FR3033831A1 - ENGINE FOR AIRCRAFT - Google Patents

Abstract

The present invention relates to a power unit (1) comprising a gas turbine engine (20), a piston engine assembly (30), and a power turbine (40), in which a power turbine (40) is arranged to be driven by both the exhaust gases from the piston engine (31) and those from the turbine (23) and wherein the compressor (32) of the piston engine (31) is coupled to the shaft the gas turbine engine (24).

Description

FIELD OF THE INVENTION The present invention relates to the field of aircraft engines.

STATE OF THE ART An aircraft or helicopter engine is sized to be able to provide a high power for a limited time generally at the time of take-off and initial climb for the propulsion systems, or at the start of the main engines for the engines. non-propulsive systems. An aircraft or helicopter engine is therefore oversized for the phase of the longest flight, typically in cruising mode for a propulsion system, and this to the detriment of the mass and performance of the engine.

Propulsion of aeronautical aircraft is provided either by piston engines, for powers below about 250kW (light aircraft and helicopters, drones), or by gas turbines (turboshaft and turboprop engines) for higher powers. Piston engines and gas turbines each have advantages and disadvantages. Piston engines, particularly diesel-cycle engines, offer excellent thermal efficiency over a wide range of operation while the efficiency of gas turbines deteriorates sharply outside the design point.

Gas turbines on the other hand offer a better weight / power ratio (typically of the order of 3 to 5kW / kg for a gas turbine instead of 0.6 to 1kW / kg for a piston engine). Gas turbines operate only above a minimum fuel burn rate, while piston engines operate only in a restricted pressure and temperature range.

Moreover, the operability of the piston engines decreases in altitude because of the limited time allowed for the ignition of the mixture. Finally, the performance of piston engines at altitude are penalized by a strong need for cooling.

Thermal-thermal hybridization solutions consisting of mechanically driving the receiver by both a gas turbine and a piston engine, with the possibility of deactivating one of the two have been proposed. In particular, an engine comprising a diesel engine and a gas turbine in parallel can be driven, each driving the receiving shaft, the diesel engine being fed by a compressor of the gas turbine. Thermal-thermal hybridization solutions do not allow the direct recovery of energy unlike electrical hybridization. They aim to optimize energy consumption at all operating points.

In this, they are particularly suitable for use cycles with high load variations, with few energy recovery phases. In the case of free-turbine gas turbines, thermal-thermal hybridization solutions do not make it possible to optimize the energy efficiency of each machine or their operating range (restart, altitude, etc.). "Thermal-electrical hybridization" of storing mechanical energy in electrical form has also been proposed. These solutions allow greater flexibility with respect to operating points, but require the storage of two different primary energies and are generally not competitive in terms of mass, even counting onboard fuel economy. SUMMARY OF THE INVENTION The invention overcomes at least one of the aforementioned drawbacks by proposing a gas and mechanical coupling between a gas turbine unit and a piston engine. The proposed gas and mechanical coupling allows a gain in performance. Moreover the two sets can be uncoupled if necessary and each set can become independent again.

To this end, the invention proposes a power unit comprising a gas turbine unit, a piston engine assembly, and a power turbine, the gas turbine unit comprising: a combustion chamber, a turbine compressor, a gas arranged to compress the intake air 10 of the combustion chamber, a turbine arranged to be driven by the exhaust gases from the combustion chamber, a gas turbine shaft, the gas turbine compressor and the turbine being coupled to the gas turbine shaft, the piston engine assembly comprising: a piston engine, a piston engine compressor arranged to compress the intake air of the piston engine, a shaft ( 34) of a piston engine coupled to a load via a transmission, the power unit being characterized in that the power turbine is arranged to be driven by both the exhaust gases from the piston engine and those from from the turbine and in that the compressor of the piston engine is coupled to the shaft of the gas turbine engine.

