Supercharging INDUCTION. Its purpose is to increase the mass of the air/fuel charge going into the engine for each revolution.

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Candace Hood
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1 Supercharging INDUCTION Its purpose is to increase the mass of the air/fuel charge going into the engine for each revolution.

2 Most supercharged engines also have constant speed propellers They are designed to keep full power, manifold pressure at or above sea level pressure for as high as possible, hence the term Altitude Engine

3 Critical altitude = that altitude where the boosted manifold pressure can no longer exceed sea level pressure. As system technology developed we eventually designed supercharged engines that exceeded ambient pressure in the intake system.

4 This can also be done at lower altitudes for maximum power during critical flight operations, Is sometimes used for limited duration s. Maximum boost is determined by the strength of the intake system, or the detonation characteristics of the engine

5 General gas law = volume of a gas is inversely proportional to the absolute pressure and is directly proportional to the temperature. (V1 * P1) / T1 = (V2 * P2) / T2

6 Many things create high cyl pressure. 1. Advanced ignition timing 2. High density air 3. Low octane, hot burning fuels 4. Excessive compression (wrong engine parts) 5. High intake temperatures

7 High pressure creates high temperature. At a certain temperature and pressure threshold, the pressure shock wave, which travels faster then the heat/burn wave, starts to spontaneously ignite the air/fuel mixture in an uncontrolled fashion.

8 This is called detonation, - FAA declares this to be a state of uncontrolled burning. Pre-ignition is when any source ignites the air/fuel charge prior to the spark plug ignition.

9 Air Density INDUCTION Standard day conditions = at sea level, at 15 c or 59 f, at 45 N lat. Factors effecting density Water and hi temps displace air molecules creating less density.

10 Avogadro s law states that any gas molecule will take up the same space at the same temperature. N2 has about twice the mass per molecule as H2O therefore the wet air has less mass per unit of volume. (Lower density)

11 Density altitude = common pilot nomenclature, higher numbers means lower density.

12 Supercharger is a non-positive displacement centrifugal air pump (compressor) that increases the air density in the intake systems and the cylinders. Can be single or multi speed up to 13 to 1 ratio to crankshaft, in low blower up to 42 inhg. hi blower = up to 80 inhg

13 When switching to high speed the manifold pressure will go up and oil pressure will drop. Supercharging is the overall term for pumping air into the engine regardless of how this is accomplished.

14 But is also the term for mechanically pumping air with a gear driven compressor. (Some auto racing applications use a 4 wide belt drive) Turbo supercharging uses exhaust to drive a turbine/compressor pump.

15 In most super chargers fuel is mixed with air before supercharging (internal), but not all (external). This helps to vaporize the fuel. Turbo superchargers have the air compressed prior to fuel metering

16 If engine cannot boost above 30.00"Hg then it is a normalized boosted engine. It can be said the normalized engine regains normal ambient pressure, up to the point where the turbo is at maximum output.

17 Those that go above 30.00"Hg are known as supercharged. Intercooler can be used on superchargers to cool the air charge after the compressor

18 With some engines there is a distribution impeller, but this not a charging impeller. (more later) On the R-985 it has an actual supercharger impeller at a 7.5 to 1 ratio to the crankshaft.

19 It is possible to have superchargers that have several stages of charging much like a turbine engine, and, or they can have several speeds of compressor RPM. Stages and speeds. Can have Stages: Speeds: 2 2 1

20 More then one compressor impeller creates the multiple stages Only the gear driven Supercharger can have different speeds (Automatic Gear box).

22 Dual speeds are controlled by solenoid switch. Engine must have low compression ratios to prevent blow ups with high pressures. Supercharger clutches are engaged with oil pressure.

23 Supercharging casing can be airfoil, vaned, venturies Supercharger efficiency is by speed of rotation, and size of impeller

24 Advantages 1. More hp, 2. shorter takeoff, 3. bigger payload, INDUCTION 4. Greater fuel efficiency, 5. higher altitude

25 Disadvantages, INDUCTION 1. premature engine wear, 2. more pre ignition and detonation, 3. closer monitoring and maintenance,

26 4. must use higher fuel grades, 5. Harder to work on higher costs, 6. low altitude restrictions due too much boost.

27 A condition, less severe than bootstrapping, is called "overshoot", where the turbo overshoots the engine one time during hard throttle application.

