chap22 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 22, the reader should be able to: • Prepare for ASE Engine Performance (A8) • • certification test content area “C” (Air Induction and Exhaust Systems Diagnosis and Repair) Discuss the purpose and function of intake manifolds Explain the differences between throttle fuelinjection manifolds and port fuel-injection manifolds Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 22, the reader should be able to: • • Describe the operation of the exhaust gas recirculation system in the intake manifold List the materials used in exhaust manifolds and exhaust systems Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: Annealing exhaust gas recirculation (EGR) hangers • helmholtz resonator micron plenum Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 AIR INTAKE FILTRATION Gasoline must mix with air to  form a combustible mixture.  Air movement into an engine  occurs due to vacuum being  created in the engine.  Like gas, air contains dirt and  other materials which cannot be allowed to reach the engine.  Just as fuel filters are used to  clean impurities from gas, an air cleaner and filter are used to remove contaminants from  the air.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 22–1 Downward movement of the piston lowers the air pressure inside the combustion chamber The pressure differential between the atmosphere and the inside of the engine forces air into the engine ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The three main jobs of the air cleaner and filter are to: Clean the air before it is mixed with fuel Silence intake noise Act as a flame arrester in case of a backfire The automotive engine uses about 9,000 gallons (34,069 liters) of  air for every gallon of gasoline burned at a ratio of 14.7 to 1.  Without proper filtering, dust and dirt in the air seriously damage  engine parts and shorten engine life While abrasive particles can cause wear any place inside the engine  where two surfaces move against each other, they first attack piston  rings and cylinder walls. Contained in blowby gases, they pass by  the piston rings and into the crankcase Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 From the crankcase, the particles circulate throughout the engine in  the oil. Large amounts of abrasive particles in the oil can damage  other moving engine parts Filter Replacement Manufacturers recommend cleaning or replacing air filter elements at periodic intervals, usually in terms of distance driven or  months of service.  It is best to replace a filter  element before it becomes  too dirty to be effective Figure 22–2 Dust and dirt in the air are trapped in the air filter so they not enter the engine A dirty air filter passes contaminants that cause engine wear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Air Filter Elements  The paper air filter element is the most common type of filter, made  of chemically treated paper stock that contains tiny passages in the fibers These passages form an indirect path for the airflow to follow.  The airflow passes through several fiber surfaces, each of which  traps microscopic particles of dust, dirt, and carbon NOTE: Do not attempt to clean a paper element filter by rapping it on a sharp object to dislodge the dirt, or blowing compressed air through the filter. This tends to clog the paper pores and further reduce the airflow capability of the filter Most filters are capable of trapping dirt and other particles larger  than 10 to 25 microns in size. One micron is equal to 0.000039 in NOTE: A person can only see objects that are 40 microns or larger in  size. A human hair is about 50 microns in diameter Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Remotely Mounted Air Filters and Ducts  Air cleaner and duct  design depend on a number of factors such as the size, shape, and  location of other engine compartment components, as well as the  vehicle body structure Port fuel­injection systems  generally use a horizontally  mounted throttle body.  Some systems also have a mass airflow (MAF) sensor between throttle body and air cleaner.  Remote air cleaners are  connected by composite  ducting. The ducting may be rigid or flexible Figure 22–3 Most air filter housings are located on the side of the engine compartment and use flexible rubber hose to direct airflow to the throttle body of the engine Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Always Check the Air Filter Always inspect the air filter and the air intake system carefully during routine service Debris or objects deposited by animals can cause a restriction to the airflow and can reduce engine performance Figure 22–4 (a) Note the discovery as the air filter housing was opened during service on a Pontiac Bonneville The nuts were obviously deposited by squirrels (or some other animal) Figure 22–4 (b) Not only was the housing filled with nuts, but also this air filter was extremely dirty, indicating that this vehicle had not been serviced for a long time Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 10 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Exhaust gas temperature will vary according to power produced by  the engine. The manifold must operate at both engine idle and  continuous full power. Under full­power conditions, the exhaust  manifold will become red­hot, causing a great deal of expansion At idle, the exhaust manifold is just warm, causing little expansion After casting, the manifold may be annealed. Annealing is a heat­ treating process that takes out the brittle hardening of the casting to  reduce the chance of cracking from the temperature changes.  NOTE: Temperature of an exhaust manifold can exceed 1500°F (815°C) During vehicle operation, manifold temperatures usually reach the  high­temperature extremes. Most exhaust manifolds are made from  cast iron to withstand extreme and rapid temperature changes. The  manifold is bolted to the head in a way that will allow expansion  and contraction.  Continued 28 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The exhaust manifold is designed to allow the free flow of exhaust  gas. Some manifolds use internal cast­rib deflectors or dividers to  guide the exhaust gases toward the outlet as smoothly as possible Some are designed to go above the spark plug, others below. The  spark plug and ignition wires are usually shielded Many exhaust manifolds have heat shields as seen here.  Figure 22–14 This exhaust manifold has a heat shield to help retain the heat and reduce exhaust emissions Exhaust systems are  especially designed for the engine­chassis  combination.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 29 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The exhaust system length, pipe size, and silencer are designed,  where possible, to make use of the tuning effect of the gas column  resonating within the exhaust system. Tuning occurs when the  exhaust pulses from the cylinders are emptied into the manifold  between the pulses of other cylinders.  