Turbofan engine assembly with gearbox

A turbofan engine assembly including an internal combustion engine in fluid communication between a compressor and a turbine, the internal combustion engine having an engine shaft, a bypass duct surrounding the internal combustion engine, and a fan drivingly engaged to the engine shaft via a gearbox, the gearbox configured to increase an output speed of the fan relative to an input speed of the engine shaft.

TECHNICAL FIELD

The application relates generally to turbofan engine assemblies and, more particularly, to such assemblies including one or more internal combustion engine(s).

BACKGROUND OF THE ART

Various configurations of turbofan engine assemblies including internal combustion engines are known. For example, in some turbofan engine assemblies, a turbine drives the fan via a first shaft while the internal combustion engine drives the compressor(s) via a second shaft rotatable independently from the first shaft. In other configurations, the shaft of the internal combustion engine is engaged to the fan via a gearbox defining a speed reduction from the engine shaft to the fan, so that the fan rotates at a slower rotational speed than the shaft of the internal combustion engine. However, existing configurations may leave place for improvement, for example in terms of thermal efficiency and thrust specific fuel consumption of the engine assembly.

SUMMARY

In one aspect, there is provided a turbofan engine assembly comprising: an internal combustion engine in fluid communication between a compressor and a turbine, the internal combustion engine having an engine shaft; a bypass duct surrounding the internal combustion engine; and a fan drivingly engaged to the engine shaft via a gearbox, the gearbox configured to increase an output speed of the fan relative to an input speed of the engine shaft.

In another aspect, there is provided a turbofan engine assembly comprising: a compressor; a plurality of rotary internal combustion engines each including an engine rotor having three apex portions mounted for eccentric revolutions within an internal cavity defined in a housing, the internal cavity having an epitrochoid shape with two lobes, the rotary internal combustion engines having an inlet in fluid communication with an outlet of the compressor through at least one first passage of an intercooler; a turbine having an inlet in fluid communication with an outlet of the rotary internal combustion engines; a bypass duct surrounding the rotary internal combustion engines, compressor and turbine; and a fan configured to propel air through the bypass duct and through an inlet of the compressor, the fan drivingly engaged to a shaft of the rotary internal combustion engines via a gearbox, the gearbox defining a speed ratio of a rotational speed of the shaft of the rotary internal combustion engines on a rotational speed of the fan, the speed ratio being smaller than 1 so that the gearbox defines a speed increase from the shaft of the rotary internal combustion engines to the fan.

In a further aspect, there is provided a method of driving a fan of a turbofan engine assembly, the method comprising: rotating a shaft with an internal combustion engine of the turbofan engine assembly; and driving the fan with the shaft of the internal combustion engine via a gearbox of the turbofan engine assembly, the gearbox configured so that the fan is rotated at a greater rotational speed than that of the shaft.

DETAILED DESCRIPTION

FIG. 1illustrates a turbofan engine assembly10in accordance with a particular embodiment. The turbofan engine assembly10is of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan12through which ambient air is propelled, a compressor section14for pressurizing the air, one or more intermittent internal combustion engines16in which the compressed air is mixed with fuel and ignited, and a turbine section18for extracting energy from the exhaust of the internal combustion engine(s)16. A bypass duct20surrounds the internal combustion engine(s)16, compressor section14and turbine section18, and the fan12is configured to propel air through the bypass duct20as well as into the inlet of the compressor section14.

The internal combustion engine(s)16is/are engaged to a common engine shaft17. In a particular embodiment, multiple internal combustion engines16are provided, each configured as a rotary intermittent internal combustion engine, for example of the type known as Wankel engine.

Referring toFIG. 3, an example of a Wankel engine which may be used as the internal combustion engine16is shown. It is understood that the configuration of the engine(s)16, e.g. placement of ports, number and placement of seals, etc., may vary from that of the embodiment shown.

The rotary internal combustion engine16comprises a housing32defining a rotor cavity having a profile defining two lobes, which is preferably an epitrochoid. A rotor34is received within the rotor cavity. The rotor defines three circumferentially-spaced apex portions36, and a generally triangular profile with outwardly arched sides. The apex portions36are in sealing engagement with the inner surface of a peripheral wall38of the housing32to form and separate three working chambers40of variable volume between the rotor34and the housing32. The peripheral wall38extends between two axially spaced apart end walls54to enclose the rotor cavity.

