Halderman J.D., Linder J. Automotive Fuel and Emissions Control Systems
Подождите немного. Документ загружается.
GASOLINE ENGINE OPERATION AND SPECIFICATIONS 51
block, the valves are operated by lifters, pushrods, and
rocker arms.
This type of engine can be called:
A pushrod engine
Cam-in-block design
Overhead valve (OHV), because an overhead valve
engine has the valves located in the cylinder head
SEE FIGURE 3–11 .
When one overhead camshaft is used, the design
is called a single overhead camshaft (SOHC) design.
When two overhead camshafts are used, the design is
called a double overhead camshaft (DOHC) design.
SEE FIGURES 3–12 AND 3–13 .
Valve and camshaft number and location. The number
of valves per cylinder and the number and location of
camshafts are major factors in engine operation. A typi-
cal older-model engine uses one intake valve and one
exhaust valve per cylinder. Many newer engines use two
intake and two exhaust valves per cylinder. The valves
are opened by a camshaft. Some engines use one cam-
shaft for the intake valves and a separate camshaft for
the exhaust valves. When the camshaft is located in the
4 CYLINDER 5 CYLINDER 6 CYLINDER
INLINE - TYPE ENGINES
V-4 ENGINE V-6 ENGINE V-8 ENGINE
V - TYPE EN
G
INE
S
FIGURE 3–7 Automotive engine cylinder arrangements.
PISTON
CRANKSHAFT
FIGURE 3–8 A horizontally opposed engine design helps to
lower the vehicle’s center of gravity.
REAR
AXLES
DIFFERENTIAL
UNIVERSAL
JOINTS
PROPELLER SHAFT
OR DRIVESHAFT
TRANSMISSION
ENGINE
CLUTCH OR
TORQUE CONVERTER
FIGURE 3–9 A longitudinally mounted engine drives the rear
wheels through a transmission, driveshaft, and differential
assembly.
PISTON
CRANKSHAFT
CONNECTING
ROD
PISTON
CRANKSHAFT
CONNECTING
ROD
FIGURE 3–6 Cutaway of an engine showing the cylinder,
piston, connecting rod, and crankshaft.
TRANSVERSE ENGINE
TRANSAXLE
TRANSMISSION
AND DIFFERENTIAL
CLUTCH
OR TORQUE
CONVERTER
HALF
SHAFTS
CLUTCH
OR TORQUE
CONVERTER
HALF
SHAFTS
LONGITUDINAL ENGINE
FIGURE 3–10 Two types of front-engine, front-wheel drive
mountings. A transaxle is used in most front wheel vehicles
and the longitudinal engine is used by Audi and some other
manufacturers.
52 CHAPTER 3
NOTE: A V-type engine uses two banks or rows of
cylinders. An SOHC design, therefore, uses two
camshafts but only one camshaft per bank (row)
of cylinders. A DOHC V-6, therefore, has four cam-
shafts, two for each bank.
Type of fuel. Most engines operate on gasoline, whereas
some engines are designed to operate on ethanol (E85),
methanol (M85), natural gas, propane, or diesel fuel.
Cooling method. Most engines are liquid cooled, but
some older models were air cooled. Air-cooled engines,
such as the original VW Beetle, could not meet exhaust
emission standards.
FIGURE 3–11 Cutaway of an overhead valve (OHV) V-8 engine
showing the lifters, pushrods, roller rocker arms, and valves.
CAM
FOLLOWER
CAM
FOLLOWER
CAMSHAFT
SINGLE OVERHEAD CAMSHAFT
CAMSHAFT CAMSHAFTLIFTER
LIFTER
DOUBLE OVERHEAD CAMSHAFT
FIGURE 3–12 SOHC engines usually require additional
components, such as a rocker arm, to operate all of the
valves. DOHC engines often operate the valves directly.
FIGURE 3–13 A DOHC engine uses a camshaft for the intake
valves and a separate camshaft for the exhaust valves in each
cylinder head.
What Is a Rotary Engine?
A successful alternative engine design is the rotary
engine, also called the Wankel engine after its in-
ventor, Felix Heinrich Wankel (1902–1988), a German
inventor. The Mazda RX-7 and RX-8 represent the
only long-term use of the rotary engine. The rotating
combustion chamber engine runs very smoothly, and
it produces high power for its size and weight.
The basic rotating combustion chamber engine
has a triangular-shaped rotor turning in a housing.
