# US 11,905,887 B2 · Restarting a gas turbine engine

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- Number: US 11,905,887 B2
- Document ID: US11905887B2
- Status: Granted
- Kind: B2
- Application number: 17/988,504
- Filed: 2022-11-16
- Published: 2023-06-15
- Granted: 2024-02-20
- Earliest claimed: 2021-12-14
- Assignees: ROLLS-ROYCE plc
- Applicants: ROLLS-ROYCE plc
- Inventors: Gareth E Moore; Paul R Davies; Stephen M Husband; David R Trainer; David P Scothern; Luke George; Douglas M M Herbert
- Web page: https://patentgrep.com/patent/US11905887B2

## CPC

- F02C 7/262: Restarting after flame-out
- F01D 15/10: Adaptations for driving, or combinations with, electric generators
- F02C 7/268: Starting drives for the rotor {, acting directly on the rotor of the gas turbine to be started}
- F02K 5/00: Plants including an engine, other than a gas turbine, driving a compressor or a ducted fan
- F05D 2220/323: for aircraft propulsion, e.g. jet engines
- F05D 2220/76: an electrical generator
- F05D 2260/85: Starting
- F05D 2270/092: in particular blow-out and relight
- F05D 2270/093: of one engine in a multi-engine system
- Y02T 50/60: Efficient propulsion technologies, e.g. for aircraft
- F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00)
- F01D: NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES (machines or engines for liquids F03; non-positive displacement pumps F04D)
- F02K: JET-PROPULSION PLANTS (features of jet-propulsion plants common to gas-turbine plants, air intakes or fuel supply control of air-breathing jet-propulsion plants F02C7/00, F02C9/00)
- F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

Multi-engine aircraft power and propulsion systems and methods of restarting an engine of a multi-engine aircraft during fight are provided. One such method comprises: determining a condition to the effect that a flame in the combustion equipment of the second gas turbine engine has been extinguished; responsive to the determination, supplying electrical power from the electrical energy storage system to one or more of the electric machines of the second gas turbine engine and operating said one or more electric machines as motors to limit a reduction in a speed of the one or more spools of the second gas turbine engine following extinguishment of the flame in its combustion equipment; and restarting the second gas turbine engine by relighting the combustion equipment of the second gas turbine engine.

## Claims

### Claim 1

A multi-engine aircraft power and propulsion system comprising:
first and second propulsive gas turbine engines, each comprising (i) combustion equipment, (ii) a plurality of spools, and (iii) first and second electric machines mechanically coupled with the plurality of spools and each comprising a first sub-machine and a second sub-machine;
an electrical system connecting the electric machines of the first gas turbine engine and the electric machines of the second gas turbine engine, whereby electrical power generated by the electric machines of the first gas turbine engine can be transferred to the electric machines of the second gas turbine engine;
an electrical energy storage system which can supply electrical power to the electric machines of each of the first and second gas turbine engines; and
a control system configured to, responsive to determining a condition to the effect that a flame in the combustion equipment of the second gas turbine engine has been extinguished, control the first and second gas turbine engines and the electrical system during an in-flight engine restart procedure, the restart procedure comprising:
supplying electrical power from the electrical energy storage system to the electric machines of the second gas turbine engine and operating one or more of the electric machines of the second gas turbine engine as one or more motors to limit a reduction in a speed of one or more of the spools of the second gas turbine engine following extinguishment of the flame in the combustion equipment of the second gas turbine engine; and
restarting the second gas turbine engine by relighting the combustion equipment of the second gas turbine engine,
wherein the electrical system comprises first and second dc distribution busses associated with each of the first and second gas turbine engines, the first and second dc distribution busses associated with the first gas turbine engine being different than the first and second dc distribution busses associated with the second gas turbine engine, and
wherein for each of the first and second gas turbine engines, (i) the first sub-machine of each of the first and second electric machines is electrically connected to the corresponding first dc distribution bus and (ii) the second sub-machine of each of the first and second electric machines is electrically connected to the corresponding second dc distribution bus.

