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AUT 112 Automotive Engines II

AUT 112 Automotive Engines II

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AUT 112 Automotive Engines II

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  1. AUT 112Automotive Engines II CHAPTER 21 TURBOCHARGING AND SUPERCHARGING

  2. OBJECTIVES After studying Chapter 21, the reader should be able to: • Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). • Explain the difference between a turbocharger and a supercharger. • Describe how the boost levels are controlled. • Discuss maintenance procedures for turbochargers and superchargers.

  3. KEY TERMS • Boost • BOV • Bypass valve • CBV • Dry system • Dump valve • Forced induction systems • Intercooler • Naturally (normally) aspirated • Nitrous oxide (N2O) • Positive displacement • Power adder • Roots supercharger • Supercharger • Turbocharger • Turbo lag • Vent valve • Volumetric efficiency • Wastegate • Wet system

  4. INTRODUCTIONAIRFLOW REQUIREMENTS • A four-stroke engine can take in only so much air, and how much fuel it needs for proper combustion depends on how much air it takes in. • Engineers calculate engine airflow requirements using three factors. • Engine displacement • Engine revolutions per minute (RPM) • Volumetric efficiency

  5. INTRODUCTIONVOLUMETRIC EFFICIENCY • Volumetric efficiency is a measure of how well an engine breathes. • It is a comparison of the actual volume of air-fuel mixture drawn into an engine to the theoretical maximum volume that could be drawn in. • Volumetric efficiency is expressed as a percentage or actual efficiency / theoretical efficiency. • In a normally aspirated engine, the volumetric efficiency will always be less that 100% of its theoretical efficiency due to turbulence and restrictions in the intake system. • A forced induction engine can operate at more than 100% of it’s theoretical efficiency. • A normal engine (newer) may be as high as 85% while a racing engine may achieve 95%.

  6. INTRODUCTIONVOLUMETRIC EFFICIENCY A Rootes type supercharger on a Ford V-8 A turbocharger on a Toyota engine.

  7. FORCED INDUCTION PRINCIPLES • The amount of force an air-fuel charge produces when it is ignited is largely a function of the charge density. • Charge density is a term used to define the amount of the air-fuel charge introduced into the cylinders. • Density is the mass of a substance in a given amount of space. • The more air and fuel that can be packed in a cylinder, the greater the density of the air-fuel charge and the greater the power output of the engine.

  8. FORCED INDUCTION PRINCIPLES • Forced induction systems use an air pump to pack a denser air-fuel charge into the cylinders. • Because the density of the air-fuel charge is greater, the following occurs. • The weight of the air-fuel charge is higher. • Power is increased because it is directly related to the weight of an air-fuel charge consumed within a given time period.

  9. FORCED INDUCTION PRINCIPLES • Atmospheric pressure decreases with increases in altitude.

  10. The effective compression ratio compared to the boost pressure. FORCED INDUCTION PRINCIPLESBOOST AND COMPRESSION RATIOS

  11. SUPERCHARGERS • A supercharger is an engine-driven air pump that supplies more than the normal amount of air into the intake manifold and boosts engine torque and power. • A supercharger provides an instantaneous increase in power without any delay. • However, a supercharger, because it is driven by the engine, requires horsepower to operate and is not as efficient as a turbocharger.

  12. SUPERCHARGERS • TYPES OF SUPERCHARGERS • Roots type • Centrifugal supercharger • Vane Type

  13. SUPERCHARGERS • A roots-type supercharger • Uses two (or more) lobes to force the air around the outside of the housing and into the intake manifold. • Is considered a positive displacement pump.

  14. SUPERCHARGERS • Centrifugal type mechanical supercharger. • Much like a turbocharger, but belt driven rather than by exhaust gasses. • Is a non-positive displacement pump

  15. SUPERCHARGERSCentrifugal Supercharger

  16. SUPERCHARGERS • A Vane type Supercharger • Normally belt driven. • Uses sliding vanes to compress air. • Is considered to be a positive displacement system.

  17. SUPERCHARGERS • The bypass actuator opens the bypass valve to control boost pressure. • When the boost pressure reaches max. • During decelleration (prevents excessive pressure) • When reverse is selected.