The housing is in the shape of a geometric figure
called a two-lobed epitrochoid. A seal on each cor-
ner, or apex, of the rotor is in constant contact with
the housing, so the rotor must turn with an eccen-
tric motion. This means that the center of the rotor
moves around the center of the engine. The eccen-
tric motion can be seen in
FIGURE 3–14 .
?
FREQUENTLY ASKED QUESTION
GASOLINE ENGINE OPERATION AND SPECIFICATIONS 53
which the power is applied to drive the vehicle. This is called the
principal end of the engine. The nonprincipal end of the engine
is opposite the principal end and is generally referred to as the
front of the engine, where the accessory belts are used.
SEE
FIGURE 3–15 .
Therefore, in most rear-wheel-drive vehicles, the engine
is mounted longitudinally with the principal end at the rear of
the engine. Most transversely mounted engines also adhere
to the same standard for direction of rotation. Many Honda
engines, and some marine applications, may differ from this
standard.
Type of induction pressure. If atmospheric air pres-
sure is used to force the air-fuel mixture into the cylin-
ders, the engine is called naturally aspirated. Some
engines use a turbocharger or supercharger to force
the air-fuel mixture into the cylinder for even greater
power.
ENGINE ROTATION DIRECTION The SAE standard
for automotive engine rotation is counterclockwise (CCW) as
viewed from the flywheel end (clockwise as viewed from the
front of the engine). The flywheel end of the engine is the end to
ECCENTRIC GEAR
ON SHAFT
MAXIMUM COMPRESSION
AND FIRING
COMPRESSION
SPARK
PLUGS
INTAKE
PORT
EXHAUST
PORT
ROTOR
INTAKE
COMPRESSIONINTAKE
EXHAUSTPOWER
FIGURE 3–14 A rotary engine operates on the four-stroke cycle but uses a rotor instead of a piston and crankshaft to achieve
intake, compression, power, and exhaust stroke.
54 CHAPTER 3
BOTTOM DEAD CENTER TOP DEAD CENTER
BORE
PISTON
DISPLACE-
MENT
STROKE
FIGURE 3–16 The bore and stroke of pistons are used to
calculate an engine’s displacement.
CENTER LINE
ROD BEARING
JOURNAL
CENTER LINE
MAIN BEARING
JOURNAL
FIGURE 3–17 The distance between the centerline of the
main bearing journal and the centerline of the connecting rod
journal determines the stroke of the engine. This photo is a little
unusual because it shows a V-6 with a splayed crankshaft used
to even out the impulses on a 90-degree, V-6 engine design.
FLEX-PLATE
(DRIVE-PLATE)
PRINCIPAL
END
DIRECTION
OF
ROTATION
DIRECTION
OF
ROTATION
NONPRINCIPAL
END
FIGURE 3–15 Inline 4-cylinder engine showing princi-
pal and nonprincipal ends. Normal direction of rotation is
clockwise (CW) as viewed from the front or accessory belt
(nonprincipal) end.
Where Does an Engine Stop?
When the ignition system is turned off, the firing of
the spark plugs stops and the engine will rotate until
it stops due to the inertia of the rotating parts. The
greatest resistance that occurs in the engine hap-
pens during the compression stroke. It has been
determined that an engine usually stops when one
of the cylinders is about 70 degrees before top dead
center (BTDC) on the compression stroke with a vari-
ation of plus or minus 10 degrees.
This explains why technicians discover that
the starter ring gear is worn at two locations on a
4-cylinder engine. The engine stops at one of the two
possible places depending on which cylinder is on
the compression stroke.
?
FREQUENTLY ASKED QUESTION
throw is the distance from the centerline of the crankshaft to the
centerline of the crankshaft rod journal. The throw is one-half of
the stroke.
SEE FIGURE 3–17 .
The longer this distance is, the greater the amount of
air-fuel mixture that can be drawn into the cylinder. The more
air-fuel mixture inside the cylinder, the more force will result
when the mixture is ignited.
NOTE: Changing the connecting rod length does not
change the stroke of an engine. Changing the connecting
rod only changes the position of the piston in the cylinder.
Only the crankshaft determines the stroke of an engine.
BORE The diameter of a cylinder is called the bore. The larger
the bore, the greater the area on which the gases have to work.
Pressure is measured in units, such as pounds per square inch (PSI).
The greater the area (in square inches), the higher the force exerted
by the pistons to rotate the crankshaft.
SEE FIGURE 3–16 .
