Diesel

One big difference between a diesel engine and a gas engine is in the injection process. Most car engines use port injection or a carburetor. A port injection system injects fuel just prior to theintake stroke (outside the cylinder). A carburetor mixes air and fuel long before the air enters the cylinder. In a car engine, therefore, all of the fuel is loaded into the cylinder during the intakestroke and then compressed. The compression of the fuel/air mixture limits the compression ratio of the engine -- if it compresses the air too much, the fuel/air mixture spontaneously ignites andcauses knocking. Because it causes excessive heat, knocking can damage the engine.

Diesel engines use direct fuel injection -- the diesel fuel is injected directly into the cylinder.

The injector ona diesel engine is its most complex component and has been the subject of a great deal of experimentation -- in any particular engine, it may be located in a variety of places. The injector has to beable to withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist. Getting the mist circulated in the cylinder so that it is evenly distributed is also aproblem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustionprocess.

Some diesel engines contain a glow plug. When a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel. The glow plug is anelectrically heated wire (think of the hot wires you see in a toaster) that heats the combustion chambers and raises the air temperature when the engine is cold so that the engine can start. According toCley Brotherton, a Journeyman heavy equipment technician:

All functions in a modern engine are controlled by the ECM communicating with an elaborate set of sensors measuring everything from R.P.M....