WASTE HEAT RECOVERY SYSTEM FOR LIQUID-COOLED INTERNAL COMBUSTION ENGINE

Abstract: In a waste heat recovery system for a liquid-cooled internal combustion engine, including a water jacket 5 of a liquid-cooled internal combustion engine 101 in which the heat generating from the engine is absorbed by the engine cooling liquid, a first heat exchanger 2 for heat absorption from the exhaust gas in which the exhaust gas heat is absorbed thereby and a second heat exchanger 4 for heat recovery in which the waste heat is recovered from the engine cooling liquid retaiing the above-mentioned heat, a second circuit 3 for waste heat recovery from the engine comprises the first heat exchanger 2 and the second heat exchanger 4 both of which are connected to the water jacket 5 in series. The second circuit 3 is adapted to return the engine cooling liquid within the water jacket 5 to the water jacket 5 through the first heat exchanger 2 and the second heat exchanger 4 by a forced circulation force or a natural circulation force. Further, a first circuit 40 for engine cooling comprises an engine cooling radiator 6a which is connected to the water jacket in the manner of circulation loop. The first circuit 40 is adapted to circulate the engine cooling liquid at least through the water jacket 5 and the engine cooling radiator 6a. And the engine cooling radiator 6a is constructed so that the heat radiation therein can be controlled by the heat radiation control means 7.

Description: The present invention relates to a waste heat recovery system for a liquid-cooled internal combustion engine, in accordance with the introductory portion of patent claim 1. A conventional waste heat recovery system for a liquid-cooled internal combustion engine, in which the engine heat absorbed by engine cooling liquid in a water jacket and the exhaust heat absorbed thereby in a first heat exchanger for heat absorption from exhaust gas (a gas/liquid heat exchanger) are adapted to be recovered from the engine cooling liquid by the radiation performed in a second heat exchanger for heat recovery (a liquid/liquid heat exchanger), is, for example, described in US-A-4 226 214. This conventional system is provided with a circuit for a waste heat recovery from an engine, which is composed of a first heat exchanger for heat absorption from exhaust gas and a second heat exchanger for heat recovery both of which are connected in series to a water jacket within an engine body and in which the engine cooling liquid in the water jacket is adapted to be returned to the water jacket through the first heat exchanger and then the second heat exchanger. Therefore, the engine cooling liquid which absorbs the heat in the water jacket also absorbs the exhaust gas heat during flowing through the first heat exchanger to reach a high temperature and then radiates the heat retained therein to an external thermal load such as a hot-water reservoir and the like through a second heat exchanger. There are, however, the following disadvantages associated with the above-mentioned prior art: In the case that the output power of an internal combustion engine is taken out as an electric power and the like during its continuous operation, when the heat radiation is stopped by the stoppage of the operation of the external thermal load or when the heat quantity radiated in the second heat exchanger gets less than that absorbed in the first heat exchanger due to a reduction of the heat quantity consumed in the external thermal load, the temperature of the engine cooling liquid gets increased excessively because the heat quantity radiated form the engine cooling liquid in the second heat exchanger decreases. Resultantly, the continuous operation of the internal combustion engine is hindered by its overheat and disadvantageously it becomes impossible to continue the takeout of its output power. Furthermore, in JP-A-58-143 151 a waste recovery system of the kind described in the introductory portion of patent claim 1 is described in which the total flow of the engine cooling liquid by means of a selector valve can either by directed into the first circuit or into the second circuit, depending on the temperature sensed in the cooling liquid. The afore-mentioned waste heat recovery system, however, does not provide for adjustable portions of the cooling liquid to be directed into the first and second circuits, respectively, depending on the heat derived from the second heat exchanger and recovered. Furthermore, the afore-described waste recovery system is constructed in such a manner that in any case, even when heat recovery from the second heat exchanger is minimum, the cooling liquid is passed through the first heat exchanger, and not only through the engine cooling radiator, so that in case of minimum heat recovery from the second heat exchanger it is not possible to keep the temperature of the cooling liquid on such a low value as it might be desireble. The present invention therefore is directed to solving the problems mentioned above and has for its object to enable the continuous operation of an internal combustion engine in the case that the operation of an external thermal load is stopped and even in the case that a heat quantity consumed in the external thermal load gets less. The afore-mentioned object is solved by the features as mentioned in the characterizing clause of patent claim 1. Prefered embodiments are subject of the subclaims. By creating the possibility that in case of minimum heat recovery from the second heat exchanger the cooling liquid is passed merely through the engine cooling radiator, bypassing the first heat exchanger, it is possible to keep the cooling liquid