GB2060766A

GB2060766A - I.C. engine with a vapour turbine driven supercharger

Info

Publication number: GB2060766A
Application number: GB8022009A
Authority: GB
Original assignee: Wallace Murray Corp
Current assignee: Wallace Murray Corp
Priority date: 1979-10-05
Filing date: 1980-07-04
Publication date: 1981-05-07
Also published as: JPS5654926A; DE3021691A1; SE8003793L; BR8003847A

Abstract

The turbine 24 driving the compressor 40 is fed with steam from an exhaust gas heated steam generator 14 supplied with water from an air cooled condenser 28 by an engine or turbine driven feed pump 32. A steam throttle valve 52 or a valve (62), Fig. 4 (not shown), in an exhaust gas bypass (64) around the generator 14 may be connected to the engine throttle so that the energy input to the turbine 24 increases with the engine fuel supply. <IMAGE>

Description

SPECIFICATION Power unit with supercharged internal combustion engine This invention relates to power units utilising super-charged internal combustion engines.

The term supercharged as used herein is intended to refer to any forced blowing of air into the air intake of an internal combustion engine, such as an internal combustion engine of the Otto or the Diesel type. The supercharging of internal combusion engines has long been practiced. In one method of supercharging, a compressor is driven directly by the internal combustion engine itself, the compressor output feeding into the air intake of the engine. In another known scheme for supercharging an internal combusion engine, the hot exhaust gases of the engine are passed through a turbine. The turbine is coupled to and drives a compressor. The output of the compressor is then fed directly to the air input of the internal combusion engine.While generally satisfactory for their intended purpose, particularly in certain applications and environments, these two known types of supercharging systems exhibit characteristics which are not suitable for other applications. For example, in the first type of supercharging, by direct coupling of the engine to drive the compressor, a gear train must often be introduced between the engine and the compressor, to thereby account for varying rotational speed requirements of the engine and the compressor. In the second type of supercharging system, the placement of a turbine in the path of the engine exhaust gases creates a back pressure. Such back pressure reduces the efficiency of the engine.

According to the present invention, there is provided a power unit comprising an internal combustion engine, an air compressor arranged to supply air for combustion to the air input of the internal combustion engine whereby the internal combustion engine is supercharged, and a Rankine cycle engine operative to drive the air compressor, the Rankine cycle engine being of the type including means for vaporizing a working fluid, an expander for extracting energy from the heated, vaporized working fluid, a condensor for condensing the working fluid, and a feed pump to return the condensed working fluid to the vaporizer, the said expander being coupled to drive the said air compressor.

In contrast to the known supercharging systems, in the present invention the compressor which supercharges the internal combustion engine is driven directly by a Rankine cycle engine.

The source of energy for the Rankine cycle engine is preferably provided by the hot exhaust gases output from the internal combustion engine: accordingly, the means for vaporising the working fluid is preferably constituted by a vapor generator in the form of a heat exchanger one side of which is connected. to receive the exhaust gases while the other side is connected to receive the working fluid. The condenser of the Rankine cycle engine can be constituted by a device not dissimilar to the common automobile radiator.

In one embodiment of the invention, the feed pump is driven directly by the expander. In a second embodiment, the feed pump is driven directly by the internal combustion engine. In a third embodiment, a throttle valve is interposed between the means for vaporising the working fluid and the expander, the throttle valve actuation being controlled by control means responsive to the operating state of the internal combustion engine. This arrangement permits a greater degree of matching between air fed to the internal combustion engine (the degree of supercharging) and its power requirements.In a fourth embodiment of the invention in which the means for vaporising the working fluid is constituted by the vapor generator connected to receive the exhaust gases, a by-pass duct is placed around the vapor generator, and a by-pass valve is inserted in this duct to control the proportion of the hot exhaust gases allowed to by-pass the generator.

This arrangement also permits greater matching of supercharging air fed to the internal combustion engine by the compressor, and power requirements of the internal combustion engine.

Four embodiments of the invention will now be particularly described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a partially schematic view of a power unit incorporating an internal combustion engine with a supercharging system according to a first embodiment of the invention; Figure 2 is a view similar to Figure 1 but illustrating a second embodiment of the invention, Figure 3 is a view similar to Figure 2, but illustrating a third embodiment of the invention; and Figure 4 is a view similar to Figure 2, but illustrating a fourth embodiment of the invention.