The invention makes it possible to have a reduced response time of the piston engine in the event of load variation on the receiver. The invention makes it possible to increase the operational range of the piston engine, in particular by facilitating its starting and its operation in cold conditions or at altitude.

The invention makes it possible to achieve an over-power on the gas turbine with a combustion temperature much lower than in an engine having only one gas turbine, thus less damage to the most critical part of the gas turbine. The invention further allows the same fuel source to be used on both thermal machines in contrast to electrical hybridization. The invention also makes it possible to dilute and post-oxidize the exhaust gases of the piston engine by mixing them with the gases of the gas turbine, thus enabling a reduction of the polluting emissions.

The power balance can be adapted according to the operating point of the motor. In an example of use, the piston engine can bring a considerable part of the power in the low power phases. At full power, the gas turbine unit will provide all the power. If a one-off booster is required, the piston engine will be used to provide the required booster on the gas turbine engine. The invention therefore makes it possible to optimize energy consumption at all operating points. The invention is advantageously supplemented by the following characteristics, taken individually or in any of their technically possible combinations. The power unit further comprises an exchanger between the compressor and the piston engine, and adapted to cool the air from the compressor. The power turbine may comprise two stages, the first stage of which would be arranged to be driven by the exhaust gases coming from the 25-piston engine, and the second stage would be arranged to be driven by the exhaust gases coming from the turbine. The power turbine is mechanically coupled to the load via the transmission and a power shaft; The transmission includes a clutch adapted to uncouple the piston engine shaft from the power turbine.

3033831 5 The clutch is used to gradually load the coupling of the gas turbine shaft and the piston engine shaft. The clutch also allows smoothing instantaneous torque variations. Furthermore, in the event of a piston engine assembly failure, the gas turbine unit 5 can regain a conventional operating cycle, the piston engine assembly being disconnectable from the power turbine if necessary to limit the friction torque. The transmission includes, for example, a gear train for adapting the rotational speed of the piston engine and the rotational speed of the power turbine to the rotational speed of the load. The transmission may also be a belt, hydraulic, or electric transmission. The transmission comprises a clutch adapted to gradually load the coupling of the gas turbine shaft and the piston engine shaft and a smoothing of instantaneous torque variations.

The power unit further comprises an air sampling circuit adapted to draw air between the piston engine compressor and the piston engine, and a sampling valve adapted to regulate the amount of air drawn. This air bleed circuit provides pressurized air and / or hot air for powering the aircraft cabin when the piston engine is not running or operating at low loads. DESCRIPTION OF THE FIGURES Other objectives, features and advantages will become apparent from the detailed description which follows with reference to the drawings given by way of nonlimiting illustration, among which: FIG. 1 is a motor according to the invention comprising a piston engine and a combustion gas turbine; - Figure 2 is a motor according to the invention comprising a 30-piston engine and two combustion gas turbines.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 to 2, a power unit 1 comprises a combustion gas turbine assembly 20, a piston engine assembly 30. Gas turbine assembly 20 The gas turbine assembly 20 may in particular be a turboprop or a turbine engine and in particular an auxiliary power unit.

The gas turbine unit 20 comprises a combustion chamber 21, a compressor 22, a turbine 23, and a shaft 24. The compressor 22 is coupled to the shaft 24. The compressor may be axial or centrifugal. In the case of an axial compressor, this consists of a series of axial stages arranged in series each comprising a rotor having the shape of a moving impeller and a stator with rectifying vanes. The rotor consists of a circular disk on which vanes (fins) are fixed and rotates in front of the stator with stator vanes. In the case of an axial compressor, the wingspan varies along the flow to compensate for changes in the density of the fluid and to maintain a constant value at the axial flow rate. The rotor sucks and accelerates the flow of intake air by deviating it from the axis of the motor. The rectifier or stator that follows, straightens the flow in the axis and slows down by transforming part of its speed into pressure. The next rotor re-accelerates the airflow by deflecting it again from the motor shaft. The next stator 25 will again straighten the flow slow down and transform its speed into pressure. Gaseous fuel or liquid spray is injected into the combustion chamber 21 where it mixes with compressed air to maintain continuous combustion. The hot gases relax as they pass through the turbine 23, where the thermal and kinetic energy of the hot gases is converted into mechanical energy. The turbine 23 3033831 7 typically consists of a fixed vane distributor, followed by a moving vane. The flue gas escapes through an exhaust duct. The rotational movement of the turbine 23 is communicated to the shaft 24 which actuates the compressor 22.

