DE102017006172B4 - Arrangement for the recovery of thermal energy in exhaust gases from an internal combustion engine - Google Patents

Abstract

Arrangement for the recovery of thermal energy in exhaust gases from an internal combustion engine (2), the arrangement comprising a heat recovery system which comprises:
- a heat recovery circuit (18) with a circulating working medium,
- An evaporator (20) in which the working medium is heated by exhaust gases from the internal combustion engine (2),
- an expander (22) and
- A heat accumulator (21), characterized in that the arrangement further comprises at least one set of heat pipes (21a-e) which is configured to transfer heat energy between the heat accumulator (21) and the exhaust gases or the working medium, the at least a set of heat pipes (21a-e) comprises a set of heat pipes (21b) configured to transfer thermal energy from the heat accumulator (21) to the working medium in a conduit (18a) that carries the working medium to the expander (22 ) directs.

Description

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to an arrangement for recovering thermal energy in exhaust gases from an internal combustion engine according to the preamble of claim 1.

A WRG system (heat recovery system) can be used to recover waste heat energy and convert it into mechanical energy or electrical energy. A heat recovery system comprises a pump that pressurizes and circulates a working medium in a closed circuit. The circuit includes an evaporator in which the working medium is heated and evaporated by a heat source, such as exhaust gases. The pressurized and heated gaseous working medium expands in an expander. The expander generates mechanical energy that can be used to support the engine and / or devices in a vehicle. Alternatively, the expander is connected to a generator that generates electrical energy. The fuel consumption of an internal combustion engine can be reduced by means of a heat recovery system. However, if the heat recovery system does not include expensive equipment that converts the thermal energy into electrical energy, the waste heat energy can generally only be used at the time it is generated. During certain operating conditions there is more heat energy in the exhaust gases than can be used by the heat recovery system. During other operating conditions there is essentially no thermal energy in the exhaust gases that can be used by the heat recovery system.

Heat pipes are used in various technical fields. A heat pipe is a closed evaporator / condenser system that consists of a sealed hollow tube, the inner walls of which are lined with a capillary structure or a wick. Thermodynamic working fluid with substantial vapor pressure at the desired operating temperature saturates the pores of the wick in a state of equilibrium between liquid and vapor. When heat is applied to the heat pipe, the liquid in the wick heats up and evaporates. As the evaporating fluid fills the hollow center of the heat pipe, it diffuses across its length. Condensation occurs where the temperature is even slightly below the temperature of the evaporation area. As it condenses, the vapor releases the heat absorbed during evaporation. This effective high heat conduction helps to maintain almost constant temperatures along the entire length of the pipe.

document WO 2014/096 892 A1 Figure 11 shows an engine assembly including an internal combustion engine and a heat recovery system in which a working fluid is sequentially pumped by a pump, heated in a heat exchanger with a heat source generated by engine operation, and expanded in an expander. The heat recovery system further comprises a heat storage device with a heat storage material which is in direct thermal contact with the working medium through a partition. Heat can be supplied from the heat source (hot exhaust gas) to the heat storage device via an intermediate fluid.

It is also from document DE 10 2012 202 150 A1 a heat storage device known which absorbs heat from an exhaust pipe and transfers it via a heat pipe to a heat storage device remote from the exhaust pipe.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an arrangement which is relatively simple in construction and which recovers thermal energy in exhaust gases from an internal combustion engine and is capable of converting it into mechanical energy when there is a need for energy.

The above-mentioned object is achieved by the control system according to the characterizing part of claim 1. The arrangement comprises a heat recovery system, which is designed with an evaporator and a heat store with a high heat storage capacity. The presence of the heat accumulator makes it possible to store heat energy during a high load when there is too much heat energy in the exhaust gases to be converted into mechanical energy by the heat recovery system. It is also possible to store thermal energy from the exhaust gases when there is no energy requirement for the heat recovery system. The stored thermal energy can be used to evaporate and overheat the working medium if the thermal energy in the exhaust gases is too low. The presence of the heat pipes makes it easy to transfer heat to and / or from the heat accumulator. Thus, no lines for a heat transfer fluid and valves that control the flow of the heat transfer fluid to and from the heat accumulator need to be used.

According to one embodiment of the invention, the working fluid in the heat pipes is cesium or antimony (III) bromide SbBr ₃ . This working fluid changes phases within temperature ranges suitable for this application. However, it is of course also possible to use other working fluids in the heat pipes.

