DESCRIPTION

Technical field

The present invention relates to the technical field of devices and methodologies for energy optimisation.

In particular, the present invention relates to a system for energy recovery applicable to vehicles, for example hybrid powered vehicles.

Prior art

The movement of vehicles requires the presence of an appropriate engine able to produce the mechanical energy necessary for the operation thereof. These engines may have different structures and types according to the specific implementation requirement, but they all share the same operating principle.

In general, the engine is able to transform an energy source, which may be in chemical form (thermal combustion engine), electrical (electric motor), or thermal (Rankine cycle engine), into mechanical energy or mechanical work through which the vehicle is moved.

A fuel cell is an electrochemical device which converts hydrogen and oxygen (taking oxygen from the environment) into electrical energy and water.

However, regardless of the specific structure of the engine and fuel used as an energy source, the energy transformation efficiency and its use for technical purposes is never equal to 100%, therefore there is inevitably waste which is to be suitably processed.

One of the main residual products of the transformation process is heat, which especially for heat engines actually represents the main output of the process in the use of the chemical energy contained in the fuel. In particular, in known devices, the energy effectively used and transformed into mechanical motion (including the friction of the engine’s kinematic mechanisms and transmission members) which can be used to move the vehicle varies from 25% to 38%, and however less than 50% whereas the remaining chemical energy is associated with the waste heat and combustion gases.

In fuel cells that use hydrogen for the production of electricity a percentage from 50% to 60% of the chemical energy is converted into electrical energy. The remaining energy is disposed of in the form of water vapour (the vapour’s latent and sensible heat).

To date this output on vehicles represents a waste which needs to be disposed of to prevent in the first place undesired overheating of the engine itself.

It therefore appears that systems of the known type are inefficient as they waste and do not process the main result of the chemical energy transformation process which they are configured to carry out.

A practical example of particular interest, in which such waste is extremely clear, is when we consider a hybrid propulsion vehicle.

A hybrid propulsion vehicle is a vehicle provided with a propulsion system that has two or more components, for example an electric motor which is coupled with a heat engine or an engine based on a fuel cell system or even a turbine engine, which work synergistically together.

In other words, hybrid vehicles are characterized by the presence of two or more forms of energy generation/storage in order to produce the necessary energy for the operation of the vehicle.

One of the main advantages of hybrid vehicles is the removal of the defects inherent in the need to start from standstill which, in conventional vehicles provided with a heat engine only, is particularly onerous because of the inevitable need for a non-null torque in order to overcome the inertia of the vehicle and place it in motion. In this context, thermal or turbine engines need a minimum speed regime in order to supply a suitable torque, whereas electric motors do not present this issue, thus being more suitable and efficient to handle the vehicle motion start-up phases.

In more detail, an internal combustion or turbine engine transforms the chemical energy of the fuel (of significant energy density and easy to supply through appropriate networks) with a reasonably acceptable efficiency especially at high speeds.

The electric motor operates instead by converting energy stored on board the vehicle in an appropriate battery pack with greater efficiency and versatility.

This battery pack must be charged so as to be able to guarantee its usability when necessary.

The battery can be charged with electric power from a grid external to the vehicle. With known technologies it is possible to charge the batteries using the vehicle’s kinetic energy during the speed reduction phase. In that case it is called regenerative braking.

A further type of known charging uses the energy produced by the heat engine and/or microturbine or turbine for charging the batteries, in particular supplying the mechanical energy to an alternator which transforms it into electrical energy which can be supplied to the battery pack.

This type of vehicle is commonly identified as a hybrid vehicle in series or range extended mode.

However, although this solution is practical from a logistical point of view (the power supply of an engine is generated through the other engine on board the vehicle itself), it is still affected by disadvantages that make the implementation not particularly efficient.

In particular, it is observed that the transformation of the chemical energy contained within the mixture of fuel and atmospheric air generates not only mechanical energy but also a high amount of waste heat. This reasoning also remains substantially valid should the vehicle comprise a fuel cell system in the place of the heat engine, in which the chemical reactions involving hydrogen and oxygen (taken from the atmosphere) also generate as an output the thermal energy normally managed as waste to be disposed of.

The advantage in fuel cells supplied by hydrogen is that the waste gas is equivalent to water vapour, thus not polluting.