### Claim 2 (depends on 1)

The aircraft power and propulsion system of claim 1, wherein the restart procedure further comprises:
operating one or more of the electric machines of the first gas turbine engine as one or more generators to extract mechanical power and generate electrical power from one or more of the spools of the first gas turbine engine; and
after supplying electrical power from the electrical energy storage system to the electric machines of the second gas turbine engine and prior to restarting the second gas turbine engine, transferring, via the electrical system, electrical power generated by the one or more electric machines of the first gas turbine engine to the one or more electric machines of the second gas turbine engine and operating the one or more electric machines as one or more motors to increase the speed of the one or more spools of the second gas turbine engine.

### Claim 3 (depends on 1)

The aircraft power and propulsion system of claim 1, wherein the electrical energy storage system comprises an energy storage device dedicated to supplying power to the electrical machines of the first and second gas turbine engines during engine restart attempts.

### Claim 4 (depends on 1)

The aircraft power and propulsion system of claim 1, wherein the control system is further configured to maintain a state of charge of the electrical energy storage system above a predetermined level.

### Claim 5 (depends on 2)

The aircraft power and propulsion system of claim 2, wherein:
the plurality of spools of each of the first and second gas turbine engines comprises a first spool and a second spool; and
for each of the first and second gas turbine engines, the first electric machine is mechanically coupled with the corresponding first spool and the second electric machine is mechanically coupled with its-the corresponding second spool.

### Claim 6 (depends on 5)

The aircraft power and propulsion system of claim 5, wherein operating the one or more of the electric machines of the first gas turbine engine as one or more generators comprises:
operating both the first electric machine and the second electric machine of the first gas turbine engine as generators to extract mechanical power and generate electrical power from both the first spool and the second spool of the first gas turbine engine.

### Claim 7 (depends on 6)

The aircraft power and propulsion system of claim 6, wherein the control system is configured te-to:
transfer the electrical power generated from both the first spool and the second spool of the first gas turbine engine to one or both of the first electric machine of the second gas turbine engine and the second electric machine of the second gas turbine engine; and
operate one or both of the first and second electric machines of the second gas turbine engine as one or more motors to drive rotation of the first spool and/or the second spool of the second gas turbine engine.

### Claim 8 (depends on 7)

The aircraft power and propulsion system of claim 7, wherein the electrical system further comprises: a dc electrical power distribution system;
a first ac-dc converter connecting the first electric machine of the first gas turbine engine to the dc power distribution system;
a second ac-dc converter connecting the second electric machine of the first gas turbine engine to the dc power distribution system;
a third ac-dc converter connecting the first electric machine of the second gas turbine engine to the dc power distribution system; and
a fourth ac-dc converter connecting the second electric machine of the second gas turbine engine to the dc distribution system.

### Claim 9 (depends on 8)

The aircraft power and propulsion system of claim 8, wherein
a bus tie connects together one of the dc distribution busses associated with the first gas turbine engine and one of the dc distribution busses associated with the second gas turbine engine, whereby electrical power generated by the first and/or the second electric machine of the first gas turbine engine can be transferred to the first and/or the second electric machine of the second gas turbine engine.

### Claim 10 (depends on 9)

The aircraft power and propulsion system of claim 9, wherein the restart procedure further comprises:
closing the bus tie to connect the dc distribution busses.

### Claim 11 (depends on 5)

The aircraft power and propulsion system of claim 5, wherein, for each respective one of the first and second gas turbine engines, a ratio, P1/T, equal to a maximum electrical power generation rating of the first electric machine divided by a maximum thrust rating of the gas turbine engine, is greater than or equal to 2.0 WN−1 and less than 7.0 WN−1.

### Claim 12 (depends on 5)

The aircraft power and propulsion system of claim 5, wherein, for each respective one of the first and second gas turbine engines, a ratio, P2/T, equal to a maximum electrical power generation rating of the second electric machine divided by a maximum thrust rating of the gas turbine engine, is greater than or equal to 3.5 WN-1 and less than 10 WN−1.

### Claim 13 (depends on 1)

The aircraft power and propulsion system of claim 1, wherein, for each respective one of the first and second gas turbine engines, a ratio defined as:
a combined rated power of all of the electrical machines mechanically coupled with the spools of the respective gas turbine engine divided by
the a maximum rated thrust of the respective gas turbine engine is greater than or equal to 4.5 WN−1 and less than 15.0 WN−1.