According to one embodiment of the invention, the at least one set of heat pipes has a high thermal conductivity in one direction and a low thermal conductivity in an opposite direction. In certain cases it is only desirable to transfer heat to and from the heat accumulator in one direction. In such cases it is possible to use diode heat pipes.

According to one embodiment of the invention, the arrangement comprises an exhaust line that guides exhaust gases through the evaporator, and an evaporator bypass line that guides exhaust gases past the evaporator, and a valve through which it is possible to reduce the exhaust gas flow through the evaporator or evaporators -Bypass line, wherein a set of heat pipes is configured to transfer heat from the exhaust gases in the evaporator bypass line to the heat accumulator. In this case it is possible to pass a suitable part of the exhaust gases through the evaporator so that the working medium evaporates and is superheated to a suitable temperature before it is passed to the expander. A possible excess part of the flue gases is routed through the evaporator bypass line, where they heat the heat accumulator via the set of heat pipes.

According to the invention, the arrangement comprises a set of heat pipes which is configured to transfer thermal energy from the heat accumulator to the working medium in a line which conducts the working medium to the expander. In this case it is possible to change the superheating of the working medium before it enters the expander. The heat accumulator can preferably be used to increase the overheating if it is too high and to reduce it if it is too high.

According to one embodiment of the invention, the arrangement comprises a first set of heat pipes which is configured to transfer thermal energy from the working medium to the heat accumulator, and a second set of heat pipes which is configured to transfer heat energy from the heat accumulator to the working medium . In this case, it is necessary to use heat pipes that transfer heat energy in one direction. If the overheating of the working medium is too high, thermal energy is transferred from the working medium to the heat accumulator, which leads to overheating of the working medium before it enters the expander. If the overheating of the working medium is too low, thermal energy is transferred from the heat accumulator to the working medium, which leads to increased overheating of the working medium before it enters the expander.

According to one embodiment of the invention, the evaporator and the heat accumulator are arranged in parallel in the heat recovery system, and the valve device comprises a valve which directs the working medium flow to the evaporator or the heat accumulator. In this case it is possible to use the evaporator or the heat accumulator for the evaporation and superheating of the working medium. It is possible to switch between the two alternatives and use the currently best alternative. In this case, the heat accumulator can be heated by exhaust gases via a set of heat pipes. As a result, the heat accumulator can have a high temperature and capacity to vaporize and overheat the working medium during most operating conditions.

According to one embodiment of the invention, it comprises a control unit which is configured to control the valve device by means of information from at least one operating parameter. The operating parameter can relate to at least one of the following parameters: the temperature of the exhaust gases, the temperature of the second heat exchanger, the load of the internal combustion engine and the energy requirement of the heat recovery system. The temperature difference between the exhaust gases and the heat accumulator can be used to determine whether it is possible to heat the heat accumulator by means of the exhaust gases. The load on the internal combustion engine is related to the exhaust gas flow and the temperature of the exhaust gases, which define the thermal energy in the exhaust gases.

According to one embodiment of the invention, the heat accumulator comprises a solid that is heated by the exhaust gases. Such a solid can, for example, be a ceramic material. Alternatively or in combination, the heat store comprises a phase change material. During a phase change process, a large amount of thermal energy can be transferred between the exhaust gases and such a material. A heat storage device that includes a phase change material does not have to be significantly heavier than the evaporator. Furthermore, a heat store provided with a phase change material has an essentially constant temperature during the phase change process of the material. The phase change material can be, for example, tin or zinc. According to a further alternative, the heat store can be a mixture of two phase change materials. In this case, the heat store can be defined as a heat energy store with two different temperature levels.

Figure list

• 1 eine Anordnung gemäß einer ersten Ausführungsform der Erfindung zeigt,
• 2 eine Anordnung gemäß einer zweiten Ausführungsform der Erfindung zeigt, und
• 3 eine Anordnung gemäß einer dritten Ausführungsform der Erfindung zeigt.

In the following, preferred embodiments of the invention are described as examples with reference to the accompanying drawings, in which:

• 1 shows an arrangement according to a first embodiment of the invention,
• 2 shows an arrangement according to a second embodiment of the invention, and
• 3 shows an arrangement according to a third embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

1 shows a schematically disclosed vehicle 1 made by a supercharged internal combustion engine 2 is driven. The internal combustion engine 2 can be a diesel engine. The vehicle 1 can be a heavy vehicle. The vehicle 1 includes an exhaust pipe 3 , the exhaust gases from the internal combustion engine 2 receives. The exhaust pipe 3 includes a turbine 4a a turbo unit 4th . The turbine 4a drives a compressor 4b of the turbocharger 4th at. The compressor 4b compresses air via a charge air line 5 to the internal combustion engine 2 to be led. The charge air line 5 includes an intercooler 6th on a front portion of the vehicle 1 is arranged.