temperature on a very low, minimum value even in case of very low heat recovery from the second heat exchanger. Furthermore, by dividing the total flow of the engine cooling liquid into two adjustable portions depending on the temperature sensed and depending on the degree of heat recovery in the second heat exchanger a smoothing of the temperature variation is achieved. It should be noted, however, that variable flow dividing valves are known as such from JP-A-58-202351 and "Modern Power and Engineering, Vol. 47, No. 1, January 1953, pages 63, 84, Maclean-Hunter Publishing Co., Ltd., Toronto, Ontario, CN. When the waste heat recovery system is fully operated according to a large external thermal load, the engine cooling radiator is changed over by the heat radiation control means so as to perform a partial radiation or to stop a radiation. In this condition, since great quantities of engine cooling liquid flows through these both heat exchangers of the water jacket and the first heat exchanger for the heat absorption from the exhaust gas, great quantities of heat are exchanged in these both heat exchangers. Accordingly, since the hot engine cooling liquid flows abundantly through the second heat exchanger, the waste heat recovery efficiency in the waste heat recovery system is enhanced. On the other hand, when the heat radiation in the second heat exchanger is stopped by the stoppage of the operation of the external thermal load or when heat quantity radiated in the second heat exchanger gets less than that absorbed in the first heat exchanger for the heat absorption from the exhaust gas due to the reduction of the heat quantity consumed in the external thermal load, the heat radiation control means is controlled as follows: The first circuit for the engine cooling is connected to the second circuit for the waste heat recovery from the engine in parallel therewith, the inlet portion of the first circuit for the engine cooling is connected to the intermediate portion between the water jacket and the first heat exchanger for the heat absorption from the exhaust gas as well as the outlet portion thereof is connected to the intermediate portion between the second heat exchanger for the heat recovery and the water jacket, the heat radiation control means is constructed by a circuit valve and the circuit changeover valve is constructed so that the engine cooling liquid can be circulated after the changeover thereof to one of the second heat exchanger for the heat recovery and the engine cooling radiator. Thereby the following advantage can be attained: When the full radiation condition is required owing to the stoppage of the operation of the external thermal load, the engine cooling liquid can be supplied abundantly to the engine cooling radiator of the first circuit for the engine cooling circuit. Hence, the engine cooling radiator can ensure great quantities of radiation heat per unit area and can be constructed compactly. By the invention, in the internal combustion engine increase of a back pressure thereof can be prevented so as to keep charging efficiency at a large value, and the output power as well as fuel consumption thereof can be improved by the improved charging efficiency. Further, since the temperature of the exhaust has can be decreased and the flow volume of the exhaust gas can be lessened, the internal combustion engine can be operated quietly without any increase of exhaust sound. Furthermore, since the flow of the engine cooling liquid can be divided to the second heat exchanger for the heat recovery and to the engine cooling radiator according to the operational condition of the external thermal load, the variation of the temperature of the engine cooling liquid can be restrained in a small extent so that the internal combustion engine can be operated within a suitable temperature range even in the case of a large variation of the external thermal load. In the case that the engine cooling liquid within the second circuit for the waste heat recovery from the engine is forcedly circulated by the water pump, since the water pump serves also as a pump which forcedly circulates the engine cooling liquid within the first circuit for the engine cooling, the necessary number of pumps can be reduced and the construction of the waste heat recovery system can be simplified. In the case that a heat radiation means for engine cooling is composed of the radiator and the radiator fan as well as they are located beyond the space provided for accomodating the second heat exchanger for the heat recovery at the lateral side of the internal combustion engine, since both the first heat exchanger for the heat recovery from the exhaust gas and the second heat exchanger for the heat recovery as well as the piping components for connecting the both heat exchangers are arranged compactly between the internal combustion engine and the radiator means for the engine cooling, the whole of the internal combustion engine can be constructed compactly. Furthermore, since the whole of the internal combustion engine can be contructed compactly, the length of each pipe line for the second circuit for the waste of recovery from the engine and the first circuit for the engine cooling can be shortened and the costs of piping materials and of the assembly thereof can be reduced. Furthermore since the second circuit for the waste heat recovery from the engine is short, the heat quantity radiated from the pipe line thereof can be reduced, the waste heat recovery efficiency can be enhanced. Furthermore since the second circuit for the waste heat recovery from the engine is short, the flow resistance of the engine cooling liquid can be