### Claim 14 (depends on 1)

The aircraft power and propulsion system of claim 1, wherein, for each respective one of the first and second gas turbine engines, one or more of the electric machines are embedded with a core of the respective gas turbine engine.

### Claim 15 (depends on 1)

An aircraft comprising the power and propulsion system of claim 1.

### Claim 16

A method of restarting a propulsive gas turbine engine of a multi-engine aircraft during flight,
the aircraft comprising:
first and second propulsive gas turbine engines, each comprising (i) combustion equipment, (ii) a plurality of spools, and (iii) first and second electric machines mechanically coupled with the plurality of spools and each comprising a first sub-machine and a second sub-machine;
an electrical system electrically connecting the electric machines of the first gas turbine and the electric machines of the second gas turbine engine, whereby electrical power generated by the electric machines of the first gas turbine engine can be transferred to the electric machines of the second gas turbine engine; and
an electrical energy storage system which can supply electrical power to the electric machines of each of the first and second gas turbine engines, and
the method comprising:
determining a condition to the effect that a flame in the combustion equipment of the second gas turbine engine has been extinguished;
responsive to the determination, supplying electrical power from the electrical energy storage system to the electric machines of the second gas turbine engine and operating one or more of the electric machines of the second gas turbine engine as one or more motors to limit a reduction in a speed of one or more of the spools of the second gas turbine engine following extinguishment of the flame in the combustion equipment of the second gas turbine engine; and
restarting the second gas turbine engine by relighting the combustion equipment of the second gas turbine engine,
wherein the electrical system comprises first and second dc distribution busses associated with each of the first and second gas turbine engines, the first and second dc distribution busses associated with the first gas turbine engine being different than the first and second dc distribution busses associated with the second gas turbine engine, and
wherein for each of the first and second gas turbine engines, (i) the first sub-machine of each of the first and second electric machines is electrically connected to the corresponding first dc distribution bus and (ii) the second sub-machine of each of the first and second electric machines is electrically connected to the corresponding second dc distribution bus.

### Claim 17 (depends on 16)

The method of claim 16, further comprising:
operating one or more of the electric machines of the first gas turbine engine as one or more generators to extract mechanical power and generate electrical power from one or more of the spools of the first gas turbine engine;
after supplying electrical power from the electrical energy storage system to the electric machines of the second gas turbine engine and prior to restarting the second gas turbine engine, transferring, via the electrical system, electrical power generated by the one or more electric machines of the first gas turbine engine to the one or more electric machines of the second gas turbine engine and operating the one or more electric machines as one or more motors to increase the speed of the one or more spools of the second gas turbine engine.

### Claim 18 (depends on 17)

The method of claim 17, wherein:
the plurality of spools of each of the first and second gas turbine engines comprises a first spool and a second spool;
for each of the first and second gas turbine engines, the first electric machine is mechanically coupled with the corresponding first spool and the second electric machine is mechanically coupled with the corresponding second spool;
operating the one or more electric machines of the first gas turbine engine as one or more generators to extract mechanical power and generate electrical power from the one or more spools of the first gas turbine engine comprises:
operating both the first and second electric machines of the first gas turbine engine as generators to extract mechanical power and generate electrical power from both the first spool and the second spool of the first gas turbine engine; and
operating the one or more electric machines of the second gas turbine engine as one or more motors to limit a reduction in speed of the one or more spools of the second gas turbine engine comprises:
operating one or both of the first electric machine and the second electric machine of the second gas turbine engine as motors to drive rotation of the first spool and/or the second spool of the second gas turbine engine.

### Claim 19 (depends on 18)

The method of claim 18, wherein a ratio defined as:
a peak electrical power generated by the electric machines of the first gas turbine engine and transferred, via the electrical system, to the electric machines of the second gas turbine engine during the restart procedure, divided by
a maximum rated thrust of the first gas turbine engine is greater than or equal to 3 WN−1 and less than 5.0 WN-−1.