Emergency power engine restart system

Abstract

An engine starting apparatus and method may allow for two methods of engine start where only one engine gearbox accessory pad exists off the aircraft engine. A gearbox lubricating apparatus may also be provided to lubricate the gearbox at altitude without added complexity. Two engine starting inputs (for example, one input for ground start and one input for in-flight engine start) are provided while avoiding complex gearbox designs. Clutches may also be used to prevent the starter gearbox from continuous operation (rotation) after the engine has started. Apparatus and methods are also provided for improving the air-fuel combustion of the hot-gas turbine start input (for in-flight engine start) to minimize the build-up of solid carbon (soot) in and around the combustor and turbine nozzle flow passages.

1 . A method for in-flight engine start using an engine start system, the method comprising:
 burning fuel and air in a combustor to drive a turbine;   turning a starter gear via the rotation of the turbine, wherein the starter gear is mounted on an accessory pad of the engine;   disconnecting a ground-based engine starter with an over-running clutch; and   driving an engine shaft through the rotation of the starter gear to affect engine start or restart.   
     
     
         2 . The method according to  claim 1 , further comprising driving a pitot pump lubrication system from rotation of the turbine to lubricate the starter gear of the engine start system. 
     
     
         3 . The method according to  claim 1 , wherein the step of burning the fuel and air in the combustion chamber includes burning the fuel incompletely. 
     
     
         4 . The method according to  claim 3 , wherein the step of burning the fuel incompletely is accomplished by at least one of the following techniques:
 the combustor has a characteristic length of less than about 486 inches;   the air to fuel ratio is below about 3.5:1; and   the fuel has a Sauter Mean Diameter of about 20 microns or greater.   
     
     
         5 . A method of starting an engine comprising:
 enabling a gearbox to be selectively connectable to turn an engine shaft;   enabling a hot gas turbine to be selectively connectable to drive the gearbox to turn the engine shaft; and   enabling an air turbine to be selectively connectable to turn the engine shaft.   
     
     
         6 . The method according to  claim 5 , wherein the hot gas turbine has a combustor with a characteristic length of less than about 486 inches. 
     
     
         7 . The method according to  claim 6 , wherein an air to fuel ratio is below about 3.5:1. 
     
     
         8 . The method according to  claim 5 , further comprising producing fuel droplets with a Sauter Mean Diameter of about 20 microns or greater. 
     
     
         9 . The method according to  claim 5 , further comprising:
 disconnecting the air turbine when torque is applied to the engine shaft by either the engine or by the gearbox.   
     
     
         10 . The method according to  claim 5 , further comprising:
 disconnecting the gearbox when torque is applied to the engine shaft by the engine.   
     
     
         11 . The method according to  claim 5 , further comprising:
 disconnecting the gearbox when the air turbine is operating.   
     
     
         12 . The method according to  claim 5 , wherein:
 the gearbox includes a starter gear, an idler gear, a compound gear, a turbine pinion gear and a pitot pump gear;   a hot gas turbine drives the turbine pinion gear;   the turbine pinion gear drives the compound gear;   the compound gear has two separate spur gears, a first spur gear which receives rotational torque from the turbine pinion gear, and a second spur gear which drives both the pitot pump gear and the idler gear; and   the idler gear turns the starter gear, which, in turn, drives the engine shaft.   
     
     
         13 . The method according to  claim 12 , wherein the starter gear, the idler gear, the compound gear, the turbine pinion gear and the pitot pump gear are spur gears. 
     
     
         14 . A method of starting an engine comprising:
 selectively connecting an air turbine starter to turn an engine shaft;   attaching a gearbox to an accessory pad of the engine, the gearbox being connected to turn the engine shaft only if the air turbine starter is disconnected from the engine shaft;   enabling a hot gas turbine to drive the gearbox to turn the engine shaft.   
     
     
         15 . The method according to  claim 14 , further comprising:
 turning oil by a gear in the gearbox to generate a circular velocity of the oil.   
     
     
         16 . The method according to  claim 15 , further comprising:
 delivering the oil to locations in the gearbox requiring lubrication.   
     
     
         17 . The method according to  claim 14 , further comprising:
 disconnecting a ground-based engine starting system when torque is applied to the engine shaft by either the engine or by the gearbox.   
     
     
         18 . The method according to  claim 14 , further comprising:
 disconnecting the gearbox when torque is applied to the engine shaft by the engine.   
     
     
         19 . The method according to  claim 14 , further comprising:
 disconnecting the gearbox when a ground-based engine starting system is operating.