The vehicle 1 includes a cooling system that has an engine intake duct 7th includes, the coolant to the internal combustion engine 2 directs. The engine inlet pipe 7th is with a pump 8th provided, which circulates a coolant in the cooling system. That the internal combustion engine 2 Leaving coolant is in an engine exhaust line 9 recorded. A first valve element 10 in the form of a three-way valve 10 is at one end of the engine exhaust pipe 9 arranged. The cooling system includes a cooler bypass line 11 and a cooler 12th . The first valve element 10 is able to get coolant from the engine exhaust line 9 to receive and part of it to the cooler bypass line 11 and a remaining part of it on the radiator 12th to distribute. The cooling system includes a second valve element 14th in the form of a three-way valve. The second valve element 14th can coolant from the cooler bypass line 11 received and it to the engine intake pipe 7th or to a condenser circuit 15th conduct in which the coolant is a working medium in a condenser 16 a heat recovery system cools. In the latter case, coolant is taken from the cooler bypass line 11 and possible coolant from the radiator 12th mixed and to the condenser circuit 15th directed. Alternatively, the second valve element receives 14th Coolant from the radiator 12th and directs it to the engine inlet pipe 7th . The condenser circuit 15th includes a condenser inlet line 15a , the coolant to the condenser 16 and a condenser outlet line 15b who have favourited the coolant from the condenser 16 to the engine inlet pipe 7th directs.

As a result, the vehicle is equipped with a WRG system (heat recovery system). The heat recovery system includes a pump 17th that are a working medium in a heat recovery circuit 18th pressurized and circulated. The working medium can be ethanol, R245fa or another type of working medium. The working medium that the pump 17th leaves, enters an evaporator 20th a. The working medium is created by exhaust gases in the evaporator 20th heated in such a way that it is evaporated and superheated before it passes through an expander inlet line 18a to an expander 22nd is directed. The overheated working medium expands in the expander 22nd the end. The expander 22nd generates a rotational movement that is via a suitable mechanical transmission to a shaft or the drive train of the vehicle 1 can be transferred. After the working medium has passed the expander 22nd it becomes the condenser 16 directed. The working medium is in the condenser 16 through the coolant in the condenser circuit 15th cooled to a temperature at which it condenses. The liquid working medium is taken from the condenser 16 to a collecting container 23 directed. Working medium is taken from the collecting tank 23 to the pump 17th sucked.

The exhaust pipe 3 includes an evaporator bypass line 3a and a valve 24 that the exhaust gas flow through the evaporator bypass line 3a controls. The valve 24 is infinitely adjustable. The valve 24 can be a throttle valve. A control unit 28 controls the valve 24 and the exhaust gas flow through the evaporator bypass line 3a . A heat store 21 can heat energy from the exhaust gases in the bypass line 3a over a first set of heat pipes 21a receive. The heat storage 21 transfers thermal energy to the working medium in the expander inlet line 18a over a second set of heat pipes 21b . The first set of heat pipes 21a and the second set of heat pipes 21b are dimensioned to transfer thermal energy within a temperature range defined by the working fluid in the heat pipes. The heat pipes can contain, for example, cesium or antimony (III) bromide SbBr ₃ , which has a suitable operating temperature range for this application.

The heat storage 21 may comprise a solid, for example a ceramic material. Alternatively or in combination, it can comprise a phase change material, for example tin, which melts at about 230 ° C., or zinc, which at melts about 430 ° C. There can also be a mixture of two phase change materials in the heat store 21 be used. A first temperature sensor 29 detects the temperature T _{1 of} the exhaust gases at one of the evaporators 20th upstream position and a second temperature sensor 30th detects the temperature T _{2 of} the second heat accumulator 21 . The control unit 25th receives information from the temperature sensors 29 , 30th . The control unit 25th can also provide information about other operating parameters, such as the load 31 of the internal combustion engine 2 and the energy requirements 32 of the heat recovery system. Weight 31 of the internal combustion engine 2 refers to the amount of thermal energy in the exhaust gases. In this case, the heat recovery system is designed in such a way that it has the capacity to absorb the entire thermal energy in the exhaust gases at a normal load of the internal combustion engine 2 to win back.