Piston Engine 30 The piston engine assembly 30 includes a piston engine 31, a piston engine shaft 34, a compressor 32, and a heat exchanger 33. The piston engine assembly 30 will preferably be a spark cycle. by compression, to allow the use of the same fuel as the turbine, but all other engine technologies can be used (spark ignition engine, Wankel engine, ...). For reasons of compactness and mass, the piston engine assembly 30 will preferably be supercharged. In the case where the piston engine assembly 30 is a four-stroke compression ignition cycle, the piston engine 31 comprises, for example, in a manner known per se, at least one air intake duct, at least one intake valve adapted to close the intake duct, at least one exhaust duct, at least one exhaust valve adapted to close the exhaust duct, at least one cylinder, at least one adapted piston to move in the axis of the cylinder, a connecting rod connecting the piston to a crankshaft. The movement of the piston in the cylinder is converted into a rotation of the crankshaft in its crankcase via the connecting rod. The compressor 32 is similar to the compressor 22 described above. The compressor 32 is coupled to the shaft 24 of the gas turbine assembly 20. The compressor 32 constitutes a first compression stage of the piston engine assembly. The rotor of the compressor 32 draws in ambient air and accelerates the flow of air by deflecting it with respect to the axis of the engine. The rectifier of the compressor 32 rectifies the flow in the axis and slows it down by transforming part of its speed into pressure. The output of the compressor 32 is connected to the inlet of the piston engine 31, and this 3033831 8 preferably via an exchanger 33 adapted to cool the air from the compressor 32. The piston engine assembly 30 operates typically in a four-cycle cycle, as follows. During an intake phase, the inlet valve opens, the piston descends and pumps into the cylinder a mass of combustion air from the intake air and compressed in the compressor 32. At the start of the motor, the movement of the piston is for example provided by an electric starter.

During a compression phase, the inlet valve is closed and the piston rises and compresses the mixture to increase the amount of work produced. At the end of compression, a metered quantity of fuel is injected into the cylinder. During a combustion and expansion phase, the pressure and temperature conditions allow ignition of the fuel. The combustion exerts, by expansion of the mixture, a pressure on the piston. The piston is pushed back, and the burned gases relax. During an exhaust phase, the exhaust valve is open and the piston flushes the flue gases through the exhaust duct.

Load 7 The piston engine assembly 30 and the gas turbine engine 20 are each coupled to a load 7, either mechanically or through their air circuit. Charge 7 is typically a propeller, but may also be an electric generator or a hydraulic pump or any other power consuming device. Power Turbine 40 The power turbine 40 is of the free turbine type, that is to say that it is not coupled directly to the turbine 23 or to the piston engine 31.

