The centrifugal compressor is shorter in length than an axial compressor and that is its main advantage. Suddenly come in The Pratt and Whitney 100 series turboprop and ask me to see the figure above. It has three shaft , two spool engine. Some compressor rotors have one piece blade and rotor units. The blades are forged as part of the disc. There one piece units are called ' Blisks' commonly used in small turbo prop and turbo shaft engines. The blade should always be check, if they break and split away, that will be like what happened at Singapore. The Qantas A380 incident. The greater the pressure ratio for a given mass airflow and thrust, the lower the engine fuel consumption. If both pressure ratio and mass airflow is increased, thrust will increase. A stronger and heavier engine is needed.
Compressor Stall
Angle of attack ( AOA ) of the compressor blade is the result of :
- inlet air velocity
- compressor RPM
NOTE : Flames do not often occur during either a surge or stall - flame in the inlet would most likely happen with a complete reversal of flow.
Compressor Bleed System
At high rotational speeds, the compressor is designed to handle maximum airflow without aerodynamic disturbance so the bleed system is scheduled closed.
How do we clean the contamination of the engine?
We clean it with walnut shell or apricot.
Generally, stall/surge bleed valves are either fully open or fully closed.
The bleed valve is fully open when the engine is :
- shutdown
- starting
- at idle to intermediate power.
The bleed valve is fully closed when the engine is :
- at takeoff
- at cruise power
This system does not meter bleed air, it is either fully open or fully closed.
I was confused on the word VBV because it pop out half way on the paragraph
The next page, i wrote on the side VBV = Variable Bleed Valves.
The EEC ( Electrical Electronic Controller ) commands the VBV to be more open during
- rapid Deceleration
- thrust reverser operation
- potential icing conditions.
The recorded measurement of blade moment weights enables each blade to be distributed around the disc in order that these unbalances are cancelled. On fans with even numbers of blades, blades with similar moment weight are replaced 180 degrees apart. Spare blades are grouped in pairs of similar moment weights. ( no more than about 200cm.g difference )
Combustion Section
All combustion sections contain the same basic elements:
- one or more combustion chambers ( combustors or cans )
- a fuel injection system
- an ignition source
- fuel drainage system
The combustion chamber, or combustor, is where the fuel and air are mixed and burned.
The fuel injection system supplies the fuel through the fuel nozzles into the combusotrs.
A typical ignition source is the high energy capacitor discharge system.
A fuel drainage system accomplishes the important task of draining the unburned fuel after engine shutdown.
The combustion process is referred to as combustion at constant pressure - pressure at exit does not alter significantly to entry pressure. Draining the unburned fuel helps to prevent gum deposits in the fuel manifold, nozzles, and combustion chambers which are caused by fuel residue.
Turbines Section
The turbine has the task of providing the power to drive the compressor and accessories and in the case of engines that do not make use solely of a jet for propulsion, of providing shaft power for a propeller or rotor.
Energy Transfer
The nozzle and blades of the turbine are twisted, the blades having a stagger angle that is greater at the tip than the root. The reason for this twist is to make the gas flow from the combustion section do equal work at all positions along the length of the blade, and to ensure that the flow enters the exhaust system with a uniform axial velocity.
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