Fuel Atomization - Delphi Multec 3.5 Applications Manual

Multec 3.5 Fuel Injector Application Manual
2.2.1.5 Non-Combustible Mixtures
2.2.2

Fuel Atomization

Note
Delphi Energy and Chassis Systems
combustible dilutant can reduce NOx. One of the most common of these
is exhaust gas, recirculated into the mixture via an EGR system. (Ref.
Delphi EGR Applications Manual for more information on this process).
Air/fuel ratios outside the combustible mixture limits (too rich or too lean)
cause engine misfire, reduced power, a significant increase in emissions
(primarily HC from unburned fuel) and poor overall engine performance.
Combustible mixture limits are dependent on many factors, some of which
are combustion chamber design, ignition system energy, fuel composition,
amount of EGR, etc.
Fuel atomization is the transformation of bulk fuel into spray. Fuel enters
the intake port as an atomized stream. The fuel droplets evaporate when
they mix with the air and also when they contact a hot surface. When the
intake valve opens, the air/fuel mixture passes into the cylinder where it
mixes with residual exhaust gases. Combustion is initiated near the end of
the compression stroke when the spark plug fires.
The optimum fuel spray characteristics for a particular application are
dependent upon the following:
• Intake manifold design
• Mixture motion control device
• Combustion chamber characteristics
• Spark plug configuration
• Injector spray targeting
• Injection timing
• The temperature of the target area
These criteria must be validated.
Combustion requires vaporized fuel. One of the functions of the fuel
injector is to atomize the fuel. Smaller fuel particles are both easier to mix
uniformly with air and require less heat to vaporize. Fuel particle size is
dependent on system fuel pressure, spray pattern, and injector spray
orifice design.
Limits to these characteristics must be totally understood. Combustion
efficiency and rate are dependent on specific application and fundamental
engine design.
Fundamentals
Revision: 11/05-1 2-7