Abstract:
A thermal energy retrieval system in which waste heat generated by an internal combustion engine is used to evaporate an organic working fluid in an evaporator. The evaporated working fluid is passed through a turbine to generate mechanical or electrical power which could be used to supplement the work done by the internal combustion engine. A unitary control valve is disposed between a feed pump and the evaporator to automatically regulate the flow of working fluid to the evaporator in accordance with the sensed temperature of the working fluid at its exit from the evaporator. This ensures the optimization of the thermodynamic efficiency of the system, which in turn leads to the provision of a more compact system useful as an add-on to motive mounted engines.

Description:
RELATED APPLICATIONS  
       [0001]    This Application is a Continuation-In-Part of U.S. application Ser. No. 09/515,919 filed on Mar. 1, 2000, pending. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a system of energy retrieval and, more particularly, to such a system which is adapted to retrieve thermal energy from waste heat generated by an internal combustion engine, such as used in a road vehicle, locomotive, water vessel or stationary power generators.  
           [0004]    2. Description of the Prior Art  
           [0005]    Environmental concerns have led to the development of internal combustion engines which are specifically designed to reduce fuel consumption and emitted pollutants.  
           [0006]    For instance, as disclosed in U.S. Pat. No. 3,979,913 issued on Sep. 14, 1976 to Yates, it has been proposed to direct engine coolant through a manifold area of an internal combustion engine to generate steam to drive a turbine. The output power from the turbine is used to supplement the basic power of the engine or, alternatively, to provide power to auxiliary equipment. A solenoid-operated valve is provided upstream of the engine manifold to allow or prevent engine coolant flow thereto depending on the temperature of the engine manifold.  
           [0007]    U.S. Pat. No. 4,031,705 issued on Jun. 28, 1977 to Berg discloses an auxiliary power system in which hot engine coolant and hot engine exhaust gas are circulated through heat exchangers to vaporize a working fluid before the same enters a vapor engine for providing extra power to the main internal combustion engine. A pressure relief valve is employed in conjunction with a linear solenoid valve to control the amount of working fluid flowing through the heat exchangers as a function of the temperature of the working fluid and the hot engine coolant.  
           [0008]    Although the systems described in the above mentioned patents are effective, their implementation has been essentially hampered by the size of the equipment needed. Accordingly, there is a need for a new thermal energy retrieval system that can be miniaturized to a size that could fit, for instance, in a truck engine environment.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an aim of the present invention to provide a relatively compact thermal energy retrieval system adapted to convert recuperated waste heat produced by an internal combustion engine into mechanical or electrical power.  
           [0010]    It is also an aim of the present invention to provide such a new thermal energy retrieval system that is adapted to be retrofitted to existing road vehicles.  
           [0011]    Therefore, in accordance with the present invention, there is provided a compact thermal energy retrieval system for an internal combustion engine, comprising a refrigerant circulated in a closed cycle, an evaporator for heating said refrigerant from a liquid state to a high pressure vapor by means of heat generated by the internal combustion engine, an expander/turbine unit through which said vapor is passed to develop power, and a condenser to cool and condense said vapor emanating from said turbine to a condensed fluid before being re-circulated through said evaporator; and a control unit for controlling the operation of said thermal energy retrieval system, said control unit including a temperature sensor mounted in said closed cycle for sensing a temperature of said refrigerant substantially at said evaporator and providing a first output signal as a function of the temperature of the refrigerant, and a fluid flow regulator incrementally adjusting a mass flow rate of circulation of said refrigerant through said evaporator in accordance with said output signal.  
           [0012]    In accordance with a further general aspect of the present invention, there is provided a compact thermal energy retrieval system for an internal combustion engine, comprising a refrigerant circulated in a closed cycle, an evaporator for heating said refrigerant from a liquid state to a high pressure vapor by means of heat generated by the internal combustion engine, an expander/turbine unit through which said vapor is passed to develop power, and a condenser to cool and condense said vapor emanating from said turbine to a condensed fluid before being re-circulated through said evaporator; and a control unit for controlling the operation of said thermal energy retrieval system, wherein said expander/turbine unit is surrounded by a jacket through which a coolant fluid is passed to cool said expander/turbine unit.  