The waste heat is identified in the heat that the combustion yields to the pistons and to the body of the engine, oil, etc. and the heat contained in the waste gases following the combustion process.

As indicated above, this waste heat represents most of the output provided by the engine and it is therefore clear how the battery pack charging process identified above implies enormous waste in which most of the energy generated is actually wasted and dissipated in the form of heat.

Object of the invention

In general terms it is therefore clear how in the sector there is a strongly felt need for new systems and configurations able to improve the efficiency of use of engines (internal combustion thermal engines, or turbines or microturbines) or comprising electrical current generating systems with fuel cells of vehicles so as to be able to tackle the enormous waste of resources currently found.

This technical task and the objects indicated are substantially achieved by a system for full energy recovery able to operate total recovery of the energy usually dissipated in the form of heat and combustion gas.

According to the present invention a system for energy recovery is shown.

In particular, a system is shown for the energy recovery from vehicles, which may for example be hybrid powered vehicles.

The system essentially comprises a storage tank, a first exchanger, a second exchanger, a first supply line and a second supply line.

The storage tank is configured and adapted to store heat energy. The first exchanger is placed in thermal contact with the storage tank and internally defines a conduit for the flow of a heat transfer fluid.

The heat exchange takes place by conduction between the walls of the exchanger and the material that performs the heat accumulation through temperature increase and/or phase change.

The second exchanger can be reversibly connected with a vehicle cooling system so as to define therewith a flow circuit for the heat transfer fluid. It is configured like a connection plate between the two circuits.

Such flow circuit is placed in thermal contact with an engine, in particular a thermal combustion engine, a turbine or microturbine engine or an engine comprising an electrical energy production system with fuel cells powered by hydrogen, installed on the vehicle.

The first supply line is configured to convey the heat transfer fluid from the first exchanger (plate/connection terminals) to the second exchanger; the second supply line is configured to convey the heat transfer fluid from the second exchanger to the first exchanger.

Advantageously, the system presented herein enables the heat generated by the vehicle’s engine during its operation to be transferred and stored, thus avoiding waste until achieving full recovery of the exhaust vapours by recovering both sensible heat and latent heat.

The dependent claims, incorporated herein by reference, correspond to different embodiments of the invention.

Brief description of the drawings

Further characteristics and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a preferred, but not exclusive, embodiment of a system for energy recovery, as illustrated in the accompanying drawings, in which:

- figure 1 shows a diagram representing the main components of a system for energy recovery according to the present invention. Detailed description of preferred embodiments of the invention

In the appended figures, the reference number 1 generically denotes a system for energy recovery, which will be referred to simply as the system 1 hereinafter in the present description.

This system 1 is specifically configured to be applied to a vehicle V which, by way of non-limiting example, may be a hybrid propulsion vehicle, or a hybrid vehicle, so as to enable the thermal energy generated during the use of its engine (internal combustion, turbine or microturbine or fuel cell system) to be recovered, for example in order to carry out a process of charging a battery pack B of the vehicle itself.

By way of non-limiting example, the vehicle V may have the structure schematically illustrated in figure 1 , in which in fact a vehicle V of the hybrid type is shown, essentially comprising a heat engine T connected to an alternator A through which the mechanical energy supplied by the heat engine T can be converted into electrical energy to be used for charging the battery pack B.

In detail, the electrical energy produced by the alternator A is directed by an appropriate control unit C to the battery pack B or to the electric motor E, which is in turn connected to the movement members M of the vehicle V.

The configuration and connections present between the components of the vehicle V shown in figure 1 define an exemplifying situation and do not exclude the compatibility of the system 1 according to the present invention being used in combination with vehicles V having different connection layouts between their elements, as long as there is always at least one element (in this case the heat engine T) provided for the generation of energy to be used directly or subsequently to appropriate transformations for moving the vehicle and such that its normal operation also implies/causes the generation of heat energy.

For ease of presentation in the following present description, explicit reference will be made to a scope in which the system 1 is used for recovering the heat generated by a heat engine T, however as indicated above the present invention is also applicable when the vehicle comprises instead of or in addition to the heat engine T an engine provided with a fuel cell system, powered by hydrogen and oxygen, a turbine or in general any engine or energy generation device that also generates heat in addition to the output directly used for the operation of the vehicle and/or its components.

Operatively, the present system 1 therefore allows the heat inevitably generated by the heat engine when active to be recovered without it being wasted.

