1.0 TITLE OF THE INVENTION
Gas Turbine electrical generator for starting of main engines on a Transport aircraft,

2.0 FIELD OF INVENTION .

The invention relates to aeronautical gas turbine engine and in particular to the design of gas turbine engine for electrical power generation, to start the main engines of a transport aircraft, on ground.

3.0 BACKGROUND OF THE INVENTION

Gas turbine engines serve as secondary power systems in starting the aircraft main engines on ground. The newly designed gas turbine electric generator coupled to a DC starter generator is capable of producing the required electrical power through supply of variable DC power catering to two modes of engine operation of a Transport aircraft.

- Smooth ground starting of main engines or

- Aircraft ground maintenance

PRIOR ART

The patent US8118253B1 discusses an APU with generator to generate the electrical power for aircraft maintenance during ground. The APU through a control module and selective coupling/ decoupling of main and secondary clutches caters to electric pneumatic or hydraulic power requirements or a combination there of, when the aircraft is on ground. However, the APU power generated is utilized only for aircraft maintenance services on ground. This APU is not employed for starting the aircraft main engines and the aircraft main engines (main motors) are kept switched off during APU operation.

The patent US8997493B2 discusses a generator with a main cavity and a shaft located in the main cavity, configured to be connected and rotated by an APU to serve as a power generation system, based on shaft rotation. The power can be utilized for various ground
maintenance services. This APU is operational with the aircraft main engines and main motors kept off, and hence not employed in starting the aircraft main engines.

4.0 SUMMARY OF THE INVENTION

The present invention relates to design and development of a gas turbine engine for electrical power generation for starting and ground maintenance of a Transport aircraft.

A DC starter generator is coupled to the engine for producing required electrical power. The engine operates in two modes; the aircraft maintenance mode and the main engine starting mode. During aircraft maintenance mode, the engine runs at idle rpm and caters to 18kW power with 28V DC for aircraft maintenance for a max duration of 2 hrs. During main engine starting mode, the engine ramps upto max. rpm as scheduled, for the given ambient and altitude conditions to deliver a maximum power of 60 kW with voltage varying from 20 to 60V DC. The main engine start cycle duration is 1 minute. On completion of the main engine start cycle, the engine returns to aircraft maintenance mode till the next main engine start command is initiated.

The engine is capable of starting the main engine 8 times with the time gap of 15 seconds for first 6 starts and 60 seconds for next 2 starts.

The precision of fuel scheduling is achieved through a dedicated digital electronic controller designed to regulate the fuel supply and engine RPM, in accordance with the varying engine loads/power demand across the range of altitude and ambient conditions for ground starts upto 3 km.

Ground starts of the aircraft main engines from sea level to higher altitudes upto 3 km including the cold and hot weather starts, have been demonstrated successfully.

5.0 BRIEF DESCRIPTION OF THE DRAWINGS

Figure T shows the cross sectional view of the the gas turbine engine coupled with DC starter generator comprising of (1) Air intake, (2) Compressor (3) Combustor Chamber
(4)Turbine (5) Exhaust, (6) Gear box, (7) Oil Cooling system and (8) DC generator (9) Engine Mounting frame (10) Oil pump and (11) Fuel pump and Pipelines
6.0 DETAILED DESCRIPTION

Gas Turbine Electrical Generator (GTEG-60) is a small gas turbine starter. The gas turbine starter is intended for starting the gas turbine engines of a transport aircraft at airfields located at a height of not more than 3 km above sea level and for energizing the aircraft mains during preparation for flight. Accordingly, it is designed to meet the specific requirements of aircraft ground start as well as stand by power supply. .

6.1 DESIGN FEATURES

The unit is a turbo-shaft engine, mainly consisting of single stage (1) Air intake, centrifugal (2) compressor; reverse flow annular (3) combustion chamber, two stage axial (4) turbine, exhaust duct (5) and (6) reduction gear box to provide drive for LRUs such as (7) Oil cooling system, (8) DC generator, (10) Oil pump and (11) fuel pump and pipelines and mountable inside the Aircraft APU bay using (9) Engine Mounting frame.

6.2 CENTRIFUGAL COMPRESSOR

The compressor consists of a radial bladed impeller and a vane less diffuser followed by radial and axial vane diffuser sections. The air is compressed to moderate pressure levels and fed into the combustion chamber.

6.3 REVERSE FLOW COMBUSTION CHAMBER

The configuration of the combustion chamber suitable for application with a centrifugal compressor is the 'annular reverse flow' type. The air from centrifugal compressor passes through an axial diffuser and experience two flow reversals in the combustion chamber prior to entering the axial turbine. A suitable fuel dispensing system is selected for the unit based on performance aspects. The system is adapted to the aviation turbine fuel normally supplied to the main propulsion engine.
6.4 AXIAL TURBINE
The gas generator turbine is a two stage axial turbine. The 2/3rd power developed by the turbine is used to drive the Centrifugal Compressor, OCS blower, Oil & Fuel pump. Remaining 1 /3rd power is extracted through DC generator as an electrical output.