28 Need to beef up the engine to handle the turbocharger or supercharger. Intercooler is heat exchanger that cools air before going into engine to increase density.

29 Two common current producers of turbosuperchargers are Ray-Jay and Garrett AirResearch.

30 RayJay were the original type of turbo, with electric on/off solenoid, then came the automatic controls. VAPC, APC, Density controller, Distribution impeller = a mixing impeller, connected directly to the crankshaft that does not provide any boosting capacity.

31 Never install a supercharger onto an engine that was not designed from the ground up to be supercharged. Conversions always loose reliability and longevity, and increase the possibility of sudden catastrophic engine departation.

32 Supercharger and *Turbosupercharger components. 1. Compressor housing 2. *Turbine housing 3. Compressor impeller 4. *Turbine impeller 5. Drive shaft

33 6. Transmission assembly (Geared superchargers only) 7. Diffuser 8. Bearing sections 9. Lubrication plumbing 10. Air ducting 11. *Exhaust ducting 12. Control systems

34 Compressor housing is made of cast aluminum, cast, then machined. Compressor impeller, centrifugal, is the upper deck pressure side, directs air from the center to the outside. Turbine housing, cast iron or steel,

35 Turbines are impulse or reaction types, can be lost wax investment casted then machined or ground to final shape. Investment casting will lessen the porosity of the casting.

36 Turbine temperatures are normally 1,700 f Turbo superchargers can operate at speeds up to 100,000 RPM.

37 Drive shaft connects the compressor impeller to the transmission assembly or to the drive turbine impeller. Transmissions are either simple geared drivelines or they can be multi-speed transmissions that are hydraulically, or electro-hydraulically controlled.

38 These latter units will include a clutch systems coupled to a sun/planetary gear system, similar to an automatic automotive transmission. Diffusers are two main types: 1. Airfoil converging/diverging duct 2. Straight vane

39 The venturi-type diffuser is equipped with plain surfaces, This type has been most widely used on medium powered, supercharged engines On large volume engines ranging from 450 hp upwards, either a vane or airfoil type diffuser is widely used.

40 Bearing housing, is usually either a floating type plain bearing with pressurized oil (turbo superchargers) or they may use a double set of ball bearings with an oil bath spray. Shaft RPM can be as high as 40,000 to 50,000 RPM on some turbo superchargers.

41 Lubrication plumbing includes standard AN hardware, hoses, and tubing, designed to handle petroleum products at or below 100 psi. The impeller shaft and gear are usually forged integrally of very high grade steel.

42 Air ducting can be anything from high pressure scat tubing to cast aluminum runners and distribution manifolds. This all needs to be considerably stronger than normally aspirated induction assemblies. Do not interchange these parts.

43 Exhaust ducting is usually made from the same materials (Stainless Steel) as the rest of the exhaust system. Since the system has so much motion from vibration and heat expansion there will probably be flex, or expansion joints installed.

44 This may be encased in heat shielding of some form, particularly when installed on aircraft with streamlined cowlings. DO NOT leave this shielding off the aircraft for any flight operations.

45 Control systems INDUCTION Some early systems were manually controlled via a push/pull vernier near the throttle control.

46 During specific altitude and power conditions the pilot would engage the supercharger clutches via oil pressure controls, or start closing the turbosupercharger wastegate.

47 Wastegate is a device used on turbo superchargers that allows exhaust gasses to bypass the drive turbine. Typically a closed wastegate means full turbine output, (the bypass is closed). Deck pressure is that pressure just after the compressor.

48 Throttle valve is between compressor and intake system. Fuel is injected into intake close to intake valves.

49 Several systems are described in the following slides. There are numerous configurations. They all function by use of pressure control or density control, or both. They can regulate waste gates or scroll valves.

50 A density regulator will measure for pressure and temperature. A pressure regulator will only regulate for pressure. The most simple system is a outside adjustable bypass screw.

51 Other smaller systems may rely on only density regulation. As temperature or pressure changes the oil pressure is allowed to build or release on the wastegate controller. These usually default to open with no pressure.

52 These controllers are on the return side of the actuator. Pressure controllers can measure pressure, density or be differential, comparing two differing pressures.

53 One Lycoming system has four main components 1. Turbo supercharger 2. Density controller 3. Differential controller 4. Bypass assembly (wastegate)

54 Turbo supercharger is a sea level boosted engine with a critical altitude of 19,000 ft. Density controller controls oil pressure of wastegate actuator only during full power operation. It is density sensing, temp. and press.

