Figure 2-2 - Air Fuel Ratio Effect On Catalytic Converter Efficiency - Delphi Multec 3.5 Applications Manual

Fundamentals
Conversion Efficiency for a Typical Three-Way Catalyst
100
80
Rich Region: where little O
available, so
be done to NO
means stripping away oxygen)
60
40
13.0
2.2.1.4 Lean Mixtures
2-6
is
2
reduction can easily
. (Reduction
X
CO
14.0

Figure 2-2 - Air Fuel Ratio Effect on Catalytic Converter Efficiency

• A mixture with "excess air"; also described by a Lambda >1.00 or an
equivalence ratio <1.00
Lean mixtures have excess oxygen and higher combustion temperatures
resulting in increased oxides of nitrogen (NO
(NO) is the primary oxide created. It forms at a significant rate when
combustion chamber temperatures are above 1200
of NO formation increases with excess oxygen concentration,
x
temperature and time at temperature. NO
stoichiometry. Lean mixtures above a 16 – 17 to 1 air/fuel ratio decrease
NO production due to the lowering of combustion temperatures.
x
While NO production is an undesirable product of running slightly lean,
x
there are several benefits that can be realized by running lean of
stoichiometry. A controlled lean combustion process can reduce the
output of hydrocarbon (HC) and carbon monoxide (CO) emissions, as well
as reducing fuel consumption. Diluting the intake charge with a non-
Multec 3.5 Fuel Injector Application Manual
Window
+/- 0.3
14.6 15.0
Air/Fuel Ratio
x
is typically highest just lean of
x
Delphi Energy and Chassis Systems
Lean Region: where excess O
available to oxidize HC & CO.
(Oxidizing means adding oxygen)
NO
16.0
) emissions. Nitric oxide
o o
F (650 C.) The rate
Revision: 11/05-1
is
2
X