OBJECTIVES <ul><li>After studying Chapter 6, the reader should be able to: </li></ul><ul><ul><ul><li>Prepare for ASE Engine Performance (A8) certification test content area “C” (Air Induction and Exhaust Systems Diagnosis and Repair). </li></ul></ul></ul><ul><ul><ul><li>Discuss the purpose and function of intake manifolds. </li></ul></ul></ul><ul><ul><ul><li>Explain the differences between throttle fuel-injection manifolds and port fuel-injection manifolds. </li></ul></ul></ul><ul><ul><ul><li>Describe the operation of the exhaust gas recirculation system in the intake manifold. </li></ul></ul></ul>(Continued)
<ul><ul><ul><li>List the materials used in exhaust manifolds and exhaust systems. </li></ul></ul></ul><ul><ul><ul><li>Discuss the need for intake manifold heating. </li></ul></ul></ul>
The three main jobs of the air cleaner and filter are to: <ul><li>Clean the air before it is mixed with fuel </li></ul><ul><li>Silence intake noise </li></ul><ul><li>Act as a flame arrester in case of a backfire </li></ul>(Continued)
Figure 6-1 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.
AIR INTAKE FILTRATION <ul><li>The automotive engine uses about 9000 gallons (34,069 liters) of air for every gallon of gasoline burned at an air-fuel ratio of 14.7 to 1. Without proper filtering of the air before intake, dust and dirt in the air seriously damage engine parts and shorten engine life. </li></ul>(Continued)
<ul><li>While abrasive particles can cause wear anyplace inside the engine where two surfaces move against each other, they first attack piston rings and cylinder walls. </li></ul>
THE AIR CLEANER <ul><li>The air cleaner housing is located on top of the throttle-body injection (TBI) unit or is positioned to one side of the engine. </li></ul>(Continued)
<ul><li>Filter Replacement </li></ul><ul><ul><li>Manufacturers recommend replacing the air filter element at periodic intervals, usually listed in terms of distance driven or months of service. The distance and time intervals are based on so-called normal driving. More frequent air filter replacement is necessary when the vehicle is driven under dusty, dirty, or other severe conditions. </li></ul></ul>(Continued)
Figure 6-2 Dust and dirt in the air are trapped in the air filter so they do not enter the engine.
Air Filter Elements <ul><li>The paper air filter element is the most common type of filter. It is made of a 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. </li></ul>(Continued)
<ul><li>Most air 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. and is a millionth of a meter. </li></ul><ul><li>NOTE: A person can only see objects that are 40 microns or larger in size. A human hair is about 50 microns in diameter. </li></ul>
Remotely Mounted Air Filters and Ducts <ul><li>Port fuel-injection systems generally use a horizontally mounted throttle body. Some systems also have a mass airflow (MAF) sensor between the throttle body and the air cleaner. </li></ul>(Continued)
<ul><li>Air temperature control is needed under these conditions to help keep the gas and air mixture combined to improve driveability and reduce exhaust emissions. </li></ul><ul><li>An air control valve or damper permits the air intake of: </li></ul><ul><ul><li>Heated air from the heat stove </li></ul></ul><ul><ul><li>Cooler air from the snorkel or cold-air duct </li></ul></ul><ul><ul><li>A combination of both </li></ul></ul>(Continued)
<ul><li>While the air control valve generally is located in the air cleaner snorkel, it may be in the air intake housing or ducting of remote air cleaners. </li></ul><ul><li>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. </li></ul>(Continued)
<ul><li>What is the purpose of the odd-shaped tube attached to the inlet duct between the air filter and the throttle body. </li></ul><ul><li>The tube shape is designed to dampen out certain resonant frequencies that can occur at certain engine speeds. </li></ul>(Continued)
<ul><li>The length and shape of this tube are designed to absorb shock waves that are created in the air intake system and to provide a reservoir for the air that will then be released into the airstream during cycles of lower pressure. </li></ul>(Continued)
<ul><li>This resonance tube is often called a Helmholtz resonator, named for the discoverer of the relationship between shape and value of frequency Herman L. F. von Helmholtz (1821-1894) of the University of H ö i zsberg in East Prussia. The overall effect of these resonance tubes is to reduce the noise of the air entering the engine. </li></ul>(Continued)
Figure 6-3 Most air filter housings are located on the side of the engine compartment and use flexible rubber hose to direct the airflow into the throttle body of the engine.
Figure 6-4 Some port fuel-injected engines use heated air taken from around the exhaust manifold.
Figure 6-5 (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. A
Figure 6-5 (continued) (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. B
Figure 6-6 A resonance tube, called a Helmholtz resonator, is used on the intake duct between the air filter and the throttle body to reduce air intake noise during engine acceleration.