Figure 22–15 Many exhaust manifolds are constructed of pressed steel and are free flowing to improve engine performance Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 30 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 22–16 A crack in an exhaust manifold is often not this visible A crack in the exhaust manifold upstream of the oxygen sensor can fool the sensor and affect engine operation Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 31 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 How Can a Cracked Exhaust Manifold Affect Engine Performance? A crack in an exhaust manifold will not only allow exhaust gases to escape and cause noise but the crack can also allow air to enter the exhaust manifold Exhaust flows from the cylinders as individual puffs or pressure pulses Behind each of these pressure pulses, a low pressure (below atmospheric pressure) is created Outside air at atmospheric pressure is then drawn into the exhaust manifold through the crack This outside air contains 21% oxygen and is measured by the oxygen sensor (O2S) The air passing the O2S signals the engine computer that the engine is operating too lean (excess oxygen) and the computer, not knowing that the lean indicator is false, adds additional fuel to the engine The result is that the engine will be operating richer (more fuel than normal) and spark plugs could become fouled, causing poor operation Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 32 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 EXHAUST MANIFOLD GASKETS Exhaust heat will expand the manifold more than it will expand  the head. It causes the exhaust manifold to slide on the sealing  surface of the head. The heat also causes thermal stress.  When the manifold is removed from the engine for service, the  stress is relieved and this may cause the manifold to warp slightly.  Exhaust manifold gaskets are included in gasket sets to seal  slightly warped exhaust manifolds. These gaskets should be used,  even if the engine did not originally use exhaust manifold gaskets.  When a perforated core manifold gasket has facing on one side  only, put the facing side against the head and put the manifold  against the perforated metal core. The manifold can slide on the  metal of the gasket as it slid on the sealing surface of the head.  33 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Gaskets are used on new engines with tubing­ or header­type  exhaust manifolds, and often include heat shields to keep exhaust  heat from the spark plugs and cables.  They may have several layers of steel for high­temperature sealing,  spot­welded together. Some are embossed for special sealing.  Many new engines do not use gaskets with cast exhaust manifolds.  The flat surface of the new cast­iron exhaust manifold fits tightly against the flat surface of the new head Figure 22–17 Typical exhaust manifold gaskets Note how they are laminated to allow the exhaust manifold to expand and contract due to heating and cooling Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 34 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Correct Tools Save Time When cast-iron exhaust manifolds are removed, the stresses built up in the manifolds often cause the manifolds to twist or bend This distortion even occurs when the exhaust manifolds have been allowed to cool before removal Attempting to reinstall distorted exhaust manifolds is often a timeconsuming and frustrating exercise However, special spreading jacks can be used to force the manifold back into position so that the fasteners can be lined up with the cylinder head Figure 22–18 An exhaust manifold spreader tool is a tool that is absolutely necessary to use when reinstalling exhaust manifolds When they are removed from the engine, they tend to warp slightly even though the engine is allowed to cool before being removed The spreader tool allows the tech to line up the bolt holes without doing any harm to the manifold Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 35 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 MUFFLERS When the exhaust valve opens, it rapidly releases high­pressure  gas sending a strong air pressure wave through the atmosphere,  which produces a sound we call an explosion. It is the same sound  produced when the high­pressure gases from burned gunpowder  are released from a gun.  In an engine, the pulses are released one after another. The  explosions come so fast that they blend together in a steady roar.  Sound is air vibration. When vibrations are large, the sound is loud.  The muffler catches the large bursts of high­pressure exhaust gas  from the cylinder, smoothing out the pressure pulses and allowing  them to be released at an even and constant rate. It does this through  the use of perforated tubes within the muffler chamber. The gases  are released to the tailpipe, silencing engine exhaust noise.   36 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Sometimes resonators are used in the exhaust system and the  catalytic converter also acts as a muffler. They provide additional  expansion space at critical points to smooth out exhaust gas flow.  Figure 22–19 Exhaust gases expand and cool as they travel through the passages in the muffler Most mufflers have a larger inlet diameter than outlet diameter. As  the exhaust enters the muffler, it expands and cools. The cooler  exhaust is more dense and occupies less volume. The diameter of  the outlet of the muffler and the diameter of the tailpipe can be  reduced with no decrease in efficiency.  The muffler and tailpipe are supported with brackets called  hangers, made of rubberized fabric with metal ends that hold the  muffler and tailpipe in position so that they do not touch any metal  37 part.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition ©©2008 2009Pearson PearsonEducation, Education,Inc Inc By James D Halderman Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Why is There a Hole in My Muffler? Many mufflers are equipped with a small hole in the lower rear part to drain accumulated water About gallon of water is produced in the form of steam for each gallon of gasoline burned The water vapor often condenses on the cooler surfaces of the exhaust system unless the vehicle has been driven long enough to fully warm the muffler above the boiling point of water (212°F [100°C]) Figure 22–20 A hole in the muffler allows condensed water to escape Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 38 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 More Airflow = More Power One of the most popular high-performance modifications is to replace the factory exhaust system with a low-restriction design and to replace the original air filter and air filter housing with a low-restriction unit The installation of an aftermarket air filter not only increases power, but also increases air induction noise, which many drivers prefer The filter housing, however, may not be able to effectively prevent water from being drawn into the engine if the vehicle is traveling through deep water Almost every modification that increases performance has a negative effect on some other part of the vehicle, or else the manufacturer would include the change at the factory Figure 22–21 A high-performance aftermarket air filter often can increase airflow into the engine for more power Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 39 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY All air entering an engine must be filtered Engines that use throttle­body injection units are equipped  with intake manifolds that keep the airflow speed through the  manifold at 50 to 300 feet per second Most intake manifolds have an EGR valve that regulates the  amount of recirculated exhaust that enters the engine to reduce  NOx emissions Exhaust manifolds can be made from cast iron or stainless  steel 40 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) The exhaust system also contains a catalytic converter,  exhaust pipes, and muffler. The entire exhaust system is  supported by rubber hangers that isolate the noise and  vibration of the exhaust from the rest of the vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 41 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 42 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458