A diesel engine compresses air to the point where it is hot enough to ignite the diesel fuel. This is why it is also called the compression engine. Basically, you compress air (making it very hot) and when you squirt the diesel fuel in with the hot air, it bursts into flame.

How Does it Work?

The diesel engine is an intermittent-combustion piston-cylinder device – in other words, it doesn’t burn fuel continuously, but in discrete stages. It operates on either a two-stroke or four-stroke cycle; however, unlike the spark-ignition engine, the diesel engine sucks only air into the combustion chamber on its intake stroke (not air and fuel, like a gasoline engine). The diesel engine gains its energy by burning fuel injected or sprayed into the compressed, hot air charge within the cylinder. The air must be heated to a temperature greater than the temperature at which the injected fuel can ignite. Fuel sprayed into air that has a temperature higher than the "auto-ignition" temperature of the fuel spontaneously reacts with the oxygen in the air and burns. Air temperatures are typically in excess of 526 C. At engine start-up, supplemental heating of the cylinders is usually required, since the temperature of the air within the cylinder can be too cold.

Diesel engines power freight trucks, large tractors, locomotives, and vessels. A limited number of automobiles also are diesel powered, as are small electric-power generators.