4
3 – What is lambda
Lambda represents the ratio between the actual mixture of air/fuel (A/F or AFR) admitted in the engine, compared to the optimum ratio
(A/F
stoichiometric
or AFR
stoichiometric
) indicating an efficient fuel combustion. Lambda can be written as:
𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿
=
𝐴𝐴
/
𝐹𝐹
𝐴𝐴
/
𝐹𝐹𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆ℎ𝑆𝑆𝑆𝑆𝐿𝐿𝑖𝑖𝑆𝑆𝑖𝑖𝑆𝑆𝑆𝑆
=
𝐴𝐴𝐹𝐹𝐴𝐴
𝐴𝐴𝐹𝐹𝐴𝐴𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆ℎ𝑆𝑆𝐿𝐿𝑖𝑖𝑆𝑆𝑖𝑖𝑆𝑆𝑆𝑆
where:
A
= parts of air (oxygen) in the combustion chamber
F
= parts of fuel in the combustion chamber
To completely burn one part of gasoline, 14.57 parts of air (AFR
stoichiometric
) are required.
This optimal combustion is also indicated as
Lambda = 1,
whatever is the fuel in use.
AFR
stoichiometric
is a fuel dependant constant. Oxygenated fuels and additives will change this value, thus it is strongly recommended to use
Lambda as reference parameter.
3.1 – Rich mixture
If the actual mixture has less than 14.57 air parts to 1 part of gasoline, the mixture is said rich.
For example An AFR of 12.2 is a rich mixture and is also indicated as:
84
.
0
57
.
14
2
.
12
=
=
Lambda
Lambda < 1
AFR < 14.57
(for gasoline)
3.2 – Lean Mixture
If the actual mixture has more than 14.57 air parts to 1 part of gasoline, the mixture is said lean.
For example an AFR of 17.5 is a lean mixture and is also indicated as:
2
.
1
57
.
14
5
.
17
=
=
Lambda
Lambda > 1
AFR > 14.57
(for gasoline)
3.3 – Stoichiometric mixture
If the actual mixture has 14.57 air parts to 1 part of gasoline, the mixture is in the stoichiometric ratio.This is also indicated as Lambda = 1