           [0013]    In accordance with a still further general aspect of the present invention, there is provided a compact evaporator for heating a working fluid from a liquid state to a high-pressure vapor. The evaporator comprises a container, a heat exchanging panel spirally rolled within the container and defining an internal serpentine passage connected in flow communication with an inlet and an outlet for allowing a working fluid to flow through the serpentine passage. Inlet and outlet means are provided for allowing a heat source fluid to flow through the container on an outside surface of the heat-exchanging panel to transfer heat to the working fluid via the heat-exchanging panel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:  
         [0015]    [0015]FIG. 1 is a schematic diagram illustrating a thermal energy retrieval system for an internal combustion engine in accordance with a first embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a schematic diagram of the thermal energy retrieval system of FIG. 1 illustrating the control system thereof;  
         [0017]    [0017]FIG. 3 is an elevation view of an evaporator forming part of the thermal energy retrieval system of FIG. 1;  
         [0018]    [0018]FIG. 4 is an end view of the evaporator of FIG. 3;  
         [0019]    [0019]FIG. 5 is an enlarged cross-sectional view of the evaporator of FIG. 3;  
         [0020]    [0020]FIG. 6 is a schematic diagram of a thermal energy retrieval system in accordance with a second embodiment of the present invention; and  
         [0021]    [0021]FIG. 7 is a schematic diagram of a thermal energy retrieval system in accordance with a third embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Referring now to FIGS. 1 and 2, there is shown a thermal energy retrieval system  10  for an internal combustion engine  12  of the type normally used to drive a road vehicle (not shown). The thermal energy retrieval system  10  is designed to fit under the hood of the vehicle and is adapted to be mounted to the chassis thereof and on the engine  12 .  
         [0023]    The thermal energy retrieval system  10  includes a reservoir (not shown) containing an organic working fluid having a low boiling point, namely a refrigerant. For instance, it is contemplated to use N-Butane as the working fluid. However, any other nonflammable organic fluids and CFC-free chemicals could be used as well. In accordance with a preferred embodiment of the present invention, TER55 (Hexafluoropropane) or TER64 (Tetrafluoroethane) are used as the working fluid. The chemical formulae of the TER55 and the TER64 could respectively be: CF 3 -CH 2 -CF 3 and CHClFCF 3 . A feed pump  14  is coupled in flow communication with an outlet port of the reservoir. The pump  14  is of standard construction and has a vane impeller (not shown). The pump  14  is driven by the crankshaft  15  of the internal combustion engine  12  via an electromagnetic clutch  16 , thereby allowing the pump  14  to be selectively connected and disconnected from the engine  12 .  
         [0024]    The output from the pump  14  passes through an evaporator  18  via flexible tubing  20 . The heat necessary to vaporize the working fluid from a liquid phase to a high-pressure vapor in the evaporator  18  is provided by the waste heat generated by the engine, such as the engine coolant emanating from the engine  12 . The evaporator  18  is thermally insulated and specially designed in a compact way to fit under the hood of the road vehicle, above the engine  12 .  
         [0025]    More particularly, as seen in FIGS.  3  to  5 , the evaporator  18  includes a cylindrical container  22  and a light roll-bond heat-exchanging panel  24  spirally wound within the cylindrical container  22  about a cylindrical core  23 . The panel  24  is in fact a double walled panel defining an internal serpentine passage  26  (see FIG. 5) for the working fluid to flow through from an inlet  25  to an outlet  27 . The serpentine passage  26  is preferably longitudinally oriented relative to the cylindrical container  22 . As seen in FIG. 5, a plurality of uniformly distributed semi-spherical bubbles  31  extend inwardly from the front and back faces of the panel  24  within the serpentine passage  26  to act as flow turbulators in order to promote heat exchange between the working fluid and the engine coolant flowing on the outside of the panel  24 .  
