Snap-On Diagnostics DGA 1000, Manual, Page: 36 / 116

2-4
Analyzer Screen Display Features
Lambda and AFR Calculation
The
DGA 1000 Gas Analyzer
uses the Brettschneider formula to
calculate Lambda (
λ
) and Air Fuel Ratio (AFR) values during the
emission tests.
Lambda (
λλλλ
) and Catalytic Converter Efficiency
Lambda is another characterization of the stoichiometric perfect
combustion point. The
λ
formula includes a factor for the specific
fuel used. Different fuels have different stoichiometric air-fuel
ratios, but optimal combustion is always achieved when Lamda =
1.00. Smaller
λ
numbers indicate a rich air-fuel ratio; larger
λ
numbers indicate a lean air-fuel ratio.
The figure below shows the relationship between certain pollutant
exhaust gases and catalytic converter efficiency. Optimal
combustion (
λ
= 1) is characterized by a highly-efficient conversion
of the pollutants
HC
,
CO
, and
NO
x
into
CO
2
,
H
2
O
, and
N
2
.
O
2
and NO
x
Measurement
O
2
and NO
x
gas concentration are measured using
electrochemical (fuel cell) sensors. A fuel cell sensor provides an
electrical response that is proportional to the concentration of the
sample gas.
Figure 2-3
: Relationship Between Certain Pollutant Exhaust Gases and Catalytic Converter Efficiency