From a structural point of view, the system 1 comprises a storage tank 2, a first exchanger 3, a second exchanger 4, a first supply line 5 and a second supply line 6.

In general terms, at least some of the constituent elements listed above contribute to defining in full or in part a path along which a heat transfer fluid can flow adapted to accumulate heat when flowing along the portion of path defined at least in part by the second exchanger 4 and to yield it to the storage tank 2 when it flows inside the portion of path defined by the first exchanger 3, according to the methods that will be explored further below.

The storage tank 2 is configured to store heat energy, in particular heat energy received from the heat transfer fluid.

According to a possible aspect of the present invention, the storage tank 2 comprises a sensible heat storage system, i.e. a system based on the absorption and subsequent release of heat through a variation (increases and decreases) in temperature of a storage means which may be in either solid or liquid form (e.g. glycol water, diathermic oil, molten salt).

Therefore, in this context, the heat storage system comprises a storage means adapted to absorb the heat from the heat exchange fluid when the latter flows inside the first exchanger 3.

In general terms also such storage means may in turn be a heat exchange fluid. Alternatively or additionally, the storage tank 2 comprises a latent heat storage system, which is based on the absorption and subsequent release of heat during the phase transition undergone by a storage means.

In particular, the latent heat storage system may comprise or be adapted to contain a phase change material configured to change phase in response to the absorption of heat by the heat exchange fluid flowing in the first exchanger 3.

Alternatively or additionally, the storage tank 2 may comprise a thermochemical storage system, whose operation is based on the energy absorbed and released during the breaking and formation of chemical or physical bonds during a completely reversible reaction.

In particular, the thermochemical storage system may comprise one or more chemical species adapted to undergo a reversible endothermic chemical reaction in response to the absorption of heat by the heat exchange fluid flowing in the first exchanger 3.

Alternatively or additionally, the storage tank 2 may comprise, or be connected to, a geothermal storage system, which enables the heat energy received from the heat exchange fluid to be conveyed into the ground so as to store it for example in the ground itself or in an underground water table, from which it can subsequently be recovered via appropriate probes.

In general, the storage tank 2 may comprise more than one storage system, which cooperate by storing and providing heat synergistically according to the use requirements of the system 1 .

For example, the storage tank 2 may comprise a sensible heat storage system used when needed to quickly exploit the heat absorbed by the heat exchange fluid, combining it with a geothermal system with which it is more efficient to store the heat energy to be exploited at a later date, even months later.

Regardless of the specific type of storage system implemented, the storage tank 2 is in thermal contact with the first exchanger 3, which internally defines a conduit for the flow of the heat exchange fluid so as to enable the latter to flow in a path along which it can gradually yield the accumulated heat to the storage tank 2.

Therefore, the first exchanger 3 receives during use a heated heat exchange fluid which flows along the flow conduit yielding its heat gradually to the storage tank 2 (in particular to its storage system).

The heat stored by the heat exchange fluid is instead obtained/absorbed in thermal contact with the heat engine T of the vehicle V.

This coupling is made possible by the second exchanger 4, which can be connected with a cooling system R of the vehicle V so as to define therewith at least a portion of a flow circuit for the heat transfer fluid.

Operatively, such flow circuit is placed in thermal contact with the heat engine T of the vehicle so as to enable the heat exchange fluid to absorb heat from the latter.

Should the heat engine T not be provided, as the vehicle V has for example a propulsion mechanism based on a fuel cell, the flow circuit is placed in thermal contact with the cooling system of such fuel cell.

Therefore, in general, the second exchanger 4 contributes to defining a flow circuit which in use is associated and in thermal contact with an element of the propulsion mechanism of the vehicle which generates heat as a consequence of its operation.

In more detail, the second exchanger 4 comprises a coupling element configured to be engaged in the cooling circuit R of the vehicle for transferring the heat exchange fluid from and to the cooling system R, thus operatively defining a by-pass of the cooling circuit.

In other words, the second exchanger 4 interfaces with the cooling system R so as to transfer the heat exchange fluid to the latter, which will flow along the normal advancement path defined by the cooling system so as to cool the engine storing heat inside it, to then return heated into the second exchanger 4 at the end of this path. In this context, the heat exchange fluid is preferably the same heat exchange fluid normally present inside the cooling system R of the vehicle V.

