Internal combustion engine with heat recovery system

Abstract

Internal combustion engine (1) with a heat recovery device (2), comprising: - a conveying unit (3) for compressing a working medium (A) that is at least largely liquid; - a heat exchanger (4) for evaporating the working medium (A) by heat transfer from a heat medium (M) to the working medium (A); - an expansion device (5) for expanding the working medium (A), wherein mechanical energy can be extracted from the expansion device; - a condensation device (6) for cooling and / or condensing the working medium (A), in which the working medium (A) can be converted from a state of matter that is at least largely gaseous to a state of matter that is at least largely liquid, wherein the conveying unit (3), the heat exchanger (4), the expansion device (5) and the condensing device (6) are connected in a circuit (CRK) in which the working medium (A) is circulating, characterized by the fact that The condensing device (6) comprises a liquid-cooled first cooler (6.1) and an air-cooled second cooler (6.2), which are sequentially permeable to the working medium (A) during operation, and the liquid-cooled first cooler (6.1) is arranged in a cooling circuit (1.1) of the internal combustion engine (1) and is designed to allow permeability with a coolant (K), so that heat transfer between the working medium (A) and the coolant (K) is possible, and the cooling circuit (1.1) of the internal combustion engine (1) is coupled to an interior heating system of a motor vehicle, and the second cooler (6.2) comprises a fan, and viewed in the direction of flow of the working medium A, the liquid-cooled first cooler (6.1) is located upstream of the air-cooled second cooler (6.2).

Description

[0001] The invention relates to an internal combustion engine with a heat recovery device comprising a delivery unit for compressing an at least largely liquid working medium, a heat exchanger for evaporating the working medium, an expansion device for expanding the working medium, wherein mechanical energy can be extracted from the expansion device, and a condensation device for cooling and / or condensing the working medium. The delivery unit, the evaporator, the expansion device, and the condensation device are interconnected to form a circuit.

[0002] Today's internal combustion engines have an efficiency of up to 40 percent. Losses are primarily dissipated as heat to a cooling medium and as exhaust heat.

[0003] In the prior art, there are various methods and devices by means of which electrical and / or mechanical energy is obtained from exhaust gas heat and / or coolant heat.

[0004] WO 2005 / 021 936 A2 discloses an internal combustion engine with a heat recovery device, which can recover energy from the exhaust heat of an internal combustion engine. The heat recovery device comprises a conveying unit in the form of a pump, a heat exchanger, an expansion device in the form of a turbine, and a condensation device with a water cooler. These elements of the heat recovery device are connected to form a circuit through which a working medium can be conveyed. The internal combustion engine enables the conversion of thermal energy into mechanical work using a so-called Rankine cycle. During operation of the internal combustion engine, exhaust heat is transferred to the working medium in the heat exchanger, causing the working medium to evaporate. The vaporous working medium is then fed to the expansion device, where it is expanded to a lower pressure.From a thermodynamic perspective, the total enthalpy of the steam is reduced as it flows through the expansion device, with the enthalpy difference being extracted from the expansion device in the form of mechanical work. The vaporous working fluid is then fed to the condenser unit, where it condenses. The working fluid is then returned to the heat exchanger in liquid form via the conveying unit.

[0005] The subsequently published DE 10 2007 056 113 A1 discloses an internal combustion engine with a heat recovery device comprising a delivery unit for compressing an at least largely liquid working medium and a heat exchanger for evaporating the working medium by heat transfer from a heat medium to the working medium and an expansion device for expanding the working medium, wherein mechanical energy can be extracted from the expansion device and a condensation device for cooling and / or condensing the working medium, in which the working medium can be converted from an at least largely gaseous state into an at least largely liquid state and wherein the delivery unit, the heat exchanger, the expansion device and the condensation device are connected in a circuit in which the working medium can be circulated.The condensation device comprises a liquid-cooled first cooler and an air-cooled second cooler, through which the working medium can flow one after the other during operation.

