Tuesday, January 1, 2008

Internal combustion: suck, squeeze, bang, and blow

Disclaimers: there are some sexual innuendos/references in this post. If you’re the squeamish type, move along, please. This post is in reference to gasoline powered engines. Diesel engines function a little bit differently. Also, this post is very simplified. There are more steps and more intricacies than I’ve listed below, but these are the basics.

Internal combustion engines (your car engine) work using four basic steps. You will remember this forever because they sound dirty.


The four steps are: suck, squeeze, bang, and blow. (There are technical terms but these are SO MUCH better.)

You’ve heard of cylinders, right? That’s where the magic takes place.

When someone refers to a car as a V-8 or a 4-cylinder, or an inline-6, they are referring to the number of cylinders in the engine and the arrangement of those cylinders. A V-6, for example, has 6 cylinders, arranged in a shape approximating a V. An inline-6, on the other hand, has 6 cylinders in, you guessed it, a line. 4-cylinder engines are nearly always arranged in a line. V-style engines are arranged in that particular way because it can allow more cylinders to fit into a smaller space. More cylinders usually means more power (thus, sports cars are trucks typically have 6, 8, or sometimes as many as 12 cylinders, while your little grocery-getter has 4). More cylinders also means, typically, more gas consumption, though factors like engine efficiency, aerodynamics, tire inflation, and a thousand other things can also impact gasoline consumption.

With me so far?

Associated with each cylinder in an engine is a piston, a spark plug, and some valves.

The pistons fit within the cylinders and move in and out. The piston is never completely out of the cylinder, but goes from a position I consider “just the tip” to being nearly all the way in. Pistons are controlled by something called a crankshaft, which is bent in such a way that half of the pistons are moving into their cylinders while the other half are moving out. The term “RPM” (revolutions per minute) refers to how many revolutions the crankshaft makes in one minute. All engines have something called a “redline,” which is the max number of RPMs you can get before the engine explodes.

Ready for those 4 steps now?

What happens is a mixture of vaporized fuel and oxygen, delivered by way of fuel injectors or, in older cars, a carburetor, is SUCKED into the cylinder by the piston moving out of the cylinder, creating a vacuum.

Then, that fuel/oxygen mixture is SQUEEZED by way of the piston moving into the cylinder, making a smaller space. The explosion, which comes next, is made stronger because of this compression.

Then the spark plug sends a spark into that compressed fuel/oxygen mixture, igniting it so it explodes. BANG. The piston is driven out of the cylinder by the force of the explosion.

In the final step, BLOW, is the piston again moves into the cylinder, pushing the exhaust from the explosion out of the valves and putting itself in position to SUCK the fuel/oxygen mixture into the cylinder again. The valves open and close and are controlled by something called a camshaft. Exhaust from the explosion goes out the valves, travels through some tubes and pipes and eventually goes through your muffler and goes out the ass end of your car.

The camshaft and the crankshaft are connected, usually with something called a timing belt. The valves and pistons have to work in a very precise order or the valves will open at the wrong time, the explosion will not be contained within the cylinder, and you’ll have all sorts of problems.

The explosion that propels the piston out of the cylinder is what makes your car go. The piston shoots out of the cylinder, driven by the force of the explosion, and that energy is transferred, by way of a series of gears and rods, to your wheels. This energy transfer includes the transmission, which can be a manual or an automatic. The transmission transfers torque (pronounced tork, sort of means power) to the wheels. More torque is need at slower speeds due to inertia, less torque is needed once the car has some momentum. The transmission also controls RPMs.

Oil is a requirement in the workings of pistons and cylinders. Much like you need lubrication for…certain activities that involve in-and-out motions, pistons and cylinders need lubrication for their in-and-out motions. Without it, the friction and heat get to be too much, and your engine will seize.

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