" cylinders of equal diameter, operate in phase. The central "passive" cylinder, of larger diameter and the same stroke, is out of phase by 180 degrees. The two outer cylinders are each fitted with inlet and exhaust valves, the latter communicating by ports to the central cylinder, which in turn is fitted with an exhaust valve.

Referring to Figure 1, during the first cycle the burning air-fuel mixture is expanding in cylinder A, with both valves ciosed. A new charge of air or air-fuel mixture is drawn into cylinder C through the open inlet valve. The exhaust valve in cylinder B is open and the contents are being expelled to the atmosphere.

During the second cycle, the exhaust valve in cylinder A is open, and the products of combustion are being transferred to the larger cylinder B, and so continue to expand and do useful work. Meanwhile, the contents of cylinder C, with both valves closed, are compressed.

In the third cycle, the inlet valve in cylinder A is open and a new charge is being drawn in. The exhaust valve in cylinder B is open and the products of combustion are being discharged to atmosphere. In cylinder C, both valves are closed and the burning air-fuel mixture is expanding.

In the fourth cycle, the charge in cylinder A is compressed, both valves being closed. The exhaust valve of cylinder C is open and the products of combustion are being transferred to cylinder B, continuing to expand and do useful work. In a spark-ignition version of the above described engine, fresh mixture is ignited by sparking in the "active" cylinders A and C and in a compression ignition version, fuel is injected into these "active" cylinders.

In a conventional engine, without the expansion cylinder B, the exhaust gases are discharged at a relatively high temperature and pressure, so wasting energy. In an engine which embodies this invention, part of this energy is converted into useful work by the expansion of the exhaust gases in cylinder B. In addition to this gain in efficiency, the retention of the burned gases within the engine for two cycles, instead of one, should promote more complete combustion. The lower temperature and pressure of the exhaust gases finally discharged would reduce exhaust noise and prolong the life of the exhaust system.

A further advantage of an engine in which the present invention is embodied is that crankshaft torque is generated more evenly than in a conventional engine: reference to Figure 1 shows that power is generated during each cycle, instead of during two of the four cycles.

The potential increase in efficiency of an engine in which the present invention is embodied can be quantified by consideration of the theoretical air-cycle efficiency, as compared to a conventional engine working under similar conditions.

Figure 2 illustrates the Otto cycle on the pressure/volume plane. Between points 1 and 2 air is compressed adiabatically. Between points 2 and 3 heat is added at constant volume, causing a rise in pressure. Between points 3 and 4 the air expands adiabatically on the power stroke. Between points 4 and 1, in a conventional engine, the heated gas is exhausted to atmosphere.

In an engine in which the present invention is embodied, transfer of the heated gases from the working cylinders A or C to the larger expansion cylinder B allows additional expansion between points 4 and 5, after which the gases are finally discharged at lower temperature and pressure. The useful work done is proportional to the area enclosed by the lines 1-2-3-4 or 1-2-3-4-5-6 respectiveiy.

Calculations show that for typical engines, whether of compression-ignition or spark-ignition type, the increase in theoretical efficiency, over the range from one-half to full power output, is from 17 to 19%.

The theoretical Otto cycle is, of course, not a true representation of the events which occur in a practical engine. In particular, the assumption, of adiabatic compression and expansion is inconsistant with the provision of cooling means, necessary for metallurgical reasons. There is therefore a loss of available heat energy to the cooling system. There are, in addition, losses in pumping of gases and in mechanical friction, and in the combustion process.

Nevertheless, it has been found that analysis based on the Otto cycle is a reliable guide to the relative, though not the absolute, efficiency of internal combustion engines operating under different prescribed conditions. There is no reason to expect, therefore, that the increase in efficiency estimated for the proposed design could not be achieved in practice.

The present invention is not limited to the embodiment described above. For example, the number of cylinders and their relative sizes may be varied, as can the ratio of "active" cylinders to "passive" cylinders. Suitable ducting or manifolding may be provided to conduct gases from more than two "active" cylinders to any one "passive" cylinder. Furthermore, any one "active" cylinder need not be exactly 1800 out of phase with an associated "passive" cylinder.

In an alternative embodiment water is added to the gases entering the "passive" cylinder. This water is caused to boil by the heat retained by the gas and thus adds to the pressure forcing the piston down the "passive" cylinder.

Claims

1. An internal combustion engine having at least one group of cylinders, there being at least three cylinders in each such group and the diameter of one of the cylinders of each such group being greater than that of each of the other cylinders of that group, said other cylinders of each such group having an exhaust port and a four stroke engine operating cycle so that products of combustion are exhausted from one of them whilst another 9f them is in its compression stroke, the exhaust ports of each of said other cylinders of each such group being in communication with an inlet of said one cylinder of the respective group, said one cylinder of each such group being arranged to operate alternate induction/expansion and exhaust strokes out of phase with the other cylinders of that group so that products of combustion exhausted from each of said other cylinders of that group are transferred to said one cylinder of that group during one of its induction/expansion strokes whereby those products of combustion continue to expand and do useful work to the end of that induction/expansion stroke, those products of combustion being exhausted from that said one cylinder during its subsequent exhaust stroke.

2. An internal combustion engine according to claim 1, wherein there are three cylinders in each such group and the diameters of said other two cylinders of each such group are equal.

3. An internal combustion engine according to claim 1 or claim 2, wherein there are three cylinders in each such group and said one cylinder of each such group is 1800 out of phase with the two other cylinders of that group.

4. An internal combustion engine according to any one of claims 1 to 3, wherein means are provided for injecting water into the products of combustion that are exhausted from said other cylinders and transferred to said one cylinder of the respective group.

5. An internal combustion engine substantially as described hereinbefore with reference to and as illustrated by the accompanying drawings.