decreased. Resultantly, the capacity of the water pump can be reduced. The foregoing and other objects and attendant advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1 is a systematic view of a preferred embodiment of a waste heat recovery system according to the invention; Figure 2 is a schematic perspective view showing an engine generator equipped with said waste heat recovery system; Figure 3 is a vertical sectional front view showing said engine generator, and Figure 4 is a horizontal sectional plan view showing said engine generator. Figures 1, 2, 4 show an embodiment of the invention in which a waste heat recovery system is combined in an internal combustion engine for an engine generator. First of all, a general arrangement of the engine generator 100 will be explained with reference to Fig. 2 as follows. In Fig. 2, the arrow of F designates the front side, the arrow of B does the back side, the arrow of L does the left side, and the arrow of R does the right side, respectively. Basing on the directions designated by those arrows, the surroundings of the engine generator 100 will be explained hereinafter. In the interior space within a soundproof casing 10 having a rectangular configuration, there are arranged an internal combustion engine 101 at the left side and a generator 103 at the right side in parallel each other. In the space at the left side of the internal combustion engine 101, there is arranged a heat radiation means 6 for engine cooling. The heat radiation means 6 for the engine cooling comprises an engine cooling radiator 6a and an electrically driven type radiator fan 6b. A battery 8 is provided in the space at the front side of the heat radiation means 6. In the space above the batttery 8, there are arranged an air cleaner 23, a second heat exchanger 4 for heat recovery and a first heat exchanger 2 for heat absorption from exhaust gas in order from the front side to the back side. In the space above the generator 103, a fuel tank 9 is provided. Now the engine generator 100 will be explained in detail with reference to Fig. 1, Fig. 3 and Fig. 4. In Figs. 3 and 4, an output shaft 11 is projected backward from an engine body 106 of the internal combustion engine 101 as well as an input 12 is projected backward from the generator 103. The output shaft 11 is connected interlockingly to the input shaft 12 by a belt type transmission means 13. The internal combustion engine 101 comprises a water-cooled horizontal Diesel engine of single cylinder type, in which a piston 16 is horizontally slidably fitted into a singly cylinder 15 formed in a cylinder body 14 and is connected interlockingly to a crankshaft 17. The output shaft 11 is formed at the rear end portion of the crankshaft 17. A cylinder head 18 and a head cover 19 are fixedly secured at the left side of the cylinder body 14 in order from the right side to the left side. A cylinder jacket 5a is formed in the cylinder body 14 and a head jacket 5b is formed n the cylinder head 18. These cylinder jacket 5a and head jacket 5b form a water jacket 5. The cylinder head 18 has an intake port 20 opened at the front side thereof and an exhaust port 21 opened at the back side thereof. The air cleaner 23 is connected to the intake port 20 through an intake pipe 22. An exhaust apparatus 1 of the internal combustion engine 101 comprises the first heat exchanger 2 and a muffler 25 which are connected to the exhaust port 21 through an exhaust pipe 24. The muffler 25 is arranged in the space below the belt type transmission means 13 so as to extend in the left and right direction and its extended outer end projects outward from the back and lower portion of the right side wall of the soundproof casing 10. Since the muffler 25 is located at a position remote from the fuel tank 9, the fuel tank 9 is effectively prevented form being heated intensively by the muffler 25 so that a vapourlock in a fuel supply system can be prevented. As a whole a waste heat recovery system 102 comprises a first circuit 40 for engine cooling and a second circuit 3 for waste heat recovery from the engine both of which are provided in the internal combustion engine 101 constructed as mentioned above. The waste heat recovery system 102 has the second heat exchanger 4 and the heat radiation means 6 for the engine cooling (the assembly of the radiator 6a and the radiator fan 6b) connected in parallel relative to the water jacket 5 of the internal combustion engine 101, constructed so as to enable the second circuit 3 for the waste heat recovery from the engine and the first circuit 40 the for engine cooling to be selectively changed over. The both circuits 3, 40 will be explained mainly with reference to Fig. 1. The second circuit 3 for the waste heat recovery from the engine is constructed as follows: The second circuit 3 has one end connected to an outlet nozzle 27 of the water jacket 5, is provided with the first heat exchanger 2, the second heat exchanger 4 and a water pump 104 arranged in order, and has the other end connected to an inlet nozzle 29 of a water jacket 5. The water pump 104 is connected interlockingly to the crankshaft 17 through the belt type transmission means 48 (refer to Figs. 3 and 4). The first circuit 40 for the engine cooling is constructed as follows: An inlet portion 40a of the first circuit 40 is branched out from the branching point 31 of the second circuit 3 and connected to an upper tank 37a of the radiator 6a through a hot water pipe 28. the outlet portion 40b is branched out from a branching point 32 of the second circuit 3 and is connected to a lower tank 37b of the radiator 6a through a cool water pipe 30. As heat radiation control means 7 for the