Turbojet Engine Efficiency: Dual Axial-Flow Compressor and Hot Section Inspections

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Questions and Answers

What is measured by a fuel flowmeter in a continuous-fuel injection system?

Fuel pressure

Fuel flow volume

Fuel flow mass

Fuel pressure drop (correct)

Which instrument should be monitored to minimize the possibility of a 'hot' start in a gas turbine engine?

RPM indicator

Turbine inlet temperature (correct)

Torque meter

Fuel flow indicator

Where are the hot and cold junctions located in an engine cylinder temperature indicating system?

Both are located at the instrument

The hot junction is located at the cylinder and the cold junction is located at the instrument (correct)

Both are located at the cylinder

The hot junction is located at the instrument and the cold junction is located at the cylinder

How do motor driven impeller and turbine fuel flow transmitters transmit data?

Using aircraft electrical system power Signup and view all the answers

In what units are turbine engine tachometers calibrated?

Actual engine RPM Signup and view all the answers

What is directly affected by a change in engine manifold pressure?

Mean effective cylinder pressure Signup and view all the answers

Under what conditions can cast iron piston rings be used?

In chrome-plated cylinders Signup and view all the answers

What actuates the pilot valve in the governor of a constant-speed propeller?

Governor flyweights Signup and view all the answers

Why are some propeller hubs permanently sealed and partially filled with dyed oil?

To make the location of cracks readily apparent Signup and view all the answers

What happens to the propeller when the engine is operating at speeds lower than those for which the constant-speed propeller control can govern in the INCREASE RPM position?

It remains in the full HIGH PITCH position Signup and view all the answers

What is the primary purpose of the front and rear cones for propellers that are installed on splined shafts?

To position the propeller hub on the splined shaft Signup and view all the answers

What operational force tends to decrease propeller blade angle?

Aerodynamic twisting force Signup and view all the answers

What is the primary function of the impeller and diffuser in a centrifugal compressor?

To compress air Signup and view all the answers

What is a possible indicator of faulty igniter plugs in a turbojet engine?

Hot spots in the combustion section Signup and view all the answers

How does a dual axial-flow compressor improve the efficiency of a turbojet engine?

By increasing the air velocity entering the combustion chamber Signup and view all the answers

What is a characteristic of subsonic air flowing through a convergent nozzle?

Its velocity increases Signup and view all the answers

When starting a turbine engine, what is recommended when indication of light-off occurs?

Release the starter switch Signup and view all the answers

How often are hot section inspections required for many modern turbine engines?

On a time or cycle basis Signup and view all the answers

What is the likely effect on a compression check if the piston ring gaps are aligned?

A false indication of a worn or defective ring Signup and view all the answers

What is engine operating flexibility?

The ability to run smoothly and give the desired performance at all speeds Signup and view all the answers

What is the function of turbine nozzle diaphragms in a gas turbine engine?

To direct the flow of gases parallel to the vertical line of the turbine blades Signup and view all the answers

If an engine misses in both the right and left positions of the magneto switch, what is the quickest method to locate the trouble?

Check each spark plug Signup and view all the answers

After spark plugs from an opposed engine have been serviced, in which position should they be reinstalled?

Next in firing order to the one from which they were removed and swapped bottom to top Signup and view all the answers

What is the purpose of a cool-off period prior to shutdown of a turbine engine?

To prevent seizure of the engine bearings Signup and view all the answers

What is meant by a shrouded turbine?

The turbine wheel is enclosed by a protective shroud to contain the blades Signup and view all the answers

What is the likely result of grinding the valves of a reciprocating engine to a feather edge?

Pre-ignition and burned valves Signup and view all the answers

What is used in turbine engines to aid in stabilization of compressor airflow during low thrust engine operation?

Variable guide vanes and/or compressor bleed valves Signup and view all the answers

Which of the following conditions can cause an engine to have an increased tendency to detonate?

High manifold pressure, high intake air temperature, and engine overheated Signup and view all the answers

In a turbine engine with a dual-spool compressor, how does the low speed compressor operate?

It seeks its own best operating speed Signup and view all the answers

What is directed into the first stage rotor vanes at the proper angle in a turbine engine?

Direct air Signup and view all the answers

Study Notes

Fuel Flow Measurement

Fuel flowmeters measure fuel flow volume, fuel pressure, and fuel flow mass in continuous-fuel injection systems.
Fuel pressure drop is measured across the metering valve, not the manifold valve or fuel nozzles.

Turbine Engine Instruments

Monitor turbine inlet temperature to minimize the possibility of a “hot” start.
Motor-driven impeller and turbine fuel flow transmitters transmit data mechanically, not using aircraft electrical system power or fuel pressure.
Tachometers are calibrated in percent of engine RPM, not actual engine RPM or percent of engine pressure ratio.

Reciprocating Engines

In a conventional reciprocating engine, the fuel/air mixture is ignited shortly before the piston reaches the top of the compression stroke.
Cast iron piston rings may be used in chrome-plated cylinders, and chrome-plated rings may be used in plain steel cylinders.

Propellers

The pilot valve in the governor of a constant-speed propeller is actuated by governor flyweights, not engine oil pressure or governor pump oil pressure.
Permanently sealing and partially filling some propeller hubs with dyed oil helps to dampen pressure surges and prevent too rapid changes in propeller blade angle.
During engine operation at speeds lower than those for which the constant-speed propeller control can govern in the INCREASE RPM position, the propeller will remain in the full LOW PITCH position.

Turbojet Engine

The velocity of subsonic air as it flows through a convergent nozzle increases.
A hot start is indicated if the exhaust gas temperature exceeds specified limits during turbine engine start-up.
Hot section inspections for many modern turbine engines are required on a time or cycle basis, not only at engine overhaul or when an over temperature or over speed has occurred.

Centrifugal Compressor

The two functional elements in a centrifugal compressor are the impeller and diffuser, not turbine and compressor or bucket and expander.

Turbine Engine Maintenance

Hot spots in the combustion section of a turbojet engine may indicate faulty igniter plugs, dirty compressor blades, or malfunctioning fuel nozzles.
A dual axial-flow compressor improves the efficiency of a turbojet engine by increasing the velocity of the air entering the combustion chamber.

Engine Performance

Engine operating flexibility refers to the ability of the engine to run smoothly and give the desired performance at all speeds, not to deliver maximum horsepower at a specific altitude or meet exacting requirements of efficiency and low weight per horsepower ratio.

Reciprocating Engine Maintenance

If piston ring gaps happen to be aligned during a differential pressure compression check on a cylinder, the test results may indicate a worn or defective ring(s).
Grinding the valves of a reciprocating engine to a feather edge can result in excessive valve clearance, pre-ignition, and burned valves.

Engine Operation

Conditions that increase an engine’s tendency to detonate include high manifold pressure, high intake air temperature, and late ignition timing.

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Description

Test your knowledge of aircraft engines, including fuel systems, injection systems, and turbine engine operation. Covers key components, measurements, and safety considerations.

Aircraft Engines and Systems