A light-automotive diesel engine typically has a higher compression ratio than a comparable gasoline engine. This high compression ratio heats the air in the combustion chamber to a temperature high enough to ignite the fuel when it is injected. High injection pressures are needed to overcome the compression and combustion pressures in the combustion chamber, and break up the fuel into small particles.
Because of these high pressures, the injector pump and the injector are made from highly polished, and accurately-sized components.
The injector pump can be an in-line type, and it is driven by the engine.
Or it can be a rotary type, also driven by the engine.
The quantity of air taken in on the intake stroke is not controlled by the driver. The driver controls how much fuel is delivered to the engine.
A characteristic of all diesel engines is that at a fixed fuel setting, the amount of fuel delivered to the engine will increase as engine speed, and pump speed increases.
This is called the rising characteristic of the fuel injection system, and unless it is controlled, over-speeding of the engine will result.
Also, because combustion pressures are greater in a diesel engine than in a comparable gasoline engine, the components are stronger and heavier. The higher mass of these reciprocating and rotating components needs to be controlled, or damaging forces could be generated.
To achieve this control, all diesel engines use a governor to control how much fuel is delivered from the injection pump, to the injectors, and into the engine.
There are several types of governors. Some operate mechanically, some are pneumatic, and some are hydraulic.
Diesel engines need assistance to make cold starting easier. Most diesel fuel injection systems inject extra fuel when starting, to ensure sufficient fuel will vaporize and burn in the combustion chamber.
Indirect injection engines may also use heater plugs, or glow plugs, which usually screw directly into the combustion chamber. They only heat the air, and do not begin the combustion.
Source: CDX Global