The rotor34is engaged to an eccentric portion42of an output shaft17to perform orbital revolutions within the rotor cavity. The output shaft17performs three rotations for each orbital revolution of the rotor34. The geometrical axis44of the rotor34is offset from and parallel to the axis46of the housing32. During each rotation of the rotor34, each chamber40varies in volume and moves around the rotor cavity to undergo the four phases of intake, compression, expansion and exhaust.

An intake port48is provided through the peripheral wall38for admitting compressed air into one of the working chambers40. An exhaust port50is also provided through the peripheral wall38for discharge of the exhaust gases from the working chambers40. Passages52for a spark plug, glow plug or other ignition mechanism, as well as for one or more fuel injectors of a fuel injection system are also provided through the peripheral wall38. Alternately, the intake port48, the exhaust port50and/or the passages52may be provided through the end or side wall54of the housing. A subchamber (not shown) may be provided in communication with the chambers40, for pilot or pre injection of fuel for combustion.

For efficient operation the working chambers40are sealed by spring-loaded peripheral or apex seals56extending from the rotor34to engage the inner surface of the peripheral wall38, and spring-loaded face or gas seals58and end or corner seals60extending from the rotor34to engage the inner surface of the end walls54. The rotor34also includes at least one spring-loaded oil seal ring62biased against the inner surface of the end wall54around the bearing for the rotor34on the shaft eccentric portion42.

The fuel injector(s) of the engine16, which in a particular embodiment are common rail fuel injectors, communicate with a source of Heavy fuel (e.g. diesel, kerosene (jet fuel), equivalent biofuel), and deliver the heavy fuel into the engine16such that the combustion chamber is stratified with a rich fuel-air mixture near the ignition source and a leaner mixture elsewhere.

Referring back toFIG. 1, the compressor section14of the embodiment shown includes a single axial compressor rotor15; it is understood that alternately, multiple compressor rotors and/or other rotor configurations could be provided; for example, the compressor can be a mixed flow or centrifugal stage compressor. In a particular embodiment, the compressor14is configured as a boost compressor. The outlet of the compressor14is in fluid communication with the inlet (e.g. intake port48) of each internal combustion engine16. In the embodiment shown, this communication is performed through the first passage(s)64′ of an intercooler64, as will be further detailed below.

In the embodiment shown, an annular compressor flow path22is defined concentric to and surrounded by the bypass duct20, with an inner wall21of the bypass duct20separating the bypass duct20from the compressor flow path22; an upstream end of the inner wall21is located immediately downstream of the fan12. The compressor rotor15extends across the compressor flow path22, and the portion of the compressor flow path22extending upstream of the compressor rotor15defines the compressor inlet14i. An annular compressor outlet scroll23is provided in fluid communication with the compressor flow path22, downstream of the compressor rotor15, and defines the outlet of the compressor section14. In the embodiment shown, vanes22′ are provided across the flow path22between the compressor rotor15and the outlet scroll23so as to turn the axial flow toward the circumferential flow direction defined by the scroll23. The outlet scroll23communicates with the first passage(s)64′ of the intercooler64, for example through a pipe24extending through the inner wall21of the bypass duct20. The first passage(s)64′ in turn communicate with an inlet manifold25extending in proximity of the internal combustion engine(s)16. The inlet (e.g. intake port48) of each internal combustion engine16is in fluid communication with the inlet manifold25.

The intercooler64is located in the bypass duct20, and includes one or more second passage(s)64″ which are in fluid communication with the bypass duct20. Accordingly, part of the air driven by the fan12to circulate through the bypass duct20circulates through the second passage(s)64″. The second passage(s)64″ is/are in heat exchange relationship with the first passage(s)64′ receiving the compressed air from the compressor14, so as to be able to cool the compressed air before it is delivered to each internal combustion engine16, using the bypass air flow of the bypass duct20.

