SEGUNDA FASE: PROXECTO DE ACTIVIDADES DOCENTES
4. Experiencia investigadora (máximo 15 puntos)
When making comparisons between turbo-chargers and internal superchargers it is inevitable that the question of “which is best?” is asked. If it was just a matter of added performance at ground level for a given cost, then the turbo-charger would probably win.
There are other considerations to be taken into account however, first of all, do we only want the added performance at ground level? Unavoidably with an aircraft the answer must be no, in which case the internal supercharger, with its ability to increase engine power with aircraft altitude, must be favourite.
Secondly, do we require that the response to throttle opening be instant? If the answer to this is yes, then once again the internal supercharger wins hands down. The turbo-charger, for all that it is the cheaper option, cannot with present day technology respond to rapid throttle opening without suffering from the phenomenon known as turbo-lag.
Turbo-lag is the result of the time it takes to speed up the turbine / compressor after the signal of low compressor output has been sent to the Absolute Pressure Controller (A.P.C.) and the waste gate actuator has reacted by closing the waste gate.
SUMMARY
SUPERCHARGER TURBOCHARGER
1 Internally driven Externally driven
2 Rotational speed controlled by RPM. Rotational speed controlled by Waste Gate position.
3 Compresses mixture Compresses air
4 ABC senses manifold pressure and
controls the throttle APC senses compressor discharge pressure and controls the waste gate 5 Compressor discharge pressure same as
manifold pressure Compressor discharge pressure greater
than manifold pressure
6 Throttle controls manifold pressure Throttle controls manifold pressure
7 Decreased exhaust back pressure in the
climb Increased exhaust back pressure in the
climb
DIESEL ENGINES
Diesel Engines also suffer from a loss of Volumetric Efficiency with altitude, high elevation take-offs and on hotter than standard days.
For this reason Turbo-Chargers (External Superchargers) may be fitted to diesel-engines so as to improve performance in a similar way to the conventional piston engine. Intercoolers are also employed to restore density after compression.
QUESTIONS
1. The Manifold Pressure Gauge fitted to a supercharged engine measures:
a. The absolute pressure in the induction manifold.
b. The differential pressure across the supercharger compressor.
c. The ratio between the atmospheric pressure and the cam rise at the supercharger inlet.
d. The pressure upstream of the throttle valve.
2. An Automatic Boost Control Unit:
a. Prevents detonation and dissociation in the cylinder.
b. Maintains an automatic preset boost pressure.
c. Maintains the correct mixture strength for the boost pressure set.
d. Sets the posiion of the waste gate to ensure the preset boost is maintained.
3. The use of a turbo-charger on an engine will:
a. Improve the exhaust scavenging efficiency.
b. Raise the volumetric efficiency of the engine.
c. Cause an automatic rise in the engine R.P.M. as altitude is gained.
d. Cause an automatic rise in engine power as altitude is gained.
4. The motive force used to drive the turbo-charger is:
a. Torque from the crankshaft via a spring drive unit.
b. Torque from the accessory gearbox.
c. Energy from the exhaust that would otherwise have been wasted.
d. Energy from the reduction gearbox.
5. The power increase that occurs with initial increase in altitude when an engine has an internal supercharger fitted, is due to:
a. The reduced weight of mixture being passed to the engine.
b. The decreasing density of the atmosphere.
c. The reducing exhausts back pressure.
d. The increasing charge temperature.
6. Rated Altitude is:
a. The height at which the boost pressure ceases to be effective with a specific R.P.M. set.
b. A comparison between the boost pressure at sea level and that at a given altitude.
c. The maximum altitude at which Rated Boost can be maintained with a specific R.P.M.
d. set.The altitude at which the waste gate becomes fully shut.
7. The speed of the turbine of a turbo-charger is controlled by:
a. The diversion of exhaust gases.
b. Controlling the exit of the exhaust gas passing out of the eye of the impeller.
c. The use of a variable controller.
d. An automatic gearbox positioned between the turbine and the impeller.
