WO2020151989A1

WO2020151989A1 - Combustion engine cooling circuit equipped with a heat recovery circuit

Info

Publication number: WO2020151989A1
Application number: PCT/EP2020/050737
Authority: WO
Inventors: Pierre Leduc; Alain Ranini
Original assignee: IFP Energies Nouvelles
Priority date: 2019-01-23
Filing date: 2020-01-14
Publication date: 2020-07-30
Also published as: EP3914817A1; FR3091898B1; JP2022518502A; FR3091898A1

Abstract

The evaporator (23) of a heat recovery circuit (24) associated with a cooling circuit (14) of a combustion engine (13) is arranged on a bypass (18) of an outlet pipe (16) outside the engine, and a valve (17) controls the distribution of the heat transfer streams between the bypass (18) and the portion parallel to the pipe (16). The flow passes fully or mainly via the bypass (18) when the motor is hot, but not when it is cold, so as to thus render the evaporator (23) inactive and so as not to prevent a normal rise in the temperature of the engine (13). By placing the evaporator (23) just at the outlet of the engine (13), a maximum flow of the heat transfer fluid passing through the cooling circuit (14) is obtained and therefore a more efficient heat recovery.

Description

COOLING CIRCUIT OF A THERMAL ENGINE EQUIPPED WITH A HEAT RECOVERY CIRCUIT

The subject of the invention is a cooling circuit for a heat engine, to which is added a heat recovery circuit.

Conventional heat engine cooling circuits pass through equipment such as radiators to transfer the heat acquired by the heat transfer fluid, generally water, passing through the engine. The heat dissipated in the radiators is however wasted, and this is why more complete devices, also including a heat recovery circuit added to the cooling circuit, have also been developed. The applicant is particularly interested in heat recovery circuits with an organic Rankine cycle, or ORC, without the present invention being limited to them.

Such heat recovery circuits are connected with the engine cooling circuit, via a heat exchanger, generally an evaporator, and the heat they recover can be used to drive a turbine. Certain documents of the prior art illustrating such embodiments are EP1925806 A2, EP2320058 A1 and WO2016 / 069455 A1.

The aim of the present invention is to strengthen the efficiency of the recovery circuit, first by placing the evaporator, or more generally the heat exchanger with the cooling circuit, at a location in the circuit where the flow of heat transfer fluid is maximum, upstream of the branches distributing the coolant from the cooling circuit to various equipment. The heat exchanger will therefore be placed at the outlet of the engine. But a drawback of this idea is that the thermal inertia of the cooling circuit is increased due to the presence of the evaporator at this location where it is made more efficient to take heat from the circuit, which will thwart the rise in temperature. of the engine during a cold start.

This problem is solved, according to a second essential characteristic of the invention, by constructing the cooling circuit with a bypass on which the heat exchanger is placed, and with a valve for distributing the fluid. coolant between the two branches: the flow will be directed more towards the supporting branch of the exchanger during stable operation, and rather towards the other branch in other circumstances, in particular when the coolant and the engine are cold.

A general definition of the invention is thus a cooling circuit of a heat engine equipped with an evaporator in heat exchange with an assistant heat recovery circuit, the cooling circuit and the heat recovery circuit being traversed by separate streams of fluids, characterized in that the evaporator is placed on a bypass of the cooling circuit, which is connected in parallel with a segment of a main part of the cooling circuit adjacent to the engine and in which the fluid has a flow maximum upstream of the bypass, a valve for distributing the flow between the bypass and the segment being placed either on the segment, or on the bypass, or in conjunction with the segment and the bypass.

The bypass and therefore the heat exchanger are in particular placed upstream of a possible engine thermostat, regulating the distribution of the flow through a radiator of the cooling circuit. They can also be located between an engine cylinder head and a possible fluid distribution unit between the branches of the cooling circuit, called water unit.

The valve can be three-way, arranged at a point of intersection of said segment and the bypass. It can also be a two-way valve, then placed either on the segment or on the bypass.