In the embodiment shown, additional heat exchangers68are located in the bypass duct20together with the intercooler64. The heat exchangers68may be configured to receive oil and/or a coolant of the internal combustion engine(s)16, and/or oil from the remainder of the engine assembly10. The heat exchangers68may thus be in fluid communication with a coolant system of the internal combustion engine16, and/or with a lubrication system of the internal combustion engine16and/or with a lubrication system of the engine assembly10as a whole. Inlet and outlet fluid conduits70,70′ provide for a circulation of the coolant (e.g. liquid coolant) and/or oil to first passage(s)68′ of the heat exchangers, which are in heat exchange relationship with second passage(s)68″ receiving part of the air circulating through the bypass duct20.

In a particular embodiment, the intercooler64and heat exchangers68located in the bypass duct20provide for heating of the flow through the bypass duct20through the heat exchanger with the air/fluid to be cooled in the intercooler64/heat exchangers68, which increases the potential for the bypass flow to provide thrust, which may increase the net efficiency (TSFC—Thrust Specific Fuel Consumption) of the engine assembly10.

In the embodiment shown, the turbine section18includes two turbines26,27each including a respective axial turbine rotor26′,27′; it is understood that alternately, a different number of turbine rotors (one, or more than two) and/or other rotor configurations could be provided. The first turbine26has an inlet in fluid communication with an outlet (e.g. exhaust port50) of each internal combustion engine16.

In a particular embodiment, the two turbines26,27have different reaction ratios from one another. Most aeronautical turbines are not “pure impulse” or “pure reaction”, but rather operate following a mix of these two opposite but complementary principles—i.e. there is a pressure drop across the blades and some reduction of flow area of the turbine blades along the direction of flow (reaction), and the direction of the flow is changed in the tangential direction (impulse), so that the speed of rotation of the turbine is due to both the acceleration and the change of direction of the flow. Pure reaction turbines would have a reaction ratio of 1 (100%), while pure impulse turbine would have a reaction ratio of 0 (0%). In a particular embodiment, the first turbine26is configured to take benefit of the kinetic energy of the pulsating flow exiting the internal combustion engines16while stabilizing the flow and the second turbine27is configured to extract energy from the remaining pressure in the flow. Accordingly, the first turbine26has a lower reaction ratio (i.e. lower value) than that of the second turbine27, so as to be closer to a “pure impulse” configuration. Alternately, the two turbines26,27may have the same or similar reaction ratios.

In the embodiment shown, a turbine inlet scroll28is provided in fluid communication with a turbine flow path29through which the rotors26′,27′ of the turbines26,27extend; the turbine inlet scroll28defines the inlet of the first turbine26and of the turbine section18. A respective exhaust pipe30extends between the outlet (e.g. exhaust port50) of each internal combustion engine16and the inlet scroll28. In a particular embodiment, the exhaust pipes30communicate with the inlet scroll28at regularly circumferentially spaced apart locations. The exhaust pipes30may each communicate with a respective section of the inlet scroll28.

The first turbine26has an outlet in fluid communication with an inlet of the second turbine27; in the embodiment shown, this is obtained by having the two turbine rotors26′,27′ located in the same turbine flow path29, with the rotor27′ of the second turbine27located downstream of the rotor26′ of the first turbine26. Other configurations are also possible.

The flow from the bypass duct20mixes with the exhaust flow from the second turbine27(i.e., exhaust flow from the turbine section18) at the downstream end of the engine assembly10. For example, a mixer66may be provided at the downstream end of the inner wall21of the bypass duct20to facilitate mixing of the two flows.

In the embodiment shown, the turbofan engine assembly10is a single shaft assembly, i.e. the fan12, the compressor rotor15and the turbine rotors26′,27′ are all drivingly engaged to the engine shaft17. A first gearbox72is provided in engagement with a forward end of the engine shaft17, and a second gearbox74is provided in engagement with a rear end of the engine shaft17. The fan12is drivingly engaged to the engine shaft17via the first gearbox72, and the turbine rotors26′,27′ are connected to a turbine shaft31drivingly engaged to the engine shaft17via the second gearbox74. The turbines26,27are accordingly compounded with the internal combustion engine(s)16.

