FR2718491A1 - Unit to recover heat from heat engine exhaust - Google Patents

Abstract

The heat recovery device consists of an annular distiller, assembled around a section of the exhaust pipe (1), carrying the combustion gas. The distiller is fed from a recovery condenser (4) via a feed pipe (3) and has an auxiliary capacity, regulated by an adjustable device (13), which acts under the combined effects of pressure and a return spring. The capacitor is located at the lowest point of the liquid circuit and has sufficient capacity to contain the total condensed fluid contained in the system, subject to the constraint of pressure. The condensing element may be a radiator, which allows the recovered heat to be passed directly to the air, used for heating the vehicle interior.

Description

 The present invention relates to a device for recovering energy, on motor vehicle exhaust to supplement the cabin heating or rapid warm-up of the engine coolant circuit.

Improving the efficiency of the engines of vehicles
automobiles, tends to reduce heat losses to the circuit
cooling.

This reduction in losses results, in particular,
in slower engine temperature, resulting in a running
prolonged unfavorable conditions: on the other hand, this situation
deprived the passenger compartment heater, which draws energy
which is needed on the cooling circuit, inputs
sufficient thermal energy to ensure a quick start in con
strong.

The present invention relates to a device for recovering
part of the energy dissipated at the exhaust of the thermal engines
which, for the purpose of using it, is directly an adjunct to heating
of the passenger compartment, ie rapid heating of the cooling circuit
which these engines are equipped with.

Among the means of transferring energy, from a circuit of
exhaust gases, to a fluid circuit at lower temperatures
such as the air for heating the passenger compartment or the
cooling circuit of an engine, it is known to use a
intermediate fluid with phase change, such as water, vapori
heat exchange through the wall of a steam exchanger
riser, with the exhaust gases and condensed along surfaces
condenser heat exchanger, with respect to the air or a heating fluid.
iron.

To understand the operation of such a device applied to
Automotive engine energy recovery, it is good to get back
bring to the figure (I) which would represent a working equipment
according to this known principle.

In this figure, we can see a section of canalisa
exhaust outlet (1) connected by one of its ends to the outlet
engine exhaust gas and the other to the evacuation of these bilge gases on this section of pipe, welded so
a jacket (2) determines an annular chamber carrying a
outlet pipe (3) connected to a heat exchanger (4)
operating on a condenser.

 In the case where the recovered energy is intended to improve the conditioning of comfort of the passenger compartment, the exchanger (4) may be a radiator, conventionally consisting of a bundle of tubes (5) filled with fins (6) and closed two water boxes (7) and (10).

 In the case where the recovered energy is intended to reduce the heat-up time of the heat engine, it may be a shell and tube heat exchanger, as shown in Figure (VI).

 The whole thus constituted. closed and sealed, is intended to contain a small amount of water or antifreeze mixture.

 When the engine of the vehicle is in operation, the exhaust gases enter the pipe (1) at high temperature. Initially, these gases heat the water contained in the jacket (2) to eventually bring it to a temperature sufficient to create boiling.

This boiling temperature for a particular fluid, such as water or antifreeze mixture, depends on the pressure prevailing in the enclosure where this boiling occurs. In the case of pure water, at atmospheric pressure, this temperature is 100 ° C. A more or less high vacuum obtained by extracting, by the plug (11), before closing the circuit, the air contained in the device, allows to dababat this temperature
Having reached its boiling point, the fluid vaporizes and its vapor emerges towards the upper part of the envelope (2). This vapor then rises through the pipe (3) to reach the radiator (). The steam then bathes the tubes (5) of this exchanger to which it transmits its latent heat of vaporization, then thence to the fins (6) which, in turn, transmit it to the circulating air through this radiator or to the engine coolant in the case of a shell-and-tube heat exchanger.

Under the effect of this heat exchange the vapor condenses along the inner face of the tubes (5) and the liquid from this condensation eventually flows along said tubes, then from there, in the box water (10) before returning, by simple gravity, to the steam jacket (2) by circulating against the steam in the connection channel (3) after passing through a pipe (9) having a syphon (9)
A closed, maintained circuit is thus formed, driving the heat taken on the exhaust gases towards the air passing through the radiator or towards the fluid circulating in the shell-and-tube heat exchanger
This operation is only a particular case of application to the specific problem of heat recovery on exhaust gas, a known principle of fluid flow hiphasic.

In practice, the operation of such a device would not be controllable
In fact, the exhaust gases of the engine of a motor vehicle are at a very variable temperature and carrying a fluctuating energy, as a function of the mechanical load applied to said engine. On the other hand, the needs for energy recovery are not constant and these are unrelated to the energy availability of the exhaust gases.

 The operation of the system, as described above, assumes that at all times a perfect equilibrium is established between the power transmitted to the boiling fluid by the exhaust gases and the power discharged by the condenser, ie to the air by the heater radiator of the passenger compartment, or to the cooling circuit by the shell-and-tube heat exchanger.

