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THE engine
The heart and soul of a car. Basically, the engine
converts air and petrol (or diesel, LPG, ethanol, etc.) into energy
to propel the vehicle.
Because most of us use petrol engines (especially
those of us who love to drive) this section will mainly look at
how a petrol engine works. If you want to know how diesel engines
work, a description can be found at Howstuffworks.com.
For you RX-7 or RX-8 owners, a brilliant description of the rotary
engine can also be found there, complete with diagrams and animations.
the basics
Almost all passenger car engines operate with
what’s known as a 4-stroke, internal-combustion
design. Other types of engines exist, such as 2-stroke
engines and rotary
engines. Like the 4-stroke, they are also internal-combustion
engines. But the 4-stroke has proven itself to be the most reliable,
efficient and cost-effective design so far.
what is internal combustion?
Internal combustion describes the process of
exploding fuel within an engine to repeatedly move the internal
components which ultimately propel the car along.
what is the 4-stroke cycle?
To understand the 4-stroke cycle, it’s
helpful to start with some basic engine anatomy (figure 1):
- Engine block – cast from a
solid block of iron or aluminium. Holds all the internal moving
parts, and provides a very sturdy environment for combustion
to take place.
- Cylinders – quite literally,
cylinder-shaped spaces bored into the engine block. There can
be as few as three cylinders, or as many as sixteen in an engine.
Most cars have four or six.
- Valves – they look like the
bottom half of a wine glass. They open and close the passageways
which allow fuel to be drawn into a cylinder (intake), or pushed
out of it (exhaust). In each cylinder, there must be at least
one valve for intake, and one for exhaust.
- Spark plugs – in petrol engines,
these are screwed into the engine block, so that one end pokes
into the top of a cylinder. Spark plugs produce a small but
powerful arc of electricity, which detonates the mixture of
air and petrol that is drawn into a cylinder.
- Pistons – they bear the brunt
of the explosion that takes place within the cylinder, and help
convert that explosive energy into controlled movement.
- Connecting rods – these slender
yet strong linkages connect the pistons to the crankshaft, and
help turn the up-and-down movement of pistons into the rotating
movement of the crankshaft.
- Crankshaft – transmits its
rotational movement to the transmission.
Inside the engine block are the cylinders. No matter how many
cylinders a car’s engine has, the process is the same: a
piston slides up and down within each cylinder, a connecting rod
links the bottom of the piston to the crankshaft, and the combined
force of all the engine’s pistons turns the crankshaft to
create power.
the four stroke cycle
Now that you’re familiar with the most basic parts, here’s
how it all works:
Stroke 1: Intake – At the start
of this stroke, the intake valve opens to allow the air/petrol
mixture to be sucked into the cylinder by the downward movement
of the piston. The mixture that gets sucked in is now a very fine
mist (figure 2).
Stroke 2: Compression – The intake
valve closes at about the time the piston starts to move upward
again. The piston doesn’t ride all the way to the top, but
goes just high enough to leave a small space within the top of
the cylinder. Since the valves are closed and the fuel now has
nowhere to escape, it gets compressed into this tiny space, which
is called the combustion chamber. At this point, the fuel is now
very volatile and ready to be ignited (figure 3).
Stroke 3: Ignition – Once the
piston reaches its highest point, the spark plug ignites the compressed
and highly volatile fuel, causing a powerful explosion within
the cylinder. This forces the piston down, which in turn pushes
down the connecting rod which twists the crankshaft around. The
more powerful the explosion, the more power the engine will produce
(figure 4).
Stroke 4: Exhaust – As the piston
starts to move upward again, the exhaust valve opens so that the
piston can push the spent fuel out of the cylinder in time for
the next intake stroke (figure 5).
The 4-stroke cycle is an amazing process because it all happens
with so much force and unimaginable speed. Even with the average
engine sitting at idle, a complete 4-stroke cycle is happening
at around 3 times every second. Each of the ten cylinders in a
typical Formula One engine, at maximum RPM, will go through this
cycle around 75
times every second!
If you'd like a more thorough description of how a petrol engine
works, and the the parts involved, you can click
this link.
This page will be continually updated.
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