IT201600079717A1 - HYBRID PROPULSION MOTOR FOR AEREONAUTICAL VEHICLES - Google Patents

Description

"ENGINE Ά HYBRID PROPULSION FOR AIRCRAFT VEHICLES"

DESCRIPTION

The present invention relates to a hybrid propulsion engine for aeronautical vehicles.

Various types of hybrid propulsion engines are known and the main known architectures can be classified into two families:

- architecture in which there is a generation of work by means of an internal combustion engine, subsequently a total transformation of the work produced by the engine into electrical energy is carried out by means of generators, with or without the aid of buffer batteries, and finally the energy is transformed electric in mechanical energy, useful for carrying out traction movements, by means of an electric motor: typical applications of this architecture are found in diesel electric locomotives for railway traction;

- architecture in which there is a generation of work by means of an internal combustion engine, subsequently a partial transformation of the work produced by the engine into electrical energy is carried out by means of generators, with or without the aid of buffer batteries, and finally the energy is transformed electric in mechanical energy, useful for carrying out traction movements, with electric motors placed in parallel with the remaining part of mechanical energy supplied directly by the internal combustion engine: typical applications of this architecture are found in the automotive sector of high-end cars.

These two architectures are an alternative to two other propulsion systems: the first, extremely conventional as well as widespread, is based solely on the production of work by means of internal combustion engines; the second is based on exclusively electric propulsion systems and is relegated, for now, only to special areas (for example forklifts, transport in protected areas such as airports or more recently on some cars).

The system based on internal combustion alone is recently showing some limits related to the need to comply with regulations and requirements related to energy saving and emission levels: the critical factor is the thermodynamic efficiency of transformation into mechanical energy, which is around 30 %, aggravated by the fact that this efficiency is typical of fixed point operation, ie constant power and rpm. However, it is known that an engine is regulated in power and rotation speed for operational requirements, and it is therefore necessary to take into account, in the global economy, the real utilization spectrum of the engine which causes the effective efficiency to drop to lower levels.

The system based on electric-only propulsion has the considerable disadvantage of having to have on board the energy necessary for its operation, which is accumulated in batteries that have a considerable weight and volume compared to the quantity of energy that can be stored, and much higher than those. of a liquid fuel such as gasoline, diesel or Jet A.

Known hybrid propulsion engines comprise an internal combustion engine, mainly used at the fixed point, which is arranged to use a fuel which has a predetermined energy density in such a way as to supply mechanical energy in the most efficient way possible. This mechanical energy is therefore:

a) used in part to perform a direct drive of the vehicle, preferably with an automatic gearbox or a CVT (Continuous Variable Transmission). b) used, for the remainder, to generate electricity through a generator, to assist or replace direct drive according to the vehicle's operating modes, to power the typical on-board electrical utilities and / or to power on-board batteries. A hybrid propulsion engine therefore comprises an electric motor which has the task of assisting traction alongside the internal combustion engine, and possibly replacing it entirely under certain operating conditions. This function can be extended to an enslavement of the CVT.

A hybrid-powered engine therefore requires:

- an electric generator of predetermined weight and dimensions to be able to perform the dedicated functions; - batteries of predetermined weight and size in such a way as to meet the needs of the hybrid propulsion system; - an electronic power management and control unit for managing the powers and adjustments of the electric motor;

- an electric motor of predetermined power for propulsion;

- a transmission system that combines the power inputs of the internal combustion engine and the electric motor.

Figure 1 shows a hybrid propulsion engine 1 according to the known art. In the following description reference will be made to an aircraft engine.

The engine 1 is designed to receive air 2 coming from the external environment, which enters a supercharging turbocharger 4 through an air intake of the aircraft, preferably oriented so as to recover the kinetic term of the flight speed so as to contribute to the compression ratio of the total thermodynamic cycle. The air is compressed by the turbocharger 4 to a predetermined pressure as a function of the power required at the flight altitude. The power is supplied by a turbine 6 which processes the power available in the vehicle exhaust gases and drives the turbocharger 4 by means of a shaft 8 which rigidly connects them. Air flow and pressure are regulated in a manner known per se by varying the number of revolutions of the turbine 6 and, at times, also with a variable geometry of the turbine ducts 6.

