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Engines and the works

Source: Www.Howstuffworks.Com
Saturday, November 24, 2012

THERE'S a two-stroke engine as well as a four— stroke engine, steam engines and external combustion engines.

The list of technical jargon is enough to make your head spin if you're a newcomer to the motor industry. But here are some common questions and answers about engines.

What is the difference between a gasoline engine and a diesel engine? In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage.

What is the difference between a two-stroke and a four-stroke engine? Most chainsaws and boat motors use two—stroke engines. A two stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle. A hole in the lower part of the cylinder wall lets in gas and air.

As the piston moves up it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. You have to mix oil into the gas in a two-stroke engine because the holes in the cylinder wall prevent the use of rings to seal the combustion chamber. Generally, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting.

Are there any advantages to steam engines and other external combustion engines? The main advantage of a steam engine is that you can use anything that burns as the fuel. For example, a steam engine can use coal, newspaper or wood for the fuel, while an internal combustion engine needs pure, high-quality liquid or gaseous fuel.

Why have eight cylinders in an engine? Why not have one big cylinder of the same displacement of the eight cylinders instead?

There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big four litre cylinder. The main reason is smoothness.

A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.