The valve can be of any known type: it can be a thermostat with autonomous operation, or a passive valve, controlled by a separate device, according to a temperature of the cooling fluid or possibly other parameters.

Other aspects of the invention are methods of controlling a cooling circuit according to the above. In one of them, the following steps are implemented:

a) when the temperature of said coolant at the outlet of said engine is below a predetermined threshold, said valve B

prevents the circulation of said cooling fluid in said evaporator, and

b) when the temperature of said coolant, said outlet of said motor is greater than a predetermined threshold, said valve allows said coolant to circulate in said evaporator.

Yet another aspect of the invention is a vehicle, otherwise ordinary and therefore not described in detail here, comprising an internal combustion engine, and a cooling circuit in accordance with the above.

The various aspects, characteristics and advantages of the invention will now be described in conjunction with the detailed description of the following figures, which represent certain purely illustrative embodiments of the invention:

[Fig. 1] is a general view of a cooling circuit and the equipment through which they pass, according to a system which is not however in accordance with the invention;

[Fig. 2] illustrates a first embodiment of the invention;

[Fig. 3] illustrates a second embodiment of the invention;

[Fig. 4] illustrates a third embodiment of the invention;

[Fig. 5] illustrates a fourth embodiment of the invention.

The conventional device of Figure 1 is now described in detail. A heat engine 1 is cooled by a cooling circuit 2 through which a heat transfer fluid delivered by a pump 3. On leaving the latter, the fluid passes through the engine 1, then by a thermostat 4 which distributes the flow in two branches of the cooling circuit 2 according to its temperature, one of which passes through a radiator 5 before returning to the pump 3, and the other passes through a heat exchanger 6 which recovers part of the calories from a exhaust gas 7, by an evaporator 8 of a heat recovery circuit 9 with an organic Rankine cycle, the working fluid of which, delivered by a second pump 10, passes through the evaporator 8, then through a turbine 11 and a condenser 12. The coolant from this branch then also returns to the pump 3, in front of which the two branches join. We will not dwell on the details of the operation of these known heat recovery circuits, which take calories from the cooling fluid at the evaporator 8 to convert them into mechanical energy at the known turbine 11. In this prior embodiment, the evaporator 8, placed between the heat exchanger 6 and the pump B, is located on one of the branches of the cooling circuit 2, upstream of the point of contact with the branch originating from the radiator 5, and its efficiency is therefore reduced, since only a partial debit borrows it. The same would apply if the evaporator 8 were located downstream of this point of contact, the fluid having passed through the radiator 5 and which would then be added to the flow passing through the evaporator 8 having been too cooled to contribute to strengthening a lot of heat exchange.

A first embodiment of the invention will now be described by means of FIG. 2. The heat engine bears the reference 13, and its cooling circuit the reference 14. A pump 15 delivers the fluid thereof through the engine 13, before it leaves through an outlet duct 16 on which is placed a valve 17. At this point, the cooling circuit is divided into a bypass 18 and a segment 28 of the outlet duct 16. The bypass 18 joins the duct of output 16 downstream of valve 17, but upstream of an engine thermostat 19 (remember that a thermostat has one input and two outputs, and for which the input and outputs are connected according to the opening an internal valve, the opening of which depends on the temperature of the fluid passing through the thermostat) which distributes the heat transfer fluid between a branch 20 passing through a radiator 21 and a branch 22 which avoids it, the branches 20 and 22 then returning to pump 15. An evaporator 23 a heat recovery circuit 24, otherwise similar to that described in FIG. 1, is arranged on the bypass 18, while the segment 28 remains unoccupied (that is to say without equipment) . For example, the heat recovery circuit 24 can be a closed circuit according to a Rankine cycle, in which circulates a heat transfer fluid (in particular an organic fluid). The closed circuit comprises a pump, the evaporator, an expansion means and a condenser. The cooling circuit 14 can pass through other equipment, not shown here, in particular heat exchangers with other sources. thermal or other equipment, and split into other branches downstream of the bypass.