The compressed air from the turbocharger 4, which heats up due to the appreciably adiabatic compression, then enters a heat exchanger 10 (called "Intercooler") which has the task of cooling it by disposing of the heat towards the external environment through external air which , in turn, it enters and exits the exchanger 10 itself preferably in a "counter cross flow" configuration, ie in countercurrent with repeated crossings of the exchanger 10 to keep compact the size and weight of the exchanger 10 itself.

The regulation of the cooling flow through the exchanger 10 can contribute to the regulation of the motor 1 as a function of the altitude and therefore of the external air temperature.

Sometimes, the heat exchanger 10 is not present.

The air coming from the exchanger 10 then enters a cylinder of an internal combustion engine 12 in a per se known manner.

The internal combustion engine 12 is a two or four stroke volumetric piston engine, or a rotating piston (Wankel) engine, and preferably operates according to the Diesel cycle.

The fuel advantageously used is diesel fuel or, for uses at higher altitudes (and therefore lower outside temperatures), Jet A.

The exhaust gases escape in a known way from the engine 12 and these exhaust gases, which still have a considerable energy content both in the form of temperature and in the form of pressure, are sent 100 to the turbine 6 and made to expand in the turbine 6 itself. generating the power necessary to drag the aforementioned turbocharger 4.

In the event of high power requirements, it may happen that the residual power available at the exhaust of the combustion engine 12 is greater than that required by the turbocharger 4: in this case, a valve called 'Vaste gate' is used which vents the exhaust gas in excess to avoid overspeeding the turbocharger 4 and thus supercharging the engine 1 beyond the structural limits for which it was designed.

Sometimes this power is not wasted but is used by making the entire flow rate in the turbine 6 expand, collecting the excess power on the same shaft 8 which also drives the turbocharger 4; this power is then sent to a main electric generator 14 which uses it to transform it into power to be supplied to a planetary reduction gear 16, as described below. When this excess power is then used, we have a "turbocompound" type engine.

In a "turbocompound" engine there are therefore two sources of mechanical power which can be combined together to supply power to the planetary reduction gear 16.

The introduction of the main electric generator 14 enslaved by the mechanical transmission transforms the engine into a so-called "hybrid" engine and allows to obtain a variable and adjustable transmission ratio thanks to the adoption of the planetary reduction gear 16, allowing the internal combustion engine 12 to be adjusted to optimum rotation speed, regardless of the rotation speed required from the propeller.

In a variant of the motor 1 described above there is an auxiliary electric generator 17 which, similarly to the main electric generator 14, is connected to the turbine 6 by which it is operated to generate electric current to be used as described below.

Figure 1 therefore shows an electrical interlocking scheme with the main electric generator 14 (and / or the auxiliary electric generator 17) which absorbs the excess power that can be generated by an optimal regulation of the motor 1. The electric power made available by the generators electric motors 14 and 17 is used, by a control unit 18, both to power on-board utilities 19 and to power an electric motor with variable revolutions 20 which controls the rotation speed of the crown of the planetary differential reduction gear 16, transforming it into a transmission with continuously variable ratio (CVT). Similarly, the internal combustion engine 12 drives the internal pinion of the planetary reduction gear 16 by means of a shaft 12a.

The engine 1 is usually managed by an electronic control system (not shown in the figure) which defines, on the basis of the maps of the characteristics of the components and the optimal regulation strategy, the respective rotation speeds by intervening on the throttle of the aircraft and on the distribution of the powers through the CVT.

The main disadvantage of the engine described above lies in the need to have both the heavy main electric generator 14 and equally heavy buffer batteries 22 which, overall, increase the weight of the vehicle and reduce its useful space.

