objectives

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 of gasoline 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 of

various alternative fuels.



AIR INTAKE FILTRATION

• Gasoline must be mixed with 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 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.




FIGURE 6-2 Dust and dirt in the air are trapped in the air filter so they do not enter the engine.




• Filter Replacement• Air Filter Elements• Remotely Mounted Air

Filters and Ducts

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.



ALWAYS CHECK THE AIR FILTER

FIGURE 6-4 (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). (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.



ENGINE AIR TEMPERATURE REQUIREMENTS

• Some form of thermostatic control has been used on 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 intake of:– Heated air from the heat stove– Cooler air from the snorkel or cold-air duct– A combination of both



WHAT DOES THIS TUBE DO?

FIGURE 6-5 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• A throttle-body fuel injector

forces finely divided droplets of liquid fuel into the incoming air to form a combustible air–fuel mixture.

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



THROTTLE-BODY INJECTION INTAKE MANIFOLDS

FIGURE 6-7 Heavy fuel droplets separate as they flow around an abrupt bend in an intake manifold.



PORT FUEL-INJECTION INTAKE MANIFOLDS

• 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.




FIGURE 6-8 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 6-9 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.



VARIABLE INTAKES

• Many intake manifolds are designed to provide both short runners, best for higher engine speed power, and longer runners, best for lower engine speed torque.

FIGURE 6-10 The air flowing into the engine can be directed through long or short runners for best performance and fuel economy.



PLASTIC INTAKE MANIFOLDS

• Plastic intake manifolds have smoother interior surfaces than do other types of manifolds, 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.



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.



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.

– 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.



EXHAUST MANIFOLD DESIGN

• The exhaust manifold is designed 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.



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 of pressed steel and are free flowing to improve engine performance.



HOW CAN A CRACKED EXHAUST MANIFOLD AFFECT ENGINE PERFORMANCE?

FIGURE 6-16 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.



EXHAUST MANIFOLD GASKETS

• Gaskets are used on new engines with tubing- or header-type exhaust manifolds.

• The gaskets often include heat shields to keep exhaust heat from the spark plugs and spark plug cables.

• They may have several layers of steel for high-temperature sealing.

FIGURE 6-17 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

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.



MUFFLERS

• 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.

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



WHY IS THERE A HOLE IN MY MUFFLER?

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



MORE AIRFLOW MORE POWER

FIGURE 6-21 A high-performance aftermarket air filter often can increase airflow into the engine for more power.



SUMMARY

1. All air entering an engine must be filtered.2. Engines that use throttle-body injection units are equipped

with intake manifolds that keep the airflow speed through the 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 engine to reduce NOX emissions.

4. Exhaust manifolds can be made from cast iron or stainless steel.

5. 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.



REVIEW QUESTIONS

1. Why is it necessary to have intake charge velocities of about 50 feet per second?

2. Why can fuel-injected engines use larger (and longer) intake manifolds and still operate at low engine speed?

3. What is a tuned runner in an intake manifold?4. How does a muffler quiet exhaust noise?



CHAPTER QUIZ

1. Intake charge velocity has to be _____ to prevent fuel droplet separation.

a) 25 feet per secondb) 50 feet per secondc) 100 feet per secondd) 300 feet per second



CHAPTER QUIZ

2. The intake manifold of a port fuel-injected engine _____.

a) Uses a dual heat riserb) Contains a leaner air–fuel mixture than does the intake

manifold of a TBI systemc) Contains only fuel (gasoline)d) Contains only air



CHAPTER QUIZ

3. Why are the EGR gases cooled before entering the engine on some engines?

a) Cool exhaust gas is more effective at controlling NOX emissions

b) To help prevent the exhaust from slowing downc) To prevent damage to the intake valved) To prevent heating the air–fuel mixture in the cylinder



CHAPTER QUIZ

4. A heated air intake system is usually necessary for proper cold-engine driveability on _____.

a) Port fuel-injection systemsb) Throttle-body fuel-injection systemsc) Both a port-injected and throttle-body injected engined) Any fuel-injected engine



CHAPTER QUIZ

5. Air filters can remove particles and dirt as small as _____.

a) 5 to 10 micronsb) 10 to 25 micronsc) 30 to 40 micronsd) 40 to 50 microns



CHAPTER QUIZ

6. Why do many port fuel-injected engines use long intake manifold runners?

a) To reduce exhaust emissionsb) To heat the incoming airc) To increase high-RPM powerd) To increase low-RPM torque



CHAPTER QUIZ

7. Exhaust passages are included in some intake manifolds. Technician A says that the exhaust passages are used for exhaust gas recirculation (EGR) systems. Technician B says that the exhaust heat is used to warm the intake charge on some engines equipped with a throttle-body-type fuel-injection system. Which technician is correct?

a) Technician A onlyb) Technician B onlyc) Both Technicians A and Bd) Neither Technician A nor B



CHAPTER QUIZ

8. The lower portion of a two-part intake manifold is often called the _____.

a) Housingb) Lower partc) Plenumd) Vacuum chamber



CHAPTER QUIZ

9. Technician A says that a cracked exhaust manifold can affect engine operation. Technician B says that a leaking lower intake manifold gasket could cause a vacuum leak. Which technician is correct?




CHAPTER QUIZ

10. Technician A says that some intake manifolds are plastic. Technician B says that some intake manifolds are constructed in two parts or sections: upper and lower. Which technician is correct?


objectives

Documents

air pressure

air movement

heated air

air filterfigure

air control valve

engine forces air

intake air temperature

air intake filtrationfigure