Referring now to Figure 1 of the drawings, the numeral 10 schematically denotes an internal combustion engine of, for example, the Otto or Diesel type. The numeral 1 2 denotes an exhaust line for the hot exhaust gases coming from the exhaust manifold of the engine, line 12 leading into a vapor generator 14 in the form of a heat exchanger. The vapor generator includes, schematically indicated, a first coil 1 6 having an output line 1 8 leading to ambient or to pollution control devices. Coil 1 6 is thus in series with the exhaust gas line. The numeral 20 schematically designates a second coil in heat exchange relation to coil 16. One end of coil 20 is coupled to line 22 leading into an expander 24. Expander 24 may assume the form of a conventional turbine wheel mounted on a rotation shaft.The output of expander 24 is fed through line 26 to a condenser 28. The output of condenser 28 is fed through line 30 to a feed pump 32 which may assume the form of a conventional liquid pump. The output of the pump is fed through line 34 back into coil 20.

Rotary shaft 36 couples the expander to a compressor 40. The input of compressor 40 is denoted by line 42, line 42 feeding, for example, directly from ambient as through a conventional air filter. The output of compressor 40 is fed through line 44 to the air input of the internal combustion engine 10.

The elements 20, 24, 28, 32, and their associated hydraulic conduits are in series with one another and define what is known as a Rankine cycle engine. The working substance of this engine may be, for example, water. The operation of the device shown in Figure 1 is as follows.

Assuming the internal combustion engine 10 to be in operation, hot exhaust gases pass through conduit 12 into vapor generator 14, passing through coil 16 and out through line 18 to either ambient or to ambient by means of a pollution control device, not illustrated. Coils 1 6 and 20 are in heat exchange relationship. Coil 20, heated by coil 16, defines the heat source for the Rankine engine. The working fluid or working substance in the Rankine cycle engine being water, water in line 22 is in the form of a vapor, i.e., steam. This steam passes through expander 24, expander 24 assuming the form of a conventional turbine wheel. After exiting from expander 24, the working fluid passes through line 26 into the condenser 28 where it is condensed from a gas or vapor to a liquid.The liquid is now passed through conduit 30 by virtue of the action of feed pump 32, the working fluid now-passing through line 34, in liquid form, into line 20 for a repetition of this cycle. The energy derived from the working fluid by expander 24 is used to turn the feed pump 32, this energy also acting through shaft 38 to operate the compressor 40. Compressor 40 compresses ambient air and passes it into the engine 10 to supercharge it.

The reader will now be in a position to comprehend that the passage of exhaust gases from the engine through conduit 12 and through coil 1 6 of vapor generator 14 creates less of a back pressure, in general, than would be the case if a turbine wheel were placed in line 12, as is customary with the so-calied turbocharger method of supercharging an internal combustion engine.

Referring now to Figure 2 of the drawings, the arrangement of elements is changed somewhat so that the feed pump 32 is actuated by the engine 10 through rotary shaft 46. As in the previously described embodiment, rotary shaft 38 couples the compressor and the expander. The mode of operation of the system shown at Figure 2 is the same as that previously described with respect to the operation of Figure 1.

Turning now to Figure 3 of the drawings, another embodiment of the invention is illustrated, this embodiment being similar to the arrangement of elements shown at Figure 2. In the system of Figure 3, an actuating element 50 is coupled to a throttle valve 52, the valve 52 being placed in line 22. Actuator 50 is controlled by a control signal derived from the internal combustion engine 10.

The operation of this system is similar to that of the systems at Figures 1 and 2, with the exception that throttle valve 52 is varied, to thereby more nearly match the power requirements of the engine with the amount of air fed to it by compressor 40. This operation takes place in the following manner. Assume that a transient power increase is desired of the engine 1 0. This power increase demand is sensed by control signal input line 54 (schematically indicated in dashed lines) and is fed to actuator element 50. Actuator element 50 causes the throttle valve 52 to open somewhat. This increased opening results in an increase in the velocity of the working fluid (steam in the example given), this increase in velocity causing an increase in speed of rotation of the expander 24.This results in an increase in the speed of rotation of compressor 40, this in turn results in an increase in the amount of air per unit time (volumeric rate of air) fed to the air intake of engine 1 0. An increase in air fed to the engine with an appropriate increase in fuel increases the combustion rate, thereby increasing the power output of the engine. Similarly, when there is a transient decrease in demand of power output from engine 10, such demand is sensed through line 54 to actuator 50, the throttle valve 52 now closing somewhat from its steady state or normal position. This results in a decrease of speed of the working fluid through the valve, thereby causing a decrease in speed of the expander 24.This in turn results in a decrease in speed of rotation of compressor 40, thereby resulting in a lessening of the volumetric rate of air fed to the air intake of engine 1 0. This in turn causes a decrease in the power output of the engine.