8. The turbo-charger waste gate is spring loaded towards:
a. The open position.
b. The closed position.
c. A neutrally balanced partly open position.
d. The maximum boost position.
9. The turbo-charger bearing is lubricated and cooled by:
a. Its own internal self contained oil system.
b. The engine oil.
c. A total loss system.
d. A tapping in the scavenge oil system.
10. Static Boost is:
a. Always the I.S.A. atmospheric pressure for the airfield altitude.
b. Obtained by opening the throttle to give a boost gauge reading of 30”He or 0 psi.
c. The boost pressure gauge reading when the engine is not running.Selecting a suitable throttle position will give the same boost gauge reading when the engine is running.
d. The difference between the induction manifold pressure and the exhaust manifold pressure.
11. The automatic boost pressure control capsules are made sensitive to:
a. Atmospheric pressure.
b. Carburettor inlet pressure.
c. Boost pressure.
d. Cabin pressure differential.
12. In order to maintain a constant boost pressure with increasing altitude, the A.B.C.:
a. Holds the throttle valve at a constant position.
b. Progressively opens the throttle valve.
c. Progressively closes the waste gate.
d. Progressively closes the throttle valve.
13. “Boost pressure” is the:
a. Inlet manifold pressure in pounds per square inch above or below standard mean sea level pressure.
b. Absolute pressure in the inlet manifold measured in inches of mercury.
c. Absolute pressure in the inlet manifold measured in millibars.
d. Inlet manifold pressure in pounds per square inch above or below atmospheric pressure.
14. “Full Throttle Height” is:
a. The height at which the engine is at Rated Boost.
b. The maximum height at which a specified boost can be maintained at a specified R.P.M.
c. The height at which the waste gate is fully closed.
15. The purpose of an intercooler is:
a. To minimise the risk of detonation.
b. To increase the volume of the charge.
c. To decrease the density of the charge.
d. To prevent overheating of the exhaust manifold.
16. The function of a diffuser in a supercharger is:
a. To decrease the temperature and increase the velocity of the charge.
b. To increase the velocity and decrease the pressure of the charge.
c. To decrease the velocity and decrease the pressure of the charge.
d. To decrease the velocity and increase the pressure of the charge.
17. Air enters the compressor of a turbo-supercharger:
a. At the tip and passes across the impeller blades to exit at the eye.
b. At the diffuser and exits at the impeller.
c. At the eye and passes across the diffuser blades before exiting at the impeller tip.
d. At the eye and passes across the impeller blades to exit at the tip.
18. The waste gate of a turbo-supercharger is fitted:
a. In the turbine by-pass.
b. In the inlet manifold.
c. To maximise exhaust back pressure.
d. In series with the turbine.
19. The waste gate is operated by:
a. The automatic boost control unit.
b. The waste gate actuator.
c. Inlet manifold pressure.
d. Exhaust gas temperature.
20. With a turbo-charger installed on the engine, its exhaust back pressure:
a. Remains the same.
b. Is decreased.
c. Is increased.
d. Decreases in the climb.
21. A high performance supercharger may require an intercooler to be placed:
a. Between the supercharger and the inlet valve.
b. At the carburettor intake.
c. Between each cylinder.
d. Between the engine block and the exhaust manifold.
22. With an increase of compressor discharge pressure the fuel flow will:
a. Increase.
b. Remain constant.
c. Decrease.
d. Increase, but only in proportion to altitude increase.
23. A turbo-charger’s rotational speed is determined by:
a. The diversion of exhaust gas.
b. The position of the throttle valve.
c. The density of the air at the compressor intake.
d. Bleeding off excess exhaust pressure.
24. During take-off from a sea level airfield with I.S.A. conditions, the position of the waste gate of a turbo-charged engine is:
a. Fully open.
b. Almost fully open.
c. Controlled by the throttle position.
d. Fully closed.
25. Maximum Continuous Power (M.C.P.) is:
a. Unrestricted, but only if economical cruising power is set.
b. The maximum power the engine will give at any time.
c. Given a 5 minute limitation.
d. Unrestricted.
