EXHAUST HEAT RECOVERY SYSTEM HAVING A WORKING FLUID CIRCUIT

Abstract

The invention relates to an exhaust heat recovery system with a working fluid circuit 1, having a heat exchanger 2a connected in an exhaust line 3 of an internal combustion engine 5, wherein the heat exchanger 2a is a part of the working fluid circuit 1 together with at least one expansion machine 11, a condenser 12 and a fluid pump 15a. According to the invention, an exhaust heat recovery system is provided which is improved as compared with known systems. This is achieved in that the exhaust heat recovery system has a protective device. The protective device protects the exhaust heat recovery system against a leakage amount of the working fluid escaping from the working fluid circuit and igniting and has a reservoir which receives a medium, wherein the reservoir is a reservoir 20 and the medium is a gas.

Claims

1. An exhaust heat recovery system comprising a working fluid circuit (1), the working fluid circuit having a heat exchanger (2a) connected in an exhaust gas line (3) of an internal combustion engine (5), the working fluid circuit (1) also having at least one expansion machine (11), a condenser (12) and a fluid pump (15a), the exhaust heat recovery system also comprising a protective device.

2. The exhaust heat recovery system as claimed in claim 1, characterized in that the protective device protects at least the exhaust heat recovery system from ignition of a leakage quantity of the working fluid escaping from the exhaust heat recovery system.

3. The exhaust heat recovery system as claimed in claim 2, characterized in that the protective device has a reservoir which receives a medium.

4. The exhaust heat recovery system as claimed in claim 3, characterized in that the reservoir is a gas reservoir (20) and the medium is a gas.

5. The exhaust heat recovery system as claimed in claim 3, characterized in that the protective device has a trigger device (23).

6. The exhaust heat recovery system as claimed in claim 5, characterized in that the trigger device (23) is part of a control unit (24) of the exhaust heat recovery system.

7. The exhaust heat recovery system as claimed in claim 5, characterized in that the trigger device (23) is connected to existing sensors.

8. The exhaust heat recovery system as claimed in claim 1, characterized in that the protective device is part of a decentralized exhaust heat recovery system.

9. The exhaust heat recovery system as claimed in claim 1, characterized in that the protective device is part of a centralized exhaust heat recovery system.

10. The exhaust heat recovery system as claimed in claim 1, characterized in that the protective device protects at least the exhaust heat recovery system from ignition of a leakage quantity of the working fluid escaping from the working fluid circuit (1).

11. The exhaust heat recovery system as claimed in claim 10, characterized in that the protective device has a reservoir which receives a medium.

12. The exhaust heat recovery system as claimed in claim 11, characterized in that the reservoir is a gas reservoir (20) and the medium is a gas.

13. The exhaust heat recovery system as claimed in claim 12, characterized in that the protective device has a trigger device (23).

14. The exhaust heat recovery system as claimed in claim 13, characterized in that the trigger device (23) is part of a control unit (24) of the exhaust heat recovery system.

15. The exhaust heat recovery system as claimed in claim 14, characterized in that the trigger device (23) is connected to existing sensors.

16. The exhaust heat recovery system as claimed in claim 15, characterized in that the protective device is part of a decentralized exhaust heat recovery system.

17. The exhaust heat recovery system as claimed in claim 15, characterized in that the protective device is part of a centralized exhaust heat recovery system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Further advantageous embodiments of the invention are shown in the description of the drawings, in which an exemplary embodiment shown in the FIGURE is described in more detail.

[0014] FIG. 1 is a circuit diagram of an exhaust heat recovery system configured according to the invention with a working fluid circuit and a protective device.

DETAILED DESCRIPTION

[0015] The exhaust heat recovery system shown diagrammatically in FIG. 1 has a working fluid circuit 1 with a first heat exchanger 2a and a second heat exchanger 2b, wherein in principle only a single heat exchanger or also more than two heat exchangers may be part of the exhaust heat recovery system. The heat exchangers 2a, 2b are here configured as or function as evaporators, and in an internal combustion engine 5, are designed to recover waste heat generated in operation of the internal combustion engine 5. An exhaust gas stream 4 from the internal combustion engine 5, forming a waste heat stream and conducted in an exhaust gas line 3 of the internal combustion engine, flows through the first heat exchanger 2a. In addition to the first heat exchanger 2a, the second heat exchanger 2b is installed in a line in the form of an exhaust gas recirculation line 6 or other heat carrier line. A part quantity of exhaust gas is taken from the exhaust gas stream 4 via the exhaust gas recirculation line 6 and supplied in controlled fashion via an exhaust gas recirculation line valve 7 to an intake system 8 of the internal combustion engine 5. The intake system 8 may preferably be configured as a charge air line system. The two heat exchangers 2a, 2b may in some cases be bypassed via heat exchanger bypass lines (not shown here) in certain operating states of the internal combustion engine 5 of a vehicle in which the internal combustion engine 5 is preferably installed. When the internal combustion engine 5 is installed in a vehicle, the internal combustion engine 5 and the exhaust heat recovery system, with the working fluid circuit 1 and the components mentioned or to be described below, are preferably installed in a engine bay of the vehicle.