         [0026]    Inlet and outlet ports  28  and  30  are defined at opposed ends of the container  22  for allowing the hot engine coolant to pass through the container  22  on the outside of the panel  24 . As seen in FIG. 1, the inlet and outlet ports  28  and  30  are in fluid communication with appropriate tubing  32  connected in fluid communication with a standard cooling line  34  (see FIG. 2) through which engine coolant is normally circulated to cool the engine  12 . As seen FIG. 2, first and second solenoid valves S 1  and S 3  are provided to selectively allow or block engine coolant flow through the evaporator  18 . It is noted that the container  22  is sized so as to relatively tightly encircle the spirally wound panel  24 . The container  22  is preferably made of aluminum alloys in particular #6061 or #6063. The panel  24  is also preferably made of aluminum alloys but in particular #1001 or #3003. It is contemplated to provide more than one spirally wound panel within the container  22 . For instance, as illustrated in FIG. 2, three distinct working fluid passages  26  could be provided within the container  22 .  
         [0027]    The high-pressure vapor is then fed to an expander/turbine unit  36  which could include a commercial turbine section of a turbo-charger to obtain expansion of the organic working fluid for driving the turbine. According to a preferred embodiment of the present invention, the expander/turbine unit  36  is, in fact, a reverse-driven turbo-charger. The expander/turbine unit  36  operates at high speeds and provides an expansion pressure ratio of between 6:1 and 2:1.  
         [0028]    The expander/turbine unit  36  includes an output shaft  38  which is connected to a reduction gear unit  40  which is adapted to reduce the output from the expander/turbine unit  36  of 80-100,000 rpm to 1,8002,500 rpm. The reduction gear unit  40  uses an overrunning clutch (not shown) to avoid loading the internal combustion engine  12  when the thermal energy retrieval system  10  is not in use.  
         [0029]    As seen in FIG. 1, the reduction gear unit  40  is connected to a light belt system  42  which is, in turn, connected to the crankshaft  15  of the internal combustion engine  12  to add waste-thermally-retrieved power thereto. The light belt system  42  includes a freewheel  44  connected to the output of the reduction gear unit  40  to transmit power to a pulley  46  mounted for rotation with the crankshaft  15 . An endless toothed belt  48  extends over the freewheel  44  and the pulley  46  to transmit power from the freewheel  44  to the pulley  46  and, thus, the crankshaft  15 . This output-recuperated energy can also be used to operate the engine auxiliaries and/or to produce electrical power through a generator running at high speed.  
         [0030]    The reduction gear unit  40  and the light belt system  42  can be combined into a single unit which produces a speed reduction factor of between 40:1 and 70:1.  
         [0031]    The spent working fluid emanating from the expander/turbine unit  36  is then directed by means of a flexible hose  50  or the like into a condenser  52 , where it is cooled and condensed from a vapor state to a liquid state by a cold fluid, such as ambient air intake. Thereafter, the condensed fluid is pumped back into the evaporator  18  to repeat the cycle.  
         [0032]    The condenser  52  includes an aluminum frame  54  in which a serpentine tube  56  sits for receiving the working fluid therethrough. The tube  56  is preferably made of aluminum alloys, such as #1001. Fins (not shown) are spirally disposed around the tube  56  in order to increase the heat exchange surface and improve the efficiency of heat transfer. The fins are preferably made of aluminum alloy wire loops.  
         [0033]    A control system is provided to ensure optimized and safe operation of the thermal energy retrieval system  10 . More particularly, the control system has a threefold function:  
         [0034]    To isolate the thermal energy retrieval system  10  when the calculated output is below the required energy to operate the system  10 ;  
         [0035]    To allow efficient operation at part load; and  
         [0036]    To protect the various units from overpressure, over-temperature and over-speed.  
         [0037]    The control system includes a microprocessor (not shown) and a control valve  58  adapted to control the flow of the working fluid on the liquid side of the cycle. The control valve  58  is disposed between the feed pump  14  and the evaporator  18 . By using the control valve  58  on the liquid side of the cycle rather than on the vapor side thereof, a more compact and cheaper control valve can be used.  
