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How a car engine works Part 2

The ­principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!
Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867.
They are:

  • Intake stroke
  • Compression stroke
  • Combustion stroke
  • Exhaust stroke

The piston is connected to the crankshaft by a connecting rod. As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:

1.The piston starts at the top, the intake valve opens, and thepiston moves down to let the engine take in a cylinder-full of air andgasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work

2.Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful.

3.When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down.

4.Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe.

Now the engine is ready for the next cycle, so it intakes another charge of air and gas.

The motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear(straight line). In an engine the linear motion of the pistons isconverted into rotational motion by the crankshaft. The rotationalmotion is nice because we plan to turn (rotate) the car's wheels withit anyway.

Come back tomorrow for the next part of the series.


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