Time to go take the kids to the big soccer game. You gather the stuff, hand out the soccer balls, make sure everyone has cleats and jerseys, almost forget your keys, get them, hop in the car, refuse yet another bathroom request or you’ll be late, and turn the key. Your car roars to life and you back out of the garage and get to the game with seconds to spare.
Of course, you expected the car to start. Those (hopefully) rare days when the car revs and dies or doesn’t even start are generally the start or cause of a rather miserable day. Having reliable engines is definitely a good thing. But how does it work, anyway?
The Engine: The Power Behind Your Car
For simplicity’s sake, we’ll just discuss the internal combustion engine that comes standard in most cars. The basic idea of an engine is to release the energy stored in gasoline (or whatever fuel source you’d like to use), harness that, and translate the energy into motion. This process starts out in a method rather like launching a potato gun, or using alka seltzer to turn a film canister into a rocket. (If you don’t know what a film canister is, I pity you.)
For all of these examples, the motion comes because tightly compressed spaces with the right kick tend to expand explosively. This expansion provides propulsion for whatever nearby surface can be prevailed upon to move. In the case of a potato gun, you might get a bit of a nasty kick from the tube but the potato gets most of the force and goes rocketing away. A film canister presses the lid to the ground, can’t expand more that way, and shoots the rest of the canister into the air at high speeds. Expanding gas in an engine pushes pistons and voila, movement!
More Details on Piston Movement
Here’s what happens specifically.
You’ve got a cylinder with two injectors at the top. One puts fuel into the engine while the other lets air in as the piston moves downwards. The piston comes up again to compress the air and gasoline, and when it reaches the apex of its movement, the spark plug ignites the gas mixture. This explodes with force, pushing the piston down. The piston returns to the top to expel the exhaust, then the process starts over. Therefore, the piston moves down and up again twice for each cycle. To visualize, this page has a handy diagram of engine pistons.
Don’t forget that this entire cycle happens about 500 times a minute when your car is in motion, give or take depending on your car’s specs.
Later, we’ll talk about how combustion turns into motion.