by Dick Stewart

Created on: April 03, 2009   Last Updated: April 05, 2009

Since technically, electric cars are powered by "motors," only combustible fuel-powered cars have "engines" (from the engineering category "heat engine," meaning they get their power from the expansion of gases caused by adding heat). Whatever the fuel, most of these engines work the same way, with a few variations.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /

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Your engine starts with a metal casting with cylinders that contain tight-fitting pistons, sort of like a really thick Pringle in a Pringles can. Each piston acts on a piston rod attached to the end of a crank arm or "throw" on a crankshaft (like the end of a crank where the handle is attached), like the crank arm the pedal is attached to on a bicycle. The piston rod is like your leg. The piston pushes down on the piston rod, which pushes down on the end of the crank arm like your foot on the pedal, turning the crank, providing the rotating force that drives your car.

Above the piston there is a space where the fuel/air mixture explodes (the combustion chamber). It is that explosion of a fuel/air mixture in the combustion chamber above the piston that increases the pressure in the combustion chamber, which pushes the piston down and creates the power that runs your car.

The volume "displaced" or swept by the piston as it travels all the way up in a cylinder is the "displacement" or size of the cylinder. That displacement is measured in cc, liters or Cubic Inches Displacement ("C.I.D."). Multiply the displacement of one cylinder by the number of cylinders, and you have the "liters" or cubic inches you see listed for an engine. It's a rough measure of how much fuel/air is exploded in one Otto cycle, so it has long been associated with the power potential of an engine.

Most modern engines work on the Otto cycle - also called "4-stroke" -named for Nicholaus Otto, a German engineer who was among the first to experiment with four-stroke engines. The four strokes refer to the piston's movement in the cylinder.

1. With the piston near the top of the cylinder, the intake valve (or valves) opens. On the down-stroke of the piston in its cylinder, the atmosphere (or a compressor called a supercharger) pushes fuel/air in past the intake valves.
2. Near the bottom of that intake (1st) stroke the intake valve(s) close, sealing the combustion chamber, and in the 2nd (compression) stroke the piston travels back up in the cylinder, compressing the fuel/air (or just air) mixture.
3. Near the top

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