Chapter 3 Engine Classifi cation, Parts Identifi cation 67
Summary
Engines can be classified in many ways.
The most commonly used classifications are by
cycle, valve location, cylinder arrangement, fuel
used, cooling, and number of cylinders. The vast
majority of auto engines are of the four-stroke
cycle type. The two-stroke cycle is used in
some small engines. Both have advantages and
disadvantages. I-head (overhead valve) engines
are used in most modern vehicles.
The most commonly used combustion chamber
shapes are the wedge and the hemispherical.
Detonation during the compression stroke can be
stopped by proper fuel and combustion chamber
design. Ricardo, in early experiments, set forth
some basic principles of combustion chamber
design that are still incorporated in modern
engines. He found that by providing turbulence
in the compressed charge, compression could be
raised without detonation.
The V-8, V-6, and inline four-cylinder
engines dominate the fi eld of engine design
and use. Some inline six-cylinder, V-10 and V-12,
and four- or six-cylinder horizontal-opposed
engines, are occasionally found. Engines are
mounted on rubber, generally using the three
point suspension system, but some vehicles can
utilize up to fi ve mounts. The diesel two-stroke
cycle engine differs from the small gasoline
engine of the same type. The diesel engine
incorporates an exhaust valve, a supercharger
and a conventional crankcase. The Wankel rotary
piston engine uses a triangular shaped rotor
that revolves inside a housing. It operates on
the four-cycle principle. It has no reciprocating
action and as a result, is very smooth running.
The rotary is a simple engine with very few
moving parts (rotor and eccentric shaft) in the
basic engine.
Experiments with new and different types
of engines are always in progress. Further
development of existing engines is also taking
place. Considerable research is being done on
natural gas, hybrid, and electric drive autos.
Review Questions
Answer the following questions using the
information provided in this chapter.
1. List the strokes in a four-cycle engine in
their proper order.
2. The two-strokes of a two-cycle engine take
place during how many revolutions of the
crankshaft?
3. What type of valves does a two-stroke
cycle gasoline engine have?
4. In a two-cycle engine, what opens and
closes the reed valve(s)?
(A) Air pressure and vacuum.
(B) A camshaft lobe.
(C) A crankshaft lobe.
(D) All of the above, depending on the
manufacturer.
5. Explain where the valves are located in the
following engines:
(1) I-head
(2) F-head
(3) L-head
(4) T-head
6. Where are the valves located in an
overhead camshaft I-head engine?
7. Valve-to-piston clearance is most important
on _____ compression engines.
8. What is detonation and how is it caused?
9. All of the following could cause
preignition, except:
(A) glowing carbon.
(B) overheated spark plug.
(C) burned valve.
(D) piece of metal extending into the
combustion chamber.
10. Additional compression can be obtained
without causing detonation if _____ in the
air-fuel mixture is increased.
11. How many cylinders do most inline
engines have that are in production today?
12. A horizontally opposed engine has _____
banks of cylinders.
13. What determines an engine’s fi ring order?
14. E85 fuels can only be used in specially
calibrated vehicles, called _____ fuel
vehicles.