Non-recuperated supercritical carbon-dioxide Brayton cycle heating for liquid natural gas-powered engines
Systems and methods for combusting liquid natural gas (LNG) for use in turbofan engines in aircraft are disclosed. Various components use a non-recuperated supercritical carbon dioxide (sCO 2 ) Brayton cycle by the sCO 2 extracting heat from a heat exchanger through which flows primary exhaust of a gas turbine engine. The sCO 2 is split into dual streams. One stream flows through a sCO 2 turbine which turns a shaft coupled to a gearbox for performing useful work. The other stream is equalized in pressure and is recombined with the stream from the sCO 2 turbine. The recombined stream flows through an evaporator in the fuel injection system, which converts LNG to gaseous natural gas (GNG) suitable for combustion.
1 . A system for a Liquid Natural Gas (LNG)-powered aircraft, comprising:
a LNG turbine engine including a burner coupled between a main compressor and a main turbine, a main shaft coupled to the main turbine and the main compressor, and a heat exchanger through which a primary exhaust gas from the LNG turbine engine flows for heating a supercritical carbon-dioxide (sCO 2 );
a fuel injection system coupled to the burner and including an evaporator, the evaporator comprising a first inlet through which the LNG flows, and comprising a first outlet;
components for implementing a non-recuperated sCO 2 Brayton cycle, the components including:
a sCO 2 turbine coupled between the heat exchanger and a second inlet of the evaporator;
a sCO 2 compressor having an input coupled to a second outlet of the evaporator and an output coupled to an input of the heat exchanger for recirculating the sCO 2 through the heat exchanger;
a sCO 2 shaft coupled to the sCO 2 turbine and the sCO 2 compressor;
a controllable bypass, comprising:
a splitter disposed between the heat exchanger and an input to the sCO 2 turbine for receiving the sCO 2 from the heat exchanger and configured to split the sCO 2 into a first portion of the sCO 2 and a second portion of the sCO 2 , the first portion of the sCO 2 entering the sCO 2 turbine, wherein the first portion of the sCO 2 from the heat exchanger flows through the sCO 2 turbine for rotating the sCO 2 shaft to operate the sCO 2 compressor, wherein the second portion of the sCO 2 from the heat exchanger bypasses the sCO 2 turbine, and wherein the sCO 2 from the second outlet of the evaporator is compressed by the sCO 2 compressor; and
a pressure control valve configured to receive the second portion of the sCO 2 from the splitter and to equalize a pressure drop between the first portion of the sCO 2 at an output of the sCO 2 turbine with the second portion of the sCO 2 ;
a mixer arranged between the output of the sCO 2 turbine and the second inlet of the evaporator, wherein the mixer is configured to recombine the first portion of the sCO 2 exiting the sCO 2 turbine with the second portion of the sCO 2 that bypassed the sCO 2 turbine for supplying sufficient heat to the second inlet of the evaporator to vaporize the LNG into a Gaseous Natural Gas (GNG); and
a controller, wherein the controller is configured to adjust a flow of the first portion of the sCO 2 to the sCO 2 turbine and a flow of the second portion of the sCO 2 to the mixer by specifying a relative quantities of the first portion of the sCO 2 and the second portion of the sCO 2 , wherein the controller is further configured to inject a controlled amount of the GNG from the evaporator into the burner for providing a prescribed amount of heat for combusting the GNG to operate the engine, wherein the controller is configured to control the pressure control valve to equalize a pressure of the second portion of the sCO 2 with a pressure of the first portion of the sCO 2 exiting the sCO 2 turbine.
2 . The system of claim 1 , wherein the engine is a turbofan engine.
3 . The system of claim 1 , wherein the pressure control valve is disposed between the second outlet of the evaporator and the sCO 2 compressor, the pressure control valve being configured to control a cycle mass flow rate of the sCO 2 .
4 . The system of claim 1 , wherein the LNG is blended with liquid hydrogen.
5 . The system of claim 1 , wherein the heat exchanger is positioned in or adjacent a primary engine nozzle.
6 . The system of claim 1 , wherein the main turbine comprises a high pressure turbine and a low pressure turbine.