THROTTLE-BODY INJECTION INTAKE MANIFOLDS <ul><li>The intake manifold is also called the inlet manifold. </li></ul><ul><li>A throttle-body fuel-injector forces finely divided droplets of liquid fuel into the incoming air to form a combustible air-fuel mixture. </li></ul>(Continued)
<ul><li>These droplets start to evaporate as soon as they leave the throttle-body injector nozzles. The droplets stay in the charge as long as the charge flows at high velocities. At maximum horsepower, these velocities may reach 300 feet per second. </li></ul>(Continued)
<ul><li>Separation of the droplets from the charge as it passes through the manifold occurs when the velocity drops below 50 feet per second. Intake charge velocities at idle speeds are often below this value. When separation occurs - at low engine speeds - extra fuel must be supplied to the charge in order to have a combustible mixture reach the combustion chamber. </li></ul>(Continued)
<ul><li>Manifold sizes represent a compromise. They must have a cross-section large enough to allow charge flow for maximum power. The cross-section must be small enough that the flow velocities of the charge will be high enough to keep the fuel droplets in suspension. </li></ul><ul><li>Fuel separation leads to poor accelerator response. </li></ul>(Continued)
Figure 6-7 A typical throttle-body injection (TBI) unit. This TBI uses two injectors. Most V-6 and V-8 engines require two throttle-body injectors, whereas 4-cylinder engines use one injector.
Figure 6-8 Heavy fuel droplets separate as they flow around an abrupt bend in an intake manifold.
MANIFOLD HEAT <ul><li>Heat is required in the manifold so that liquid fuel in the charge will evaporate as the charge travels from the intake to the combustion chamber. When heat is taken from the air in the intake charge by fuel evaporation, the charge temperature is lowered. </li></ul>(Continued)
<ul><li>Additional heat is supplied to the charge when it is needed. The added heat gives good fuel evaporation for smooth engine operation when the engine is cold. An intake charge temperature range of about 100 degrees to 130 degrees F (38 degrees to 55 degrees C ) is necessary to give good fuel evaporation. </li></ul>(Continued)
<ul><li>In some engines, heat is supplied to the intake manifold during low-temperature operation by a system known as a thermostatic air cleaner (TAC) . </li></ul><ul><li>A thermostatically controlled bimetallic switch adjusts a vacuum motor. It controls the amount of heated air used. </li></ul>(Continued)
<ul><li>Another thermostatic valve, called a heat riser, directs exhaust gases against the underside of the intake manifold. On V-type engines, exhaust gas is routed through a passage called an exhaust heat crossover. Part of the exhaust gas is directed against the intake manifold directly under the throttle body. </li></ul>(Continued)
Figure 6-9 Heat radiating from the exhaust manifold heats the intake air on engines equipped with a carburetor or throttle-body-type fuel injection.
Figure 6-10 The heat crossover passage allows exhaust gases to flow under and heat the manifold to improve cold engine operation.
PORT FUEL-INJECTION INTAKE MANIFOLDS <ul><li>The size and shape of port fuel-injected engine intake manifolds can be optimized because the only thing in the manifold is air. The fuel injection is located in the intake manifold about 3 to 4 inches (70 to 100 mm) from the intake valve. Therefore, the runner length and shape are designed for tuning only. </li></ul>(Continued)
<ul><li>Long runners build low-RPM torque. </li></ul><ul><li>Shorter runners provide maximum high-RPM power. </li></ul>(Continued)
<ul><li>Some engines with four valve heads utilize a dual or variable intake runner design. At lower engine speeds, long intake runners provide low-speed torque. At higher engine speeds, shorter intake runners are opened by means of a computer-controlled valve to increase high-speed power. </li></ul>(Continued)
Figure 6-11 The graph shows the effect of sonic tuning of the intake manifold runners. The longer runners increase the torque peak and move it to a lower RPM. The .600-mm-long intake runner is about 24 inches long.
Figure 6-12 Airflow through the large diameter upper intake manifold is distributed to smaller diameter individual runners in the lower manifold in this two-piece manifold design.
PLASTIC INTAKE MANIFOLDS <ul><li>Most thermoplastic intake manifolds are molded from fiberglass-reinforced nylon. The plastic manifolds can be cast or injection molded. Some manifolds are molded in two parts and bonded together. Plastic intake manifolds are lighter than aluminum manifolds and can better insulate engine heat from the fuel injectors. </li></ul>(Continued)
Figure 6-13 This DaimlerChrysler V-6 engine uses an intake manifold tuning valve that is controlled by the engine computer to switch where the air is directed through the passages of the manifold to allow the engine to produce the most torque possible at every engine speed.
