FR3042538A1 - ENGINE ASSEMBLY WITH OPTIMIZED COOLING CIRCUIT - Google Patents

Abstract

An engine assembly (100) comprising an internal combustion engine comprising an engine block (1), a cooling circuit (2) configured to exhaust heat generated by the engine block, and a Rankine system (5). The motor assembly is configured such that the thermal energy produced by the engine block (1) is transmitted to the Rankine system (5) via the cooling circuit (2). Advantageously, the cooling circuit (2) is the fluid circuit of the Rankine system.

Description

FIELD OF THE INVENTION The invention relates to an engine assembly, that is to say a system comprising at least one engine to provide mechanical power. The invention particularly relates to an engine assembly comprising both a main engine, providing the bulk of the mechanical power produced, but also an auxiliary engine for providing additional mechanical power from the heat produced by the main engine. Advantageously, an engine assembly of this type has a better energy efficiency than the main engine, because the heat produced by the main engine is upgraded by the auxiliary engine in the form of mechanical power. The invention relates more particularly to the case where the main engine is an internal combustion engine, in particular a piston engine, and more particularly still a piston aircraft engine.

BACKGROUND

Piston engines have a motor efficiency of 20 to 50%. The rest of the energy consumed is converted into heat and released into the ambient air via the engine cooling system and the exhaust gases. The cooling system usually consists of a coolant circuit, which passes through the engine block to collect heat generated therefrom, and further comprises a cooling radiator for exhausting ambient air through the engine block. heat thus collected. The fluid is circulated by means of a cooling circuit pump.

Moreover, exhaust heat energy recovery systems are conventionally used to convert a portion of thermal losses of the engine into work and thus improve the efficiency of the system. We talk about cogeneration.

These systems are unfortunately too heavy to allow their integration into an aircraft.

Various known technologies can be envisaged for producing the auxiliary motor: a Rankine system, a Stirling engine, a Seebeck effect cell, or a Turbocompound system.

However, none of these solutions is satisfactory and exploitable for an aircraft engine, for various reasons: the excessive mass of the auxiliary engine, for the Rankine system and the Stirling engine; the low power that can be generated for the seebeck cell, or the negative impact on the main engine, namely the exhaust back pressure, for the Turbocompound system.

PRESENTATION OF THE INVENTION

Accordingly, the object of the invention is to provide an engine assembly comprising a main motor and an auxiliary motor to provide additional mechanical power from the heat produced by the main engine, having a relatively high energy efficiency, of moderate cost, and if possible relatively small mass so that it can be used in an aircraft.

This objective is achieved with an engine assembly comprising an internal combustion engine comprising an engine block, a cooling circuit configured to evacuate a heat released by the engine block, and a Rankine system with at least one pump, an evaporator, a expander and a condenser interposed on a fluid circuit; the motor assembly being configured such that thermal energy produced by the engine block is transmitted to the Rankine system via the cooling circuit, and characterized in that, at least in one mode of operation, the cooling circuit is the fluid circuit of the Rankine system.

In the preceding definition, a Rankine system is a system comprising successively, in the same closed circuit of two-phase fluid: the pump, for compressing the fluid, the evaporator in which the fluid undergoes a vaporization, the expander in which the fluid expands generating a work, and the condenser in which the fluid undergoes condensation.

The pump generally designates any compressor or pressurizing means for circulating the fluid in the fluid circuit and to raise the fluid pressure in the liquid phase leaving the condenser. It can be a set of several pumps.

The expander therefore constitutes a component in which the work provided by the fluid is transmitted to an output member which serves to transmit the mechanical power, for example an output shaft intended to transmit a torque. The expander can in particular be a turbomachine, in particular a turbine. The evaporator is a device that allows the vaporization of the fluid; it comprises at least the engine block.

Spraying can be done in one step; in this case, the evaporator for example may comprise only one chamber in which the fluid is injected into the liquid phase, and extracted in the vapor phase.

In another embodiment, the vaporization is done gradually. The evaporator can then comprise, for example, several stages of heating and / or vaporization. It may comprise, for example, one or more heating chambers in which the temperature of the fluid is progressively raised to the boiling temperature, and one or more vaporization chambers at the end of which the fluid is vaporized.

