Auto Fundamentals, 11th Edition Page 59 (77 of 656)

Chapter 3 Engine Classifi cation, Parts Identifi cation 59
diesel engine repeatedly burns glow plugs, the
technician should fi rst determine whether bio-
diesel is being used.
One of the principal differences in these
engines is in method of fuel delivery and conver-
sion to a burnable form. Gasoline, LNG, CNG,
and LPG utilize the same basic type of engine,
but LNG, CNG, and LPG utilize a slightly dif-
ferent fuel delivery setup. Diesel engines do not
use an ignition system. Due to the pressures and
stresses involved, diesel engines are constructed
very rigidly. The theory of diesel engines is cov-
ered in the diesel injection section in Chapter 10,
Fuel Injection Systems. Diesel engines are either
two- or four-stroke cycle types.
Natural Gas Engines
Natural gas is piped to millions of homes,
where it is burned in water heaters, furnaces,
and stoves. In addition, some vehicles oper-
ate on natural gas. The vehicle holds the gas in
a high pressure storage tank, since it must be
under high pressure in order to stay liquid. The
gas must be maintained in a liquid state, as the
vehicle could not carry enough to go very far if
the gas were in its vapor state. The high pres-
sure tank gives the natural gas vehicle a cruis-
ing range similar to that of a gasoline powered
engine.
A natural gas engine is an internal combus-
tion engine similar to a gasoline engine. In fact,
most natural gas engines are production gaso-
line engines with a modified fuel system. The
fuel system is modified to allow the natural gas
to vaporize and mix with the incoming air. A
simple mixing valve arrangement replaces the
carburetor or fuel injectors. The natural gas sys-
tem can even be adapted to work with the exist-
ing computer control system.
The advantage of natural gas is that it pro-
duces much less pollution and is readily avail-
able in large quantities. The disadvantage of
natural gas is that the high pressure tank adds
weight and price to the vehicle. Also, since most
vehicles are gasoline powered, refueling sta-
tions are hard to fi nd. Refueling time is slightly
longer than for gasoline. If natural gas powered
vehicles become more common, it may be pos-
sible in the future for homeowners to refuel their
vehicles from their home gas system.
Engine Mounting
It is common practice to mount the engine
on fl uid-filled or rubber pads, usually called
engine mounts. This helps isolate engine vibra-
tions from the vehicle body. It also eases torque
(twisting strain) loading of the drive line.
Mounts are used to support the engine and
Figure 3-24.
E85 gasoline contains 85% alcohol and should be used
on fl ex fuel vehicles only. E85 pumps are clearly marked.
Goodheart-Willcox Publisher
Figure 3-25.
Biodiesel can be used in most diesel engines with no
modifi cations. It is made from plants and cooking oils that
would otherwise be discarded.
Goodheart-Willcox Publisher

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Extracted Text (may have errors)

Chapter 3 Engine Classifi cation, Parts Identifi cation 59
diesel engine repeatedly burns glow plugs, the
technician should fi rst determine whether bio-
diesel is being used.
One of the principal differences in these
engines is in method of fuel delivery and conver-
sion to a burnable form. Gasoline, LNG, CNG,
and LPG utilize the same basic type of engine,
but LNG, CNG, and LPG utilize a slightly dif-
ferent fuel delivery setup. Diesel engines do not
use an ignition system. Due to the pressures and
stresses involved, diesel engines are constructed
very rigidly. The theory of diesel engines is cov-
ered in the diesel injection section in Chapter 10,
Fuel Injection Systems. Diesel engines are either
two- or four-stroke cycle types.
Natural Gas Engines
Natural gas is piped to millions of homes,
where it is burned in water heaters, furnaces,
and stoves. In addition, some vehicles oper-
ate on natural gas. The vehicle holds the gas in
a high pressure storage tank, since it must be
under high pressure in order to stay liquid. The
gas must be maintained in a liquid state, as the
vehicle could not carry enough to go very far if
the gas were in its vapor state. The high pres-
sure tank gives the natural gas vehicle a cruis-
ing range similar to that of a gasoline powered
engine.
A natural gas engine is an internal combus-
tion engine similar to a gasoline engine. In fact,
most natural gas engines are production gaso-
line engines with a modified fuel system. The
fuel system is modified to allow the natural gas
to vaporize and mix with the incoming air. A
simple mixing valve arrangement replaces the
carburetor or fuel injectors. The natural gas sys-
tem can even be adapted to work with the exist-
ing computer control system.
The advantage of natural gas is that it pro-
duces much less pollution and is readily avail-
able in large quantities. The disadvantage of
natural gas is that the high pressure tank adds
weight and price to the vehicle. Also, since most
vehicles are gasoline powered, refueling sta-
tions are hard to fi nd. Refueling time is slightly
longer than for gasoline. If natural gas powered
vehicles become more common, it may be pos-
sible in the future for homeowners to refuel their
vehicles from their home gas system.
Engine Mounting
It is common practice to mount the engine
on fl uid-filled or rubber pads, usually called
engine mounts. This helps isolate engine vibra-
tions from the vehicle body. It also eases torque
(twisting strain) loading of the drive line.
Mounts are used to support the engine and
Figure 3-24.
E85 gasoline contains 85% alcohol and should be used
on fl ex fuel vehicles only. E85 pumps are clearly marked.
Goodheart-Willcox Publisher
Figure 3-25.
Biodiesel can be used in most diesel engines with no
modifi cations. It is made from plants and cooking oils that
would otherwise be discarded.
Goodheart-Willcox Publisher

