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The purpose of a
gasoline car engine is to convert gasoline into
motion so that your car can move. Currently the
easiest way to create motion from gasoline is to
burn the gasoline inside an engine. Therefore, a car
engine is an internal combustion engine --
combustion takes place internally.
The principle behind
any reciprocating internal combustion engine: If you
put a tiny amount of high-energy fuel (like
gasoline) in a small, enclosed space and ignite it,
an incredible amount of energy is released in the
form of expanding gas. You can use that energy to
propel a potato 500 feet. In this case, the energy
is translated into potato motion. You can also use
it for more interesting purposes. For example, if
you can create a cycle that allows you to set off
explosions like this hundreds of times per minute,
and if you can harness that energy in a useful way,
what you have is the core of a car engine!
The internal combustion engine is an engine in which
the combustion of a fuel occurs with an oxidizer
(usually air) in a combustion chamber. In an
internal combustion engine the expansion of the high
temperature and pressure gases, which are produced
by the combustion, directly applies force to a
movable component of the engine, such as the pistons
or turbine blades and by moving it over a distance,
generate useful mechanical energy. The term internal
combustion engine usually refers to an engine in
which combustion is intermittent, such as the more
familiar four-stroke and two-stroke
piston engines
Today, internal
combustion engines in cars, trucks, motorcycles,
aircraft, construction machinery
and many others, most commonly use a four-stroke
cycle. As their name implies, operation of a four
stroke internal combustion engines have 4 basic
steps that repeat with every two revolutions of the
engine:
1) Intake - Combustible mixtures are emplaced in the
combustion chamber
2) Compression - The mixtures are placed under
pressure
3) Combustion/Expansion - The mixture is burnt,
almost invariably a deflagration, although a few
systems involve detonation. The hot mixture is
expanded, pressing on and moving parts of the engine
and performing useful work.
4) Exhaust - The cooled combustion products are
exhausted into the atmosphere
Here is what happens as
the engine goes through its cycle:
-
The piston starts
at the top, the intake valve opens, and the
piston moves down to let the engine take in a
cylinder-full of air and gasoline. This is the
intake stroke. Only the tiniest drop of gasoline
needs to be mixed into the air for this to work.
(Part 1 of the figure)
-
Then the piston
moves back up to compress this fuel/air mixture.
Compression makes the explosion more powerful.
(Part 2 of the figure)
-
When the piston
reaches the top of its stroke, the spark plug
emits a spark to ignite the gasoline. The
gasoline charge in the cylinder explodes,
driving the piston down. (Part 3 of the figure)
-
Once the piston
hits the bottom of its stroke, the exhaust valve
opens and the exhaust leaves the cylinder to go
out the tailpipe. (Part 4 of the figure)
Many engines overlap
these steps in time; jet engines do all steps
simultaneously at different parts of the engines.
Now let's look at all the parts that work together
to make this happen.
Cylinder |
Spark Plug |
Valve |
Piston |
Piston Ring
| Connecting
Rod |
Crankshaft |
Sump
Cylinder
The core of
the engine is the cylinder, with the piston moving
up and down inside the cylinder. The engine
described above has one cylinder. That is typical of
most lawn mowers, but most cars have more than one
cylinder (four, six and eight cylinders are common).
In a multi-cylinder engine, the cylinders usually
are arranged in one of three ways: inline, V or flat
(also known as horizontally opposed or boxer), as
shown in the following figures.
Inline - The cylinders are
arranged in a line in a single bank. =>
<= Flat - The cylinders are
arranged in two banks on opposite sides of the
engine.
V - The cylinders
are arranged in two banks set at an angle to one
another. =>
Different
configurations have different advantages and
disadvantages in terms of smoothness, manufacturing
cost and shape characteristics. These advantages and
disadvantages make them more suitable for certain
vehicles.
Spark Plug
The spark plug supplies
the spark that ignites the air/fuel mixture so that
combustion can occur. The spark must happen at just
the right moment for things to work properly.
Valve
The intake and exhaust valves open at
the proper time to let in air and fuel and to let
out exhaust. Note that both valves are closed during
compression and combustion so that the combustion
chamber is sealed.
Piston
A piston is a cylindrical piece of
metal that moves up and down inside the cylinder.
