Basic Engine Operation Section 1:
starts with the piston at TDC.
intake stroke
is the main moving part in an engine
piston
The air-fuel mixture is uniformly mixed together to be present in the combustion chamber at a chemically exact ratio of
14.7, which is known as stoichiometric air-fuel ratio
One horsepower is equivalent to
33,000 ft
A typical automobile crankshaft will complete anywhere from _____ revolutions or more every minute
500 to 6,000
means higher thermal efficiency or that portion of the heat supplied to the engine that is turned into work.
A higher compression
is the diameter of the cylinder
Bore
shows that the pressure of a gas is inversely proportional to the volume of its containe
Boyle's law
An engine is normally described in one of two ways:
By the amount of power it produces By the size of the engine
s the ratio of the volume at BDC to the volume at TDC (clearance volume)
Compression ratio
s defined as work per unit of time. It's the rate of doing work or torque and is the unit of measurement that expresses the power output of an internal combustion engine.
Horsepower
Four Stages (Strokes) of Engine Operation
Intake, Compression, Power, Exhaust
is a complete run through all four stages of operation—intake, compression, power, and exhaust
One engine cycle
This term is used to describe an engine in which the cylinder bore diameter is exactly equal to the piston stroke dimension. When bore and stroke values are expressed, bore always appears before stroke
Square Engine
is the movement of the piston from the top to the bottom of the cylinder
Stroke
What opens to allow the exhaust gases produced by the burning mixture to exit the cylinder
The exhaust valve
What opens to allow the air-and-fuel mixture to enter the cylinder.
The intake valve
begins shortly after the spark plug arc ignites the air-fuel mixture in the combustion chamber and gasoline (reactant) burns, supported by oxygen
The power stroke
When the piston is at its highest position in the cylinder, it's said to be at
Top dead center (TDC).
is a force that tries to turn or twist something around and is defined as the product of a force and the perpendicular distance between the line of action of the force and the axis of rotation.
Torque
What is done during the intake stroke?
air that has been mixed with fuel is drawn into the cylinder.
four-stroke engine will contain at least two mechanical valves:
an intake valve and an exhaust valve
When a piston is at its lowest position in the cylinder, it's said to be at
bottom dead center (BDC)
Piston rings are designed to be springy so that
can stretch to fit over the outside of the piston and then snap back into their grooves
The space between the piston and the cylinder head when the piston is at TDC is the
clearance space or is sometimes called the compression or combustion space
The volume of this clearance space is known as the
clearance volume
The process of burning the air-and-fuel mixture in the cylinder is called
combustion
small, open space above the piston is called the
combustion chamber
The ratio of the largest cylinder volume to the smallest cylinder volume is called the
compression ratio
When the piston reaches BDC, the intake valve closes, sealing the cylinder, and the
compression stroke begins.
The connecting rods are attached to the rod journals. The main journals are used to mount the
crankshaft to the engine blockcrankshaft to the engine block
is a hollow metal tube that's drilled into the metal engine block
cylinder
In an actual engine, the top of the cylinder is sealed by a metal cover called the
cylinder head
In an automotive engine, fuel is sent directly to the _______, where it's burned inside to produce the power that's used to run a vehicle.
engine
is the volume of space that the piston must travel from the very bottom of its path to the very top of its path and is measured in units of volume
engine displacement
the size of the space inside the engine where the air-and-fuel mixture is burned. The size of this space is called the
engine displacement
In an internal combustion engine, fuel is burned inside the
engine to produce power.
The piston then begins to rise in the cylinder, beginning the
exhaust stroke
is a stroke that produces no work but expends a quantity of energy to push exhaust gases from the cylinder.
exhaust stroke
is allowed to close, by spring pressure, shortly after the piston begins its downward movement.
exhaust stroke
fuel is burned outside the engine.
external combustion engine
When the piston is at the bottom of its stroke, or BDC, the crank is at a point
farthest from the cylinder
Torque is generally expressed in
foot-pounds or Newton-meters
When a piston is in place inside a cylinder, the piston rings will press outward against the walls of the cylinder. This action helps
form a tight seal between the piston and the cylinder
the piston requires _________ to complete one full engine cycle.
four strokes
the fuel is injected directly into the combustion chamber where the air and fuel are mixed together, similar to a diesel engine.
gasoline direct injection (GDI)
There are two types of journals on a crankshaft—
he rod journals and the main journals
The sparking action of the spark plug is controlled by the engine's
ignition system
The engines that are used in automobiles
internal combustion engines.
The internal combustion engine produces
mechanical energy directly by burning fuel
When the piston is at the top of its stroke or TDC, the crank is at a point
nearest the cylinder
n a two-stroke engine, the intake and compression stages are combined and completed by
one piston stroke
When the bore is larger than the stroke, the engine is ________, and most of its power is dependent upon revolutions per minute (rpm) and generated at higher rpm values
oversquared
is a can-shaped metal component that can move up and down inside the cylinder.
piston
Note that the outside surface of a piston has several horizontal grooves cut into it. Each of these grooves holds a metal ring called
piston ring
is a circular piece of metal that's split at one point
piston ring
In the combustion chamber, a mixture of air and gasoline is burned to produce
power
the standard unit of horsepower is used to describe the
power output of a gasoline engine.
When the air-and-fuel mixture burns in the combustion chamber, it produces a small, contained explosion. The air expansion produced by this explosion is strong enough to force the piston downward in the cylinder and uses the reciprocating motion of the piston to turn the crankshaft in rotary motion, hence the term
reciprocating engine
When the piston is forced downward in the cylinder, the piston's downward motion is transferred to the
rod and crankshaft
The bottom end of the piston is connected to a
rod and crankshaft assembly
The rod and crankshaft then convert the up-and-down motion of the piston into
rotary motion
he power and exhaust stages are combined and completed by a
second piston stroke
is an example of an external combustion engine.
steam engine/ boiler
What is done during the power stage?
the air-and-fuel mixture is ignited by a spark, and the contained explosion of the fuel presses the piston back down in the cylinder.
burns fuel to produce steam, and then steam is sent to the engine to produce power.
the boiler
What is done During the exhaust stage?
the burned exhaust gases are released from the cylinder. The four stages then begin all over again
The length of the rod journal determines the
the distance the piston travels, or stroke, and is the lever
What is done during the compression stage?
the piston rises and compresses the air-and-fuel mixture that's trapped in the combustion chamber
is force (f) multiplied by length.
torque
the piston takes only _______ to complete one full engine cycle of intake
two strokes
What is the reason thatTwo-stroke engines aren't used in any current automobiles, but seen in motorcycles and small motors?
two-stroke engines aren't very fuel efficient and tend to produce more pollution than four-stroke engines
When the stroke is larger than the bore, the engine is _________, with most of its power dependent on torque.
undersquared
as defined as the product of a force and the distance through which the force acts.
work
is defined as the product of a force and the distance through which the force acts.
work