radiator 6a there is provided a variable flow dividing valve 41 (7) capable of adjustably separating the engine cooling water into both circuits 3, 40, possibly of a thermostat type or an electrically driven type automatic dividing valve. This valve 41 (7) is provided at the branching point 31. The first heat exchanger 2 for the heat recovery from the exhaust gas comprises a gas/liquid type heat exchanger and serves to recover the residual heat of the exhaust gas which flows through the interiors of small tubes whilst the engine cooling water (the engine cooling liquid) flows outside the small tubes. The second heat exchanger 4 comprises a liquid/liquid type heat exchanger and serves to recover the heat of the engine cooling water which flows through the interiors of small tubes thereof, by fresh water 89 for heat recovery which flows outside the small tubes. A heat absorbing portion 40a of the second heat exchanger 4 for the waste heat recovery is connected through the cool water pipe 33 and the hot water pipe 24 to a hot water reservoir 90 which is provided outside the engine generator 100. An electrically driven type circulation pump 91 is interposed in the cool water pipe 33. The circulation pump 91 comprises an electrically driven pump which is supplied with electric power from the generator 103 as a driving source, and is arranged in the space below the second heat exchanger 4 within the soundproof casing 10 (refer ti Fig. 4). The flow of the engine cooling water in the waste heat recovery system 102 will be explained with reference to Fig. 1. In the case that the waste heat from the internal combustion engine 101 is required to be fully recovered owing to a large hot water feeding load in the hot water reservoir 90, the circuit changeover valve 41 (7) is set so as to allow the water flow to the first circuit 40. Accordingly, the engine cooling water from the water jacket 5 is adapted to be returned to the water jacket 5 through the dividing valve 41 (7), the first heat exchanger 2, the second heat exchanger 4, the branching point 32 and the water pump 104 so that the heat of the engine body 106, and the exhaust gas heat can be recovered in the second heat exchanger 4. To the contrary, in the case that the hot water feeding loads gets decreased or the hot water feeding is stopped in the hot water reservoir 90 and then the temperature of the engine cooling water gets increased, for example to not less than 95°C at the inlet side of the water jacket 5, the operation of the waste heat recovery is stopped. That is the water flow to the second circuit 3 is blocked and the water flow to the first circuit 40 is allowed by the changeover of the dividing valve 41 (7) to the radiation side. Thereupon, the engine cooling water from the water jacket 5 is returned to the water jacket 5 through the dividing valve 41 (7), the hot water pipe 28, the radiator 6a, the cool water pipe 30 and the water pump 104 so that solely the engine body 106 can be cooled. Between the afore discribed explained position the dividing valve 41 (7) can vary the portions of the slow into the two circuits 3, 40 over a white range. As shown in Figs. 3 and 4, since the water pump 104 and the electrically driven type circulation pump 91 etc. are arranged in the space between the engine body 106 and the radiator 6a in addition to the arrangement of the first and the second heat exchangers 2, 4 and the piping components for forming the first and the second circuits 40,3, the whole of the engine generator 100 can be constructed compactly. Therefore, the piping lengthes of the first and the second circuits 40, 3, can be shortened. Since the piping length of the second circuit 3 is comparatively short in that way, the radiation areas of the arranged pipes can be reduced so as to lessen the heat loss. And since the piping length of the first circuit 40 is also comparatively short, the resistance of water passage can be reduced and the cooling water can be circulated smoothly in the engine cooling system. Furter, since the radiator fan 6b is of a forced draft type in which cooling air is adapted to be forcedly discharged to the radiator 6a located at the left side thereof, the pipes and the like arranged in the space at the right side of the radiator fan 6b don't act as a draft resistance to the radiator fan 6b so as to enhance the cooling efficiency. By the way, as shown by an alternate long and two short dashes line as a phantom line in Fig. 1, the upper reaches of the second circuit 3 relative to the first heat exchanger 2 and the lower reaches thereof relative to the water pump 104 may be connected by an auxiliary flow line 43 and a bypass control valve 46 comprising a throttling valve, or a stop valve may be provided in this auxiliary flow line 43. In this case, even though the water flow to the second circuit 3 is blocked by the circuit changeover valve 41, the first heat exchanger 2 can be cooled sufficiently by the delivery of the engine cooling water from the bypass control valve 46 thereto 2. By the way, as the internal combustion engine 101 according to the present invention, a gasoline engine or a gas engine may be employed instead of the Diesel engine. And instead of the horizontal engine, a vertical engine of a vertical shaft type engine having a crankshaft arranged in a vertical manner may be employed. Further, the heat radiation means 6 for the engine cooling may be merely the assembly of the radiator and the radiator fan. The heat radiation means 6 may be a condenser or a hopper instead of the radiator. And as the engine cooling liquid, the engine cooling water may be replaced with other cooling liquid such as cooling oil and the like.