Help

58 Auto Fundamentals
Higher compression ratios can be used in
the V-type engine without block distortion under
load. The short, heavy crankshaft is more resis-
tant to torsional vibration. In the past, V-12 and
V-16 engines were widely used. Current produc-
tion V-type engines are the V-6 and V-8, along
with a few V-10 and V-12 designs, Figure 3-22.
Horizontally Opposed Engines
The horizontally opposed engine, some-
times called a boxer engine, is like a V-type
engine, except that both banks lie in a horizontal
plane. The advantage here is an extremely low
overall height, which makes this engine ide-
ally suited to installations where space is lim-
ited. Figure 3-23 shows a horizontally opposed
engine. It is an air-cooled, six-cylinder engine.
Firing Order
Firing order refers to the sequence in which
the cylinders fi re. Firing orders are given in order
from the front of the engine to the rear. The order
in which the engine must fi re is determined by
the number of cylinders and the arrangement of
the crankshaft throws. Firing order can be found
in the service information for the vehicle being
serviced. Firing orders vary between engines,
and must be obtained from the service informa-
tion. On some engines, the fi ring order is shown
on the valve cover or intake manifold.
Cooling Classifi cation
As you have learned, engines are either
liquid-cooled or air-cooled. Most vehicles use
liquid-cooled engines. Air-cooled engines are
used in limited numbers on modern vehicles,
but are widely used to operate chain saws, lawn
mowers, scooters, and other equipment. Both
types have advantages and disadvantages.
Air cooling is simple and has no coolant to
leak or freeze in cold weather. However, air-cooled
vehicles are very uncomfortable in cold weather,
since there is no effi cient or safe way to transfer
engine heat to the passenger compartment.
Fuel Classifi cation
Automobile engines can use gasoline, diesel
fuel, gasohol (mixture of gasoline and alcohol),
alcohol, LNG (liquefied natural gas), CNG (com-
pressed natural gas), or LPG (liquefied propane
gas). Gasoline powers the majority of vehicles, but
diesel fuel is used in some vehicles. Gasohol, LNG,
CNG, and LPG are beginning to see wider use.
Some gasohol is called E85 fuel. E85 fuels
are 85% high ethanol (grain alcohol), and can
only be used in specially calibrated vehicles,
usually called fl ex fuel vehicles. E85 fuels are
available in many areas. E85 pumps are clearly
marked to avoid confusion with other types of
gasoline, Figure 3-24. Do not attempt to use E85
in a vehicle that is not calibrated to use it.
Biodiesel is made from plants and animal
fats and is available in many parts of the United
States. Figure 3-25 shows a biodiesel pump. Bio-
diesel is interchangeable with diesel made from
crude oil, without engine modifications. Exhaust
emissions are lower when biodiesel is used
instead of crude oil diesel fuel. Most biodiesel
is mixed with crude oil diesel in a 20/80 ratio.
This is called B20 biodiesel. Some biodiesel has a
higher cetane number and may slightly increase
combustion chamber temperatures. When a
Figure 3-22.
Crankshaft, connecting rods, and pistons of a V-8 engine.
Zelfi t/Shutterstock.com
Figure 3-23.
Crankshaft, connecting rods, and pistons of a horizontally
opposed engine.
Subaru

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60 Auto Fundamentals
to minimize torque defl ections. Small shock
absorbers are sometimes employed, especially
on diesel engines, to further control vibration.
The three-point suspension, used mostly
on rear-wheel drive vehicles, is one of the most
popular. This method uses one mount on either
side of the engine near the front and one at the
back, usually under the transmission. However,
other setups use two-, three-, four-, or fi ve-point
engine mount arrangements. This varies from
each model and manufacturer. Figure 3-26
shows a fi ve-point mounting pattern.
Other Engine Designs
Although most automobiles and light trucks
use four-stroke, reciprocating, gasoline engines,
there are a number of other engine types used
in late-model vehicles. Some of these engines
burn a fuel other than gasoline. Others are vari-
ations of the conventional four-cycle engine. A
few of the more common alternative engines are
detailed in the following sections.
Two-Stroke and Four-Stroke Cycle
Diesel Engines
A two-stroke cycle diesel engine is some-
what different than the two-stroke gasoline
engine discussed earlier in this chapter. The two-
stroke cycle diesel engine utilizes an exhaust
valve. No fuel mixture enters the crankcase.
Due to the pressures involved, a supercharger is
used to force air into the cylinder intake ports.
Figure 3-27 shows the two-stroke cycle opera-
tion in a diesel engine. Notice that air rushing in
through the cylinder liner ports helps scavenge
the cylinder by fl owing out the exhaust passage
for a portion of the piston travel. Since only air
enters the cylinder, there is no loss of fuel.
Figure 3-28 shows a typical four-stroke
cycle, four-cylinder automotive diesel engine.
Inline fi ve-, six-, and V-8 diesels are also used,
Figure 3-29. Diesel fuel injection system opera-
tion is discussed in Chapter 10, Fuel Injection
Systems.
Rotary Engines
The rotary engine was used on a few vehi-
cles for many years and was not produced in
large numbers. The rotary engine is very power-
ful for its size. This engine is often referred to as
a Wankel engine.
The rotary engine has fewer moving parts
than a piston engine. Since it has no recipro-
cating motion, the rotary engine produces less
vibration and offers more horsepower. Draw-
backs of the rotary engine included difficulty
meeting emission control standards, and poor
fuel economy compared to a piston engine of
similar power output.
Rubber
Fluid
Orifice
Diaphragm
Air chamber
Movable
plate
Right
mount
Center
mount
Front
mount
Rear mount
Left mount
Figure 3-26.
One type of front-wheel drive engine mount. The fl uid sealed in the mount absorbs low speed vibrations.
Toyota

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