[0016] In operation, the internal combustion engine 5 receives fuel and combustion air which burn in the combustion chambers of the internal combustion engine 5, generating working power as hot exhaust gas which forms the exhaust gas stream 4 in operation of the internal combustion engine 5. The exhaust gas stream 4 is finally discharged through the exhaust gas line 3, from which the exhaust gas recirculation line 6 also branches, to the environment. Exhaust silencers 9 and devices 10 for after-treatment of the exhaust gas, for example in the form of a catalytic converter and/or a filter, may be installed in the exhaust gas line 3 upstream and/or downstream of the first heat exchanger 2a, in any order. The internal combustion engine 5 is for example a self-igniting internal combustion engine operated on diesel fuel. The diesel fuel is here for example injected into the combustion chambers by means of a common rail injection system. The internal combustion engine may however also be an externally ignited, petrol-operated internal combustion engine which may also have an common rail injection system.

[0017] The first heat exchanger 2a and the second heat exchanger 2b, as stated above, are each part of the working fluid circuit 1 which comprises, in addition to the heat exchangers 2a, 2b, an expansion machine 11, a condenser 12, in some cases a condenser pump 13, an expansion tank 14, and one or two fluid pumps 15a, 15b. The fluid pump 15a is fluidically connected via a first supply line 16a to the first heat exchanger 2a, and the second fluid pump 15b is fluidically connected via a second supply line 16b to the second heat exchanger 2b. The fluid pumps 15a, 15b may be autonomous pumps, or for example be designed in the form of a double-stroke vane pump. For example, a double-stroke vane pump can be set such that, with a constant or adjustable total delivery quantity of the working fluid, the division of delivery quantity to the first heat exchanger 2a and the second heat exchanger 2b can be set increasinglyand accordingly decreasinglybetween 0% and 100%. The total delivery quantity may for example be set by changing the rotation speed of the fluid pumps 15a, 15b. As indicated above however, also only one single fluid pump 15 may be present, wherein then control valves are fitted in the first supply line 16a and in the second supply line 16b in order to set the distribution of the delivery quantity. If only a single heat exchanger is provided, naturally the delivery quantity distribution described above is not required.

[0018] The expansion machine 11 may for example be a piston machine or a turbine. In the case of a turbine, normally a reduction gear is fitted downstream in order to reduce the high turbine rotation speeds and adapt these to the rotation speeds of a downstream working machine or other consumer.

[0019] In operation of the exhaust heat recovery system, the fluid pumps 15a, 15b pressurize a fluid suitable for a Rankine process, for example ethanol or cyclopentane, to a high pressure and supply it to the heat exchangers 2a, 2b. The fluid is heated in the heat exchangers 2a, 2b and transferred into the gaseous state under high pressure. The resulting vapor is supplied to the expansion machine 11 and drives this under expansion of the working fluid. In order to conduct the working fluid circuit 1 past the expansion machine 11, a bypass line 17 may be provided with a bypass valve 18, via which the expansion machine 11 can be bypassed.

[0020] The working fluid supplied to the expansion machine 11 expands here, performing mechanical shaft work which is discharged via an output shaft. The output shaft 19 may for example be coupled to a generator to generate electrical power. Then the cold vapor is condensed in a condenser 12 and finally returned to the fluid pumps 15a, 15b. The expansion tank 14 is connected in the connecting line between the condenser 12 and the double-stroke vane pump 16. As well as the above-mentioned components, arbitrary further components may be provided, in particular sensors for determining temperatures and pressures in various portions of the working fluid circuit 1. Furthermore, a control unit is present for controlling the exhaust heat recovery system.

[0021] According to the invention, the exhaust heat recovery system has a protective device which may reliably prevent the ignition of a leakage quantity of the working fluid escaping from the working fluid circuit 1. For this, the protective device has a reservoir formed as a gas reservoir 20, in which a medium is stored in the form of a pressurized gas. Any number of nozzles 21 may be connected directly or via nozzle lines to the gas reservoir 20, and directed at various regions of the working fluid circuit 1. Furthermore, the gas reservoir 20 has a control connection 22 for a trigger device 23, which may be part of a control unit 24 of the exhaust heat recovery system. The control unit 24 or the trigger device 23 is connected to sensors which respond for example in the event of a vehicle crash or airbag deployment, or on detection of a suddenly rising concentration of the working fluid in the engine bay. If such a state is determined, the protective device is activated and the nozzles 21 of the gas reservoir 20 open, so that the gas present in the gas reservoir 20 can flow out and for example reduce the temperature of surrounding components of the working fluid circuit 12 below a critical ignition temperature. This prevents ignition or explosion of the leakage quantity of the working fluid. The gas reservoir 20 may also be provided with a filling device for the gas.