The power turbine 40 typically consists of a rotor comprising a power turbine shaft 44 on which vanes are fixed and a stator 3033831 9 consisting of a housing carrying fixed deflectors, generally consisting of two parts. assembled in an axial plane. The power turbine 40 can be single or double. In the case where the power turbine 40 is double, it comprises a first stage 42 adapted to the large continuous flow of gas from the assembly 20 and a second stage 41 adapted to the lower pulsed flow of gas from the piston engine. 31, in order to optimize the energy recovery in the exhaust gases. The power turbine 40 recovers energy from the gases from both the piston engine assembly 30 and the gas turbine assembly 20 to provide torque to the load 60. The exhaust pipe piston engine is connected to the power turbine 40, which recovers energy from the combustion of gases to drive the load shaft 60. During an exhaust phase of the piston engine 31, the The exhaust valve 15 is opened and the piston flushes the flue gas into the free turbine 40 to make room for a new air charge. At this point the cycle resumes the admission time. The exhaust duct of the turbine 23 is connected to the power turbine 40. Instead of evacuating the energy lost by the exhaust duct, the power turbine 40 located downstream of the turbine 23 extracts the exhaust gas. exhaust gas enthalpy. Transmission 50 The power turbine shaft 44 and the piston engine shaft 34 are coupled to the load 60 via a transmission 50. From the point of view of the piston engine, the power turbine 40 plays the role of mechanical energy recovery system (commonly called 'mechanical turbo compound'). For this purpose the transmission 50 directly transfers the power of the crankshaft and the free power turbine 40 to the load. In an exemplary embodiment, for high power, the piston engine assembly 30 is of lower power than the gas turbine engine 20, which limits the inherent defects of the piston engine, namely the low power density, the need for cooling, and the acyclisms. The transmission 50 advantageously comprises a clutch 52 adapted to uncouple the piston engine assembly 30 from the power turbine 40. Thus, in the event of a failure of the piston engine assembly 30, the gas turbine unit 20 can recover a conventional operating cycle, the piston engine assembly 30 being uncoupled from the power turbine 40 if necessary to limit the friction torque.

The transmission 50 comprises a gear train 51 configured to match the rotational speed of the piston engine 31 and that of the free turbine to be compatible with that of the load 60. In a possible variant, a clutch allows also progressive loading of the coupling of the two shafts 24 and 34 and a smoothing of the variations of instantaneous torque. The combination of the exhaust gases from the turbine assembly 20 and the piston engine assembly 30 into the power turbine 40 allows the exhaust gases of the piston engine 31 to be diluted and post-oxidized by mixing them. with the gases of the gas turbine 20, which allows a reduction of polluting emissions. The coupling of a piston engine and a gas turbine unit makes it possible to use the same energy source on the two thermal machines in contrast to electrical hybridization.

Furthermore, the air supply of the piston engine 31 by the first stage 32 of compression of the gas turbine allows: - to have a reduced response time of the piston engine in case of load variation on the receiver ; to increase the operational range of the piston engine, in particular facilitating its start-up and its operation in cold conditions or at altitude; - supplying pressurized air and / or hot air to power the aircraft cabin when the piston engine is not running or operating at low load.

Tank 10 The engine is powered by a tank 10 and comprises a fuel management system 11. The engine may advantageously comprise a single tank 10 supplying the two sets 20 and 30, the fuel dosage of the two sets 20 and 30 remaining independent .