The fluid leaves the evaporator entirely in the form of steam or possibly a liquid-vapor mixture. Preferably, the fraction of the fluid which is in the vapor phase at the outlet of the evaporator is greater than 80%. In some cases, in particular because of the operating constraints of certain regulators, it may be imperative for the fluid to be entirely in the vapor phase at the outlet of the evaporator.

In the Rankine system, the fluid thus undergoes cyclic vaporization, expansion, condensation and compression.

The basic principle of the invention therefore consists in making the engine cooling circuit, at least in one operating mode, the fluid circuit of the Rankine system. The evaporator is then constituted directly by the engine block, or at least comprises at least the engine block. As will be detailed below, the evaporator may optionally also include additional heat exchangers, for example to collect the calories contained in the engine lubricant, in the exhaust gas, and / or in the air. in particular if the engine is supercharged, and / or from any other heat source present.

In one embodiment, the radiator of the cooling circuit generally serves as a condenser for the system

Rankine. The motor assembly then advantageously comprises only a condenser or cooling radiator.

In one embodiment, the cooling pump of the cooling circuit is used as a drive pump of the Rankine system. The motor assembly then advantageously comprises only one pump.

In one embodiment, the internal combustion engine is a piston engine.

In one embodiment, the fluid circuit includes a portion of the engine block cooling circuit located within the engine block, and wherein during said mode of operation, the transfer fluid absorbs heat generated by the engine block. engine.

The fluid of the Rankine system fluid circuit passes inside the portion of the engine block cooling circuit, which leads to its heating and possibly its partial or total vaporization. Conversely, the flow of fluid through the engine block to cool it.

In one embodiment, during the operating mode in which the Rankine system is implemented, the fluid exiting the portion of the engine block is in the liquid phase. The vaporization of the fluid therefore occurs in a portion of the evaporator located downstream of the engine block.

In one embodiment, it can be further provided that the fluid circuit comprises a circuit portion in bypass in order to be able, if desired, to bypass the "hot loop" of the fluid circuit, that is to say the part of the fluid circuit in which the temperature is highest and the fluid is mainly or totally in the vapor phase. The hot loop thus includes the portion of the fluid circuit that extends from the portion of the evaporator in which the fluid is vaporized to the condenser.

Also, in an improvement of the foregoing embodiment, the fluid circuit further comprises a bypass circuit portion arranged in a shunt between a fluid sampling point in the fluid circuit downstream of the block cooling circuit portion. engine, and upstream of a vaporization portion of the evaporator in which the fluid is vaporized, and a fluid feed point in the fluid circuit downstream of the expander.

The bypass circuit portion allows the motor assembly to be operated in a second mode of operation, in which no fluid circulates in the hot loop.

In this second mode of operation, the cooling circuit does not implement the Rankine system. It can then in particular function as a conventional cooling circuit, in which the fluid carried at high temperature at the outlet of the engine block cooling circuit portion is cooled by a heat exchanger. This exchanger is preferably the condenser of the Rankine system. This is typically the engine cooling radiator.

To control the distribution of the fluid between the hot loop and the bypass circuit portion, the flow in these circuits is normally controlled by a valve, which may be disposed on the circuit portion in bypass or on the hot loop, including a valve regulation.

The closing of the "hot loop" can be useful for the following reasons: - In the case of partial load operation, reducing the flow rate in the hot loop makes it possible to promote the vaporization of the working fluid, which is more favorable for operation of the regulator. In particular, this can prevent wear phenomena by erosion / cavitation. - The opening of the circuit portion in bypass allows to return to a conventional operation of the cooling circuit, without implementation of the Rankine system. The opening of the bypass circuit portion can be controlled to prevent overheating of the working fluid.

Conversely, closing the circuit portion in bypass may allow a faster temperature rise of the engine during startup and low load phases.

In one embodiment, the internal combustion engine further comprises a lubrication circuit comprising a heat exchanger; and this heat exchanger is part of the evaporator and thus is configured to contribute to the vaporization of the fluid by allowing a heat transfer of a lubricant circulating in the fluid lubrication circuit.

This heat exchanger cools the lubricant and keeps it at an acceptable temperature

In one embodiment, the internal combustion engine further comprises a turbocharger with an air compressor disposed on an air supply circuit portion of the internal combustion engine and a turbine disposed on an exhaust circuit portion. of the internal combustion engine.

In an improvement of this embodiment, the air supply circuit portion comprises an upstream heat exchanger; this upstream heat exchanger is part of the evaporator and thus is configured to contribute to the vaporization of the fluid by allowing a heat transfer of the air flowing in the air supply circuit portion to the fluid.