         [0038]    The operation of the system  10  at part load is effected by controlling the mass flow rate of circulation of the working fluid. This is done automatically by the control valve  58 .  
         [0039]    When the calorific energy in the engine coolant reduces, the temperature of the working fluid at the exit from the evaporator  18  will drop. As seen in FIG. 2, a temperature sensor TC 1  senses the change and alters the opening of the control valve  58  such that less working fluid flows to the evaporator  18 , the rest being discharged through an overflow line  60  back to the inlet side of feed pump  14 . Accordingly, the control valve  58  have two output ports (not shown), one being connected in flow communication with the evaporator  18  and the other with the overflow line  60 .  
         [0040]    The opposite occurs when there is excess energy in the engine coolant. The temperature of the working fluid at exit from the evaporator  18  rises and the control valve opens so as to allow more working fluid to flow to the evaporator  18 .  
         [0041]    By so optimizing the efficiency of the cycle, it becomes possible to keep the dimensions of the evaporator as small as possible. It is noted that the choice of the working fluid has also a significant influence on the thermodynamic efficiency of the cycle and, thus, on the physical size of the elements forming the thermal energy retrieval system  10 .  
         [0042]    As mentioned hereinbefore, the control system through its microprocessor is adapted to activate the thermal energy retrieval system  10  only when sensed engine operating conditions are such that a positive power output can be obtained from the system  10 . The thermal energy retrieval system  10  can be readily deactivated or isolated by switching off the feed pump  14 . This is done by switching off the electromagnetic clutch  16  between the pulley  46  and the pump  14  itself.  
         [0043]    As seen in FIG. 2, the control system further includes a working fluid flow rate meter FM 1  mounted between the control valve  58  and the evaporator  18  to provide an output signal as a function of the flow rate of the working fluid directed to the evaporator  18 . The output signals from the flow rate meter FM 1  and the temperature sensor TC 1  are input into the microprocessor which is preprogrammed to calculate the power output of the thermal energy retrieval system  10  under these conditions. If the calculated power output is less than the consumption level of the feed pump  14 , plus an allowance for frictional losses, then the electromagnetic clutch  16  is switched off, and the system  10  ceases to operate. Thereafter, the normally open solenoid valves S 3  and S 1  are switched to close, thus returning the engine to normal radiator cooling and preventing engine coolant flow to the evaporator  18 . It is important for the switching sequence to occur in the order indicated above to avoid water hammer occurring. The microprocessor must be programmed accordingly.  
         [0044]    The reverse sequence occurs when the thermal energy retrieval system  10  is switched on again. The parameters used by the microprocessor to determine whether the thermal energy retrieval system  10  should be activated or not are obtained by a second flow meter FM 2  mounted in the engine cooling line  34  at an exit of the engine  12  and by a pair of temperature sensors TC 4  and TC 5  disposed in the cooling line  34  to sense the temperature of the engine coolant downstream and upstream of the engine  12 . The temperature sensor TC 4  and TC 5  could, for instance, consist of conventional thermocouples. The thermal energy retrieval system  10  is re-activated when the engine coolant flow rate, indicated by the second flow meter FM 2 , and the difference between the temperatures sensed by the sensors TC 4 -TC 5  indicates that a positive power input, plus frictional losses, can be expected. The calculation is done within the programmed microprocessor.  
         [0045]    For safety purposes, the thermal energy retrieval system  10  must not be subjected to overpressure. The most sensitive part is the evaporator  18  which is effectively a pressure vessel. As seen in FIG. 2, the pressure in the evaporator  18  is sensed by a piezoelectric gauge P 1  and the reading is conveyed to the microprocessor. If the pressure rises above a specified threshold, the system  10  is deactivated via the clutch  16 . When N-butane is used as the working fluid, it is not possible to have a normal pressure relief valve, since N-butane cannot be vented to atmosphere. A lower threshold is also specified within the microprocessor below which the pressure will need to drop before the system  10  is allowed to switch on again.  