The valve 17 is a three-way valve which governs the distribution of the heat transfer fluid to pass it through the evaporator 23 or on the contrary to avoid it through the segment 28 and directly reach the engine thermostat 19. The predominant flow can pass. via the bypass 18 or remain in the outlet branch 16, in particular according to the temperatures of the heat transfer fluid, or even of the motor 13 or of the evaporator 23, according to the operating possibilities described below. If the valve 17 is controlled only in temperature, it could be a thermostat. It may also consist of a passive valve controlled by a separate device, not shown and sensitive to various sensors, in particular the temperature of the heat transfer fluid or the temperature of the engine 13. Finally, the valve 17 can be in two states, or admit. intermediate states.

Figure 3 illustrates an alternative embodiment, which differs from the previous one in that the engine thermostat 19 at the separation between branch 20 and bypass 22 is omitted and replaced by an engine thermostat 25 located at the point where these branches 20 and 22 meet before returning to the pump 15. The device is not otherwise modified.

The embodiment illustrated in Figure 4 differs from that of Figure 2 in that the valve 17 is replaced by a two-way valve 26 placed either on the bypass 18 or on the segment 28 of the outlet duct 16 between its junctions with its ends of the bypass 18. The valve 26 can also be a thermostat or a passive valve with separate control device. It also makes it possible to distribute the heat transfer fluid between the bypass 18 and said segment 28, which is parallel to the latter.

In all these embodiments, the bypass 18 can be placed immediately downstream of the engine 13, or even adjacent to the latter, or be separated from it by heat exchangers, with the exhaust gas pipe for example, which allow the heat transfer fluid to be further heated; and if the cooling circuit 14 is divided at the location of the engine 13, for example into several parallel branches to cool the cylinder head of the engine 13 or an additional branch to cool the circuit lubrication, the bypass 18 is placed downstream of the points where these different branches meet at the outlet of the motor 13, in order to reform a single outlet pipe 16, in order to have all the flow of the cooling circuit 14 for the benefit of heat exchange with the recovery circuit 24.

In the case where the cooling circuit 14 comprises what is called a water outlet box 27, the function of which is to distribute the heat transfer flows to various branches of the cooling circuit 14 from the outlet of the engine 13, FIG. 5 illustrates that this water outlet housing 27 is not attached directly to the motor 13, but via a spacer 29 which contains at least part of the bypass 18, and the valve 17 or 26. In the Example shown, the water outlet housing 27 distributes the heat transfer flow between the branches 20 and 22, the first of which serves the radiator 21 and the second avoids it.

The operation of the devices of the invention is now described. During the heat-up phase of the engine 13, the evaporator 23 is avoided so that the flow of heat transfer fluid does not circulate, or very little, through the bypass 18. The flow passes entirely or mainly in the segment 28 of the output branch 16, without leaving the latter. The rise in temperature of the motor 13 is therefore not delayed by the additional thermal inertia represented by the evaporator 23. Once the motor 13 is hot, which corresponds for example to reaching a predefined threshold of temperature at the outlet of the engine 13, or at the instant when the thermostat of the engine 19 or 25 begins to open the branch 20 of the cooling circuit 14 which leads to the radiator 21, the valve 17 or 26 for controlling the flow rate to the evaporator 23 is activated, so as to send all or part of the fluid flow at the outlet of the motor 13 to the evaporator 23. The heat recovery circuit 24 then begins to receive calories and can begin to operate. If the valve 17 or 26 for controlling the flow rate to the evaporator 23 is of the continuously controlled type, it is possible to control the heat flow sent to the evaporator 23 if it is desired to modulate the operating power of the recovery circuit. For this, the flow control valve 17 or 26 is set to an intermediate position between full opening and full closure. Finally, after stopping the engine 13 having led to the start of a drop in temperature of the cooling fluid, the invention makes it possible to accelerate the rise in temperature of the engine 13: if the temperature in the evaporator 23 is higher than that of the coolant when restarting, the valve 17 or 26 can be adjusted so that the fluid leaving the motor 13 is directed to the evaporator 23, so as to use it to heat the fluid more quickly, so that the engine 13 returns to a warm operating state more quickly.