55 Bellows regulates oil valve when deck pressure is below maximum output for those conditions. Differential controller controls oil pressure of wastegate actuator by means of a differential diaphragm with deck pressure on one side and post throttle MAP on the other side.

56 The differential controller will try to maintain a pressure drop across the throttle valve of 2-4 Hg. When it opens the waste gate opens. This valve will remain closed during wide open throttle operation since there is not enough differential to open it.

57 Another system uses a variable-pressure controller instead of a density and differential controllers. This device works similar to the differential controller but it also has a cam and plunger that is actuated by throttle linkage.

58 Over high deck pressure pushes the poppet down and open on the top end, and the cam pushes the poppet follower up and open from the bottom end during lower power settings. A vacuum filled bellows and several balancing springs work to keep the poppet valve closed. Unliscensed copyrighted material - W. North 1998 Unliscensed copyrighted material - W. North 1998

59 Continential had earlier units which used three controllers and later units combined these into one unit with cam/throttle linkages. These are: absolute pressure controller rate of change controller pressure-ratio controller

60 In similar fashion as they bleed off waste gate control oil opening the waste gate. They are hooked up in parallel so that each may independently dump exhaust gas.

61 Absolute pressure controller is a maximum upper deck pressure limiter. Rate of change controller bypasses wastegate oil if the deck pressure changes faster then 6.5 in Hg/S

62 The engine can over boost momentarily during rapid throttle application. This may only oscillate the power, or it may cause detonation for a short period.

63 Pressure ratio controller will maintain a pressure ratio between the deck pressure and inlet ram air of 2.2:1 at any altitude above 16,000 ft. This prevents excessive heat buildup in the deck airstream which can cause detonation.

64 The variable absolute pressure controller combines these three units and it functions in a manner identical to the Lycoming variable controller. This system also incorporates a overpressure MAP relief valve.

65 It uses varible fuel pressure as the operating force. Another turbo supercharger control system uses an adjustable orifice that also includes an overpressure relief valve

66 Adjustment criteria, at component replacement, or engine overhaul Test run on ground, Calibrate MAP gauge, Slowly advance throttle watching MAP

67 Install thermocouple to know temperature at specified port in compressor, then use chart to check temp against pressure read. Slow smooth throttle movement.

68 Frequent oil changes for any turbo supercharged engines. Plan on higher service requirements inspection wise as well. One quote is $1.50 per hour flight time in additional costs.

69 Bootstrapping is when as you increase power, turbo increases more, then you are over powered in a cyclic manner. It is an undesirable cycle of turbocharging events causing the manifold pressure to drift in an attempt to reach a state of equilibrium.

70 Bootstrapping occurs when the waste gate is closed or mostly closed. Rapid movement of the throttle can cause a certain amount of manifold pressure drift in a turbocharged engine. Bootstrapping is when the drift persists.

71 Intercoolers may exist on any of these devices. They provide pressurized intake air cooling. Sonic venturis are used to increase cabin air volume input, sacrificing limited amounts of air pressure.

72 Over boost is when the MAP upper pressure limit has been exceeded. This will break parts, cause detonation and break more parts.

73 Turbo compounding The turbocompound engine consists of a conventional, reciprocating engine in which exhaust driven turbines are coupled to the engine crankshaft.

74 This system of obtaining additional power is sometimes called a PRT (power recovery turbine) system. Power recovery turbine systems, because of weight and cost considerations, are used exclusively on very large reciprocating engines.

75 The net yield from them is not sufficient to justify their use on smaller engines.

77 Turbo supercharger problems 1. Aircraft fails to reach critical altitude. 2. Exhaust system leaks. 3. Faulty turbocharger bearings. 4. Waste gate will not close fully. 5. Waste gate will not open.

78 6. Engine surges. 7. Bootstrapping. INDUCTION 8. Waste gate malfunction. 9. Controller malfunction. 10. Waste gate bypass valve bearings tight. 11. Oil inlet orifice blocked. 12. Broken waste gate linkage.

79 Differential controller malfunctions. 1. Seals leaking. 2. Diaphragm broken. 3. Replace controller. 4. Controller valve stuck.

80 Density controller malfunctions. 1. Bellows damaged. 2. Valve stuck.

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