[0006] DE JP S58-12 819 A discloses an internal combustion engine with a heat recovery device comprising a delivery unit for compressing an at least largely liquid working medium and a heat exchanger for evaporating the working medium by heat transfer from a heat medium to the working medium and an expansion device for expanding the working medium, wherein mechanical energy can be extracted from the expansion device and a condensation device for cooling and / or condensing the working medium, in which the working medium can be converted from an at least largely gaseous state into an at least largely liquid state and wherein the delivery unit, the heat exchanger, the expansion device and the condensation device are connected in a circuit in which the working medium can be circulated.The condensation device comprises a first cooler cooled by the working medium and an air-cooled second cooler, through which the working medium can flow one after the other during operation.

[0007] The subsequently published DE 10 2007 061 032 A1 discloses an internal combustion engine with a heat recovery device comprising a delivery unit for compressing an at least largely liquid working medium and a heat exchanger for evaporating the working medium by heat transfer from a heat medium to the working medium and an expansion device for expanding the working medium, wherein mechanical energy can be extracted from the expansion device and a condensation device for cooling and / or condensing the working medium, in which the working medium can be converted from an at least largely gaseous state into an at least largely liquid state and wherein the delivery unit, the heat exchanger, the expansion device and the condensation device are connected in a circuit in which the working medium can be circulated.The condensation device comprises a liquid-cooled first cooler and an air-cooled second cooler, through which the working medium can flow one after the other during operation. The liquid-cooled first cooler is arranged in a cooling circuit of the internal combustion engine and is designed to allow a coolant to flow through it, allowing heat transfer between the working medium and the coolant. The cooling circuit of the internal combustion engine is coupled to a motor vehicle interior heating system, and the second cooler comprises a fan.

[0008] The invention is based on the object of providing an internal combustion engine with a heat recovery device in which the conversion of thermal energy into mechanical and / or electrical energy is improved.

[0009] This object is achieved by an internal combustion engine having the features of claim 1. The condensation device comprises a liquid-cooled first cooler and an air-cooled second cooler, through which the working medium can flow one after the other during operation. Condensation of the working medium is provided in the first and / or second cooler, so that the working medium can be converted at least largely completely from a gaseous phase into a liquid phase. The arrangement of two coolers in the condensation device has the advantage that a large amount of heat can be dissipated via the condenser device, thus improving the efficiency of the heat recovery device.

[0010] The liquid-cooled first cooler is arranged in a cooling circuit of the internal combustion engine and is designed for a coolant to flow through, enabling heat transfer between the working fluid and the coolant. In this way, the first cooler is coupled to an existing cooling circuit, so that only a few additional components are required to implement the heat recovery device. Furthermore, with this design, the coolant can be heated quickly during a cold start of the internal combustion engine, thus improving cold-start characteristics.

[0011] The liquid-cooled first cooler is positioned upstream of the air-cooled second cooler in the direction of flow of the working fluid. This allows the working fluid to be supplied to the first cooler at a comparatively high temperature, and the cooling fluid in the first cooler can be heated quickly.

[0012] An embodiment of the invention is explained in more detail below with reference to drawings.

[0013] Showing: Fig. 1 schematically shows a circuit diagram of an internal combustion engine according to the invention with a heat recovery device, and Fig. 2 possible process sequences in a pressure-enthalpy diagram.

[0014] In Fig. 1 shows an internal combustion engine 1 with a heat recovery device 2 according to the prior art. The heat recovery device 2 comprises a delivery unit in the form of a pump 3, a heat exchanger 4, an expansion device in the form of a turbine 5, and a condensation device 6, which are connected in a circuit CRK, wherein a working medium A can be circulated in this circuit CRK. The working medium A can be, for example, water, ammonia, ethanol, n-butane, or another organic compound, as well as mixtures of the aforementioned media. The heat recovery device is suitable for implementing a Clausius-Rankine cycle.