Referring now to Figure 4 of the drawings, a system is disclosed which is similar to the system of Figure 3 in that engine power requirements are more nearly matched to the air fed into it by compressor 40. There, dashed line 66 denotes a control signal line coupled to a valve actuator 60, the actuator 60 in turn controlling a by-pass valve 62 in line 64. Line 64 by-passes or shunts coil 16 of vapor generator 14, as indicated, by the by-pass line feeding back to output line 1 8.

The system of Figure 4 operates in the following manner. If engine 10 produces more power, as by increasing its rate of fuel supply, it will demand more air from compressor 40 (to thereby maintain a predetermined air-fuel ratio).

Expander 24, to enable compressor 40 to supply more air to engine 10, will extract more energy from the working fluid in the Rankine cycle engine.* The pressure of the working fluid will then drop.

Such pressure decrease (energy content) is sensed, by conventional means, and fed to actuator 60 through line 66, causing valve 62 to close somewhat. More hot exhaust gas will now pass through coil 1 6 than before, thus still further heating coil 20 and the working fluid therein. Such additional heat will now raise the pressure in the working fluid, thereby increasing its energy content.

Should the engine 10 decrease its power output, thereby reducing the amount of air fed to it by compressor 40, a similar, but opposite, action will result in pressure in the working fluid increase, and actuator 60 will now open somewhat valve 62, thereby increase the hot exhaust gases bypassed around coil 1 6 of vapor generator 14.

If desired, the control arrangements of Figures 3 and 4 may be combined.

The several elements of the system illustrated may assume several forms. For example, the expander and the compressor may be rotary turbine wheel devices, or may be of the sliding vane or lobe type expanders and compressors, as well as the noted dynamic machines, such as axial flow or centrifugal compressors and turbines. The choice between any one of the four embodiments illustrated depends, generally, on intended use in a particular environment. For example, the embodiment of Figure 2 may be employed instead of that of Figure 1 when the expander and the compressor both operate at high speed and where a low speed feed pump is desired.

The selection of which of the four embodiments illustrated will depend upon the particular working fluid chosen and the performance requirements of the vapor cycle system. As an example, the following calculated parameters are given for a system using water as the working fluid and with the performance requirement of a compressor pressure ratio of 2.5. Since the compressor and expander are likely to be similar types of machines, since they rotate at the same speed, the expander expansion ratio should be approximately equal to the compressor pressure ratio. The compressor and expander also should be approximately the same size, thereby the inlet volume flow rate of the compressor should be approximately equal to the discharge volume flow rate of the expander.Using a typical compressor adiabatic efficiency of 75%, air entering the compressor at 850 F. is found to be discharged at 21 80F. Using an expander adiabatic efficiency of 70% and a mechanical efficiency of 90% to account for losses in bearings and seals, and calculating the power balance between the compressor and expander, the expander discharge pressure is found to be 60 psia of saturated steam at 2900 F. At this condition, the expander discharge volume flow rate is slightly greater than the compressor inlet flow rate. The compressor and expander are therefore approximately the same size. The expander inlet conditions are found to be 145 psia at 3550 F. Steam at that pressure is slightly super heated at that temperature.The steam flow rate through the expander is approximately 2.5 times the air flow rate through the compressor.

The exhaust manifold temperature of a diesel engine varies from approximately 1 0000 F. for a two cycle engine to approximately 13000 F. for a four cycle engine. The design of the evaporator, which is required to supply slightly superheated steam at 3550F. can easily be accomplished, since the heat is transferred from gas at 1 ,0000F.

or higher. The condensor for the water system must condense steam at a saturation temperature of 2900 F. which is easily accomplished witka relatively small heat exchanger cooled by ambient air. The internal pressure of the Rankine cycle engine system is low, being approximately 1 45 psia thus simplifying sealing problems and permitting the use of readily available shaft seal elements.

The Rankine cycle engine itself is well known.

Further, it is also well known to employ a Rankine cycle engine in a compound arrangement. Thus, it is known to couple a Rankine cycle engine with a usual internal combustion engine of the Otto or the Diesel type in the following manner. A source of heat from the internal combustion or primary engine is used to vaporize a working fluid in a heat exchanger. The working fluid is expanded through a power producing device. The power produced is supplied to the crankshaft of the primary or internal combustion eingine. The working fluid is then condensed and pumped by a feed pump back to the vaporizer. Such a Rankine cycle compound system suffers from the disadvantage, however, that the operational speed of the power producing expander frequently does not match the speed of the primary or internal combustion engine.

