In this simplified animation, the green device attached to the left side of the cylinder is a fuel injector. However, the injector on a 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 be able 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 a problem, 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 combustion process. 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 rather than direct injection.
In a car engine, therefore, all of the fuel is loaded into the cylinder during the intake stroke and then compressed. A diesel compresses only air, so the compression ratio can be much higher. The higher the compression ratio, the more power is generated. Some Diesel engines contain a glow plug of some sort that is not shown in this figure. When a Diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel.