A diesel engine is powered by extreme air pressure that ignites the fuel in the cylinders to create internal combustion. This is why diesel vehicles require drivers to wait several seconds after attempting to start the ignition. The waiting period gives the air pressure time to accumulate in the cylinders.
Unlike gasoline engines, diesel engines have no spark plugs. Instead, they use forced compressed air to create sufficient pressure for an explosion. In modern vehicles, this is monitored by a computer in the vehicle.
The combustion cycle for a diesel engine consists of four strokes, just like a gasoline engine. The first stroke opens the intake valve, then the second stroke creates compressed air with the piston. The third stroke injects fuel into the cylinder and returns the piston to its original position, and the final stroke releases the exhaust from the fuel combustion.
The longer a diesel engine runs, the more fuel-efficient it becomes. This is because it uses less fuel as compressed air in the cylinder gets hotter. This is why some models come with glow plugs, which generate heat independent of the cylinder so the combustion can take place faster.
The diesel engine was invented by Rudolf Diesel in 1897. However, the engine continues to experience changes and developments as manufacturers find new ways to make it more efficient.