MEP.1.1.2.2 Turbochargers

Question 1

What’s the name of turbocharger in older actf?

Answer 1

Supercharger

Question 2

What’s a turbocharger system used for?

Answer 2

Boosting or pressurising the fuel-air mixture that is being supplied to the intake manifold

Question 3

How is it driven?

Answer 3

By exhaust gases from the engine

Question 4

How do we achieve the amount of pressurisation?

Answer 4

It is a balance between what the engine can cope with and the capacity of the turbo

Question 5

What happens if there’s a lot of turbo?

Answer 5

The engine is over boosted and can be damaged

Question 6

What happens at higher altitudes?

Answer 6

Engine can cope, but turbo cannot sustain the equivalent fuel-air mixture for full power.

Above is full throttle height, thus maximum power cannot be sustained

Question 7

What do modern systems have in order to overcome this problem?

Answer 7

An automatic wastegate, which adjusts the turbo (bur) on older systems

Question 8

What does the pilot do to control the wastegate?

Answer 8

Controls it manually, but must exert care not to over boost the engine at lower altitudes

Question 9

What are exhaust gas-driven supercharger known as?

Answer 9

Turbochargers

Question 10

What are turbochargers driven by?

Answer 10

By a turbine running off the exhaust gas from the engine

Question 11

What does this turbine drive?

Answer 11

A centrifugal compressor

Question 12

Why have turbochargers become very popular, especially in smaller engines?

Answer 12

They do not need the heavy and expensive gearing of the supercharger.

They are reliable and reasonably efficient means of restoring power to engines at high altitudes

Question 13

What is the heart of a turbo?

Answer 13

Very high-speed turbine operating at very high temperature.

Question 14

To what is it vulnerable?

Answer 14

Sudden changes in engine speed and temperature

Question 15

How is the control of a turbocharger achieved?

Answer 15

Through a wastegate which can spill the exhaust gas straight into the exhaust system when it is open, or, when closed, force all the gas to go through the turbine before entering the exhaust system, thus providing maximum power to the compressor

Question 16

How is the control of the wastegate achieved?

Answer 16

Variable wastegate
Fixed wastegate

Question 17

How does a variable wastegate work?

Answer 17

It is able to move from fully open (no turbocharging) to fully closed (full turbocharging)

Question 18

What are the three systems used to vary the wastegate?

Answer 18

• Level or second throttle operated by the pilot.
  • On climb, when the normal throttle is fully open, the wastegate can be gradually closed to give more power as required.
• Wastegate can be connected directly to the throttle so that as the throttle is opened, the wastegate is closed and the turbocharger comes in.
  • It is simpler to use by operators must be careful as little movement of the throttle can give a big power increase
• Automatic movement as needed and determined by sensors
  • Complex and expensive, although the most efficient
  • Variable wastegate system usually has a pressure relief valve to dump any over boosted air

Question 19

How does a fixed wastegate system work?

Answer 19

It is the simplest although it has many drawbacks.

It has a set position (adjustable on the ground), pilot does not have to worry about it.

Question 20

What is one of the drawbacks?

Answer 20

At no stage is all the exhaust gas available to supply the turbine.

Thus, the amount of boost available at higher altitudes is limited.

Question 21

What happens at lower altitudes?

Answer 21

Some turbocharging is in operation even though it is not needed.

Question 22

What care needs to be taken regarding this?

Answer 22

During take-off and early part of the climb over boosting will occur if the throttle is fully opened

Question 23

How should power changes be in all types of turbochargers?

Answer 23

Smooth and anticipated so that throttle movement is even slower than you were used to in the normally aspirated single.

Question 24

How many seconds will take from idle to full power and viceversa?

Answer 24

4’’

Question 25

What’s the significant caution with turbochargers?

Answer 25

Thermal stress

Question 26

Why?

Answer 26

They turn at extremely high RPM and cannot tolerate sudden temperature changes

Question 27

What is the critical time?

Answer 27

Reducing power for a descent, simulating engine failures and stabilising the temperature prior to shut down.

Question 28

What’s the minimum run-down time?

Answer 28

2 minutes, where the engines are allowed to idle, so that temperature stabilizes before the engines are shutdown