[0015] Before entering pump 3, the working medium A is in the liquid phase. It has an initial, comparatively low temperature T1 and a lower process pressure p1 (compare Fig. 2). In pump 3, the liquid working medium can be compressed approximately adiabatically and isentropically to an upper process pressure p2. After compression, the working medium has a second temperature T2, which at least approximately corresponds to the first temperature T1 or slightly exceeds it (depending on the working medium used and the operating condition).

[0016] The working medium A can then be fed to the heat exchanger 4. In the heat exchanger 4, a heat transfer from an exhaust gas of the internal combustion engine 2 to the working medium A can be realized. The heat transfer takes place largely isobarically. As it flows through the heat exchanger 4, the working medium A is initially heated in the liquid phase largely isobarically to an upper boiling point T sheated and then evaporated isobarically and isothermally. The gaseous portion of the working medium increases continuously during evaporation until the working medium A is completely in the gaseous phase. The gaseous working medium is then superheated in the heat exchanger, largely isobarically, to a third temperature T3.

[0017] After flowing through the heat exchanger 4, the gaseous working medium A can be fed to the turbine 5, where it can be expanded essentially adiabatically to at least approximately the lower process pressure p1. Mechanical work can be extracted from the turbine 5 at a shaft (not shown). During the expansion, the working medium cools to a fourth temperature T4.

[0018] The working medium A can then be fed to the condensation device 6. The condensation device 6 comprises a liquid-cooled first cooler 6.1 and an air-cooled second cooler 6.2. The liquid-cooled first cooler 6.1 is coupled to a cooling circuit 1.1 of the internal combustion engine and, during operation, is flowed through by a coolant K. In the first cooler 6.1, a heat transfer from the working medium A to the coolant K can be realized. While flowing through the first cooler 6.1, the working medium A is initially largely isobarically cooled to a lower boiling temperature T ucooled. As the flow continues through the first cooler 6.1, further heat is extracted from the working medium A, so that a portion of the working medium A changes into a liquid phase. The partially condensed working medium A can then be fed to the second cooler 6.2. In the second cooler 6.2, heat can be transferred from the working medium into the ambient air, so that the remaining gaseous portion of the working medium A condenses. As the flow continues through the second cooler 6.2, the at least largely liquid working medium is cooled to approximately the first temperature T1. According to the invention, the second cooler 6.2 comprises a fan to improve the heat transfer and thus the cooling performance.

[0019] After flowing through the condensation device 6, the working medium A can be fed back to the pump 3 in at least a largely liquid phase, so that the circuit CRK is closed.

[0020] In the following, Fig. 2 possible process sequences under different operating conditions are described in a pressure-enthalpy diagram.

[0021] In the diagram, a boundary line S L , S G Areas are demarcated in which the working medium is present in different phases. The boundary line can be divided into a boiling line S L and a saturated steam limit S G which at a critical point T K merge into each other. The boiling point curve S L and the saturated steam limit S G Together they define a so-called wet steam region NG, in which the working fluid exists in both a liquid and a gaseous phase. With a reduction in enthalpy (e.g., by reducing the temperature at constant pressure) to below the boiling point S Lthe working fluid has completely entered the liquid phase; the area of ​​the pressure-enthalpy diagram bounded by the ordinate and the boiling point is therefore also referred to as the liquid region FG. An increase in enthalpy beyond the saturated vapor limit S G leads to a complete phase change into the gaseous phase, and the corresponding area of ​​the pressure-enthalpy diagram is called the so-called dry steam region TG.