STROKE The stroke of an engine is the distance the piston
travels from top dead center (TDC) to bottom dead center (BDC).
This distance is determined by the throw of the crankshaft. The
ENGINE MEASUREMENT
GASOLINE ENGINE OPERATION AND SPECIFICATIONS 55
DISPLACEMENT Engine size is described as displace-
ment. Displacement is the cubic inch (cu. in.) or cubic centi-
meter (cc) volume displaced or how much air is moved by all
of the pistons. A liter (L) is equal to 1,000 cubic centimeters;
therefore, most engines today are identified by their displace-
ment in liters:
1 L 1,000 cc
1 L 61 cu. in.
1 cu. in. 16.4 cc
CONVERSION
To convert cubic inches to liters, divide cubic inches
by 61.02:
Liters 5
Cubic inches
61.02
To convert liters into cubic inches, multiply by 61.02:
Cubic inches Liters 61.02
CALCULATING CUBIC INCH DISPLACEMENT The
formula to calculate the displacement of an engine is basically
the formula for determining the volume of a cylinder multiplied
by the number of cylinders.
The formula is:
Cubic inch displacement π (pi) R
2
Stroke
Number of cylinders
R Radius of the cylinder or one-half of the bore.
The πR
2
part is the formula for the area of a circle.
Applying the formula to a 6-cylinder engine:
Bore 4.000 in.
Stroke 3.000 in.
π 3.14
R 2 inches
R
2
4 (2
2
or 2 2)
Cubic inches 3.14 4 (R
2
) 3 (stroke) 6 (number of
cylinders).
Cubic inches 226 cubic inches
Because 1 cubic inch equals 16.4 cubic centimeters, this
engine displacement equals 3,706 cubic centimeters or, rounded
to 3,700 cubic centimeters, 3.7 liters.
SEE CHART 3–1 for
an example of engine sizes for a variety of bore and stroke
measurements.
ENGINE SIZE CONVERSION Many vehicle manufactur-
ers will round the displacement so the calculated cubic inch
displacement may not agree with the published displacement
value.
SEE CHART 3–2 .
How Fast Can an Engine Rotate?
Most passenger vehicle engines are designed to
rotate at low speed for the following reasons:
• Maximum efficiency is achieved at low engine
speed. A diesel engine used in a large ship,
for example, will rotate at about 100 RPM for
maximum efficiency.
• Piston ring friction is the highest point of friction in
the engine. The slower the engine speed, the less
loss to friction from the piston rings.
However, horsepower is what is needed to get a
vehicle down the road quickly. Horsepower is torque
times engine speed divided by 5,252. Therefore, a
high engine speed usually indicates a high horse-
power. For example, a Formula 1 race car is limited
to 2.4 liter V-8 but uses a 1.6 in. (40 mm) stroke. This
extremely short stroke means that the engine can
easily achieve the upper limit allowed by the rules of
18,000 RPM while producing over 700 horsepower.
The larger the engine, the more power the en-
gine is capable of producing. Several sayings are
often quoted about engine size:
“There is no substitute for cubic inches.”
“There is no replacement for displacement.”
Although a large engine generally uses more
fuel, making an engine larger is often the easiest way
to increase power.
TECH TIP
DEFINITION Compression ratio (CR) is the ratio of the
difference in the cylinder volume when the piston is at the bot-
tom of the stroke to the volume in the cylinder above the piston
when the piston is at the top of the stroke. The compression
ratio of an engine is an important consideration when rebuilding
or repairing an engine.
SEE FIGURE 3–18 .
COMPRESSION RATIO
If Compression Is Lower If Compression Is Higher
Lower power Higher power possible
Poorer fuel economy Better fuel economy possible
Easier engine cranking Harder to crank engine,
especially when hot
More advanced ignition
timing possible without
spark knock (detonation)
Less ignition timing required to
prevent spark knock (detonation)
56
V-8 ENGINE
Stroke 3.50 3.75 3.875 4.00 4.125
Bore Cu. In. Cu. In. Cu. In. Cu. In. Cu. In.
3.00 199 212 219 226 233
3.125 214 229 237 244 252
3.250 232 249 257 265 274
3.375 251 269 277 286 295
3.500 269 288 298 308 317
3.625 288 309 319 330 339
3.750 309 332 343 354 365
3.875 331 354 366 378 390
4.00 352 377 389 402 414
4.125 373 399 413 426 439
6-CYLINDER ENGINE
Stroke 3.50 3.75 3.875 4.00 4.125
Bore Cu. In. Cu. In. Cu. In. Cu. In. Cu. In.