The system 11 allows the fuel flow rate in both sets 20 and 30 to be independently metered according to their operating point. In particular, it will be possible to favor the fuel flow rate in the piston engine 31 in the low power phases. At full power, only the gas turbine unit 20 will be fueled. If a one-off boost is required, the 15-piston engine 31 will again be used to provide the required boost to the gas turbine engine 20. As shown in FIG. 2, the piston engine 31 may be used as a backup for a two-turbine propulsion system having two gas turbine assemblies 20 and 20 '. These two gas turbine units 20 and 20 'can be of equal power, the piston engine 31 then serving to support gas turbine assemblies 20 and 20' for the high power phases. One can also have an architecture with a main gas turbine unit 20, and a second equivalent power engine comprising the piston engine 3 and a secondary turbine unit 20 '. In this configuration, the assembly 20 provides its power continuously on its nominal operating point, while the piston motor 31 and the secondary turbine unit 20 'are used according to the power requirement. For example, the piston motor 31 for low power, the second set 20 'for intermediate powers which correspond to its nominal point, and the two gas turbine units 20 and 20' for high powers are preferred. In the case of a twin-turbine engine associated with a piston engine 31, the coupling of the three machines makes it possible, in the event of a malfunction of one of the five gas turbines, to supply the piston engine with the other engine and therefore to ensure a sufficient level of power with the two remaining machines. Air sampling circuit 70 The engine may further comprise an air sampling circuit 70 adapted to draw air downstream of the compressor 32. This air can then be used to pressurize the cabin of the aircraft or prevent the formation of ice on critical parts of the aircraft, such as the leading edges of the wings. The air sampling circuit 70 is located between the outlet of the compressor 32 and the inlet duct of the piston engine assembly 30. In the event of a stopping of the piston engine 31 or of low-load operation, any or part of the air flow from the compressor 32 can be taken, via the air sampling circuit 70, to supply the pressurization of the appliance cabin and the heating system. This flow can also be directly released to the exhaust if none of these needs are present. 1: Power Group 10 Package: Fuel Tank 11: Fuel Management System 25 20/20 ': Gas Turbine Assembly 21/21': Gas Turbine Combustion Chamber 22/22 ': Turbine Compressors 23/23 ': Turbine of the gas turbine 24/24': Primary shaft of the gas generator 30 30: Piston motor assembly 31: Piston motor 3033831 13 32/32 ': Piston motor compressor 33: Exchanger (charge air cooling) 34: Piston motor power shaft 35/35 ': Compressor gas sampling valve 32 5 40/40': Power turbine assembly 44/44 ': Power shaft 50 : Transmission unit 51: Transmission (gears, clutch, ...) 52: Link with the piston engine assembly 10 53/53 ': Link with the gas turbine unit 60: Receiver (rotor, propeller, generator ,. ..) 70/70 ': Compressed air sampling circuit

Claims (7)

REVENDICATIONS1. Power unit (1) comprising a gas turbine engine assembly (20), a piston engine assembly (30), and a power turbine (40) connected to a load (60), the gas turbine engine assembly (20) comprising: a combustion chamber (21), a gas turbine compressor (22) arranged to compress the intake air of the combustion chamber (21), a turbine (23) arranged to be driven by the combustion gases; exhaust from the combustion chamber (21), a gas turbine shaft (24), the gas turbine compressor (22) and the turbine (23) being coupled to the gas turbine shaft (24) the piston engine assembly (30) comprising: a piston engine (31), a piston engine compressor (32) arranged to compress the intake air of the piston engine (31), a shaft (34), ) of a piston engine coupled to a load (60), via a transmission (50) the power unit (1) being characterized in that the power turbine (40) is arranged to be driven both the exhaust gases from the piston engine (31) and those from the turbine (23) and that the compressor (32) of the piston engine (3) is coupled to the shaft ( 24) of gas turbine. 2. Power unit (1) according to the preceding claim, further comprising an exchanger (33) between the compressor (32) and the piston engine (31), and adapted to cool the air from the compressor (32). 3033831 15 3. power unit (1) according to one of the preceding claims, wherein the power turbine (40) comprises two stages, a first stage (41) arranged to be driven by the exhaust gas from the motor 5 pistons (3) and a second stage (42) arranged to be driven by the exhaust gases from the turbine (23). 4. Power unit (1) according to one of the preceding claims, wherein the transmission (50) comprises a clutch (52) adapted to uncouple the piston engine shaft (34) from the power turbine (40). ). 5. power group (1) according to the preceding claim, wherein the clutch (52) is adapted to smooth instantaneous torque variations. 15 6. power unit (1) according to one of the preceding claims, wherein the transmission (50) comprises a gear train (51) adapted to adapt the speed of rotation of the piston engine (31) and the speed of rotating the power turbine (40) at the rotational speed of the load (60). 20 7. power unit (1) according to one of the preceding claims, further comprising an air sampling circuit (70) adapted to draw air between the compressor (32) piston engine (31) and the piston engine (31), and a sampling valve (35) adapted to regulate the amount of air withdrawn. 25