The control unit receives during operation 25th information about the temperature T _{1 of} the exhaust gases in the exhaust pipe 3 , the temperature T _{2 of} the heat accumulator 21 , the load of the internal combustion engine 31 and the energy requirements of the heat recovery system 32 . When an energy demand 32 of the heat recovery system is present, the control unit initially checks whether the exhaust gases have a temperature T ₁ that is high enough to allow the working medium in the evaporator 20th to evaporate. During normal engine load 2 the exhaust gases essentially always have a temperature T ₁ which is high enough for the working medium in the evaporator 20th to evaporate and superheat to a suitable temperature. The working medium has a temperature T ₃ when it enters the evaporator 20th leaves. In the expander inlet line 18a overheating of the working medium by the heat accumulator 21 over the second set of heat pipes 21b be changed before the working medium enters the expander 22nd entry. By means of the information about the temperature T _{1 of} the exhaust gases in the exhaust pipe 3 and the temperature T _{2 of} the heat accumulator 21 regulates the control unit 25th the valve 24 such that a suitable part of the exhaust gas flow is used to generate the working medium in the evaporator 20th to heat, and a remaining part of the exhaust gas flow is used, the heat storage 21 about the first set of heat pipes 21a to warm up. As a result, the working medium enters the expander 22nd with a suitable overheating. If the heat recovery system does not need any energy, the control unit switches 25th the heat recovery system and opens the valve 24 so that the exhaust gas flow through the evaporator bypass line 3a is directed. In this case, the heat accumulator 21 by the thermal energy in the exhaust gases through the first set of heat pipes 21a warmed up.

2 shows an alternative embodiment of the arrangement. In this case it is the heat accumulator 21 over a first set of heat pipes 21c and a second set of heat pipes 21d with two points of the expander inlet line 18a thermally connected. In this case the heat pipes are 21c , 21d in such a way that they can only transfer heat in one direction. Such heat pipes 21c , 21d can be diode heat pipes. The control unit receives during operation 25th information about the temperature T _{1 of} the exhaust gases in the exhaust pipe 3 , the temperature T _{2 of} the heat accumulator 21 , the load of the internal combustion engine 31 and the energy requirements of the heat recovery system 32 . When an energy demand 32 WRG system is present, the control unit initially checks whether the exhaust gases have a temperature T ₁ that is high enough to keep the working medium in the evaporator 20th to evaporate. If this is the case, the control unit starts 17th the pump 17th of the heat recovery system. That the vaporizer 20th the evaporated and superheated working medium leaving it has a temperature T ₃ . In the case in which the temperature T _{3 of} the working medium is lower than the temperature T _{2 of} the heat accumulator 21 is, the working medium is through the heat accumulator 21 about the first set of heat pipes 21c warmed up. In the case in which the temperature T _{3 of} the working medium is higher than the temperature T _{2 of} the heat accumulator 21 is the heat storage 21 through the working fluid through the second set of heat pipes 21d warmed up.

In the event that the exhaust gases have a very high temperature T ₁ , the working medium is in the evaporator 20th get too high overheating to a temperature T ₃ , which is higher than the temperature T _{2 of} the heat accumulator 21 is. In such a case, part of the thermal energy in the working medium becomes the heat store 20th over the second set of heat pipes 20d transfer. In this case, the initially excessive overheating of the working medium is reduced to a suitable overheating temperature before it enters the expander 22nd entry. In the event that the exhaust gases have a very low temperature T ₁ , the working medium is in the evaporator 20th achieve too low overheating to a temperature T ₃ , which is lower than the temperature T _{2 of} the heat accumulator 21 is. In such a case, part of the in the heat accumulator 21 stored thermal energy through the first set of heat pipes 21c transferred to the working medium. In this case, the initially too low superheating of the working medium is increased to a suitable superheating temperature of the working medium before it enters the expander 22nd entry. As a result, it is possible to overheat the working medium in a suitable manner in the event of fluctuating temperatures T _{1 of} the exhaust gas in the exhaust line 3 to obtain.

3 Figure 3 shows a further alternative embodiment of the arrangement. In this case it is the heat accumulator 21 in an evaporator bypass line 20a of the heat recovery cycle 18th arranged. The heat recovery system also includes a valve 34 that the working medium flow through the evaporator 20th controls, and a valve 34 that the working medium flow through the evaporator bypass line 20a controls. A set of heat pipes 21e provides a heat transfer between the exhaust gases in the exhaust pipe 3 and the heat storage 21 ready.