3.00 148 159 164 169 175
3.125 161 172 178 184 190
3.250 174 186 193 199 205
3.375 188 201 208 215 222
3.500 202 216 223 228 238
3.625 216 232 239 247 255
3.750 232 249 257 265 273
3.875 248 266 275 283 292
4.00 264 283 292 301 311
4.125 280 299 309 319 329
4-CYLINDER ENGINE
Stroke 3.50 3.75 3.875 4.00 4.125
Bore Cu. In. Cu. In. Cu. In. Cu. In. Cu. In.
3.00 99 106 110 113 117
3.125 107 115 119 123 126
3.250 116 124 129 133 137
3.375 125 134 139 143 148
3.500 135 144 149 152 159
3.625 144 158 160 165 170
3.750 155 166 171 177 182
3.875 165 177 183 189 195
4.00 176 188 195 201 207
4.125 186 200 206 213 220
CHART 3–1
To find the cubic inch displacement, find the bore that is closest to the actual value, then go across to the closest stroke value.
GASOLINE ENGINE OPERATION AND SPECIFICATIONS 57
CHART 3–2
Liters to cubic inches is often not exact and can result in representing several different engine sizes based on their advertised size
in liters.
LITERS TO CUBIC INCHES
Liters Cubic Inches Liters Cubic Inches Liters Cubic Inches
1.0 61 3.2 196 5.4 330
1.3 79 3.3 200 / 201 5.7 350
1.4 85 3.4 204 5.8 351
1.5 91 3.5 215 6.0 366 / 368
1.6 97 / 98 3.7 225 6.1 370
1.7 105 3.8 229 / 231 / 232 6.2 381
1.8 107 / 110 / 112 3.9 239 / 240 6.4 389 / 390 / 391
1.9 116 4.0 241 / 244 6.5 396
2.0 121 / 122 4.1 250 / 252 6.6 400
2.1 128 4.2 255 / 258 6.9 420
2.2 132 / 133 / 134 / 135 4.3 260 / 262 / 265 7.0 425 / 427 / 428 / 429
2.3 138 / 140 4.4 267 7.2 440
2.4 149 4.5 273 7.3 445
2.5 150 / 153 4.6 280 / 281 7.4 454
2.6 156 / 159 4.8 292 7.5 460
2.8 171 / 173 4.9 300 / 301 7.8 475 / 477
2.9 177 5.0 302 / 304 / 305 / 307 8.0 488
3.0 181 / 182 / 183 5.2 318 8.8 534
3.1 191 5.3 327
COMPRESSION RATIO = 8:1
CLEARANCE
VOLUME
PISTON
DISPLACEMENT
TOP
DEAD
CENTER
BOTTOM
DEAD
CENTER
CYLINDER
VOLUME
3
4
1
2
5
6
7
8
FIGURE 3–18 Compression ratio is the ratio of the total
cylinder volume (when the piston is at the bottom of its stroke)
to the clearance volume (when the piston is at the top of its
stroke).
CALCULATING COMPRESSION RATIO The compres-
sion ratio (CR) calculation uses the formula:
CR 5
Volume in cylinder with piston at bottom of cylinder
Volume in cylinder with piston at top center
SEE FIGURE 3–19 .
For example: What is the compression ratio of an engine with
50.3 cu. in. displacement in one cylinder and a combustion cham-
ber volume of 6.7 cu. in.?
CR 5
50 1 6.7 cu. in
6.7 cu. in
5
57.0
6.7
5 8.5
CHANGING COMPRESSION RATIO Any time an engine
is modified, the compression ratio should be checked to make
sure it is either the same as it was originally or has been
changed to match the diesel compression ratio. Factors that
can affect compression ratio include:
Head gasket thickness. A thicker than stock gasket will
decrease the compression ratio and a thinner than stock
gasket will increase the compression ratio.
58 CHAPTER 3
certain distance by a force. If the object is moved in 10 seconds
or 10 minutes does not make a difference in the amount of work
accomplished, but it does affect the amount of power needed.
Power is expressed in units of foot-pounds per minute and
power also includes the engine speed (RPM) where the maxi-
mum power is achieved. For example, an engine may be listed
as producing 280 hp @ 4,400 RPM.
Increasing the cylinder size. If the bore or stroke is
increased, a greater amount of air will be compressed
into the combustion chamber, which will increase the
compression ratio.