Accordingly, often complicated gearing and clutching arrangements are required to match the speeds of these two parts of the entire system.

The reader will now be in a position to recognize that such a known arrangement is similar to that shown, for example, in Figure 1 of the drawings, except that the compressor 40 is not present in such an arrangement. Instead, the expander 24 was coupled directly to the crankshaft of the engine 10, although as noted above, often through complicated gearing and clutching arrangements. The reader will now recognize that by the virtue of the arrangement shown, for example, in Figure 1, that by causing the Rankine cycle expander 24 to drive a compressor, the compressor in turn providing air to the engine 10, the expander and compressor can operate at the most appropriate speed. This will depend upon the type of expander and compressor used, and is independent of the speed of the engine 1 0.

The actuator 50 and control signal line 54 of the embodiment of Figure 3 and the actuator 60 and control signal line 66 of Figure 4 may assume a variety of forms. For example, the control signal line (54, 66) may be a lever which is attached to the throttle of the internal combustion engine 10, the position of the lever corresponding to the position of the throttle, in turn corresponding to the rate of fuel consumed by the engine. The lever may be coupled, for example, to an actuator handle for the throttle valve 52 of Figure 3 or the by-pass valve 62 of Figure 4. The reader will recognize that, instead of a mechanical arrangement such as described, the control signal line may be an electrical line or a hydraulic line, with a suitable actuator such as an electric motor or a hydraulic motor, for actuating the valves 52 or 62.

Claims

1. A power unit comprising an internal combustion engine, an air compressor arranged to supply air for combustion to the air input of the internal combustion engine whereby the internal combustion engine is supercharged, and a Rankine cycle engine operative to drive the air compressor, the Rankine cycle engine being of the type including means for vaporizing a working fluid, an expander for extracting energy from the heated, vaporized working fluid, a condensor for condensing the working fluid, and a feed pump to return the condensed working fluid to the vaporizer, the said expander being coupled to drive the said air compressor.

2. A power unit according to Claim 1, wherein the means for vaporizing the working fluid comprises a heat exchanger connected on one side to receive the hot exhaust gases from the said internal combustion engine and on its other side to receive the working fluid of the said Rankine cycle engine, whereby the said working fluid is arranged to take up heat from the said exhaust gases and become vaporized.

3. A power unit according to Claim 1 or Claim 2, wherein the feed pump is driven directly by the expander.

4. A power unit according to Claim 1 or Claim 2, wherein the feed pump is driven directly by the internal combustion engine.

5. A power unit according to any one of the preceding claims, further comprising a throttle valve provided in the Rankine cycle engine between the means for vaporizing the working fluid and the expander, and control means operative to control said throttle valve in dependence on the power requirements of the internal combustion engine, such that when power is required from the internal combustion engine, the throttle valve is actuated to move to a more open configuration whereby to cause an increase in the velocity of working fluid passing therethrough to thereby increase the speed of the expander and produce an increase in the rate of air fed to the internal combustion engine by the compressor, the control means being operative upon a power decrease being required from the internal combustion engine to cause the throttle valve to move to a more closed position whereby to cause a decrease in the velocity of working fluid passing therethrough, and thereby decrease the speed of the expander.

6. A power unit according to Claim 2 or to any one of Claims 3 to 5 when dependent thereon, of Claims 3 to 5 when dependent thereon, including a by-pass valve provided in a by-pass duct which is connected across the said one side of the heat exchanger to enable a portion of the hot exhaust gas coming from the internal combustion engine to be by-passed around the heat exchanger, sensing means operative to sense the energy content of the working fluid of the Rankine cycle engine, and actuator means arranged to actuate the by-pass valve in accordance with the sensed energy content of the working fluid, the arrangement of the said sensing and actuating means being such that when a power increase from the internal combustion engine occurs, with attendant increase in the rate of air fed by the compressor, the decreased energy content of the working fluid is sensed, and the bypass valve is moved to a more closed position to by-pass less hot exhaust around the heat exchanger, and conversely when a power decrease from the internal combustion engine occurs, the increased energy content of the working fluid is sensed and the by-pass valve moves to a more open position to by-pass more hot exhaust gas around the heat exchanger.

7. A power unit substantially as hereinbefore described with reference to anyone of Figures 1 to 4 of the accompanying drawings.