Published: 14 September, 2005

Series of explosions pushes pistons in order to move car

How does burning gasoline make a car move?

We can draw many similarities between an engine in a car and the human body on a bicycle. Your body is the bicycle's engine. While you need food, water, and air, the gasoline engine needs gasoline, electricity, and air.

There are various types of combustible fluids such as diesel and gasoline used in engines. A gasoline engine mixes air and gasoline in a specific proportion called the stoichiometric ratio, ensuring the fuel has the right amount of oxygen for combustion. Once ignited, power is generated: Air + Gasoline + Spark = Power

A gasoline engine is an internal combustion engine; basically a block of metal, called the engine block, inside of which gasoline ignites in a controlled manner. A typical engine has three mechanical components directly exposed to the explosion; the cylinder, the pistons, and the valves.

Cylinders: Engine blocks have cylinders, typically 4, 6, or 8, each about the size of a soda can. The total volume inside the cans gives the engine displacement, typically in liters or cubic inches. A stoichiometric ratio of air/fuel mixture is sprayed into the cylinder and ignited. The cylinders will contain explosions in sequence, or firing order.

Pistons: The piston is like the plunger in a syringe and compresses the air/fuel mixture in each cylinder. In a gasoline engine, this pressurized mixture is ignited by the spark plug. The explosion pushes the piston with great force. The piston acts like your leg pushing on the pedal when riding a bike.

Valves: Each cylinder has at least one opening for air/fuel mist to enter, and at least one for the exhaust gas to escape after the explosion. The intake and exhaust valves open and close at the right times so the whole process can occur with the best results.

Cars have four stroke engines. The four stokes, or stages in each cylinder are: Intake (air/fuel enters intake valve), Compression (valves closed), Combustion (valves closed, explosion), and Exhaust (exhaust valve opens).

In order to get that power to the wheels, every piston is attached to the crankshaft, similar to your legs attached to a bike's pedals. The explosion pushes the piston and turns the crankshaft, just like your muscles make your leg push and turn the bike's pedal.

While one leg pushes down, the other leg rests on the other pedal and is pushed up. This also happens in the engine block. While one piston is being pushed down by an explosion, another will be pushed up by the rotating crankshaft to compress the air/fuel mixture in another cylinder. Each piston is at a different point of the cycle, providing a steady delivery of power.

A bike uses a chain to send power to the rear wheel. The crankshaft sends power to the wheels through various driveshafts. Between the crankshaft and the driveshafts are various gears, in the transmission, to make the most out of the engines power. You can shift those gears like you would shift the bike's gears.

Next time you see an engine while it's running, imagine looking inside it and seeing over a thousand controlled explosions every second where gasoline, air, and a spark have come together. To make it happen, those pistons and valves need to move very fast.