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CHAPTER 21 TURBOCHARGING AND SUPERCHARGING

CHAPTER 21 TURBOCHARGING AND SUPERCHARGING. 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).

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CHAPTER 21 TURBOCHARGING AND SUPERCHARGING

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  1. 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. 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 KEY TERMS

  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.

  6. FIGURE 21–1 A supercharger on a Ford V-8. FIGURE 21–2 A turbocharger on a Toyota engine. INTRODUCTIONVOLUMETRIC EFFICIENCY

  7. FIGURE 21–3 The more air and fuel that can be packed in a cylinder, the greater the density of the air-fuel charge. 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.

  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. FIGURE 21–4 Atmospheric pressure decreases with increases in altitude. FORCED INDUCTION PRINCIPLES

  10. 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 • SUPERCHARGER BOOST CONTROL • SUPERCHARGER SERVICE

  13. FIGURE 21–5 A roots-type supercharger uses two lobes to force the air around the outside of the housing and into the intake manifold. SUPERCHARGERS

  14. FIGURE 21–6 The bypass actuator opens the bypass valve to control boost pressure. SUPERCHARGERS

  15. FIGURE 21–7 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. SUPERCHARGERS

  16. 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.

  17. 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. • OPERATION • TURBOCHARGER OPERATION • TURBOCHARGER SIZE AND RESPONSE TIME

  18. FIGURE 21–8 A turbocharger uses some of the heat energy that would normally be wasted. FIGURE 21–9 A turbine wheel is turned by the expanding exhaust gases. TURBOCHARGERS

  19. FIGURE 21–10 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. FIGURE 21–11 Engine oil is fed to the center of the turbocharger to lubricate the bushings and returns to the oil pan through a return line. TURBOCHARGERS

  20. BOOST CONTROL • BOOST CONTROL FACTORS • WASTEGATE • RELIEF VALVES • Compressor bypass valve (CBV) • Blow-off valve (BOV)

  21. FIGURE 21–12 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. BOOST CONTROL

  22. FIGURE 21–13 A wastegate is used on many turbocharged engines to control maximum boost pressure. The wastegate is controlled by a computer-controlled valve. BOOST CONTROL

  23. FIGURE 21–14 A blow-off valve is used in some turbocharged systems to relieve boost pressure during deceleration. BOOST CONTROL

  24. 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.

  25. FIGURE 21–15 A dual turbocharger system installed on a small block Chevrolet V-8 engine. If One Is Good, Two Are Better

  26. TURBOCHARGER FAILURES • SYMPTOMS OF FAILURE • PREVENTING TURBOCHARGER FAILURES

  27. 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.

  28. NITROUS OXIDE • PRINCIPLES • ENGINE POWER ADDER • PRESSURE AND TEMPERATURE • WET AND DRY SYSTEM • ENGINE CHANGES NEEDED FOR N2O • SYSTEM INSTALLATION AND CALIBRATION

  29. NITROUS OXIDE

  30. FIGURE 21–16 Nitrous bottles have to be mounted at an angle to ensure that the pickup tube is in the liquid N2O. NITROUS OXIDE

  31. 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.

  32. FIGURE 21–17 An electrical heating mat is installed on the bottle of nitrous oxide to increase the pressure of the gas inside. Increase Bottle Pressure

  33. 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.

  34. 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.

  35. 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?

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

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

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

  39. 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

  40. 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

  41. 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

  42. 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

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

  44. 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

  45. 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

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