10 POUNDS
1 FOOT
FIGURE 3–20 Torque is a twisting force equal to the dis-
tance from the pivot point times the force applied expressed
in units called pound-feet (lb-ft) or newton-meters (N-m).
TORQUE AND HORSEPOWER
DEFINITION OF TORQUE Torque is the term used to
describe a rotating force that may or may not result in motion.
Torque is measured as the amount of force multiplied by the
length of the lever through which it acts. If you use a 1 ft long
wrench to apply 10 pounds (lb) of force to the end of the wrench
to turn a bolt, then you are exerting 10 pound-feet (lb-ft) of
torque.
SEE FIGURE 3–20 .
Torque is the twisting force measured at the end of the
crankshaft and measured on a dynamometer. Engine torque is
always expressed at a specific engine speed (RPM) or range
of engine speeds where the torque is at the maximum. For
example, an engine may be listed as producing 275 lb-ft @
2,400 RPM.
The metric unit for torque is newton-meters, because the
newton is the metric unit for force and the distance is expressed
in meters.
1 pound-foot 1.3558 newton-meters
1 newton-meter 0.7376 pound-foot
DEFINITION OF POWER The term power means the rate
of doing work. Power equals work divided by time. Work is
achieved when a certain amount of mass (weight) is moved a
Is Torque ft-lb or lb-ft?
The definition of torque is a force (lb) applied to
an object times the distance from that object (ft).
Therefore, based on the definition of the term, torque
should be:
lb-ft (a force times a distance)
Newton-meter (N-m) (a force times a distance)
However, torque is commonly labeled, even on
some torque wrenches, as ft-lb.
?
FREQUENTLY ASKED QUESTION
Quick-and-Easy Engine Efficiency Check
A good, efficient engine is able to produce a lot of
power from little displacement. A common rule of
thumb is that an engine is efficient if it can produce
1 horsepower per cubic inch of displacement. Many
engines today are capable of this feat, such as the
following:
Ford: 4.6 liter V-8 (281 cu. in.): 305 hp
Chevrolet: 3.0 liter V-6 (207 cu. in.): 210 hp
Chrysler: 3.5 liter V-6 (214 cu. in.): 214 hp
Acura: 3.2 liter V-6 (195 cu. in.): 260 hp
An engine is very powerful for its size if it can
produce 100 hp per liter. This efficiency goal is harder
to accomplish. Most factory stock engines that can
achieve this feat are supercharged or turbocharged.
TECH TIP
DECK HEIGHT
PISTON TOP
AT TDC
PISTON TOP
AT BDC
COMPRESSED
HEAD GASKET
0.020 INCH
STROKE
COMBUSTION CHAMBER VOLUME
FIGURE 3–19 Combustion chamber volume is the volume
above the piston with the piston is at top dead center.
GASOLINE ENGINE OPERATION AND SPECIFICATIONS 59
3. Most engines rotate clockwise as viewed from the front
(accessory) end of the engine. The SAE standard is coun-
terclockwise as viewed from the principal (flywheel) end of
the engine.
4. Engine size is called displacement and represents the vol-
ume displaced by all of the pistons.
SUMMARY
1. The four strokes of the four-stroke cycle are intake, com-
pression, power, and exhaust.
2. Engines are classified by number and arrangement of cyl-
inders and by number and location of valves and cam-
shafts, as well as by type of mounting, fuel used, cooling
method, and type of air induction.
1. What are the strokes of a four-stroke cycle?
REVIEW QUESTIONS
2. If an engine at sea level produces 100 hp, how many
horsepower would it develop at 6,000 ft of altitude?
1. All overhead valve engines ______________ .
a. Use an overhead camshaft
b. Have the valves located in the cylinder head
c. Operate by the two-stroke cycle
d. Use the camshaft to close the valves
2. An SOHC V-8 engine has how many camshafts?
a. One c. Three
b. Two d. Four
3. The coolant flow through the radiator is controlled by the
______________ .
a. Size of the passages in the block
b. Thermostat
c. Cooling fan(s)
d. Water pump
4. Torque is expressed in units of ______________ .
a. Pound-feet
b. Foot-pounds
c. Foot-pounds per minute
d. Pound-feet per second
5. Horsepower is expressed in units of ______________ .
a. Pound-feet
b.