26. The primary purpose of a supercharger is to:
a. Raise the temperature of the charge entering the cylinder.
b. Increase the mass of the charge entering the cylinder.
c. Improve the engine’s exhaust scavenging capability, and hence increase its power output.
d. Allow the use of high octane fuel.
27. The type of fuel used in a turbo-charged engine would be:
a. AVTUR.
b. AVGAS.
c. AVTAG.
d. AVPIN.
28. At an idle or low power condition, the turbo-charger waste gate is normally:
a. Partially open.
30. The construction of a turbo-charger ensures that the turbine and the compressor:
a. Are on the same shaft.
b. Are on different shafts.
c. Are connected by mechanical gearing.
d. Are controlled by the A.B.C.
31. The waste gate fitted to a turbo-charger regulates the quantity of:
a. The mixture that enters the induction manifold.
b. The atmosphere that can enter the compressor.
c. The exhaust gas that will by-pass the turbine.
d. The exhaust gas that leaves the compressor.
32. The main function of a supercharger is to:
a. Increase the thermal efficiency of the engine.
b. Increase the compression ratio of the engine.
c. Maintain sea level pressure in the engine to above rated altitude.
d. Increase the volumetric efficiency of the engine.
33. The response of a turbo-charged engine to rapid throttle opening, when compared to a normally aspirated engine:
a. Is initially better, but exhaust back pressure will cause a flat spot.
b. Is always better.
c. Is worse.
d. Is identical.
34. With a constant manifold pressure set during the climb, the power output from a supercharged engine:
a. Decreases.
b. Increases.
c. Remains constant.
d. Is unaffected by altitude change.
35. An internal supercharger is one which:
a. Is driven by exhaust gases.
b. Compresses the air.
c. Compresses the exhaust gases.
d. Compresses the mixture.
36. If the waste gate of a turbo-charged engine seizes in the climb before critical altitude has been reached:
a. Engine power will be automatically adjusted by the A.B.C.
b. Engine power will rise by approximately 10%.
c. Reducing back pressure will compensate for any loss in power.
d. Engine power will fall as the climb continues.
37. To prevent large acceleration loads on the compressor and the drive shaft of an internal supercharger, it is usual to:
a. Prohibit “slam” acceleration.
b. Incorporate a spring drive mechanism in the driving gears.
c. Rely on the inertia absorbing qualities of the exhaust gases.
d. Use a Vernier drive coupling.
38. The rotational speed of the turbo-charger of an engine which is at full throttle at low altitude is:
a. The exhaust gas temperature to decrease due to a decrease in exhaust back pressure.
b. The waste gate to open.
c. The waste gate to progressively close.
d. The diffuser rotational speed to increase.
40. Over boosting an engine fitted with a turbo-charger is prevented by the installation of:
a. An automatic boost control unit.
b. A manifold pressure gauge.
c. A waste gate pressure controller d. A suck in flap.
41. A turbo-charger which is designed to maintain sea level pressure at altitude is termed:
a. An altitude-boosted turbo-charger.
b. A turbo-supercharger.
c. An internal supercharger.
d. A ground boosted turbo-charger.
42. With the power lever opened for take off power at sea level, the throttle butterfly of an engine fitted with an internal supercharger would be:
a. Fully open.
b. In a choked position.
c. Partially open.
d. Fully closed.
43. “Static Boost” is the manifold pressure indicated on the boost pressure gauge when:
a. The engine is stopped.
b. The engine is running at the manufacturer’s recommended idle speed.
c. The engine is running at its rated power.
d. The manifold gauge needle is opposite the lubber line.
44. The limit of the amount of supercharging that an engine can tolerate is reached when:
a. Maximum R.P.M. is reached.
b. The engine is at its rated altitude.
c. Maximum boost pressure is obtained.
d. The engine starts to suffer from detonation.
45. The rotational speed of a turbo-charger is dependant upon:
a. Engine R.P.M. and waste gate position.
b. Engine R.P.M. only.
c. Throttle position only.
d. Propeller pitch and altitude.