The buffer batteries 22 are necessary to power the control unit 18 and the variable speed electric motor 20 to compensate in transients the imbalances of electrical energy generated by the generators 14 and 17 with respect to that required by the variable speed motor 20 and by the users on board 19.

The power generated by the generators 14 and 17 then arrives at the control unit 18 which operates as a power controller: if all the power received is used by the variable speed motor 20 is sent all in those direction, only a part is needed, the the remaining power must be recharged the buffer batteries 22 if they have residual storage capacity, if also in this case the power is exuberant, then the control unit 18 intervenes on the regulation of the internal combustion engine 12 and on the excitation of the electric generators 14 and 17 to decrease the amount of power generated.

The aim of the present invention is therefore to propose an innovative hybrid propulsion engine for vehicles which overcomes the disadvantages of the engines of the prior art.

This and other objects are achieved with a hybrid propulsion engine for vehicles whose characteristics are defined in claim 1.

Particular embodiments form the subject of the dependent claims, the content of which is to be understood as an integral part of the present description.

Further characteristics and advantages of the invention will appear from the following detailed description, carried out purely by way of non-limiting example, with reference to the attached drawings, in which:

Figure 1, described above, shows a schematic diagram of a hybrid "turbocompound" propulsion engine according to the known art;

Figure 2 shows a schematic diagram of a hybrid propulsion engine according to the present invention; And

- Figure 3 shows an enlargement of the area of the fuel cell of Figure 2.

In summary, the hybrid propulsion engine of the present invention combines the advantages and compensates for the disadvantages of the engines of the prior art, so as to mitigate the negative effects and enhance the positive ones.

Figure 2 illustrates a schematic diagram of an engine according to the present invention which includes all the components described above belonging to an engine of the known art (and the same references will therefore be used).

Part of the mechanical power is supplied to the planetary gearbox 16 directly through the shaft 12a which connects the internal combustion engine 12 to the internal (solar) pinion of the planetary gearbox 16, while another part of power is supplied to the outer crown of the gearbox 16 through the shaft 8 which connects the turbine 6 and the turbocharger 4 to the reducer 16.

However, this type of exclusively mechanical coupling establishes a fixed and immutable transmission ratio, but the flight conditions and the power demands lead both the engine components, i.e. the turbocharger 4 and the turbine 6 on the one hand, and the engine to internal combustion 12 on the other hand, to work at unsuitable speeds for obtaining an optimal efficiency, which can only be reached for a certain power at a certain altitude.

The engine of the present invention comprises, in place of the buffer batteries 22 and the recharging generators 14 and 17, a plurality of hydrogen cells powered by hydrogen stored in liquid LOHC + (Liquid Organic Hydrogen Carrier loaded with hydrogen) materials in a per se known manner. .

In the aeronautical propulsion application of the present invention the liquid LOHC- is used as fuel of the internal combustion engine 12 exploiting some characteristics of the process of catalytic dissociation or dehydrogenation of LOHC + in LOHC- in terms of thermodynamic recovery as described below.

In summary, with reference to Figure 2:

- a liquid LOHC + 50 is stored in a tank 51, typically placed inside the wings of the aircraft, and with suitable pumps known per se it is sent to a catalyst 52 which carries out the dehydrogenation; preferably the liquid 50 passes through a counter-current exchanger 53 (see Figure 3, which shows an enlargement of the area of the fuel cell of Figure 2);

- the catalyst 52 is kept at a predetermined temperature by exploiting the latent heat of the exhaust gases that come out of the turbine 6, carrying out a first part of thermodynamic recovery;

at the outlet of the catalyst 52 we obtain:

i) hot gaseous hydrogen which is sent to at least one fuel cell 54, where it reacts with air taken from the outside, generating electrical energy to power the electric motor 20;

ii) liquid LOHC-56 in the vapor state which is sent to the internal combustion engine 12 and generates power by exploiting the heat of vaporization of the fuel, carrying out a second part of the thermodynamic recovery. For the part possibly exceeding the instantaneous requirement of the internal combustion engine 12, the LOHC-56 is sent back to the tank 51 through the previous heat exchanger 53, so as to return to liquid and contribute to the heating of the dehydrogenation process, thus effecting a third part of thermodynamic recovery.

