Halderman ch024 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

INTAKE AND EXHAUST SYSTEMS

24

24 INTAKE AND EXHAUST SYSTEMS



ObjectivesObjectives

• The student 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 air system components.




ObjectivesObjectives

• The student should be able to:– Explain the differences between throttle-

body fuel-injection manifolds and port fuel-injection manifolds.

– List the materials used in exhaust manifolds and exhaust systems.

– Describe the purpose and function of the exhaust system components.




AIR INTAKE FILTRATIONAIR INTAKE FILTRATION




Air Intake FiltrationAir Intake Filtration

• Need for Air Filtering– Gasoline must be mixed with air for

combustion– Air movement into engine occurs due to

vacuum created in engine




Figure 24-1 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.





• Need for Air Filtering– Dirt in air cannot reach engine– Air filter and cleaner remove contaminants





• Need for Air Filtering– Three jobs of air cleaner and filter

• Clean air before it is mixed with fuel• Silence intake noise





• Need for Air Filtering– Three jobs of air cleaner and filter

• Act as flame arrester in case of backfire





• Need for Air Filtering– Automotive engine uses 9,000 gallons

(34,000 liters) of air per gallon of gasoline in air-fuel ratio of 14.7:1 by weight

– Abrasive particles cause wear inside engine





• Need for Air Filtering– Filter is in air cleaner housing

• Stamped steel• Composite (usually nylon reinforced plastic)





• Air Filter Elements– Paper air filter element most common– Paper stock contains tiny passages in fibers





• Air Filter Elements– Airflow passes through several fiber

surfaces– Fiber surfaces trap microscopic particles





• Air Filter Elements– Most air filters trap particles larger than 10

to 25 microns– NOTE: A person can see objects 40 microns

or larger in size. Human hair is about 50 microns in diameter.




Figure 24-2 Dust and dirt in the air are trapped in the air filter so they do not enter the engine.





• Filter Replacement– Manufacturers recommend cleaning or

replacing air filter elements at periodic intervals

– Replace filter before it becomes too dirty to be effective





• Remotely Mounted Air Filters and Ducts– Air cleaner and duct design depend on size,

shape, location, and vehicle body construction

– Port fuel-injection systems generally use horizontally mounted throttle body





• Remotely Mounted Air Filters and Ducts– Some systems have mass airflow (MAF)

sensor between throttle body and air cleaner

– Design issues make it is more efficient to use remote air cleaner placement




Figure 24-3 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.





• Remotely Mounted Air Filters and Ducts– Turbocharged engines require remote air

filter placement– Air filter connects to air inlet elbow on

turbocharger





• Remotely Mounted Air Filters and Ducts– Heat generated by turbocharger requires

remote placement of air filter– Air filter connected to turbocharger by

composite ducting





• Air Filter Restriction Indicator– Connections must be airtight– Vehicles driven in dusty conditions often

have air filter restriction indicators





• Air Filter Restriction Indicator– Device warns if filter is restricted and

needs replacement– Device operates by detecting drop in air

pressure





• Air Filter Restriction Indicator– Typical calibration of indicator

• 15 to 20 in. of water (in. H2O) for gasoline engines





• Air Filter Restriction Indicator– Typical calibration of indicator

• 20 to 30 in. of water (in. H2O) for diesel engines





• Air Filter Restriction Indicator– Unit of inches of water measures difference

in air pressure before and after air filter





• Air Filter Restriction Indicator– 28 in. of water equals pound per square

inch (PSI)– Some air filter restriction indicators use

electrical switch to light dash-mounted warning light

?




Figure 24-4 A typical air filter restriction indicator used on a General Motors truck engine. The indicator turns red when it detects enough restriction to require a filter replacement.




Figure 24-5 (a) Note the discovery as the air filter housing was opened during service on a Pontiac. The nuts were obviously deposited by squirrels (or some other animal).




Figure 24-5 (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.