In an improvement of embodiments in which the internal combustion engine comprises a turbocharger, the exhaust circuit portion comprises a downstream heat exchanger; the downstream heat exchanger is part of the evaporator and thus is configured to contribute to the vaporization of the fluid by allowing a heat transfer of the gases flowing in the exhaust circuit portion to the fluid.

Each of the heat exchangers indicated above, namely the heat exchanger of the lubrication circuit, the upstream heat exchanger, the downstream heat exchanger, makes it possible to supply energy in thermal form to the fluid, which contributes to increase the thermal power collected by the Rankine system and thus to improve the energy efficiency of the engine assembly. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings, in which: - Figure 1 is a schematic view of a motor assembly illustrating a first embodiment of the invention; FIG. 2 is a schematic view of an engine assembly illustrating a second embodiment of the invention, similar to the engine assembly of FIG. 1, but whose engine further comprises a turbocharger; and FIG. 3 is a diagrammatic view of a motor assembly illustrating a third embodiment of the invention, similar to the motor assembly of FIG. 2, but whose fluid circuit further comprises a portion of a circuit in FIG. bypass.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, a motor assembly 100 constituting a first embodiment of the invention will now be described. The motor assembly 100 comprises an internal combustion engine 10 with a motor block 1, and a Rankine system 5, the fluid circuit 2 is also the cooling circuit of the engine block. The internal combustion engine 10 is a piston engine.

In the motor assembly 100, the motor 10 is the main motor, and the Rankine system 5 the auxiliary motor. The motor assembly 100 further comprises a lubrication circuit 12 and an oxidizing air circuit 13, respectively for the lubrication and for the supply / exhaust of the engine 10. The combustion air circuit 13 is composed of a portion an air supply circuit 131 and an exhaust circuit portion 132 for exhausting the combustion gases. The engine block 1 is mechanically connected to a load 3.

The fluid circuit 2 contains ethanol as the working fluid; other analogous compounds may be used in the context of the invention.

The fluid circuit 2 has a dual function: to evacuate calories from the engine block and thus to ensure the cooling of the engine block 1; produce mechanical power using the Rankine 5 system.

For this purpose, the circuit 2 comprises a pump 21, a portion of the engine block cooling circuit 11 located inside the engine block, a pressure regulation system 22, a heat exchanger 23, a radiator 24, and an expander 25.

The pressure regulating system 22 is typically an expansion vessel or accumulator. Its position as shown in Figure 1 is arbitrary and does not presage the position it may have in practice in the motor assembly.

The function of this pressure control system is to set the pressure at a point in the circuit to a value or range of value, to ensure that the regulator can operate in the vapor phase (preferably dry) and that the pressure fluid remains at an optimum value for the operation of the motor assembly.

In the circuit 2, the fluid is set in motion by the pump 21. This pumps the fluid in the liquid phase; the fluid first passes through the heat exchanger 23. This allows a first supply of heat to the fluid: the heat exchanger 23 makes it possible to transmit to the fluid the heat of the lubricant circulating in the lubrication circuit 112. The exchanger 23 is configured to maintain the lubricant in its optimum operating temperature range.

At the outlet of the heat exchanger 23, the fluid is directed into the engine block 1 and more precisely into the portion of the engine block cooling circuit 11.

As the fluid passes through this portion of the engine block cooling circuit, it absorbs the heat generated by the engine block and vaporizes. The vaporization allows it to absorb a large amount of heat and to cool the engine block very effectively.

At the output of the engine block 1, the hot fluid, in the vapor phase, is injected into the expander 25. This consists of a turbine. The fluid relaxes by passing through the turbine and provides work to the rotor of the turbine, which rotates the output shaft thereof. The mechanical power thus communicated to the output shaft of the turbine 25 is transmitted to a load 3 '.

At the outlet of the turbine, the fluid then passes through the cooling radiator 24, in which it is liquefied; the heat is dissipated in the ambient air.

The fluid in the liquid phase is then sucked into the intake port of the pump 21; he can then start the previous cycle again.

Thus in this embodiment, the heat exchanger 23, in which the fluid is heated, in association with the engine block cooling circuit portion 11 in which the fluid is heated again and vaporized, form an evaporator 20 within the meaning of the invention, which ensures the vaporization of the fluid discharged by the pump 21 and allows its injection into the high pressure vapor phase in the expander (the turbine 25). The mechanical power produced on the output shaft of the turbine improves the efficiency of the engine 10.