EXHAUST GAS RECIRCULATION PASSAGES <ul><li>To reduce the emission of oxides of nitrogen (NOx), engines have been equipped with exhaust gas recirculation (EGR) valves. </li></ul>(Continued)
<ul><li>The EGR valve opens at speeds above idle on a warm engine. When open, the valve allows a small portion of the exhaust gas (5% to 10%) to enter the intake manifold. Here, the exhaust gas mixes with and takes the place of some of the intake charge. This leaves less room for the intake charge to enter the combustion chamber. </li></ul>(Continued)
<ul><li>The recirculated exhaust gas is inert and does not enter into the combustion process. The result is a lower peak combustion temperature. As the combustion temperature is lowered, the production of oxides of nitrogen is also reduced. </li></ul>(Continued)
<ul><li>The exhaust gases are more effective in reducing oxide of nitrogen (NOX) emissions if the exhaust is cooled before being drawn into the cylinders. This tube is often designed to be long so that the exhaust gas is cooled before it enters the EGR valve. </li></ul>(Continued)
Figure 6-14 The exhaust gas recirculation system is more efficient at controlling NOX emissions if the exhaust gases are cooled. A long metal tube between the exhaust manifold and the intake manifold allows the exhaust gases to cool before entering the engine.
UPPER AND LOWER INTAKE MANIFOLDS <ul><li>Many intake manifolds are constructed in two parts. </li></ul><ul><li>A lower section, usually called the plenum, attaches to the cylinder heads and includes passages from the intake ports. </li></ul>(Continued)
<ul><li>An upper manifold connects to the lower unit and includes the long passages needed to help provide the ram effect that helps the engine deliver maximum torque at low engine speeds. The throttle body attaches to the upper intake. </li></ul>
EXHAUST MANIFOLD DESIGN <ul><li>The exhaust manifold is designed to collect high-temperature spent gases from the head exhaust ports. </li></ul>(Continued)
<ul><li>The hot gases are sent to an exhaust pipe, then to a catalytic converter, to the muffler, to a resonator, and on to the tailpipe, where they are vented to the atmosphere. This must be done with the least possible amount of restriction or back pressure while keeping the exhaust noise at a minimum. </li></ul>(Continued)
<ul><li>Some exhaust manifolds are designed to go above the spark plug, whereas others are designed to go below. The spark plug and carefully routed ignition wires are usually shielded from the exhaust heat with sheet-metal deflectors. </li></ul>(Continued)
<ul><li>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. </li></ul>(Continued)
Figure 6-15 The exhaust gases are pushed out of the cylinder by the piston on the exhaust stroke.
Figure 6-16 Example of heat deflector shields placed between the exhaust manifold and the spark plugs and plug wires. Even high-temperature-resistant silicone jacket spark plug wires cannot withstand the high exhaust manifold temperatures.
Figure 6-17 Original-equipment (OE) type of tubular steel exhaust manifold.
Figure 6-18 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.
EXHAUST MANIFOLD GASKETS <ul><li>Exhaust heat will expand the manifold more than it will expand the head. </li></ul><ul><li>When a perforated core exhaust 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 just as it slid on the sealing surface of the head. </li></ul>(Continued)
Figure 6-19 Typical exhaust manifold gaskets. Note how they are laminated to allow the exhaust manifold to expand and contract due to heating and cooling.
The Correct Tools Save Time <ul><li>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 time-consuming and frustrating exercise. </li></ul>(Continued)
<ul><li>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. </li></ul>(Continued)
Figure 6-20 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 technician to line up the bolt holes without doing any harm to the manifold.
MUFFLERS <ul><li>When the exhaust valve opens, it rapidly releases high-pressure gas. This sends a strong air pressure wave through the atmosphere, which produces a sound we call an explosion. </li></ul>(Continued)
<ul><li>Sound is air vibration. When the vibrations are large, the sound is loud. The muffler catches the large bursts of high-pressure exhaust gas from the cylinder, smoothing out the pressure pulses and allowing them to be released at an even and constant rate. </li></ul>(Continued)
Figure 6-21 Exhaust gases expand and cool as they travel through the passages in the muffler.
HIGH PERFORMANCE TIP <ul><li>Many mufflers are equipped with a small hole in the lower rear part to drain accumulated water. About 1 gallon of water is produced in the form of steam for each gallon of gasoline burned. </li></ul>(Continued)
<ul><li>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 degrees F [100 degrees C ]). </li></ul>(Continued)
<ul><li>More Airflow = More Power </li></ul><ul><li>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 </li></ul>(Continued)
<ul><li>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. </li></ul>(Continued)
Figure 6-22 A hole in the muffler allows condensed water to escape.
Figure 6-23 A high-performance aftermarket air filter often can increase the airflow into the engine for more power.