How Does An Engine Work?

HOW DOES AN ENGINE WORK?

by 

Elias Dodge (age 12)

The gasoline engine is an internal combustion engine. This means that fuels are burned inside it to provide power. The engine has something inside in it called an intake valve and an exhaust valve. Older engines have one intake valve and one exhaust valve. Some engines have two intake valves and one exhaust valve. Most high-performance engines have two intake valves and two exhaust valves. The intake and exhaust valves hang from the camshaft.

There is also something called an injector. The injector opens and lets out a mixture of fuel and air, then the intake valve[s] open, letting the mixture into the cylinder [the compartment containing the piston]. The piston is what is pushed when the fuel is burned. After the fuel is injected, the piston goes up, compressing the air inside the cylinder. The more compressed the air is inside the cylinder, the easier it is to burn fuel.

Then inside the engine, a spark plug ignites a spark and the fuel explodes, pushing the piston back down. Each time a piston goes down it turns something called a crankshaft around. The crankshaft is a revolving shaft that is driven by, or drives a crank.When the crankshaft goes around, the timing belt makes the camshaft open the valves at the right time.

The crankshaft is usually connected to the flywheel and the clutch. The flywheel is on the end of the crankshaft. When the crankshaft is spun around, the flywheel goes around. The flywheel has gear teeth around the edge, and when you engage the starter, it has a gear that engages those teeth and turns the flywheel. Turning the flywheel moves the crankshaft, which opens the valves. Then the process starts over.

The PCM [a computer] tells the injectors and the spark plugs when to fire. The flywheel also holds kinetic energy [energy in motion]. This is mainly to help smooth shifts and to keep engine RPMs [revolutions per minute] up, but it's a balancing act. A heavier flywheel requires more time and energy for the engine to get the RPMs up. A heavier flywheel also makes the engine lose RPMs more slowly because more kinetic energy is present in the rotating assembly and/or the drivetrain. Keeping the RPMs up is good for smoother shifts, but of course the flywheel shoudn't be to heavy, because it would slow the car's accelerartion. Lightweight flywheels are faster and are prefered by performance enthusiasts because they keep the RPMs up. Cars with automatic transmision have a flex plate instead of a flywheel, which is thinner. The timing belt runs from the flywheel or flex plate to the camshaft, and makes it so the camshaft opens the valves at the right time.

WHAT ARE OCTANE NUMBERS?

When you go to the gas station, you choose what type of gas you want. You might have wondered what the numbers on the buttons you hit to start the pump are. These numbers are called octane numbers. The octane number is the indication for antiknock quality. Well what exactly is antiknock? Gasolines are graded by their ability to resist exploding too soon or too quickly during the compression process within the cylinders of a gasoline engine. These explosions reduce energy and could damage the engine, and create a "knocking" or "pinging" sound. A gasoline's ability to resist knocking and to burn smoothly is its antiknock quality. Higher octane numbers mean the gasoline has greater antiknock qualities. So if you hit the 93 button that is higher antiknock quality, although it is more expensive.


(edited with help for Homeschool Project Fair)


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