The thermodynamic cycle that the fluid undergoes in the Rankine system 5 is as follows:

During the passage of the fluid in the pump 21, the latter undergoes isochoric compression in the liquid phase and is brought to a pressure of about 3.5 bar.

The fluid is then transferred to the evaporator 20 in which it is vaporized: its temperature reaches at least the vaporization temperature of the ethanol, ie about 80 ° C. In practice, the temperature reaches about 150 ° C. The fluid therefore leaves the evaporator 20 entirely in the vapor phase; its pressure is about 2.5 Bars.

The fluid then undergoes expansion as it passes through the expander 25; its pressure decreases and reaches about atmospheric pressure. During this relaxation, the enthalpy of the fluid is transformed into work.

Following this expansion, the fluid is condensed during its passage through the condenser 24; its temperature drops to 70 ° C.

The fluid in liquid form is then directed towards the inlet of the pump 21.

In the motor assembly 100, compared with a configuration comprising only the engine 10 and a cooling circuit in liquid phase with cooling radiator, the additional mass induced by the modification of the cooling system to make a Rankine system is mainly the adding the turbine 25 to generate the mechanical power. Given the low weight of the latter, the increase in weight is negligible, while on the other hand advantageously the engine efficiency is improved.

Figure 2 shows a motor assembly 100 which constitutes a second embodiment of the invention. This second embodiment is identical to the first embodiment with the exception of the differences that will be indicated below.

In this second embodiment, the piston engine 1 is supercharged using a turbocharger 14.

The combustion air circuit 13 is modified. The turbocharger 14 comprises an air compressor 141 disposed on the air supply circuit portion 131 of the internal combustion engine and a turbine 142 disposed on the exhaust circuit portion 132 of the engine 10.

The heat conveyed by the air of the feed circuit portion 131, and the heat conveyed by the exhaust gas can thus be recovered in order to further improve the efficiency of the motor assembly 100.

For this purpose, in addition to the heat exchanger 23 and the engine block cooling circuit portion 11, the evaporator 20 includes a supply air heat exchanger 26 and a gas heat exchanger. exhaust 27.

Naturally, in other embodiments and depending on the desired application, it is possible for the evaporator to include a supply air heat exchanger (such as exchanger 26) but no heat exchanger. Exhaust gas heat (such as exchanger 27), or conversely, includes an exhaust gas heat exchanger but no supply air heat exchanger. The combustion air contained in the supply circuit portion 131 is cooled by means of the exchanger 26 and transfers its calories to the fluid flowing in the cooling circuit 2.

The gases contained in the exhaust circuit portion 132 yield part of their enthalpy to the turbocharger 14 and a portion of the remaining calories is transferred to the fluid through the exchanger 27.

Moreover, as in the first embodiment, the fluid also collects the calories from the engine block cooling circuit portion 11 of the engine 1 and the lubrication circuit 12.

The energy efficiency gain of the engine 10 provided by the invention can be evaluated as follows.

In the embodiment shown, the motor 10 is capable of providing a driving power equal to 100kW, and a power close to 100kW can be collected in the form of heat via the various heat exchanges. When the fluid expands in the expander, it then delivers at the output a mechanical power of about 3.6 kW, of which about 0.2 kW are used to drive the pump 21.

By comparison, in the absence of the Rankine system and using conventional cooling around 1.5 kW are required to drive the pump 21 (instead of 0.2 kW). Indeed in this case, the pump generally compresses a higher fluid flow rate to ensure that the fluid temperature remains below the vaporization temperature.

Also in total, the invention increases the available mechanical power of 4.9 kW, a reduction in consumption of nearly 5%.

In addition, in terms of mass, the fact of having recourse to thermal exchanges in two-phase medium makes it possible to optimize the volume of the portion of the engine block cooling circuit 11, and the volume of the oil / coolant exchangers ( exchanger 23), supply air / cooling fluid (exchanger 26) and thus reduce the mass of the engine 10.

In addition, the pump 21 has a flow rate fifteen times less than in the configuration without Rankine system: it can therefore be lighter. Only the exchanger between the exhaust gas and the fluid (exchanger 27) increases the mass of the engine assembly. It can therefore legitimately be considered that the addition of a Rankine system according to the invention allows a reduction of the mass of the motor assembly or at least does not lead to an increase thereof.