46. The inlet manifold pressure of a turbo-charged engine in an aircraft which is climbing will:
a. Increase to full throttle height and then fall.
b. Increase to critical height and then remain constant.
c. Remain constant to critical altitude and then fall.
d. Decrease to critical altitude and then remain constant.
47. The type of compressor normally used in a supercharger is:
a. An axial compressor.
b. A Rootes compressor.
c. A centrifugal compressor.
d. A reciprocating thrunge compressor.
48. The compressor output pressure of an internal supercharger is:
a. The same as manifold pressure.
b. Greater than the manifold pressure.
c. Sometimes greater, sometimes less than the manifold pressure.
d. Less than the manifold pressure.
49. The position of the waste gate in a turbo-charged engine is:
a. In the inlet manifold.
b. Downstream of the turbine.
c. In parallel with the turbine.
d. In parallel with the compressor.
50. The maximum engine Brake Horse Power with a specified R.P.M. and manifold pressure set which permits continuous safe operation is termed:
a. Maximum Power.
b. Take Off Power.
c. Critical Power.
d. Rated Power.
51. The compressor output of a turbo-charger unit is:
a. The same as the manifold pressure.
b. Greater than the manifold pressure.
c. Sometimes greater, sometimes less than the manifold pressure.
d. Less than manifold pressure.
52. Within the compressor of a turbo-charger:
a. The pressure increases and the temperature decreases.
b. Both the pressure and the temperature increase.
c. Both the pressure and the temperature decrease.
d. The pressure increases and the temperature remains constant.
53. The type of compressor normally fitted to turbo-chargers and superchargers would compress the air:
55. To maintain the Rated Boost of a supercharged engine while reducing the R.P.M.:
a. The throttle valve must be opened.
b. The waste gate must be closed.
c. The waste gate must be opened.
d. The throttle valve must be closed.
56. The effect of selecting Rated Boost, but less than Rated R.P.M. on the climb, would be that:
a. The Rated Altitude would be lower.
b. The Full Throttle Height would be less.
c. The Rated Altitude would be higher.
d. The Full Throttle Height would be higher.
57. The Automatic Boost Control Unit operates:
a. The Boost Control Lever.
b. The waste gate.
c. The throttle butterfly.
d. The R.P.M. gauge and the manifold pressure gauge.
58. Boost pressure is indicated on:
a. The cylinder head temperature gauge.
b. The manifold pressure gauge.
c. The fuel pressure gauge.
d. The R.P.M. gauge and the manifold pressure gauge.
59. With an increase of compressor discharge pressure, the fuel flow will:
a. Decrease.
b. Remain constant.
c. Initially increase, but subsequently decrease.
d. Increase.
60. Superchargers are used to overcome:
a. The decrease in density due to the increase in altitude.
b. The increase in temperature due to the increase in altitude.
c. The fuel density variation that occurs with an increase in altitude.
d. The exhaust back pressure.
61. The boost pressure of a turbo-charged engine is controlled by:
a. Adjusting the throttle position.
b. Varying the speed of the turbo-charger.
c. The A.B.C.
d. Changing engine R.P.M.
62. In a supercharger, the mixture:
a. Enters through the eye of the impeller and leaves at the periphery.
b. Enters at the periphery and leaves through the eye.
c. Enters through the turbine and leaves through the compressor.
d. Enters through the compressor and leaves through the turbine.
ANSWERS
1 A 21 A 41 A 61 A
2 B 22 A 42 B 62 A
3 B 23 A 43 A
4 C 24 B 44 C
5 C 25 D 45 A
6 C 26 B 46 C
7 A 27 B 47 C
8 A 28 C 48 A
9 B 29 A 49 C
10 C 30 A 50 D
11 C 31 C 51 B
12 B 32 D 52 B
13 A 33 C 53 D
14 B 34 B 54 B
15 A 35 D 55 A
16 D 36 D 56 B
17 D 37 B 57 C
18 A 38 A 58 B
19 B 39 C 59 D
20 C 40 B 60 A
CHAPTER TWELVE