Diesel engines are the power behind our biggest machines - trucks, trains, ships and submarines.On the surface, they are similar to regular gasoline engines, but they produce more power and are more efficient in slightly different ways.Let's take a closer look.
Like a gasoline engine, a diesel engine is an internal combustion engine.An internal combustion engine is a place where fuel burns in the main part of the engine (the cylinder).This is very different from the external combustion engines used in older steam locomotives.In a steam engine, there is a big fire at one end of the boiler, and water can be heated to make steam.The steam flows down the long tube to the cylinder at the other end of the boiler, where it pushes the piston back and forth to move the wheels.This is external combustion, as the fire is outside the cylinder (in fact, usually 6-7 meters or 20-30 feet away).
In a gasoline or diesel engine, fuel burns inside the cylinder.The internal combustion wastes much less energy because heat does not have to flow out of the place where the cylinder is made: everything happens in the same place.This is why internal combustion engines are more efficient than external combustion engines (they produce more energy from the same volume of fuel).
Both gasoline and diesel engines use internal combustion, but in slightly different ways.In a gasoline engine, fuel and air are injected into small metal cylinders.A small spark from the spark plug ignites the compressed mixture of pistons, causing the mixture to explode, generating power to push the piston against the cylinder and (through the crankshaft and gears) turn the wheels.
Diesel engines are simpler.First, air enters the cylinder and compresses it.Diesel engines compress air much better than gasoline engines.In a gasoline engine, the fuel-air mixture is compressed to about one-tenth of its original volume.But in a diesel engine, the air is compressed 14 to 25 times.Compressed gas produces heat. Imagine how much heat is produced by forcing air to take up 14 to 25 times less space than it normally does.So much heat, and the air became very hot - usually at least 500°C (1000°F), and sometimes even hotter.Once the air is compressed, the fuel is typically (in modern engines) injected into the cylinder by an electronic fuel injection system that resembles a complex aerosol tank.The air is so hot that the fuel ignites and explodes instantly without the need for a spark plug.This controlled explosion pushes the piston back from the cylinder, creating the power to drive the vehicle or machine that installs the engine.As the piston returns to the cylinder, exhaust gas is pushed out through the exhaust valve, and the process is repeated hundreds or thousands of times per minute!