A third embodiment is illustrated in FIG. 3. With respect to the embodiment of FIG. 2, it also includes a bypass circuit portion 61 so as to be able, if it is desired to bypass the "hot loop" of the fluid circuit. , referenced 65.

The bypass circuit portion 61 is arranged in shunt. It extends from a fluid sampling point 63 to a fluid re-injection point 64.

The fluid sampling point 63 is downstream of the engine block cooling circuit portion 11; thus the fluid flowing in the bypass circuit portion contains the heat taken from the engine block 1. Also, even without using the Rankine system via the hot loop, cooling the fluid of the circuit portion bypass can allow ensure the cooling of the fluid.

In the fluid circuit 2, the fluid is injected in the liquid phase into the exchanger 26; a partial vaporization of the fluid generally occurs in this exchanger (depending on the operating mode of the engine, the ambient conditions, etc.); the vaporization continues in the exchanger 27 at the outlet of which the fluid is entirely in the vapor phase.

Also the 'vaporization portion' of the evaporator, that is to say the part of the evaporator in which the fluid is vaporized, is constituted by the exchangers 26 and 27.

The fluid sampling point 63 is upstream of the heat exchanger 26 and therefore the vaporization portion of the evaporator 20. As a result, the fluid flowing in the bypass circuit portion is in the liquid phase.

The point 69 of fluid reinjection in the fluid circuit is located downstream of the expander (of the turbine) 25.

The flow of fluid in the bypass circuit portion is controlled by a valve 62 which makes it possible to short-circuit the hot loop 65.

The control of the valve 62 may be all-or-nothing or proportional type.

Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that various modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In addition, individual features of the various embodiments mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims (8)

An engine assembly (100) comprising an internal combustion engine (10) comprising an engine block (1), a cooling circuit (2) configured to exhaust heat generated by the engine block, and a Rankine system (5). ) with at least one pump (21), an evaporator (1,23,26,27), an expander (25) and a condenser (24) interposed on a fluid circuit; the motor assembly being configured such that heat energy produced by the engine block (1) is transmitted to the Rankine system (5) via the cooling circuit (2), and characterized in that, at least in a mode of operation, the cooling circuit (2) is the fluid circuit of the Rankine system. 2. Engine assembly (100) according to claim 1, wherein the internal combustion engine (10) is a piston engine, and whose expander (25) is a turbomachine. An engine assembly according to claim 1 or 2, wherein the fluid circuit (2) comprises a portion of the engine block cooling circuit (11) located within the engine block, and wherein during said In operation, the transfer fluid absorbs heat generated by the motor (10). The motor assembly of claim 3, wherein the fluid circuit further comprises a bypass circuit portion (61) arranged in a shunt between a fluid sampling point (63) in the fluid circuit downstream of the portion engine block cooling circuit (11), and upstream of a vaporization portion of the evaporator in which the fluid is vaporized, and a fluid re-injection point (64) in the fluid circuit downstream of the expansion valve (25). An engine assembly according to any one of claims 1 to 4, wherein the internal combustion engine further comprises a lubrication circuit (12) comprising a heat exchanger (23); said heat exchanger (23) of the lubrication circuit is part of the evaporator (20) and thus configured to contribute to vaporization of the fluid by allowing heat transfer of a lubricant circulating in the lubrication circuit (12) to the fluid. 6. Engine assembly according to any one of claims 1 to 5, wherein the internal combustion engine further comprises a turbocharger (14) with an air compressor disposed on a portion of circuit (131) for supplying air. an internal combustion engine and a turbine disposed on an exhaust circuit portion (132) of the internal combustion engine. The engine assembly of claim 6, wherein the air supply circuit portion comprises an upstream heat exchanger (26); the upstream heat exchanger (26) is part of the evaporator (20) and thus is configured to contribute to the vaporization of the fluid by allowing a heat transfer of the air flowing in the air supply circuit portion (131) to the fluid. 8. Engine assembly according to claim 6 or 7, wherein the exhaust circuit portion comprises a downstream heat exchanger (27); the downstream heat exchanger (27) is part of the evaporator (20) and thus is configured to contribute to the vaporization of the fluid by allowing a heat transfer of the gases flowing in the exhaust circuit portion (132) to the fluid.