Foot-pounds
c. Foot-pounds per minute
d. Pound-feet per second
6. A normally aspirated automobile engine loses about
______________ power per 1,000 ft of altitude.
a. 1% c. 5%
b. 3% d. 6%
CHAPTER QUIZ
7. One cylinder of an automotive four-stroke cycle engine
completes a cycle every ______________ .
a. 90 degrees
b. 180 degrees
c. 360 degrees
d. 720 degrees
8. How many rotations of the crankshaft are required to com-
plete each stroke of a four-stroke cycle engine?
a. One-fourth
b. One-half
c. One
d. Two
9. A rotating force is called ______________ .
a. Horsepower
b. Torque
c. Combustion pressure
d. Eccentric movement
10. Technician A says that a crankshaft determines the stroke
of an engine. Technician B says that the length of the con-
necting rod determines the stroke of an engine. Which
technician is correct?
a. Technician A only
b. Technician B only
c. Both Technicians A and B
d. Neither Technician A nor B
HORSEPOWER AND ALTITUDE Because the density of
the air is lower at high altitude, the power that a normal engine
can develop is greatly reduced at high altitude. According
to SAE conversion factors, a nonsupercharged or nonturbo-
charged engine loses about 3% of its power for every 1,000 ft
(300 m) of altitude.
Therefore, an engine that develops 200 brake horsepower at
sea level will produce only about 116 brake horsepower atthe top
of Pike’s Peak in Colorado at 14,110 ft (4,300 m) (3% 14 – 42%).
Supercharged and turbocharged engines are not as greatly af-
fected by altitude as normally aspirated engines, which are those
engines that breathe air at normal atmospheric pressure.
60 CHAPTER 4
chapter
4
OBJECTIVES: After studying Chapter 4 , the reader should be able to: • Prepare for ASE Engine Performance (A8) certification
test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair). • Explain how a diesel engine works.
• Describe the difference between direct injection (DI) and indirect injection (IDI) diesel engines. • List the parts of the typical diesel
engine fuel system. • Explain how glow plugs work. • List the advantages and disadvantages of a diesel engine.
KEY TERMS: Diesel exhaust fluid (DEF) 74 • Diesel exhaust particulate filter (DPF) 71 • Diesel oxidation catalyst (DOC) 71
• Differential pressure sensor (DPS) 72 • Direct injection (DI) 62 • Glow plug 67 • Heat of compression 60 • High-pressure
common rail (HPCR) 64 • Hydraulic electronic unit injection (HEUI) 64 • Indirect injection (IDI) 62 • Injection pump 60
• Lift pump 63 • Opacity 78 • Particulate matter (PM) 71 • Pop tester 77 • Regeneration 72 • Selective catalytic reduction
(SCR) 74 • Soot
71 • Urea 74 • Water-fuel separator 63
A diesel engine has several disadvantages compared to a
similar size gasoline-powered engine, including:
1. Engine noise, especially when cold and/or at idle speed
2. Exhaust smell
3. Cold weather startability
4. Vacuum pump that is needed to supply the vacuum needs
of the heat, ventilation, and air-conditioning system
DIESEL ENGINE OPERATION
AND DIAGNOSIS
EXHAUST
VALVE
INJECTOR
AIR
INTAKE
VALVE
FIGURE 4–1 Diesel combustion occurs when fuel is injected
into the hot, highly compressed air in the cylinder.
DIESEL ENGINES
FUNDAMENTALS In 1892, a German engineer named
Rudolf Diesel perfected the compression ignition engine that
bears his name. The diesel engine uses heat created by com-
pression to ignite the fuel, so it requires no spark ignition
system.
The diesel engine requires compression ratios of 16:1 and
higher. Incoming air is compressed until its temperature reaches
about 1,000°F (540°C). This is called heat of compression.
As the piston reaches the top of its compression stroke, fuel
is injected into the cylinder, where it is ignited by the hot air.
SEE FIGURE 4–1 .
As the fuel burns, it expands and produces power.
Because of the very high compression and torque output of
a diesel engine, it is made heavier and stronger than the same
size gasoline-powered engine.
A diesel engine uses a fuel system with a precision injec-
tion pump and individual fuel injectors. The pump delivers fuel
to the injectors at a high pressure and at timed intervals. Each
injector sprays fuel into the combustion chamber at the precise
moment required for efficient combustion.
SEE FIGURE 4–2 .
ADVANTAGES AND DISADVANTAGES A diesel engine
has several advantages compared to a similar size gasoline-
powered engine, including:
1. More torque output
2. Greater fuel economy
3. Long service life