7 . The system of claim 1 , wherein the main shaft comprises a high pressure shaft and a low pressure shaft.
8 . The system of claim 1 , wherein the main compressor comprises a high pressure compressor and a low pressure compressor.
9 . The system of claim 1 , wherein the engine further includes a gearbox positioned between the main turbine and the main shaft, wherein the gearbox is coupled to the sCO 2 shaft, such that the sCO 2 shaft and the gearbox are configured to provide additional power via the sCO 2 from the heat exchanger that flows through the sCO 2 turbine.
10 . The system of claim 9 , wherein the controller is configured to control, using the controllable bypass, a first amount of energy used to generate the additional power and a second amount energy used to heat the LNG.
11 . The system according to claim 1 , further comprising:
a first fluid channel between the heat exchanger and the evaporator for delivering the sCO 2 to the second inlet of the evaporator such that the sCO 2 flowing through the heat exchanger causes the LNG to convert to the GNG as the GNG flows through the first outlet of the evaporator;
a second fluid channel between the second outlet of the evaporator and the sCO 2 compressor for repressurizing the sCO 2 ; and
a third fluid channel between the output of the sCO 2 compressor and the heat exchanger for recirculating the sCO 2 back through the heat exchanger, wherein
the GNG is configured to controllably flow through a conduit to the burner to enable combustion for a sustained operation of the engine to power the aircraft.
12 . The system of claim 11 , wherein the controller is configured to control an amount of heat energy of the sCO 2 sufficient to convert the LNG into the GNG.
13 . A method for a Liquid Natural Gas (LNG)-powered gas turbine engine, comprising:
circulating a primary exhaust of the gas turbine engine through a heat exchanger arranged at or adjacent a primary exhaust nozzle to thereby absorb heat energy;
receiving a supercritical carbon-dioxide (sCO 2 ) from the heat exchanger;
splitting the sCO 2 into a first portion and a remaining portion, wherein relative quantities of the first portion and the remaining portion are specified by a controller;
passing the first portion of the sCO 2 through a sCO 2 turbine, the sCO 2 turbine being coupled with a sCO 2 shaft, the sCO 2 shaft being coupled with a sCO 2 compressor;
bypassing the remaining portion of the sCO 2 through a different channel;
recombining the first portion of the sCO 2 with the remaining portion of the sCO 2 ;
passing the LNG through a first inlet of an evaporator arranged in a fuel injection system;
routing the sCO 2 to a second inlet of the evaporator, the sCO 2 having a heat energy sufficient to vaporize the LNG into a Gaseous Natural Gas (GNG) at a first outlet of the evaporator;
sending the sCO 2 exiting a second outlet of the evaporator through the sCO 2 compressor;
recirculating the sCO 2 flowing out the sCO 2 compressor through the heat exchanger;
injecting a controlled amount of the GNG from the evaporator into a burner disposed in the engine for combusting the GNG, the burner being coupled between a main compressor and a main turbine through which a primary airstream from a main inlet of the engine passes to provide energy for operating the main turbine and thereby rotating a main shaft of the engine; and
passing the remaining portion of the sCO2 through a pressure control valve and equalizing a pressure drop of the remaining portion of the sCO2 with the first portion of the sCO2 exiting the sCO2 turbine.
14 . The method of claim 13 , wherein an amount of the heat energy of the sCO 2 and the controlled amount of the GNG are regulated by the controller.
15 . The method of claim 13 , further comprising controlling a cycle mass flow rate, comprising passing the sCO 2 exiting the evaporator through another pressure control valve prior to sending the sCO 2 through the sCO 2 compressor.
16 . The method of claim 13 , further comprising engaging, by the sCO 2 shaft, a gearbox positioned in the engine between the main turbine and the main shaft to generate an additional power.
17 . The method of claim 13 , wherein the fuel injection system is positioned at a predetermined distance from the primary airstream.
18 . The method of claim 13 , wherein:
the main turbine comprises a plurality of turbines;
the main compressor comprises a plurality of respective compressors; and
the main shaft comprises a plurality of respective shafts.