AUTOplus manual
Page 42
B. LAMBDA CALCULATION
The value for Lambda is a determinant for the burning efficiency of an engine.
The value depends on the composition of the fuel, the air that is used for the
combustion and on the combustion products as found in the exhaust gases.
A basic formula, taking into account:
•
Components of the fuel: carbon, hydrogen, oxygen and water content;
•
Water content of the air;
•
Components of the exhaust gases: carbon dioxide, carbon monoxide,
hydrocarbons and nitrogen oxide;
has been developed by J. Brettschneider and published in Bosh Technishe
Berichte, Volume 6 (1979), No. 4, page 177-186.
A simplified formula, derived from the basic formula, and based upon the
assumption that the water content of the fuel and air and the NOx content in the
exhaust gases are negligible, allows the computation of Lambda when certain
components of the exhaust are measured.
B.1 Oxygen balance formula
For Lambda calculation, based upon measurements of CO, CO2, HC and O2, the
following formula is standardized: Displayed on the analyzer as LAMBDA (O)
λ
= CO
2
+ (CO/2) + O
2
+ [H
CV
/4
×
{3.5 / (3.5 + CO/CO
2
)} – O
CV
/2]
×
(CO
2
+ CO)
(1 + H
CV
/4 - O
CV
/2)
×
{(CO
2
+ CO) + (K
1
×
HC)}
Where:
CO = Carbon monoxide % volume measured.
CO
2
= Carbon dioxide % volume measured.
HC = Hydrocarbon ppm volume measured.
O
2
= Oxygen % volume measured.
K
1
= Conversion factor for HC is expressed in ppm vol n-hexane (C
6
H
14
)
equivalent. Its value in this formula is 6.10
-4
H
cv
= Atomic ratio hydrogen to carbon in the fuel. Nominal value is 1.7261
O
cv
= Atomic ratio oxygen to carbon in the fuel. Nominal value is 0.0176