Piston rings
Piston rings provide a
sliding seal between the outer edge of the piston
and the inner edge of the cylinder. The rings serve
two purposes:
-
They prevent the fuel/air mixture
and exhaust in the combustion chamber from
leaking into the sump during compression and
combustion.
-
They keep oil in the sump from
leaking into the combustion area, where it would
be burned and lost.
Most cars that "burn oil" and have to have a
quart added every 1,000 miles are burning it
because the engine is old and the rings no
longer seal things properly.
Connecting Rod
The connecting rod
connects the piston to the crankshaft. It can rotate
at both ends so that its angle can change as the
piston moves and the crankshaft rotates.
Crankshaft
The crankshaft turns the
piston's up and down motion into circular motion
just like a crank on a jack-in-the-box does.
Sump
The sump surrounds the
crankshaft. It contains some amount of oil, which
collects in the bottom of the sump (the oil pan).
What can go wrong
with engines?
So you go out one morning and your
engine will turn over but it won't start... What
could be wrong? Now that you know how an engine
works, you can understand the basic things that can
keep an engine from running. Three fundamental
things can happen: a bad fuel mix, lack of
compression or lack of spark. Beyond that, thousands
of minor things can create problems, but these are
the "big three." Based on the simple engine we have
been discussing, here is a quick rundown on how
these problems affect your engine:
Bad fuel mix - A bad fuel mix
can occur in several ways:
-
You are out of gas, so the engine
is getting air but no fuel.
-
The air intake might be clogged,
so there is fuel but not enough air.
-
The fuel system might be
supplying too much or too little fuel to the
mix, meaning that combustion does not occur
properly.
-
There might be an impurity in the
fuel (like water in your gas tank) that makes
the fuel not burn.
Lack of compression - If the
charge of air and fuel cannot be compressed
properly, the combustion process will not work like
it should. Lack of compression might occur for these
reasons:
-
Your piston rings are worn
(allowing air/fuel to leak past the piston
during compression).
-
The intake or exhaust valves are
not sealing properly, again allowing a leak
during compression.
-
There is a hole in the cylinder.
The most common "hole" in a cylinder
occurs where the top of the cylinder (holding the
valves and spark plug and also known as the cylinder
head) attaches to the cylinder itself. Generally,
the cylinder and the cylinder head bolt together
with a thin gasket pressed between them to ensure a
good seal. If the gasket breaks down, small holes
develop between the cylinder and the cylinder head,
and these holes cause leaks.
Doing regular engine
maintenance
can help you avoid future
repairs.
Lack of spark -
The spark might be nonexistent or weak for a number
of reasons:
-
If your spark plug
or the wire leading to it is worn out, the spark
will be weak.
-
If the wire is cut
or missing, or if the system that sends a spark
down the wire is not working properly, there
will be no spark.
-
If the spark occurs
either too early or too late in the cycle (i.e.
if the ignition timing is off), the fuel will
not ignite at the right time, and this can cause
all sorts of problems.
Many other things
can go wrong. For example:
-
If the battery is
dead, you cannot turn over the engine to start
it.
-
If the bearings
that allow the crankshaft to turn freely are
worn out, the crankshaft cannot turn so the
engine cannot run.
-
If the valves do
not open and close at the right time or at all,
air cannot get in and exhaust cannot get out, so
the engine cannot run.
-
If someone sticks a
potato up your tailpipe, exhaust cannot exit the
cylinder so the engine will not run.
-
If you run out of
oil, the piston cannot move up and down freely
in the cylinder, and the engine will seize.
In a properly running
engine, all of these factors are within tolerance.
As you can see, an engine has a number of systems
that help it do its job of converting fuel into
motion. Lack of maintenance is the most important
reason for a car to break down.
Tips to keep the engine in a good
shape.
1. Regular oil
change is most important factor to keep the
engine running. If you do it more often than
suggested by manufacturer’s schedule, that’s even
better.
2. Try to avoid engine overheating.
3. Tune Up - Changing spark plugs, air
filter, timing belt and other items from maintenance
schedule will save you from expensive repairs.
4. Regularly examine your vehicle in order to fix
any small problem before it turns into a serious
damage.
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