At 43 Ch 6 Intake and Exhaust

8/7/2019 At 43 Ch 6 Intake and Exhaust

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Automotive Fuel and Emissions Control Systems, 2/eBy James D. Halderman and Jim Linder

2009 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES

After studying Chapter 6, the reader should be able to:1. Describe how the proper grade ofgasoline affects

engine performance.

2. List gasoline purchasing hints.

3. Discuss how volatility affects driveability.

4. Explain how oxygenated fuels can reduce CO

exhaust emissions.

5. Discuss the advantages and disadvantages ofvarious alternative fuels.


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AIR INTAKE FILTRATION

Gasoline must be mixedwith air to form a

combustible mixture.

Air movement into an

engine occurs due to low

pressure (vacuum) being

created in the engine.

FIGURE 6-1 Downward movement ofthepiston 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.


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FIGURE 6-2 Dust and dirt in the air are trapped in

the airfilter so they do not enter the engine.


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Filter Replacement

Air Filter Elements

Remotely Mounted Air

Filters and Ducts

FIGURE 6-3 Most airfilter

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.


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ALWAYS CHECK THE AIR FILTER

FIGURE 6-4 (a) Note the discovery as the airfilter housing was opened during service

on a Pontiac Bonneville. The nuts were obviously deposited by squirrels (or some

other animal). (b) Not only was the housing filled with nuts, but also this airfilter was

extremely dirty, indicating that this vehicle had not been serviced for a long time.


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ENGINE AIR TEMPERATURE REQUIREMENTS

Some form of thermostatic control has been usedon vehicles equipped with a throttle-body fuel

injection to control intake air temperature for

improved driveability.

An air control valve or damper permits the air intakeof:

Heated airfrom the heat stove

Cooler airfrom the snorkel or cold-air duct

A combination ofboth


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WHAT DOES THIS TUBE DO?

FIGURE 6-5 A resonance tube, called a Helmholtz resonator, is used on the intake

duct between the airfilter and the throttle body to reduce air intake noise during

engine acceleration.


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THROTTLE-BODY INJECTION INTAKE

MANIFOLDS

Athrottle-body

fuel injector

forces finely divided

droplets of liquid fuel into

the incoming air to form a

combustible airfuel

mixture.

FIGURE 6-6 A throttle-body injection (TBI)

unit used on a GM V-6 engine.


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THROTTLE-BODY INJECTION INTAKE

MANIFOLDS

FIGURE 6-7 Heavy fuel droplets separate as they

flow around an abrupt bend in an intake manifold.


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PORT FUEL-INJECTION INTAKE MANIFOLDS

The size and shape ofport fuel-injected engineintake 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 intakevalve.

Therefore, the runner length and shape are

designed for tuning only.


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FIGURE 6-8 The graph shows the effect ofsonic 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.


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FIGURE 6-9 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.


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VARIABLE INTAKES

Many intake mani

folds aredesigned to provide both

short runners, best for

higher engine speed power,

and longer runners, best for

lower engine speed torque.

FIGURE 6-10 The airflowing into the

engine can be directed through long or

short runners for best performance and

fuel economy.


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PLASTIC INTAKE MANIFOLDS

Plastic intake mani

foldshave smoother interior

surfaces than do other

types ofmanifolds,

resulting in greater airflow.

FIGURE 6-11 Many plastic intake

manifolds are constructed using many

parts glued together to form complex

passages for airflow into the engine.


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PLASTIC INTAKE MANIFOLDS

FIGURE 6-12 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.


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UPPER AND LOWER INTAKE MANIFOLDS

Many intake manifolds are constructed in two parts. A lower section, usually called the plenum, attaches to

the cylinder heads and includes passages from the intake

ports.

A

n upper manifold connects to the lower unit and includesthe 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.


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EXHAUST MANIFOLD DESIGN

The exhaust mani

fold isdesigned to collect high-

temperature spent gases

from the head exhaust

ports.

FIGURE 6-13 The exhaust gases are

pushed out of the cylinder by the piston on

the exhaust stroke.


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EXHAUST MANIFOLD DESIGN

FIGURE 6-14 This exhaust manifold has a

heat shield to help retain the heat and help

reduce exhaust emissions.

FIGURE 6-15 Many exhaust manifolds are

constructed ofpressed steel and are free

flowing to improve engine performance.


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HOW CAN A CRACKED EXHAUST MANIFOLD

AFFECT ENGINE PERFORMANCE?

FIGURE 6-16A 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.


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EXHAUST MANIFOLD GASKETS

Gaskets are used on newengines with tubing- or

header-type exhaust

manifolds.

The gaskets often include

heat shields to keepexhaust heat from the spark

plugs and spark plug

cables.

They may have severallayers ofsteel for high-

temperature sealing.

FIGURE 6-17 Typical exhaust manifoldgaskets. Note how they are laminated to

allow the exhaust manifold to expand and

contract due to heating and cooling.


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THE CORRECT TOOLS SAVE TIME

FIGURE 6-18 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 technician to line up the bolt holes without doing

any harm to the manifold.


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MUFFLERS

Sound is air vibration. When the vibrations are large, the sound is loud.

The muffler catches the large bursts ofhigh-pressure

exhaust gas from the cylinder, smoothing out the pressure

pulses and allowing them to be released at an even and

constant rate.

FIGURE 6-19 Exhaust gases expand and cool as they travel through the passages in the muffler.


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WHY IS THERE A HOLE IN MY MUFFLER?

FIGURE 6-20A hole in the muffler allows condensed water to escape.


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MORE AIRFLOW MORE POWER

FIGURE 6-21 A high-performance aftermarket airfilter often can increase airflow

into the engine for more power.


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SUMMARY

1. All air entering an engine must be filtered.

2. Engines that use throttle-body injection units are equippedwith intake manifolds that keep the airflow speed throughthe manifold at 50 to 300 feet per second.

3. Most intake manifolds have an EGR valve that regulates

the amount of recirculated exhaust that enters the engineto reduce NOX emissions.

4. Exhaust manifolds can be made from cast iron or stainlesssteel.

5. The exhaust system also contains a catalytic converter,

exhaust pipes, and muffler. The entire exhaust system issupported by rubber hangers that isolate the noise andvibration of the exhaust from the rest of the vehicle.

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At 43 Ch 6 Intake and Exhaust