Alternatively, the second exchanger 4 can only be connected in thermal contact with the cooling system R without there being any exchange of fluids between the two and so as to receive and absorb from the latter the heat originally generated by the heat engine T.

In general, the second exchanger 4 may be provided in the form of a coupling plate which has a first face connected or that can be connected with the first supply line 5 and the second supply line 6 and a second face that can be connected with the cooling system R (can be connected in simple heat exchange or even with mutual exchange of heat exchange fluid).

In other words, the second exchanger 4 operatively defines the interface between the vehicle V (specifically its cooling system) and the system 1 (specifically the storage tank 2).

In its possible embodiments such second exchanger 4 can therefore be a real heat exchanger, should it define only an interface, a conduit or a circuit in thermal contact with the cooling circuit R, or an exchanger in the sense of an element designed to exchange the heat exchange fluid with the cooling circuit should it define the interface and therefore in fact the connector through which the supply lines 5, 6 are engaged in the cooling system R for exchanging the heat exchange fluid with them.

In general, in a use configuration, the transfer of heat exchange fluid from the first exchanger 3 to the second exchanger 4 and vice versa is thus operated by the first and the second supply line 5, 6 which define respective conduits connected to the exchangers 3, 4.

In particular, the first supply line 5 receives the heat exchange fluid from the first exchanger 3 and conveys it to the second exchanger 4, while the second supply line 6 brings the heat exchange fluid back from the second exchanger 4 to the first exchanger 3. Therefore, during use, the second exchanger 4 is connected to the cooling system R of the vehicle V and the activation of the system 1 ensures that the heat exchange fluid flows along the first supply line 5 reaching the inside of the second exchanger 4, whereby flowing in thermal contact with the heat engine T (with the mediation of the cooling system R itself) it absorbs heat and heats up.

At this point the heat exchange fluid is supplied to the second supply line 6 which brings it back into the first exchanger 3, flowing inside which the heat exchange fluid yields the heat previously accumulated at the storage tank 2.

Advantageously, through the use of the present system 1 , the heat transferred to the storage tank 2 can therefore be stored to be used (immediately or later) for supplying a utility, preferably a domestic or industrial or commercial utility (single or multiple).

For that purpose, the storage tank 2 can be connected to such utility, for example in direct thermal contact so as to enable a direct transfer of the stored heat, or through one or more transfer lines 7 which convey the element used for absorbing the heat of the heat exchange fluid to the effective point of use thereof and bring it back into the storage tank 2 after the latter has yielded the stored heat to the utility of interest.

Such system 1 thus enables the heat generated by the heat engine T (or internal combustion engine, turbine or microturbine or fuel cell) to be recovered during the operation thereof, reducing waste and using an output of the charging process normally wasted in a particularly efficient and effective way.

Preferably, the system 1 comprises at least one detection sensor S configured to monitor at least one temperature and/or flow rate of the heat transfer fluid in the first supply line 5 and in the second supply line 6.

This sensor may be for example coupled or installed on the second exchanger 4 or however configured to be housed in its vicinity. In this way it is possible to determine the temperature of the heat exchange fluid and the amount of heat effectively transferred from the heat engine T to the storage tank 2, also enabling the flow rate of the heat exchange fluid conveyed along the system 1 to be controlled and possibly varied according to the requirements to increase/reduce the amount of heat transferred or even only conveyed.

In particular, the management of the flow rates of the heat exchange fluid and the control of the heat transferred thanks to the system can be carried out through an appropriate control unit 8 which may comprise or be connected with such detection sensor S (e.g. by means of a cabled connected 8a as shown in figure 1 ) for receiving the data acquired therefrom and therefore control the flow rate of the heat exchange fluid (e.g. by activating appropriate valves).

Advantageously, the system 1 may further comprise an exhaust line 9 which can be coupled to an exhaust pipe of the vehicle V (or however in general to a line of the vehicle provided for the evacuation of the waste gases of the energy generation process from the heat engine T) and configured to receive an exhaust gas of the vehicle V itself.

The exhaust line 9 is configured to promote a strong reduction of the temperature of the exhaust gas so as to condense it and thus obtain the recovery of the sensible and latent heat of the gas as well as the abatement with removal of the harmful combustion products.

