Engine parts, engine description, accessories and technology,fuel system,oil system,fuel control system,starting and ignition accessories, engine operation and storage.
There are two fuel systems for starting the ATAR 09 C turbojet engine which are both independent: - the self-contained kerosene starter fuel system, - the engine fuel system. A. Self contained kerosene starter fuel system When the engine is started the fuel used by the self-contained kerosene starter is take from the inlet connection fixed on the fuel pump. It is then a pressure between 1 and 2.5 bar. The fuel passes through a pipe to the electric pump unit from where it flows at a pressure of 4.5 bar.
Up on operation of the three way solenoid valve the fuel flows through it to the fuel control unit. The fuel is metered according to the "P2 starting pressure".
When the engine is operating, the centrifugal starting speed detector interrupts the electrical supply to the self-contained kerosene starter. The electric pump unit and three way solenoid valve are no longer supplied with current. The valve allows fuel in the fuel control unit to flow to the drain connection. Note that a pipe is connected between the starter and the purge valve. The valve is designed to allow the unburned fuel to leave the gas generator combustion chamber as soon as the starter stops. During operation the pressure in the combustion chamber retains the valve on its seat thus preventing any gas from escaping. B. Engine starting fuel system Under impulse from the self-contained kerosene starter, the engine begins to rotate. The fuel pump secured to the accessory support supplies the main fuel control unit.
The starting block pressure reducer valve supplies the starting injectors at a constant pressure of 2.6 bar. This supply is continued as long as the starter solenoid valve is energized. Fuel sprayedinside the ignition antechamber, is, alighted by the igniter plugs, thus the combustion of the fuel sprayed by the two-flow injectors begins.
Note that, to flow to the starter injectors, the fuel must pass through the double check-valve. This prevents the combustion gases from escaping into the starter fuel system during dry engine operation. Note also that the fuel remaining in the starter injectors after thy have operated is drawn in through a drain piping. The piping is fitted on the junction section.
The 80 bar starting by-pass solenoid valve limits the fuel flow admitted to the two-flow injectors. The flow increases as rapidly permitted by the double-stop control device of the main fuel control unit. The engine continues to accelerate and when the speed reaches 1900 rpm, the centrifugal starting speed detector cuts-off the supply to the starter solenoid valve(6 bar) and the starting by-pass solenoid valve (80 bar). Dry engine operation then begins.
* A rotor comprising a series of discs fitted with blades
* A stator comprising two half-shells fitted with rows of vanes which fit between the blades on each rotor disc.
Note
A row of vanes or blades constitutes a cascade.
The grouping of a cascade of blades with a cascade of vanes constitutes a complete compressor stage.
The compressor of the ATAR 09 C engine comprises 9 stages whom the compression ratios varying from 1.2 to 1.3. The total compression ratio is about 5.5.
Since the volume of the air mass diminishes during compression, the section of the airflow will decrease progressively despite a simultaneous reduction of the axial speed.
The increase of the total energy of air is caused by the rotational of the blades which are driven by the turbine wheel.
Each blade assembly imparts a certain speed to the air flow which is transformed into pressure party in blade assembly and party in the vane assembly.
The operation of the compressor can be described thus; each blade or vane can be compared to a wing and follows aero-dynamic laws. Allowing for the effect of the neighboring blades or vanes (cascade effect)
The phenomenon of loss of lift or "stalling" encountered on an aircraft wing occurs in the compressor in the form of malfunctioning (in particular "compressors stall") if abnormal operating conditions are accidentally imposed on the engine.
Axial thrusts act to compressor and turbine. Their intensity varies following operation requirements but:
A part is compensated by pressures (controlled by the clearance in the labyrinth seals) on the front and rear flanges of the compressor.
The other part is beared by the front bearing compressor constituted by a ball bearing with three contact points and deep groove.
Central casing
Attached to rear of compressor it works like diffuser decreasing substantially the flow speed of P2 air. Speed decreasing, static pressures increases before to supply burners. The latter located in the primary flow, are secured to the rear part of the central casing.
Burners are made in such way to create turbulences to stabilize the flame. They allows a correct mixing of air and fuel sprayed by two-flow injectors.
The combustion chamber
The combustion chamber is of the annular type.
Part of the air flowing from the compressor ensures the complete combustion of the fuel, which is injected and sprayed by the injectors: it is the primary air.
Combustion which is behind burners, requires an "air/fuel" ratio closely to these of stoichiometric value, consequently primary air is heated to a temperature between 1500°Cmass and 1800 °C.
Gases at this high temperature must no enter the turbine. So, the reminder of the air or secondary air, first cools the chamber and then through the dilution apertures, mix with and cool the burned gases.
Some of these secondary approximately 2.5 to 3 percent of the total flow cools the bearings N° 2 and 3, the turbine 1 st-stage guide vane assembly and turbine discs.
For complete combustion the "air/fuel" mass ratio should be 15/1. The practical ratio is 60/1. The excess air, mixed with gases can be used in the afterburner after a second injection of fuel down-stream from the turbine. An "afterburner ignition" injector in the combustion chamber gives aflame which passes through the turbine and ignites the fuel distributed by the afterburner injection manifolds.
The air intake duct is before the turbojet engine and pipes air required to thermodynamics operation of the later. It must ensure an axial flow supply giving highly efficient operation with the minimum loss and disturbance.
Above a given air speed, dynamic compression takes place in the air intake duct ( increasing as the speed increases ). This duct is adapted to a predetermined range of air speeds outside which a greater loss results; in particular during ground running the losses are considerable and thrust of the engine on aircraft is often less than that obtained on the test bench this is due to efficient difference between the two duct.
The air intake duct is a part of the airframe. At higher flight speed the duct has a great effect on the operation of the engine and plays an important part in obtaining performance.
The intake casing
The intake casing which is located between the duct and compressor, determines the cross sectional area of the compressor intake. The ring of vanes upstream from the first group of blades is secured to the casing.
This part is positioned at the front end of the engine and a hot air supply is required to prevent icing.
Summary of the fuel system accessories
Self-contained kerosene starter Allows engine starting and drives it during clearing operations
Electric pump unit Supplies fuel to the self-contained kerosene starter>
Fuel control unit
Controls the fuel flow for the self-contained kerosene starter
Starting speed detector
Stops the self-contained kerosene starter when the engine reaches 1800 Starting block comprising: - pressure reducer valve
Limits the pressure of the fuel supply to the starter injectors to 2.6 bar
-Master control valve
Shuts off the fuel supply to the two flow injectors when throttle control is turned to "stop"
-Starting solenoid valve (6 bar)
Allows fuel to flow to the starter injectors when starting or re-lighting in flight.
- Starting by-pass solenoid valve (80 bar)
Limit the pressure of fuel supplying the two-flow injectors while starting on the ground.
- Double check valve To prevent combustion gases flowing back to the starter system (through the starting injectors)
-Starting injectors
To spray the fuel in the ignition antechambers while starting on the ground or relighting in flight.
To control the fuel supply to the afterburnerignition injector.
Afterburner ignition check valve
To prevent the gases from the combustion chamber flowing back to theafterburner.
Afterburner ignition injector
To inject the afterburner ignition fuel upstream from the turbine 1 st-stage nozzle guide vane assembly to produce a flame which reaches the burner rings.
Ionization probe
To detect the afterburner ignition and send an electric signal to the flame detector amplifier.
Electronic amplifier for flame detection
To amplify the signal transmitted by the ionization probe and thus control the afterburner ignition system.
Afterburner ignition pressure switch
To supply the afterburner ignition warning light on the aircraft panel.