  18. SUPERCHARGERS • A Ford supercharger cutaway display showing the roots-type blower and air charge cooler (intercooler). • The air charge cooler is used to reduce the temperature of the compressed air before it enters the engine to increase the air charge density.

  19. Faster Moves More Air • One of the high-performance measures that can be used to increase horsepower on a supercharged engine is to install a smaller diameter pulley. • The smaller the pulley diameter, the faster the supercharger will rotate and the higher the potential boost pressure will be. • The change will require a shorter belt, and the extra boost could cause serious engine damage.

  20. TURBOCHARGERS • A turbocharger uses the heat of the exhaust to power a turbine wheel and therefore does not directly reduce engine power. • In a naturally aspirated engine, about half of the heat energy contained in the fuel goes out the exhaust system.

  21. TURBOCHARGERSLubrication • The exhaust drives the turbine wheel on the left which is connected to the impeller wheel on the right through a shaft. • The bushings that support the shaft are lubricated with engine oil under pressure. • Engine oil is fed to the center of the turbocharger to lubricate the bushings and returns to the oil pan through a return line. • Sometimes engine coolant will be used to help cool the turbocharger bearings.

  22. BOOST CONTROL • BOOST CONTROL FACTORS • With increased boost, temperature is increased. • Increased temperatures increase the risk of detonation. • If pressures are not controlled, the higher temperatures/pressures can cause engine/turbocharger damage. • Boost pressure and temperature may be controlled by: • Intercoolers • Wastegates • Relief Valves • Compressor bypass valve (CBV) • Blow-off valve (BOV)

  23. BOOST CONTROL • INTERCOOLER • The unit on top of this Subaru that looks like a radiator is the intercooler, which cools the air after it has been compressed by the turbocharger.

  24. BOOST CONTROL • WASTEGATE • A wastegate is used on many turbocharged engines to control maximum boost pressure. • When activated, it allows exhaust gasses to bypass the turbine. • The wastegate is controlled by a computer-controlled valve. • Older installations may be controlled by a mechanical pressure regulator.

  25. BOOST CONTROL • RELIEF VALVES • A BLOW-OFF VALVE (BOV)is used in some turbocharged systems to relieve boost pressure during deceleration. • Excess pressure is vented to the atmosphere. • A COMPRESSOR BYPASS VALVE (CBV) reroutes excess air back to the inlet side of the compressor.

  26. If One Is Good, Two Are Better • A turbocharger uses the exhaust from the engine to spin a turbine, which is connected to an impeller inside a turbocharger. • This impeller then forces air into the engine under pressure, higher than is normally achieved without a turbocharger. The more air that can be forced into an engine, the greater the power potential. • A V-type engine has two exhaust manifolds and so two small turbochargers can be used to help force greater quantities of air into an engine.

  27. Turbocharger Operation • http://www.youtube.com/watch?v=vGhlgphrBxA

  28. TURBOCHARGER FAILURES • SYMPTOMS OF FAILURE • Noticeable drop in power. • Excessive or continuous oil consumption. • PCV system failure. (not truly a turbo failure) • Clogged air filter. • Clogged oil return.

  29. TURBOCHARGER FAILURES • PREVENTING TURBOCHARGER FAILURES • Regular oil/filter changes (synthetic best) • Be sure to follow recommended maintenance/inspection schedule. • Allow the turbocharger to cool/spin down before shutting engine off.

  30. NITROUS OXIDE • Nitrous oxide is used for racing or high-performance only, and is not used from the factory on any vehicle. • This system is a relatively inexpensive way to get additional power from an engine, but can cause serious engine damage if not used correctly or in excess amounts, or without proper precautions.

  31. NITROUS OXIDE • PRINCIPLES • Oxidizer • Manufactured or artificial gas. • 36% molecule weight is oxygen. • ENGINE POWER ADDER • Provides extra oxygen to the fuel air mixture allowing more fuel to be burned. • PRESSURE AND TEMPERATURE • Requires 770 PSI to become a liquid at 70 deg F. • Becomes a gas at room/seal level pressures and temperatures. • WET AND DRY SYSTEM • Wet system has additional fuel nozzles. • Dry system depends on ECU and existing injectors to provide additional fuel. • ENGINE CHANGES NEEDED FOR N2O • Forged pistons • Greater piston to cylinder wall clearance. • Forged crank and connecting rods. • Oil cooler. • SYSTEM INSTALLATION AND CALIBRATION • Usually installed as a kit. • Purchased with nozzel sets for desired HP increase. • Includes a switch to limit NOX use to WOT.