In the embodiment ofFIG. 1, the compressor14is located between the internal combustion engine(s)16and the fan12, and the compressor rotor15is also engaged to the engine shaft17via the first gearbox72, such as to be rotatable at the same speed as the fan12. The fan12and compressor rotor15are connected to a same shaft19engaged to the engine shaft17via the first gearbox72. The first gearbox72is configured to increase an output speed of the fan12and of the compressor rotor15relative to an input speed of the engine shaft17, i.e. the gearbox72defines a speed ratio of a rotational speed ωeof the engine shaft17on a rotational speed ωfof the fan12(and of the compressor rotor15) which is smaller than 1 (i.e. ωe/ωf<1). In use, the rotational speed of the fan12and of the compressor rotor15is thus greater than the rotational speed of the engine shaft17. In a particular embodiment, the speed ratio ωe/ωfof the first gearbox72is 0.5 or approximately 0.5, i.e. the fan shaft19(fan12, compressor rotor15) rotates at a rotational speed double or approximately double the rotational speed of the engine shaft17.

In a particular embodiment, the first gearbox72is configured as a single stage epicyclic gearbox. Other configurations are also possible.

In the embodiment shown, the second gearbox74is an accessory gearbox. The assembly10includes engine accessories76(e.g. fuel pump(s), oil pump(s), cooler pump(s), electric machine(s)) which are also engaged to the second gearbox74. Some of the accessories76may rotate at different rotational speeds from one another. In a particular embodiment, the second gearbox74is also an epicyclic gearbox. Other configurations are also possible.

Referring toFIG. 2, a turbofan engine assembly110in accordance with another particular embodiment is shown, where elements similar to that of the engine assembly10ofFIG. 1are identified by the same reference numerals and will not be described in further detail therein.

In this embodiment, the compressor114is located between the internal combustion engine(s)16and the first turbine26. The compressor114is configured as a centrifugal compressor, with the compressor flow path122extending radially at the compressor outlet to communicate with the compressor outlet scroll23. It is understood that the configuration of the compressor could be different than that shown; for example, the compressor could be a single or multiple stage(s) axial or mixed flow compressor.

The compressor inlet114iis defined by a duct extending radially inwardly from a scoop or other axial component configured to raise the air pressure and located in the bypass duct20downstream of the internal combustion engine(s)16. The compressor flow path122then turns along the axial direction adjacent the leading edge of the compressor rotor115. Accordingly, the compressor flow path122extends first radially inwardly then radially outwardly from the bypass duct20to the compressor outlet scroll23.

Variable inlet guide vanes78are optionally provided in the compressor flow path122, upstream of the compressor rotor115. Although not shown, variable inlet guide vanes may also be provided in the assembly ofFIG. 1.

In this embodiment, the flow accordingly goes rearwardly across the compressor114, then forwardly from the compressor outlet scroll23through the intercooler64and into the inlet of the internal combustion engine(s)16, then rearwardly again from the internal combustion engine(s)16through the exhaust pipe(s)30, turbine inlet scroll28and turbines26,27. In contrast, the flow through the engine assembly10ofFIG. 1goes in generally rearwardly from the compressor inlet to the turbine exhaust.

In a particular embodiment, the first gearbox72of the assembly110is configured to increase an output speed of the fan12relative to an input speed of the engine shaft17, i.e. the first gearbox72defines a speed ratio of a rotational speed ωeof the engine shaft17on a rotational speed ωfof the fan12which is smaller than 1 (i.e. ωe/ωf<1). In use, the rotational speed of the fan12is thus greater than the rotational speed of the engine shaft17, similarly to the assembly ofFIG. 1.

In this embodiment however, the compressor rotor115is drivingly engaged to the engine shaft17via the second gearbox74so as to be rotatable at a same rotational speed as the turbine rotors26′,27′, i.e. the turbine rotors26′,27′ and the compressor rotor115are connected to a same shaft31drivingly engaged to the engine shaft17via the second (e.g. accessory) gearbox74.

In a particular embodiment, the engine assembly10,110allow to achieve a thermal efficiency which is superior to a gas turbine turbofan engine of a similar size.