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Figure 2. Inline - The cylinders are arranged in a line in a single bank.
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Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.
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Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.
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.
Displacement
The combustion chamber is the area where compression and combustion take place. As the piston moves up and down, you can see that the size of the combustion chamber changes. It has some maximum volume as well as a minimum volume. The difference between the maximum and minimum is called the displacement and is measured in liters or CCs (Cubic Centimeters, where 1,000 cubic centimeters equals a liter).
Here are some examples:
- A chainsaw might have a 40 cc engine.
- A motorcycle might have a 500 cc or a 750 cc engine.
- A sports car might have a 5.0 liter (5,000 cc) engine.
If you have a 4-cylinder engine and each cylinder displaces half a liter, then the entire engine is a "2.0 liter engine." If each cylinder displaces half a liter and there are six cylinders arranged in a V configuration, you have a "3.0 liter V-6."
Generally, the displacement tells you something about how much power an engine can produce. A cylinder that displaces half a liter can hold twice as much fuel/air mixture as a cylinder that displaces a quarter of a liter, and therefore you would expect about twice as much power from the larger cylinder (if everything else is equal). So a 2.0 liter engine is roughly half as powerful as a 4.0 liter engine.
You can get more displacement in an engine either by increasing the number of cylinders or by making the combustion chambers of all the cylinders bigger (or both).
Other Parts of an Engine
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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.
Valves
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.
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?
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.
- 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.
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.
- 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.
As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. Most of these subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine. Let's look at all of the different subsystems used in modern engines in the following sections.