The control unit receives during operation 25th information about the temperature T _{1 of} the exhaust gases in the exhaust pipe 3 , the temperature T _{2 of} the heat accumulator 21 , the load of the internal combustion engine 31 and the energy requirements of the heat recovery system 32 . When an energy demand 32 of the heat recovery system is present, the control unit checks 25th initially, whether the exhaust gases have a temperature T ₁ , which is high enough to the working medium in the evaporator 20th to evaporate and overheat. If this is possible, the control unit opens 25th the valve 33 and closes the valve 34 so that the working medium passes through the evaporator 20th is directed. If this is not possible, the control unit checks 25th whether the heat storage 21 has a temperature T ₂ which is high enough to evaporate and overheat the working medium. If this is possible, the control unit closes 25th the valve 33 and opens the valve 34 so that the working medium through the heat accumulator 21 is directed. In this embodiment, the control unit 25th allows to switch between the two alternatives in order to evaporate and overheat the working medium during operation. If the heat recovery system does not need any energy, the control unit switches 25th the heat recovery system and controls the valves 33 , 34 such that the exhaust gases pass through the evaporator bypass line 20a be directed. The exhaust gases heat the heat accumulator 21 to a temperature T ₂ , which is normally high enough to evaporate and overheat the working medium, and to a suitable temperature when the heat recovery system requires energy.

The invention is not restricted to the embodiment described, but can be varied freely within the scope of the claims.

Claims (12)

Arrangement for recovering thermal energy in exhaust gases from an internal combustion engine (2), the arrangement comprising a heat recovery system which comprises: - a heat recovery circuit (18) with a circulating working medium, - an evaporator (20) in which the working medium is heated by exhaust gases from the internal combustion engine (2), - an expander (22) and - a heat accumulator (21), characterized in that the arrangement further comprises at least one set of heat pipes (21a-e) which is configured to generate thermal energy between the heat accumulator (21) and the exhaust gases or the working medium, wherein the at least one set of heat pipes (21a-e) comprises a set of heat pipes (21b) which is configured to transfer heat energy from the heat accumulator (21) to the Transferring the working medium in a line (18a) which conducts the working medium to the expander (22). Arrangement according to Claim 1 , characterized in that the working fluid in the heat pipes (21a-e) is cesium or antimony (III) bromide SbBr ₃ . Arrangement according to one of the preceding claims, characterized in that at least one set of heat pipes (21c, 21d) comprises diode heat pipes which have a high thermal conductivity in one direction and a low thermal conductivity in an opposite direction. Arrangement according to one of the preceding claims, characterized in that the arrangement has an exhaust gas line (3) which routes exhaust gases through the evaporator (20) and an evaporator bypass line (3a) which routes exhaust gases past the evaporator (20), and a valve (24) which enables the flow of exhaust gases to be directed through the evaporator (20) or the evaporator bypass line (3a), a set of heat pipes (21a) configured to remove heat from the exhaust gases in the Evaporator bypass line (3a) to lead to the heat accumulator (21). Arrangement according to Claim 3 , characterized in that the arrangement comprises a first set of heat pipes (21c) which is configured to transfer thermal energy from the working medium to the heat accumulator (21), and a second set of heat pipes which is configured to transfer heat energy from the heat accumulator (21) to transmit to the working medium, comprises. Arrangement according to one of the preceding Claims 1 until 3 , characterized in that the heat accumulator (21) is arranged in a line (20a) parallel to the evaporator (20) in the heat recovery system (18) and that the working medium is sent to the evaporator ( 20) or the heat accumulator (21). Arrangement according to Claim 6 , characterized in that the heat accumulator (21) is configured to be heated by thermal energy from the exhaust gases via a set of heat pipes (21e). Arrangement according to one of the preceding claims, characterized in that it comprises a control unit (25) which is configured to control the heat recovery system by means of information from at least one operating parameter. Arrangement according to Claim 8 , characterized in that the operating parameter relates to at least one of the following parameters: the temperature T _{1 of} the exhaust gases, the temperature T _{2 of} the heat accumulator (21), the load (31) of the internal combustion engine (2) and the energy requirement (32) of the heat recovery system . Arrangement according to one of the preceding claims, characterized in that the heat accumulator (21) comprises a solid to be heated. Arrangement according to one of the preceding claims, characterized in that the heat accumulator (21) comprises a phase change material to be heated. Arrangement according to one of the preceding claims, characterized in that the heat store (21) comprises a mixture of two phase change materials to be heated.

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