6.5 CONTROL SYSTEM

The control system is designed to cater to fuel scheduling for starting, acceleration, speed governing, variable loads and power demands across the range of altitude conditions for ground start. A microprocessor based electronic fuel control system, known as the ‘Turbo Generator Electronic Control Unit (TGECU) is advantageously used to save weight, cost and integration efforts. The TGECU provides full authority control of fuel flow to the starter unit. TGECU is an on-board processor system, which comprises of dual lane control .Both lanes are designed and programmed identically to prevent over speed, over temperature and run away conditions. At any given point of time, only one lane will be in control and the other will be in hot standby mode. TGECU receives power from aircraft batteries or ground power unit.

The TGECU performs the following-functions:

• Controls the fuel flow during the starting cycle, ensuring smooth light up

• Controls fuel flow to achieve a surge free acceleration

• Regulates fuel flow to maintain required engine rpm under various load conditions

• Safely shuts down the engine in case of gas turbine over speed or over temperature, ensuring overall engine and aircraft safety

6.6 REDUCTION GEAR BOX

The Reduction gear box is designed to meet the requirements of GTEG-60 engine. The gear box mainly consists of front gear box casing, rear gear box casing, compounded gear train arrangement and supported bearings etc.,. The casings are made of aluminum alloy. The front gear box casing has mounting pads to mount the generator, generator
cooling system, fuel pump and oil pump. The rear gear box casing is designed integral with air intake arrangement and has provision to mount the gas turbine engine.

The gear box is designed to step down the engine speed (45000 rpm) to the different RPMs for the accessories. The compounded gear train consists of three gear train loops and all gears are spur gear type. The pinion is common gear for all three gear train loops. Three different double gears are mounted equi-spatially around the pinion. The first gear train loop arrangement reduces speed from pinion (input speed is 45000 rpm) to the generator (output speed is 6472 rpm) through first double gear. The secondary gear train loop arrangement reduces speed from pinion to generator cooling system (output speed is 23935 rpm) through second double gear. The tertiary gear train loop arrangement reduces speed from pinion to oil and fuel pump drive (each running at 14896 rpm) through the third double gear. All the geared shafts are supported in simply supported manner with their respective ball bearings. Different bosses are provided on gear box casings for oil supply, oil drain, vent to the atmosphere and speed measurement purposes.

6.7 DC STARTER GENERATOR

A DC starter generator is coupled to the engine for producing required electrical power in two modes of operation.

i) Starting mode: The DC generator draws power from aircraft batteries 24V, 520 Amps max., starts and ramps the gas turbine engine upto idle RPM

ii) Power generation mode:

a) The generator can produce 18 kW (28V, 600 amps) power to aircraft mains for a continuous duration, upto 2hrs, at regulated speed proportional to engine idle rpm.

b) The generator produces upto 60 kW power with variable DC voltage between 30 to 60V, 1000 amps to cater to 1 Minute duration starting cycles of the aircraft main engines (AI-20D), at regulated speed proportional to engine max rpm.
6.8 LUBRICATION SYSTEM
GTEG-60 has a closed loop oil lubrication system to lubricate its bearings and gears. The engine has an oil tank which supplies oil for lubrication. The oil used conforms to MIL-PRF-23699. Two gear pumps mounted on the front gearbox casing of GTEG-60 serve as the Pressure Pump (PP) and the Scavenge Pump (SP) for the lubricating oil circuit. Oil is drawn by pressure pump from the oil tank through a filter. A pressure relief valve relieves the outlet of pressure pump into its inlet if the outlet pressure exceeds 2.75 bar (40 psi). This is essential to prevent very high pressures from being generated in the pump. The oil from Pressure Pump branches off into two streams. The first one is the main stream, which flows through a filter into the different lubricating jets of GTEG-60, which are 20 in number. The second stream which is the bypass flow flows through a metering orifice whose size is varied to fine-tune the pressure of the main stream oil.

During rig testing of the pump, the flow characteristics are obtained with different sizes of metering jet (also referred as 'bypass jet') to facilitate the selection of the appropriate size of this jet on the starter. The bypass flow returns to the scavenge pump through an ejector type T connector.

6.9 ROTOR SYSTEM

The rotor systems are mounted on rolling element bearings. The gas generator rotor is supported by a ball bearing at cold end which takes both axial and radial loads and a roller bearing at hot end which takes only radial loads. 16 ball bearing with different sizes are used in gear box for supporting the all geared shafts in a simply support manner. Pressure pump supplies the high pressure lubrication oil to all these bearings.