Figure 24-6 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 THROTTLE-BODY INJECTION INTAKE INJECTION INTAKE

MANIFOLDSMANIFOLDS




Throttle-Body Injection Intake Throttle-Body Injection Intake ManifoldsManifolds

• Terminology– Intake manifold also called inlet manifold– Smooth engine operation occurs only when

each combustion chamber produces same pressure





• Terminology– All cylinders must receive exactly same

quality and quantity of charge– Charges must have same physical

properties and air-fuel mixture





• Terminology– Throttle-body fuel injector forces tiny

droplets of liquid fuel into incoming air to form combustible air-fuel mixture




Figure 24-7 A throttle-body injection (TBI) unit used on a GM V-6 engine.





• Intake Air Speeds– Droplets begin to evaporate when they

leave throttle-body injector nozzles– Droplets stay in the charge as long as

charge flows at high velocities





• Intake Air Speeds– At maximum engine speed, velocity may

reach 330 ft per second– Separation of droplets from charge as it

passes through manifold occurs when velocity drops below 50 ft per second





• Intake Air Speeds– At idle speed, intake charge velocities may

drop below 50 ft per second





• Intake Air Speeds– Manifold sizes and shapes represent

compromise• Cross section large enough for maximum

power






compromise• Cross section small enough so equal

mixtures reach each cylinder






compromise• Racing manifolds must be large enough to

reach maximum horsepower






compromise• Large size allows charge to move slowly






compromise• Fuel separation occurs at low engine speeds






compromise• Fuel separation leads to poor accelerator

response




Figure 24-8 Heavy fuel droplets separate as they flow around an abrupt bend in an intake manifold.





• Intake Air Speeds– Standard passenger vehicle engines

designed for economy under light load, partial-throttle operation





• Intake Air Speeds– Manifolds have smaller cross-sectional area

than racing engines– Small sizes keep flow velocities high

through normal operating speeds




PORT FUEL-INJECTIONPORT FUEL-INJECTIONINTAKE MANIFOLDSINTAKE MANIFOLDS




Port Fuel-Injection Intake ManifoldsPort Fuel-Injection Intake Manifolds

• Terminology– Size and shape of port fuel-injected engine

intake manifolds can be optimized because only air is in the manifold





• Terminology– Fuel injector located in intake manifold 3 to

4 in (70 to 100 mm) from intake valve





• Terminology– Runner length and shape designed for

tuning only– No need to keep air-fuel mixture

homogenized





• Terminology– Intake manifolds tuned to improve

performance• Long runners build low-RPM torque





• Terminology– Intake manifolds tuned to improve

performance• Shorter runners provide maximum high-RPM

power




Figure 24-9 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 intake runner is about 24 in. long.




Figure 24-10 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.





• Variable Intakes– Some engines with four valve heads use

dual or variable intake runners– At low engine speeds, long intake runners

give low-speed torque





• Variable Intakes– At high engine speeds, shorter intake

runners increase high-speed power– Many intake manifolds have both long and

short intake runners– Valves that control air flow are computer

controlled




Figure 24-11 The air flowing into the engine can be directed through long or short runners for best performance and fuel economy.





• Plastic Intake Manifolds– Most intake manifolds are made from

thermoplastic molded – Some manifolds are molded in two parts

and bonded together





• Plastic Intake Manifolds– Plastic intake manifolds have smoother

interior surfaces for greater airflow




Figure 24-12 Many plastic intake manifolds are constructed using many parts glued together to form complex passages for airflow into the engine.





• Upper and Lower Intake Manifolds– Many intake manifolds are constructed in

two parts• Lower section attaches to cylinder heads

and have passages from intake ports






two parts• Upper manifold, called plenum, connects to

lower unit






two parts• Upper manifold includes long passages






two parts• Throttle body attaches to upper intake





• Upper and Lower Intake Manifolds– Two-part intake manifolds allow easier

manufacturing and assembly– Two-part intake manifold create additional

locations for leaks





• Upper and Lower Intake Manifolds– Leak in lower intake manifold can affect

operation of engine– Leak in upper intake manifold results in

vacuum leak only




EXHAUST GASEXHAUST GASRECIRCULATION RECIRCULATION

PASSAGEPASSAGE




Exhaust Gas Recirculation PassagesExhaust Gas Recirculation Passages

• Purpose and Function– To reduce emission of oxides of nitrogen

(NOx), engines have exhaust gas recirculation (EGR) valves





• Purpose and Function– Most EGR valves are mounted on intake

manifold– Some newer engines do not require EGR

system





• Purpose and Function– EGR valve opens at speeds above idle– EGR valve allows small portion of exhaust