  32. Temperature/pressure relation for nitrous oxide: The higher the temperature, the higher the pressure. NITROUS OXIDE

  33. NITROUS OXIDE • Nitrous bottles have to be mounted at an angle to ensure that the pickup tube is in the liquid N2O.

  34. Increase Bottle Pressure • To increase the pressure of the nitrous oxide in a bottle, an electrical warming blanket can be used. • The higher the temperature, the higher the pressure and the greater the amount of N2O flow when energized.

  35. Increase Bottle Pressure • An electrical heating mat is installed on the bottle of nitrous oxide to increase the pressure of the gas inside.

  36. SUMMARY • Volumetric efficiency is a comparison of the actual volume of air-fuel mixture drawn into the engine to the theoretical maximum volume that can be drawn into the cylinder. • A supercharger operates from the engine by a drive belt and, although it consumes some engine power, it forces a greater amount of air into the cylinders for even more power. • There are two types of superchargers: roots-type and centrifugal. • A turbocharger uses the normally wasted heat energy of the exhaust to turn an impeller at high speed. The impeller is linked to a turbine wheel on the same shaft and is used to force air into the engine.

  37. SUMMARY • A bypass valve is used to control the boost pressure on most factory installed superchargers. • An intercooler is used on many turbocharged and some supercharged engines to reduce the temperature of air entering the engine for increased power. • A wastegate is used on most turbocharger systems to limit and control boost pressures, as well as a relief valve, to keep the speed of the turbine wheel from slowing down during engine deceleration. • Nitrous oxide injection can be used as a power adder, but only with extreme caution.

  38. REVIEW QUESTIONS • What are the reasons why supercharging increases engine power? • How does the bypass valve work on a supercharged engine? • What are the advantages and disadvantages of supercharging? • What are the advantages and disadvantages of turbocharging? • What turbocharger control valves are needed for proper engine operation?

  39. CHAPTER QUIZ 1. Boost pressure is generally measured in ________. • in. Hg • PSI • in. H2O • in. lb

  40. CHAPTER QUIZ 2. Two types of superchargers include ________. • Rotary and reciprocating • Roots-type and centrifugal • Double and single acting • Turbine and piston

  41. CHAPTER QUIZ 3. Which valve is used on a factory supercharger to limit boost? • Bypass valve • Wastegate • Blow-off valve • Air valve

  42. CHAPTER QUIZ 4. How are most superchargers lubricated? • By engine oil under pressure through lines from the engine • By an internal oil reservoir • By greased bearings • No lubrication is needed because the incoming air cools the supercharger

  43. CHAPTER QUIZ 5. How are most turbochargers lubricated? • By engine oil under pressure through lines from the engine • By an internal oil reservoir • By greased bearings • No lubrication is needed because the incoming air cools the supercharger

  44. CHAPTER QUIZ 6. Two technicians are discussing the term turbo lag. Technician A says that it refers to the delay between when the exhaust leaves the cylinder and when it contacts the turbine blades of the turbocharger. Technician B says that it refers to the delay in boost pressure that occurs when the throttle is first opened. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

  45. CHAPTER QUIZ 7. What is the purpose of an intercooler? • To reduce the temperature of the air entering the engine • To cool the turbocharger • To cool the engine oil on a turbocharged engine • To cool the exhaust before it enters the turbocharger

  46. CHAPTER QUIZ 8. Which type of relief valve used on a turbocharged engine is noisy? • Bypass valve • BOV • Dump valve • Both b and c

  47. CHAPTER QUIZ 9. Technician A says that a stuck open wastegate can cause the engine to burn oil. Technician B says that a clogged PCV system can cause the engine to burn oil. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

  48. CHAPTER QUIZ 10. What service operation is most important on engines equipped with a turbocharger? • Replacing the air filter regularly • Replacing the fuel filter regularly • Regular oil changes • Regular exhaust system maintenance