[0022] The internal combustion engine is preferably designed for an operating point in which a comparatively small amount of heat is transferred from the exhaust gas to the working medium (e.g., partial load). The design is such that the working medium A evaporates in the heat exchanger 4 and cools down to a third temperature T 3**Subsequently, the working medium A is expanded in the turbine 5 to the saturated steam limit SG. After the expansion, the working medium has a fourth temperature T 4** which corresponds to the lower boiling point T u In the first cooler 6.1 and the second cooler 6.2, the working medium A is then condensed and optionally further cooled in the liquid phase. In modified embodiments, the internal combustion engine can also be designed such that the working medium A, when the internal combustion engine is operating at the design operating point in the turbine 5, expands slightly into the dry steam region TG or slightly into the wet steam region NG and thus, after the expansion, reaches a temperature T 4o** or T 4u** has.

[0023] If the amount of heat transferred in heat exchanger 4 increases (for example, due to an increase in the load of the internal combustion engine), the working fluid A has a higher third temperature T3 after flowing through the heat exchanger 4. After expansion in the turbine 5, the working fluid is therefore generally in the gaseous phase.

[0024] In a modified embodiment, the condensation device 6 is designed such that the working medium A can be condensed at an operating point or in an operating range up to the boiling point SL. The working medium A is then fed to the pump 3 and compressed there, so that after compression it reaches the second pressure p2 and a second temperature T 2* has.

[0025] In further, modified exemplary embodiments, the internal combustion engine is designed such that, at an operating point or in an operating range, the working medium can be completely condensed in the first cooler or completely in the second cooler. When the working medium expands in the turbine into the dry steam region TG, cooling of the working medium in the gaseous phase is provided in the first cooler before condensation begins. Furthermore, the internal combustion engine can be designed such that, at an operating point or in an operating range, after complete condensation in the first cooler, the working medium can be fed to the second cooler in the liquid phase and is cooled in the second cooler. Furthermore, it is also possible to design the internal combustion engine such that a small proportion of the working medium condenses in the turbine 5 during the expansion.In a further, modified embodiment, the internal combustion engine is designed such that the working fluid is cooled in the first cooler in the gaseous phase and fed to the second cooler in the gaseous phase. The working fluid is then condensed in the second cooler.

[0026] The internal combustion engine is installed in a motor vehicle. The cooling circuit passing through the first radiator is preferably coupled to an interior heating system of the motor vehicle. The rapid heating of the coolant K in the heat exchanger during a cold start thus leads to a rapid warming of the interior of the motor vehicle and increased comfort for the occupants.

[0027] The arrangement of two coolers in the condensation unit has the advantage of optimally utilizing the available installation space. Furthermore, the internal combustion engine according to the invention advantageously ensures the most complete condensation possible and sufficient cooling of the working fluid.

Claims

[1] Internal combustion engine (1) with a heat recovery device (2), comprising: - a conveying unit (3) for compressing an at least largely liquid working medium (A); - a heat exchanger (4) for evaporating the working medium (A) by heat transfer from a heat medium (M) to the working medium (A); - an expansion device (5) for expanding the working medium (A), wherein mechanical energy can be extracted from the expansion device; - a condensation device (6) for cooling and / or condensing the working medium (A), in which the working medium (A) can be converted from an at least largely gaseous state into an at least largely liquid state, wherein the conveying unit (3), the heat exchanger (4), the expansion device (5) and the condensation device (6) are connected in a circuit (CRK) in which the working medium (A) can be circulated, characterized by , that the condensation device (6) comprises a liquid-cooled first cooler (6.1) and an air-cooled second cooler (6.2), through which the working medium (A) can flow one after the other during operation, and the liquid-cooled first cooler (6.1) is arranged in a cooling circuit (1.1) of the internal combustion engine (1) and is designed so that a coolant (K) can flow through it, so that heat transfer between the working medium (A) and the coolant (K) can be realized, and the cooling circuit (1.1) of the internal combustion engine (1) is coupled to an interior heating system of a motor vehicle, and the second cooler (6.2) comprises a fan, and viewed in the flow direction of the working medium A, the liquid-cooled first cooler (6.1) is arranged upstream of the air-cooled second cooler (6.2).

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