Claims: 1. A waste heat recovery system for a liquid-cooled internal combustion engine, including a second circuit (3) for waste heat recovery form the engine comprising a first heat exchanger (2) for heat absorption from the exhaust gas in an exhaust apparatus (1) and a second heat exchanger (4) for heat recovery both of which being connected to a water jacket (5) within an engine body (106) in series, said second circuit (3) being constructed so that the engine cooling liquid being circulated in order through the water jacket (5), the first heat exchanger (2), the second heat exchanger (4) and the water jacket (5) to absorb the heat generating from the engine body (106) in the water jacket (5), absorb the exhaust gas heat in the first heat exchanger (2) and then radiate the heat thereof in the second heat exchanger (4), said water jacket (5) being connected to an engine cooling radiator (6a) in the manner of a circulation loop so as to form a first circuit (40) for engine cooling, said first circuit (40) for the engine cooling being constructed so that the engine cooling liquid is circulated at least through the water jacket (5) and the radiator (6a) to absorb the heat generating form the engine body (106) in the water jacket (5) and then radiate the heat thereof in the radiator (6a), and said engine cooling radiator (6a) being so arranged that the heat radiation therein is able to be controlled by a heat radiation control means (7), wherein the first circuit (40) for the engine cooling is connected to the second circuit (3) for the waste heat recovery from the engine in parallel therewith, characterized in that an inlet portion (40a) of the first circuit (40) for the engine cooling is connected to the intermediate portion between the water jacket (5) and the first heat exchanger (2) for the heat absorption from the exhaust gas as well as an outlet portion (40b) thereof (40) is connected to the intermediate portion between the second heat exchanger (4) for the heat recovery and the water jacket (5); and that the heat radiation control means (7) comprises a variable flow dividing valve (41 (7)) adapted to divide the flow of the engine cooling liquid into two portions to the second heat exchanger (4) for the heat recovery and to the engine cooling radiator (6a) as well as to vary its dividing proportion adjustably; 2. A waste heat recovery system according to claim 1, characterized in that a water pump (104) is interposed between the second heat exchanger (4) for the heat recovery and the water jacket (5). 3. A waste heat recovery system according to claim 1 or 2, characterized in that the enginge cooling radiator (6a) and the radiator fan (6b), of which a heat radiation means (6) for engine cooling is composed, are located beyond the space provided at the lateral side of the internal combustion engine (101) for accomodating heat recovery component devices, and that the first heat exchanger (2) for the heat absorption from the exhaust gas and the second heat exchanger (4) for the heat recovery are located within said space as well as the air within the space is discharged to the engine cooling radiator (6a) by the radiator fan (6b).

Inventors: ISODA, MITSUMASA C/O KUBOTA LTD., NISHITSUJI, TAMOTSU C/O KUBOTA LTD., TAKAMATSU, YOSHIMICHI C/O KUBOTA LTD., TAKAMIYA, KATSUNORI C/O KUBOTA LTD.
Applicants: KUBOTA LTD.
Application year: 1988
Main classification: F02G5
IPC codes: F02B1, F01P3, F02G5, F02B3