Delphi Multec 3.5 Applications Manual page 21

Multec 3.5 Fuel Injector Application Manual
2.2.1.3 Rich Mixtures
Delphi Energy and Chassis Systems
design, fuel quality (contaminants and other non-combustibles) and the
limited time available to complete the process (especially at high engine
rpm.) all contribute to less than ideal combustion.
A catalytic converter is usually used in the exhaust system to transform
the harmful by-products of combustion to less harmful gases:
HC, CO, NOx Three-way catalyst
Figure 2-2 illustrates the relationship between the air/fuel ratio and
catalytic converter efficiency. Optimum converter efficiency is achieved
at 14.5 +/- 0.3 A/F.
• A mixture with "excess fuel"; also described by a Lambda < 1.00 or an
equivalence ratio >1.00
Rich mixtures have a larger proportion of fuel relative to the
stoichiometric ratio, which typically results in increased fuel consumption
and hydrocarbon emissions. As the amount of fuel in the ratio increases, it
displaces intake air, and thus oxygen, in the mixture. This lack of oxygen
results in some portion of the fuel to be incompletely combusted, thus
increasing hydrocarbon emissions. If excessively rich, the lack of oxygen
can also result in a large increase in carbon monoxide emissions (CO).
Controlled rich mixtures are regularly used at vehicle start-up when the
engine is cold. This is done to help ensure vehicle start and performance
quality, as it is more difficult for fuel to vaporize under these conditions.
Rich mixtures may also be used under conditions where maximum engine
power is required, or to help protect the catalytic converter under high
load conditions.
Fundamentals
H O, CO , N
2 2 2
Revision: 11/05-1 2-5