Advantageously, the exhaust line 9 is specifically configured to operate a condensation of the exhaust gases, so as to enable not only the latent heat but also the sensible heat to be recovered/absorbed therefrom, thus obtaining complete recovery of the energy produced by the combustion process that generated such gas.

For that purpose, the system 1 comprises a condenser device coupled to the exhaust line 9 and inside which the exhaust gas undergoes a change of state promoted by the yield of heat which can thus be transferred and stored for example inside the storage tank 2, which can be placed in thermal contact with the condenser device.

Therefore, advantageously, the system 1 also comprises a condensate neutraliser comprising a container inside which substances are placed, in particular chemical ones, appropriately selected according to the fuel and/or additives used in the combustion process (salts or equivalent chemical components) and specifically configured to modify, e.g. to increase, the pH of the condensed exhaust gases (due to the effect of the heat exchange and the action of the condenser device) and/or neutralise any harmful residues of the combustion process (such as, for example, nitrogen oxides), thus reducing the danger to the environment in the event of discharging them.

Such condensate neutraliser is in particular positioned downstream of the condenser device so as to be able to receive a condensed exhaust gas from it.

The condensed exhaust gas interacts with the substances present inside the condensate neutraliser causing a change in the pH of the condensates in order to make them less harmful for humans and the environment.

Preferably, the system 1 can further comprise a purifier device 10 coupled to an end or intermediate portion of the exhaust line 9 and configured to promote the complete removal of at least one polluting chemical species of the exhaust gas.

In this way, thanks to the exhaust line it is possible to completely recover also the energy contained in the exhaust gas and at the same time make it inert in order to eliminate any potential risks for the environment and for people’s health.

Specifically, the purifier device 10 can comprise one or more catalysts and/or filters configured both to trap the polluting chemical agents (facilitating their subsequent disposal and preventing their release into the environment) and to promote chemical reactions such as to transform them into non-hazardous chemical compounds for the health of people and/or the environment. Structurally, to recover heat, the exhaust line 9 can also comprise at least one section coupled in thermal contact with the storage tank 2 (or also with the first exchanger 3), thus enabling also the residual heat present in the exhaust gas downstream or upstream of the purifier device 10 (when provided) to be absorbed and recovered.

Alternatively, the exhaust line can comprise a tubular element along which the exhaust gases are conveyed and a dedicated tank in thermal contact with the tubular element so as to enable the transfer and storage of the heat contained in the exhaust gases.

Therefore, in this context, cooling of the exhaust gases is obtained with the consequent transfer of the energy which can be advantageously stored.

This operation can also enable the condensation of the exhaust gases, making their evacuation from the system 1 easier and possibly also enabling more simple storage in the event of any specific disposal procedures not simply possible near the system 1 being required or necessary.

Thanks to the structure just indicated, it is possible to obtain substantially complete recovery of the energy from the combustion process as the exhaust gases generated by it are processed so as to recover all of the energy possible, also promoting the neutralisation thereof, which makes it possible for its safe and harmless introduction into the external environment without having to require complex storage and/or transfer operations.

In particular, the complete removal of the polluting agents produced by the combustion process is obtained thanks to the combination of effects produced by the mechanical filtration of the exhaust gases and/or the addition of additives that optimise the combustion process and/or the neutralisation through appropriate substances, for example the already mentioned chemical substances such as salts, acidic condensates generated by the condenser device for the complete recovery of the energy (both latent and sensible heat) of the exhaust gases.

Additionally to the exhaust line 9 and, when present, to the purifier device 10, the system 1 may comprise a third supply line (not illustrated in the figures) which can be connected to the heat engine T for supplying it with at least one additive adapted to promote a combustion process of a fuel inside the heat engine T itself.

In other words, the third supply line conveys into the heat engine T a substance which improves the combustion process as a whole thus enabling the amount of waste substances (i.e. polluting substances) generated to be reduced and therefore disposed of or removed.

By way of example, this additive can comprise liquid oxygen, and/or hydrogen peroxide and/or hydrogen in gaseous form through which it is possible to reduce the level of nitrogen oxides generated during the combustion process.

Advantageously, the system 1 can further comprise also a charging line 1 1 that can be connected to an alternator A or to the control unit C of the vehicle V so as to receive electrical energy from the latter in order to transfer it as a supply to a utility U, for example the already mentioned individual or collective domestic or industrial or commercial utility or one or more battery packs through which to store the electrical energy produced.

