Emergency start of a gas turbine engine
A starting apparatus for a first gas turbine engine of a plurality of gas turbine engines of an aircraft. The apparatus includes an air turbine starter, an electric machine, and a controller. The controller is configured to receive an emergency restart command for the first gas turbine engine while the aircraft is in-flight, determine whether the first gas turbine engine is in operation, determine whether at least a second gas turbine engine of the plurality of gas turbine engines is in operation, and, responsive to receiving the emergency restart command and determining that at least the second gas turbine engine of the plurality of gas turbine engines is in operation and that the first gas turbine engine is not in operation, perform an emergency restart of the first gas turbine engine.
1 . A starting apparatus for a first gas turbine engine of a plurality of gas turbine engines of an aircraft, the starting apparatus comprising:
an air turbine starter configured to cause rotation of a spool of the first gas turbine engine of the plurality of gas turbine engines using compressed air derived from an air source external to the first gas turbine engine;
an electric machine configured to cause rotation of the spool of the first gas turbine engine; and
a controller configured to:
receive an emergency restart command for the first gas turbine engine while the aircraft is in-flight;
determine whether the first gas turbine engine is in operation;
determine whether at least a second gas turbine engine of the plurality of gas turbine engines is in operation; and
responsive to receiving the emergency restart command and determining that at least the second gas turbine engine of the plurality of gas turbine engines is in operation and that the first gas turbine engine is not in operation, perform an emergency restart of the first gas turbine engine by at least simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine, wherein simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine comprises simultaneously supplying pneumatic energy to the air turbine starter that causes the air turbine starter to deliver torque to the spool and supplying electrical energy to the electric machine that causes the electric machine to deliver torque to the spool, wherein simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine cause the spool to reach a threshold speed for a restart to be executed during the emergency restart relatively more quickly than only a single one of the air turbine starter or the electric machine, and wherein:
the air source external to the first gas turbine engine comprises at least two air sources comprising a first air source and a second air source, and
the controller is configured to cause the first air source and the second air source to simultaneously deliver compressed air to the air turbine starter.
2 . The starting apparatus of claim 1 , wherein the second gas turbine engine is an auxiliary power unit (APU).
3 . The starting apparatus of claim 1 , wherein the controller is further configured to:
introduce fuel to a combustor of the gas turbine engine at a first threshold rotational speed during a starting operation in which a vehicle comprising the gas turbine engine is grounded, wherein the controller is configured to introduce fuel to the combustor at a second threshold rotational speed during a starting operation in which the vehicle is in-flight,
wherein the second threshold rotational speed is lower than the first threshold rotational speed,
wherein introducing fuel at the second threshold rotational speed results in a second temperature in a turbine of the gas turbine engine,
wherein introducing fuel at the first threshold rotational speed results in a first temperature in the turbine of the gas turbine engine, the first temperature cooler than the second temperature.
4 . The starting apparatus of claim 1 , wherein the first air source comprises bleed air from a second gas turbine engine.
5 . The starting apparatus of claim 1 , wherein the second air source includes an auxiliary power unit (APU).
6 . The starting apparatus of claim 1 , wherein the electric machine is configured to receive electrical energy from a generator of the second gas turbine engine, a battery, an on-board electrical system, or combinations thereof.
7 . The starting apparatus of claim 3 , wherein the second threshold rotational speed is at least 10% lower than the first threshold rotational speed.
8 . The starting apparatus of claim 1 , wherein the first gas turbine engine is a turboprop engine, wherein the turboprop engine comprises a propeller driven by a free power turbine of the gas turbine engine.
9 . The starting apparatus of claim 8 , further comprising:
a generator configured to generate electrical power using mechanical energy extracted from a windmilling operation of the propeller of the first gas turbine engine,
wherein the electric machine uses the generated electrical power for performing the emergency restart of the first gas turbine engine.
10 . The starting apparatus of claim 9 , wherein the controller is further configured to command an unfeathering of the propeller.
11 . The starting apparatus of claim 10 , wherein, responsive to determining that the first gas turbine engine is not in operation and the aircraft is in-flight, the controller is further configured to command a feathering of the propeller.
12 . The starting apparatus of claim 3 , further comprising:
a generator configured to generate electrical power using mechanical energy extracted from a windmilling operation of a propeller of the first gas turbine engine,
wherein the electric machine uses the generated electrical power for performing the emergency restart of the first gas turbine engine.
13 . A method of starting a first gas turbine engine of a plurality of gas turbine engines of an aircraft in-flight, the method comprising:
receiving, via a controller, an emergency restart command for the first gas turbine engine of the plurality of gas turbine engines while the aircraft is in-flight;
determining, via the controller, whether the first gas turbine engine is in operation;
responsive to determining that the first gas turbine engine is not in operation, determining whether at least a second gas turbine engine of the plurality of gas turbine engines is in operation; and
responsive to receiving the emergency restart command and determining that at least the second gas turbine engine of the plurality of gas turbine engines is in operation and that the first gas turbine engine is not in operation, performing an emergency restart of the first gas turbine engine by at least simultaneously causing an air turbine starter and an electric machine to cause rotation of a spool of the first gas turbine engine by supplying pneumatic energy to the air turbine starter that causes the air turbine starter to deliver torque to the spool and supplying electrical energy to the electric machine that causes the electric machine to deliver torque to the spool, wherein simultaneously causing the air turbine starter and the electric machine to cause rotation of the spool of the first gas turbine engine cause the spool to reach a threshold speed for a start to be executed during the emergency restart relatively more quickly than only a single one of the air turbine starter or the electric machine, and
wherein the air turbine starter uses compressed air sourced from a first air source and a second air source, the first air source external to the first gas turbine engine and the second air source external to the first gas turbine engine, and wherein the method includes causing, by the controller, the first air source and the second air source to simultaneously deliver compressed air to the air turbine starter.
14 . The method of claim 13 , further comprising:
introducing fuel to a combustor of the gas turbine engine at a first threshold rotational speed during a starting operation in which a vehicle comprising the gas turbine engine is grounded,
introducing fuel to the combustor at a second threshold rotational speed during a starting operation in which the vehicle is in-flight,
wherein the second threshold rotational speed is lower than the first threshold rotational speed,
wherein introducing fuel at the second threshold rotational speed results in a second temperature in a turbine of the gas turbine engine,
wherein introducing fuel at the first threshold rotational speed results in a first temperature in the turbine of the gas turbine engine, the first temperature cooler than the second temperature.
15 . The method of claim 13 , wherein the first gas turbine engine is a turboprop engine, wherein the turboprop engine comprises a propeller driven by a free power turbine of the gas turbine engine.
16 . The method of claim 13 , further comprising:
commanding an unfeathering of a propeller of the first gas turbine engine;
generating electrical power from a windmilling operation of the propeller; and
supplying the generated electrical power to the electric machine for performing the emergency restart of the first gas turbine engine.
17 . The starting apparatus of claim 1 , wherein the controller is configured to cause the first air source, the second air source, and a third air source to simultaneously deliver compressed air to the air turbine starter.
18 . The starting apparatus of claim 17 , wherein the third air source is a compressed air tank.