Delphi Multec 3.5 User Manual

Fundamentals Multec 3.5 Fuel Injector Application Manual
2-18 Delphi Energy and Chassis Systems
Revision: 11/05-1
2.2.7.3 Cold Engine/ Cold Ambient Effects on Combustion
During cold engine starts, additional fuel is required to make a
combustible mixture due to the fact that the fuel will not vaporize as
readily on the cold engine surfaces. Fuel atomization and spray
distribution are extremely critical during this phase since there is little heat
for fuel vaporization. The engine controller compensates by commanding
a richer air-fuel mixture until intake valve and cylinder temperatures are
adequate for fuel vaporization, typically estimated by using a coolant
temperature sensor. Once adequate operating temperatures are reached,
the engine controller typically reverts back to a stoichiometric A/F.
Due to the lack of heat to completely vaporize fuel, the richer A/F, and the
exhaust catalyst not being up to full operating temperature for maximum
efficiency, exhaust emissions (especially HC and CO) during the period
just after start-up has a significant contribution to overall emissions
output. Focus on reduction of start-up exhaust emissions generation has
increased with the implementation of SULEV / PZEV (Super Ultra Low
Emissions Vehicle / Partial Zero Emissions Vehicle) exhaust
requirements.
Injector spray quality and spray targeting options can affect the cold start
HC emissions. Engine development and calibration should include
injector spray optimization where cold start HC emissions are a concern.
Note:
When sizing injectors, verify the injector’s ability to supply extra cold
engine fuel to accommodate lower numerical A/F ratios. This often
requires vehicle cold weather testing with the engine under high load.
2.2.7.4 Injector Tip Icing
Normal combustion processes generate large quantities of water vapor.
Other sources, such as exhaust gas recirculation (EGR), also contribute to
the quantity of water vapor within the intake system. When the engine is
shut off and allowed to cool, water vapor will condense on the coolest
surfaces within the intake manifold, such as the intake air passages and the
tips of the fuel injectors. If ambient temperatures are low enough and the
engine soak time is long enough, this condensate will freeze, potentially
restricting or completely blocking the flow of fuel.
This phenomenon must be considered during the design of both the
manifold passage shape and the placement of the injector in the manifold
or head. Cold weather test procedures need to address this possibility.
Since EGR can be a major source of water vapor, disabling EGR at low
ambient temperatures is an option if icing is a problem. However, care
should be taken when disabling EGR for extended periods, as this lack of

Delphi Multec 3.5 Specifications

General

Brand	Delphi
Model	Multec 3.5
Category	Laboratory Equipment
Language	English