In particular, when the system 1 is made to operate with a hybrid propulsion vehicle, the charging line 1 1 is configured to activate a transfer of electrical energy produced by the alternator A in response to the completion of a charging process of a battery pack B of the vehicle V.

Advantageously, the system 1 itself can comprise an alternator, so as to be able to convert the mechanical energy generated by the heat engine T (or thermal combustion engine, turbine or microturbine or fuel cell system) into electrical energy even when the system 1 is instead used to operate with a different type of vehicle, such as a vehicle without an alternator A.

Operatively, such conversion takes place when the mechanical energy produced is not to be used to move the vehicle, e.g. when the vehicle is parked with the heat engine T operating.

In this way, the electrical energy which is generated by the alternator A during the operation of the heat engine T (regardless of the fact that such an alternator A is on board the vehicle V or the system 1 ) is never wasted but can also be used directly for supplying the utility or be stored for subsequent use.

In this context, the operation of the charging line 1 1 can be controlled and monitored by the control unit 8, which can be interfaced with the control unit C of the vehicle V, activating the transfer of electrical energy through the charging line 11 when useful, for example when the latter communicates that the battery pack B has been completely charged or the vehicle is not in movement although the heat engine T is still operating.

Furthermore, there may also be an auxiliary charging line 1 1 a which supplies one or more resistors placed in thermal contact with the storage tank 2 and/or with the first exchanger 3 so as to enable the electrical energy generated by the alternator A to be exploited for generating heat energy and transferring it to the storage tank 2 directly or through the first exchanger 3. In other words, the electrical energy generated by the alternator A can be further directed along the auxiliary charging line 11 a (in particular once the battery pack of the vehicle V has been completely charged) so as to be able to exploit it to generate further heat to be stored inside the storage tank and thus avoid wasting the energy produced by the alternator A.

Therefore, advantageously, the present invention achieves the proposed objects, overcoming the disadvantages complained of in the known art by providing for the user a system for energy recovery which enables the heat generated during the operation of a heat engine T to be efficiently exploited, thus reducing the waste connected with the operation thereof.

The advantages can in part be listed according to how and where the system 1 is installed.

Some specific implementation examples may be:

A_1 ) the system 1 is external to the vehicle V and can be reversibly coupled thereto.

In this context the system 1 can be in a stationary position and if such hybrid propulsion vehicle with series configuration is stopped, i.e. not moving, then the system 1 enables the batteries to be charged and at the same time heat to be recovered and the exhaust gases to be possibly abated/removed.

Advantageously, in this way, there is total recovery of the heat also associated with the exhaust gases further enabling the harmful subproducts of the combustion process to be removed thus also being applicable in the context of cogeneration and/or tri-generation plants.

In other words, the system 1 according to the present invention enables the exploitation of the energy contained in the fuel to be optimised/maximised. Furthermore, in the subsequent step of moving the hybrid vehicle with series configuration, as long as the batteries serving the electric motor are charged, the movement takes place without producing any heat or polluting emissions.

A_2) the system 1 is installed on board the vehicle V and firmly constrained thereto.

In this context the system 1 can also be operated when the vehicle V is moving therefore, considering the already mentioned hybrid powered vehicle V with series configuration, in the phase of producing electrical current, there would be simultaneous recovery and storage for deferred use of the heat of the cooling circuit and possibly the exhaust gases.

In this way, the vehicle would move, significantly limiting the heat and polluting gas emissions produced as a whole by the heat engine or in general terms by the system/device provided for the combustion of fuel.

In general, the system 1 can be coupled (according to one of the methods set out above, i.e. reversibly or stably) to a heat engine T (internal combustion engine, turbine or microturbine) but which uses the mechanical energy for the movement of the vehicle, without generating electrical current the advantages mentioned above would be obtained in any case, as if the system 1 is external to the vehicle V it would be possible to recover and exploit fully and integrally the waste heat energy, both of the heat exchange fluid of the cooling system, and of the exhaust gases, whereas if the system 1 were fitted on board the vehicle V, the vehicle V would be moved with the complete recovery and storage of the heat generated by the heat engine obtaining less dispersion into the atmosphere both of the heat energy and any polluting gases, thus guaranteeing excellent exploitation of the energy contained in the fuels used.