The advantages of the invention can be stated as follows. The positioning of the evaporator 23 in the cooling circuit 14 at the outlet of the engine 13 and before the branches of the circuit 14 allows the evaporator 23 to be passed through by the entire flow of cooling fluid from the engine 13. This is generally the point of circuit 14 where the fluid flow rate is the highest. The transfer of calories from the fluid to the working fluid of the recovery circuit 24 is thus optimized. For a quantity of heat to be transferred, this makes it possible to use an evaporator 23 that is more compact, and therefore also lighter and less expensive than if it were placed elsewhere in the cooling circuit 14 of the engine 13.

If the evaporator 23 could not be avoided by the flow, its presence in the cooling circuit 14 would constitute an additional thermal inertia which would delay the rise in temperature of the coolant of the engine 13. The delay in the rise in temperature of the engine 13 would be harmful to fuel consumption, due in particular to greater friction and increased thermal losses at the walls of the combustion chambers, with a cold engine. Combustion is also less efficient as long as the walls of the combustion chambers are colder, and the pollution control means in the engine exhaust line also being less efficient when cold, the pollutants would also be greater.

The valve 17 or 26 for controlling the flow in the bypass 18 of the evaporator 23 also makes it possible, once the engine is warm, to manage, if necessary, the heat flow reaching the evaporator 23. It thus becomes possible to modulate, by controlling an intermediate position between the two extreme positions of the valve 17 or 26, the heat flow sent to the evaporator and captured by the recovery circuit. After stopping the engine 13 long enough for a drop in the cooling water temperature to be initiated, it is possible, conversely, to take advantage of the heat in the recuperator circuit to heat up the engine 13 more quickly, as well as it was mentioned.

Claims

1. Cooling circuit of a thermal engine (13) equipped with an evaporator (23) in thermal exchange with an assistant circuit (24) for heat recovery, the cooling circuit and the heat recovery circuit being traversed by separate flows of fluids, characterized in that the evaporator (23) is placed on a bypass (18) of the cooling circuit (14), which is connected in parallel to a segment (28) of a main part (16 ) of the cooling circuit adjacent to the engine and in which the fluid has a maximum flow upstream of the bypass, a valve (17, 26) for distributing the flow between the bypass (18) and the segment being placed either on the segment ( 28), either on the derivation (18), or in a competition of the segment and the derivation.

2. Cooling circuit of a heat engine according to claim 1, characterized in that the heat recovery circuit is an organic Rankine cycle circuit.

3. Cooling circuit of a heat engine according to claim 1 or 2, characterized in that the bypass (18) is upstream of an engine thermostat (19, 25), regulating a distribution of the flow through a radiator. (21).

4. Cooling circuit of a heat engine according to any one of claims 1 to 3, characterized in that the bypass is located between the engine and an outlet housing (27) of the fluid, which distributes the fluid between branches. (20, 22) of the cooling circuit.

5. Cooling circuit of a heat engine according to any one of claims 1 to 4, characterized in that the valve is a three-way valve arranged in conjunction with the segment (28) and the bypass (18).

6. Cooling circuit of a heat engine according to any one of claims 1 to 4, characterized in that the valve is a two-way valve.

7. Cooling circuit of a heat engine according to any one of claims 1 to 6, characterized in that the valve is a thermostat.

8. Cooling circuit of a heat engine according to any one of claims 1 to 6, characterized in that the valve is controlled according to a temperature of the fluid of the cooling circuit.

9. A method of controlling a cooling circuit according to any one of the preceding claims, in which the following steps are implemented:

a) when the temperature of said coolant at the outlet of said engine (13) is below a predetermined threshold, said valve prevents the circulation of said coolant in said evaporator (23), and

b) when the temperature of said coolant, said outlet of said motor is greater than a predetermined threshold, said valve allows said coolant to circulate in said evaporator (23).

10. Vehicle comprising an internal combustion engine and a cooling circuit (14) according to one of claims 1 to 8.