         [0046]    Overheating can occur in the control valve and the overflow line  60  in cases when the majority of the flow is returned to the inlet of the feed pump  14  via the overflow line  60 . Accordingly, a thermocouple TC 2  has been provided to sense the temperature of the working fluid entering in the pump  14  and send an output signal to the microprocessor to deactivate the system  10  when a specified threshold is exceeded.  
         [0047]    Overheating can also occur in the expander/turbine unit  36  and the gear reducer unit  40 . As seen in FIG. 2, the expander/turbine unit  36  and the gear reducer unit  40  are cooled by the engine oil. To avoid overheating in the expander/turbine unit  36  and the gear unit  40 , a sensor, such as a thermocouple TC 3  is provided to sense the temperature of the return oil and send an output signal to the microprocessor in order to deactivated the system  10  when a specified threshold is exceeded.  
         [0048]    In each case, the thermal energy retrieval system  10  is allowed to switch on again when the temperatures sensed by TC 2  and TC 3  falls below a specified lower threshold.  
         [0049]    There is, additionally, the danger that, if a belt transmission, such as belt  48  (see FIG. 1) breaks while the expander/turbine unit  36  is driving, then the expander/turbine unit  36  will over-speed and damage itself or the gear unit  40 . Hence rider pulleys (not shown), positioned on each transmission belt; are provided to operate micro-switches, such as those designated by MS 1  and MS 2  in FIG. 2. In the event that a belt breaks, the associated rider pulley will trigger the associated micro-switch, thereby sending a signal to the microprocessor to shut down the system  10 .  
         [0050]    The design specifications for the microprocessor are as detailed in the above paragraphs. Additionally, warning lights and malfunction lights are provided for each function, and displayed on an instrument panel.  
         [0051]    It is also contemplated to circulate the engine exhaust gas through the evaporator  18  in order to evaporate the working fluid.  
         [0052]    [0052]FIG. 6 illustrates a second embodiment of the present invention wherein a large expansion chamber  80  is directly connected to the outlet of the expander/turbine unit  36  to reduce flow velocity and gas pressure, thus improving performance of the expander/turbiune unit  36  by increasing the ratio of expander entry pressure to exit pressure. At the same time, this will reduce the pressure losses in the condenser  52  leading to improvement in condenser performance. In order to assist in cooling the refrigerant (working fluid), it is contemplated to add some fins  82  on the hose or tube  50 . This additional cooling will reduce the pressure at the condenser inlet and reduce the cooling load, which will improve the overall system efficiency. Instead of connecting the feed pump  14  to the crankshaft  15  as illustrated in FIG. 1, the pump  14  is drivingly coupled to the power-take-off  84  of the truck transmission. This will result in more efficient pump performance due to the elimination of belt slippage. Likewise, the power generated from the expander/turbine unit  36  can be input into the power-take-off  84  of the truck transmission. This will also result in improved performance due to the elimination of belt slippage. On must truck transmissions there are two power-takeoffs  84  (see FIG. 6). This allows the feed pump  14  and the recuperated power to be connected to the transmission at the same time. Installation will also be universal, since all truck transmissions are equipped with similar power-take-offs. The second embodiment also differs from the first embodiment in that the expander/turbine unit  36  and the turbo-gear reducer  40  are surrounded by a jacket  86  through which the refrigerant is passed before being directed into the evaporator  18 . In this way, the heat removed from the expander/turbine unit  86  and the turbo-gear reducer  40  can advantageously be used to pre-heat the refrigerant before entering into the evaporator  18 , thus allowing a reduction in size of the evaporator  18 .  
         [0053]    [0053]FIG. 7 illustrates a third embodiment of the present invention wherein a turbo-alternator  88  is coupled to the expander/turbine unit  36  to convert mechanical energy into electricity. The turbo-alternator  88  generates heat and requires cooling. Therefore, it is contemplated to enclose the alternator  88  into a jacket  86 ′ similar to jacket  86 . The refrigerant will be flowed through the jacket  86 ′ to remove the required heat from the turbo-alternator  88  and the pre-heated refrigerant will then be directed into the evaporator  18 , as set forth hereinabove.