 In the opposite case, the system would experience significant variations in vapor pressure: a pressure drop that could go as far as stopping the system, as soon as the energy level of the exhaust gases is no longer sufficient to maintain the boiling temperature, pressure rise up to destruction of the device in case of significant availability of energy on the exhaust circuit exceeding the needs for recovery energy.

 The object of the present invention is to confer on the system described above, a perfect safety of use and a constant adaptation of the power exchanged for instantaneous needs for energy recovery.

To understand the particularities of editing, it is good, at first, to refer to the figure <Il)
In this figure, we can see the device shown in Figure (x) completed schematically a deformable capsule (13) connected by a small conduit (12) to the lower part of the water jacket (2) of the vaporizer.

 The possibilities of deformation of the capsule (13) are li mited by the action of a spring (14) calibrated at a suitable value.

This complement to the device shown in Figure (I) fundamentally alters the operation of the assembly. The invention will be better understood and other objects will appear more clearly in the course of the description which follows, with reference to the accompanying schematic drawings, given solely by way of example, illustrating several embodiments of the invention and in which
- Figures IIa, IIb, lic represent the device according to the invention in three characteristic operating states
FIG. iii represents an alternative arrangement of the elements of a device according to the invention.

FIG. IV represents a particular diposition simplifying the device while remaining in accordance with the invention
- Figure V represents a preferred embodiment of the device according to the invention.

 - Figure VI shows the device according to the invention in the case where it is intended to transfer the energy to the cooling circuit of a heat engine, through a shell heat exchanger.

 At first, tal shown in FIG. 11, the sys theme being stopped in the absence of circulation of exhaust gas, the fluid contained in the water chamber (2) is cold and the relative pressure in the enclosure is null (even negative, if a certain void had been previously created in the enclosure).

 Under these conditions, as shown in Figure 11a, as the system is not operating, under the action of the spring (14) the capsule (13) is compressed, and most of the water it was likely to contain is pushed back into the annular chamber (2) of the vaporizer around the exhaust pipe (1).

 Under these conditions, the circulation of the exhaust gases in the pipe (1), the operation of the system follows the mode described above.

 This mode of operation continues as long as the pressure in the chamber remains moderate and lower than the calibration pressure of the spring (14). As soon as this pressure exceeds the rating limit of this spring, the action of this pressure on the underside of the capsule (13) tends to deform the latter and increase its capacity, as shown in Figure IIb. In this case, a certain amount of water is taken from the annular chamber (2) of the vaporizer, to enter: in the deformable capsule through the conduit (12). The level of the liquid in the vaporization chamber (2) then lowers, reducing the active wet exchange surface, with respect to the exhaust gases of the exhaust manifold (1).

 This decrease in active area results in a reduction of the energy taken from the gases. In turn, this reduction of the recovered energy tends to lower the pressure in the chamber and this until again a perfect balance is established between the power exchanged on the exhaust gas and the power evacuated on the circuit of use.

 The terminal shown in FIG. 1c, the increase in the imbalance between the power recovered on the exhaust gas and that discharged to the condenser should continue, the pressure in the air would still tend to rise and cause deformation. more and more important of the capsule (13) and the compression of the setting spring (14), so much that all the fluid contained in the device would be found in said capsule.

 In this extreme case, due to a lack of liquid to vaporize, the pump stops working, until the pressure in the assembly has lowered, the deformable capsule returns a small amount of water to the vaporization chamber allowing the normal cycle to resume.

 Under these conditions, it can be seen that the system automatically tends to operate at constant vapor pressure, whatever the energy available on the exhaust gas and whatever the dissipation to the recovery circuit.

 The system thus described thus ensures, in addition to a perfect adaptation to the needs of power exchanged, total operational safety, since in no case the vapor pressure could rise in the enclosure, beyond the setting pressure of the compensating spring.

 In a preferred embodiment, taking into account the geometric arrangement of the elements in a motor vehicle, and without departing from the operating principle described above, the assembly can advantageously be made according to the indications of Figure (III).

 In this figure can be seen, as in the previous figures the exhaust pipe (1) and the water chamber of a boiler (2) formed by a jacket, welded sealingly on this pipe. It also shows a pipe (3) connecting the water chamber (2) and the upper box (7) of the condenser <4).

In the figure it is also possible to see, in the same arrangements as before, the condenser constituted in this case by a heat exchanger on the air (4) formed by the tube bundle (7) and the fins (8). ) closed by an upper box (9) provided with its emptying plug (10)
In this embodiment, on the other hand, the deformable capacity (13) and the setting spring (14) are connected at the bottom of the condensate outlet siphon.

Coins in the previous case, the deformable capsule (13), although no longer connected to the low point of the device, allows to accumulate a greater or lesser portion of the condensed liquid, depending on the pressure in the incense closed, trap this liquid as soon as it leaves the condenser
Figure V represents a preferred embodiment of the device. In this embodiment, one can see the special provisions of the condensate receiving box enabling it to fulfill the functions of deformable capsule.

