Fuel Delivery Systems

For many years, diesel engines have been controlled by mechanical governors through intricately designed linkages, levers, and springs. The mechanical governors are phenomenal in their smoothness of operation and accuracy. When studying these old governors, one cannot help but marvel at the genius it took to design and build them. However, with the new strict emission regulations established to protect the environment, the old reliable friends have to go.

Modern diesel engines need to make fuel adjustments in milliseconds, mid-revolution of the crankshaft. Therefore, the industry must now turn to electronics for fuel control. Nearly all diesels today are manufactured with EDC. Examples of today’s fuel injection control system are the common rail system and the hydraulically actuated electronically controlled unit injectors, which will be discussed later in this chapter.

Fuel injection is now done under much higher pressures for complete atomization of fuel sprayed directly into the superheated air of the combustion chamber. Furthermore, electronic control means varying rates of fuel delivery per cylinder and degree of crankshaft movement. Additionally, it must be done under varying speed and load conditions for quieter and smoother performance. EDC can also compensate for extremes in temperature by injecting the precise amount of fuel to match ambient temperatures.

New combustion chamber design methods also aid fuel delivery to make engines cleaner and quieter. As an example, one method to reduce ignition clatter at idle is the use of a smaller pilot spray to initiate the combustion cycle, with greater amounts of fuel following ignition. Delivery tapers off near the completion of the combustion cycle for complete burn and low emissions. This and other innovative designs are possible through research, and are important to improve efficiency and meet new emission standards for diesel engines.

Modern high-pressure fuel injection systems can easily spray fuel into your body. Always wear eye protection and do not search for a fuel leak by placing your hand on a fuel injection line.