gas (5% to 10%) to enter intake manifold





• Purpose and Function– EGR system interconnects exhaust and

intake manifolds– EGR valve controls gas flow through

passages• On V-type engines, intake manifold

crossover provides exhaust gas





• Purpose and Function– EGR valve controls gas flow through

passages• On inline-type engines, external tube carries

exhaust gas to EGR valve





• Exhaust Gas Coolers– Exhaust gases are more effective in

reducing NOx emissions if exhaust is cooled before entering cylinders

– Tube is long so exhaust gas is cooled before entering EGR valve




Figure 24-13 A typical long exhaust gas line used to cool the exhaust gases before being recirculated back into the intake manifold.




EXHAUST MANIFOLDSEXHAUST MANIFOLDS




Exhaust ManifoldsExhaust Manifolds

• Purpose and Function– Exhaust manifold collects high-temperature

spend gases from head exhaust ports and connects them to exhaust system




Figure 24-14 The exhaust gases are pushed out of the cylinder by the piston on the exhaust stroke.





• Purpose and Function– Hot gases are sent to exhaust pipe,

catalytic converter, muffler, resonator, and tailpipe





• Purpose and Function– Exhaust system designed to meet these

needs• Provide least possible restriction or

backpressure





• Purpose and Function– Exhaust system designed to meet these

needs• Keep exhaust noise to minimum





• Purpose and Function– Exhaust gas temperature varies





• Purpose and Function– Manifold must operate at engine idle and

full power





• Purpose and Function– Temperature of exhaust manifold can

exceed 1,500°F (815°C)





• Construction– Most exhaust manifolds are made from the

following• Cast iron• Steel tubing





• Construction– Manifold temperature usually reaches high-

temperature extremes– Manifold is bolted to head to allow

expansion and contraction





• Construction– Many manifolds have heat shields to

protect spark plug wires and improve emissions




Figure 24-16 Many exhaust manifolds are constructed of steel tubing and are free flowing to improve engine performance.





• Exhaust Manifold Gaskets– Exhaust heat expands manifold more than

head– Heat causes exhaust manifold to slide on

sealing surface of head





• Exhaust Manifold Gaskets– Heat causes thermal stress– Removing manifold for service may cause

manifold to warp





• Exhaust Manifold Gaskets– Manifold gaskets seal slightly warped

manifolds– If gasket has facing on one side only, put

facing against head





• Exhaust Manifold Gaskets– Gaskets are used on new engines with

tubing- or header-type exhaust manifolds– Gaskets may have several layers of steel

for high-temperature sealing

?




Figure 24-18 Typical exhaust manifold gaskets. Note how they are laminated to allow the exhaust manifold to expand and contract due to heating and cooling.




Figure 24-19 An exhaust manifold spreader tool is absolutely necessary when reinstalling exhaust manifolds. When they are removed from the engine, the manifolds 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 harming the manifold.





• Exhaust Manifold Gaskets– Many new engines do not use gaskets with

cast exhaust manifolds




MUFFLERSMUFFLERS




MufflersMufflers

• Purpose and Function– When the exhaust valve opens, it releases

a strong air pressure– The air pressure produces an explosion




MufflersMufflers

• Purpose and Function– Muffler catches bursts of high-pressure

exhaust in perforated tubes – Smoothing out bursts of pressure quiets

exhaust




Figure 24-20 Exhaust gases expand and cool as they travel through passages in the muffler.




MufflersMufflers

• Construction– Most mufflers have larger inlet diameter

than outlet diameter– Cooler exhaust is denser and requires less

volume




MufflersMufflers

• Construction– Resonators and catalytic converters also

functions as mufflers– Tailpipe releases exhaust gases away from

vehicle




MufflersMufflers

• Construction– Muffler and tailpipe are supported by

hangers– Hangers isolate exhaust noise from vehicle




MufflersMufflers

• Construction– Types of exhaust system hangers

• Rubberized fabric with metal ends• Rubber materials that look like rubber bands

?




Figure 24-21 A hole in the muffler allows condensed water to escape.




Figure 24-22 A high-performance aftermarket air filter often can increase airflow into the engine for more power.