In this design, without departing from the scope of the invention, the deformable capacity (13) and its calibration spring (14) are replaced by an elastic membrane (15) constituting the bottom of an auxiliary capacity of the lower box ( 10) receiving condensate from the exchanger.

In this arrangement, the elastic deformation forces of the diaphragm play the same role as the calibrated spring (14) of the preceding representations.
In this case also, to take account of the forces induced by the movement of the vehicle (vibrations, centrifugal force ...) the capacity (10) can usefully be filled with a spongy material fixing the accumulated liquid in the holding capacity (15) both that the membrane remains under the influence of pressure.

In the case of this embodiment, the operation remains in all respects identical to that previously described
The exhaust gases from the heat engine exchange part of their energy through the wall of the duct (1) with the liquid contained in the annular chamber (2), which under the influence of this calorific input that it vaporizes partially.

The steam produced rises from the bottom upwards through the ducting (3) to the condenser exchanger (4)
In this exchanger, the steam gives up its latent heat of vaporization to the tube bundle (5), this heat is dissipated by the fins (6) towards the air passing through the radiator, or as shown in FIG. (VI), directly through the tubes (5) to the fluid flowing in the shell of the exchanger.

 Under the effect of this heat exchange, the fluid resumes its liquid phase by condensing on the inner face of the tubes to eventually flow to the condensate receiving box (10).

 From there, the liquid returns to the annular enclosure by taking the conduit (8), then the conduit (3) in which it flows from top to bottom, against the current with the steam, thus forming a closed circulation circulation circuit, as long as the heat gains recovered from the exhaust gases are eliminated by the condenser heat exchanger.

 As soon as the heat gains by the exhaust gases tend to exceed the level of energy-evacuated pa! the heat exchanger (4), the temperature of the coolant tends to rise, causing a rise in pressure in the chamber.

 This pressure is transmitted directly to the deformable membrane (15) in the lower part of the receiving box (10).

 Under the influence of this increase in pressure, the membrane deforms by increasing the capacity of the lower part of the receiver box. The condensates produced, instead of returning as previously to the annular enclosure, are primarily accumulate in the volume and clear of the condensate retention box (in).

 Under these conditions, the liquid level in the annular boiling chamber tends to drop, reducing the exchange capacity with respect to the exhaust gases and thereby reducing the difference between the energy inputs and the possibilities. evacuation of the recuperator.

 If, however, this gap continues to increase, as in the case shown in Figure Vc, the pressure in the chamber continues to rise; it would follow an even greater deformation of the elastic membrane (1S) which would increase the condensate retention capacity of the receiving box (10) to the point that all the fluid contained in the installation would be retained.

In this case, the system would stop working due to lack of liquid in the annular chamber portion serving as boiler. This situation would only persist for the time necessary for a sufficient lowering of temperature, therefore of pressure, so as to release a part of the stresses applied to the elastic membrane. This by returning to its original shape, would restore a portion of the fluid accumulated in the condensate receptacle (10) thus allowing the resumption of the normal cycle of operation.

Without departing from the scope of the invention, the system could be designed to operate under a relative vacuum whose object, at first, to ensure the degassing of the coolant (mixture of water and antifreeze) and then to favor the exchange of heat at relatively low temperature (less than 100 ° C.)
In this case, the elastic membrane (16) at the stop of the system would experience a pre-deformation in the direction indicated in Figure Va, the most important part of the fluid contained in the installation then being in the chamber of ring exchange (2). In the opposite case of operating at the highest pressure, the membrane would be deformed as indicated by Figure Vc allowing the capacity (10) to contain all the fluid introduced into the installation.

Claims (6)

RKvKNDlCATIONS 1 device for recovering energy from a motor vehicle engine exhaust, characterized in that it comprises an annular boiler (2) assembled on a section of flue gas discharge pipe (1), connected by a pipe ( 3) a recuperator condenser (4) and an auxiliary capacity deformable under the effect of the pressure (13), located at a low point of the liquid circuit, of sufficient capacity to receive under pressure stress, the entire fluid coolant contained in the system. 2 Device according to claim 1, characterized in that the condenser element may be a radiator (4) for releasing the recovered energy directly to the air for heating the passenger compartment of the motor vehicle. 3 Device according to claim 1, characterized in that the condenser element can be a shell heat exchanger (17) for transferring the recovered energy to the cooling liquid circuit of the heat engine.  4 Apparatus according to one of claims 1 to 3, characterized in that the deformable capacity (13) can be connected to the lower part of a siphon condensate discharge output condenser exchanger. 5 Device according to claim 1 to 3, characterized in that the deformable auxiliary capacity (13) can be incorporated in the receiver box condansats radiator (10) or the shell heat exchanger (17) in the form of an elastic membrane . 6. Device according to one of claims 5 to 5, characterized in that the device can operate under partial vacuum.