PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
3.
(1) Methods. There are two methods of injecting fuel into a
compressionignition engine. One method is air injection. This method uses
a blast of air to force a measured charge of fuel into the combustion
chamber. The other method is solid injection, where direct mechanical
pressure is placed on the fuel itself to force it into the combustion
chamber. Only the solid injection system will be discussed in this task
because air injection is virtually unused in automotive applications.
(2) Fuel Atomization and Penetration. The fuel spray entering the
combustion chamber must conform to the chamber's shape so that the fuel
particles will be well distributed and thoroughly mixed with the air. The
shape of the spray is determined by the degree of atomization and
penetration produced by the orifice through which the fuel enters the
chamber. Atomization is the term used to indicate the size of the droplets
into which the fuel is broken down. Penetration is the distance from the
orifice that the fuel droplets attain at a given phase of the injection
period. The dominant factors that control penetration are the length of the
nozzle orifice, the diameter of the orifice outlet, the viscosity of the
fuel, and the injection pressure of the fuel. Increasing the ratio of the
length of the orifice to its diameter will increase penetration and decrease
atomization. Decreasing this ratio will have an opposite effect. Because
penetration and atomization are opposed mutually and both are important, a
compromise is necessary if uniform fuel distribution is to be obtained. The
amount of fuel pressure for injection is dependent on the pressure of the
air in the combustion chamber, and the amount of turbulence in the
combustion space.
(3) Function of the Injection System. It is impossible to cover the
this lesson. However, the operation of the more common systems will be
discussed. If the three basic functions of diesel fuel injection are kept
in mind while studying the operation of the systems, it will be easier to
understand how they work. The three basic functions are:
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