In a variant of the invention, this still hot vapor or liquid is conveyed inside an anti-icing system 60 of the aircraft (typically the leading edge of the wings) further contributing to a thermodynamic recovery.

In a variant of the invention, there is an additional electrical generator 80 operating as described above with reference to the main 14 and auxiliary 17 electrical generators.

The liquid LOHC-, a waste product of the catalytic dissociation process carried out by the hydrogen cells, is used as fuel for the internal combustion engine 12 instead of being stored to be taken to the recharging system at the end of the flight.

The reuse of the LOHC- liquid is the determining factor of the invention and the other regenerative aspects described above are different and very important aspects as they are combined with the reuse of the waste liquid.

During flight, the lighter the plane becomes because it burns fuel, the less lift it requires; since there is an optimal fixed ratio for each aircraft between lift and drag (called "aerodynamic finesse") it follows that the more the weight drops, the less resistance it opposes and therefore the less power it requires to maintain flight speed at a given altitude .

The known solution which uses simple batteries does not cause the batteries to lose weight as they become discharged, while the solution of the present invention which envisages not returning the LOHC- liquid (by burning it in the internal combustion engine as described in the present invention) instead makes it lose weight to the aircraft by progressively decreasing the lift requirement and induced drag, and therefore thrust and power necessary for the flight, with advantages on consumption, autonomy and operating costs. As a further example, you can have a demonstrator or special aircraft that exploits the only method of using the LOCH + in a fuel cell for electric-only propulsion with conservation of the LOCH-exhausted, without burning it in an internal combustion engine. This aircraft, while not exploiting the advantage of hybridization as described above, allows to have a considerable advantage of energy density (kWh / kg) of the LOHC + compared to batteries, with a factor of about ten. However, this advantage is mitigated by the weight of the catalyst and the fuel cell, which is a fixed and immutable weight in flight, therefore, this solution becomes more and more advantageous the greater the autonomy required by the aircraft, as for example in drone systems. MALE (Medium Altitude Long Endurance).

Naturally, the principle of the invention remaining the same, the embodiments and construction details may be widely varied with respect to what has been described and illustrated purely by way of non-limiting example, without thereby departing from the scope of protection of the present document. invention defined by the appended claims.

Claims (5)

CLAIMS 1. Hybrid propulsion engine (1) for an airplane comprising: - an internal combustion engine (12) and an electric engine (20); - a plurality of hydrogen cells fed by a predetermined liquid stored in a tank (51), in which said hydrogen cells comprise a respective catalyst (52) suitable for carrying out a process of dehydrogenation of said liquid, obtaining a liquid exhausted; in which, at the end of said dehydrogenation process, hot gaseous hydrogen is obtained which is sent to at least one fuel cell (54) where it reacts with air coming from outside to generate electrical energy to power said electric motor (20) , and in which the exhausted liquid is sent to the internal combustion engine (12) in such a way as to generate power. 2. Hybrid propulsion engine according to claim 1, wherein said engine (1) is arranged to receive air (2) coming from the external environment, which enters a supercharging turbocharger (4) of said engine (1 ) so as to be compressed by the turbocharger (4) at a predetermined pressure, in which the power necessary to carry out the compression is supplied by a turbine (6) connected to the turbocharger (4) and in which the catalyst (52) is maintained at a predetermined temperature by exploiting the latent heat of the exhaust gases that come out of said turbine (6), carrying out a thermodynamic recovery. 3. Engine according to claim 1 or 2, in which part of the liquid is sent back to the tank (51) so as to return liquid and contribute to the heating of the dehydrogenation process, thus carrying out a further thermodynamic recovery. 4. Engine according to claim 1 or 2, in which said liquid is conveyed inside an anti-ice system (60) of the aircraft contributing to a thermodynamic recovery. 5. Engine according to claim 1 or 2, wherein the engine (1) comprises an additional electrical generator (80).