Engines

Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.

Photo courtesy DaimlerChrysler
2003 Jeep® Grand Cherokee Engine

You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." What does all of that mean?

If you have ever wondered about this kind of stuff, then read on -- In this article, we'll discuss the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how to increase performance.

The Basics
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. Two things to note:

There are different kinds of internal combustion engines. Diesel engines are one form and gas turbine engines are another. See also the articles on HEMI engines, rotary engines and two-stroke engines. Each has its own advantages and disadvantages.
There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats is the best example of an external combustion engine. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. Internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus an internal combustion engine is a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

Inside a typical car engine

Almost all cars today use a reciprocating internal combustion engine because this engine is:

Relatively efficient (compared to an external combustion engine)
Relatively inexpensive (compared to a gas turbine)
Relatively easy to refuel (compared to an electric car)

These advantages beat any other existing technology for moving a car around.

Combustion is Key
To understand the basic idea behind how a reciprocating internal combustion engine works, it is helpful to have a good mental image of how "internal combustion" works. One good example is an old Revolutionary War cannon. You have probably seen these in movies, where the soldiers load the cannon with gun powder and a cannon ball and light it. That is internal combustion, but it is hard to imagine that having anything to do with engines.

A more relevant example might be this: Say that you took a big piece of plastic sewer pipe, maybe 3 inches in diameter and 3 feet long, and you put a cap on one end of it. Then say that you sprayed a little WD-40 into the pipe, or put in a tiny drop of gasoline. Then say that you stuffed a potato down the pipe. Like this:

I am not recommending that you do this! But say you did... What we have here is a device commonly known as a potato cannon. When you introduce a spark, you can ignite the fuel.

What is interesting, and the reason we are talking about such a device, is that a potato cannon can launch a potato about 500 feet through the air! There is a huge amount of energy in a tiny drop of gasoline.

Continued