Lambda Values: Definition & Regulations (Articles)

The lambda value (λ) indicates whether there is an excess of air or fuel during combustion in the engine. It is measured using a lambda sensor (G39, G108). In most modern engines, the lambda value can be displayed via the OBD system.

A Lambda value of 1 indicates that there is exactly the amount of combustion air needed for complete fuel combustion. In this case, we are talking about the stoichiometric fuel-air ratio.

λ greater than 1: There is too much combustion air present.

λ less than 1: This indicates that there is insufficient combustion air. Many gasoline engines use excess fuel for internal cooling under full load, which helps to lower the temperatures during combustion. Therefore, a lambda value less than 1 at full load is often normal.

In diesel engines, the lowest lambda values are typically greater than 1.2. Values below this level result in excessive soot formation during combustion. Normal values for soot-free combustion under full load are approximately 1.25-1.30.
In diesel engines, power control is primarily achieved through the amount of fuel injected. Consequently, the lambda value increases as the load decreases.

The lambda sensor measures the residual oxygen content in the exhaust gases of a diesel engine. This measurement is essential for enabling low-emission operation of the engine.
When exhaust gas temperatures are too high in a diesel engine, the lambda value must be increased.

Unlike diesel engines, gasoline engines operate within a range of λ (air-fuel ratio) between 1 and 1.1, as this allows for fuel-efficient and low-emission operation. The catalytic converter only functions correctly when λ is equal to 1.
In a gasoline engine, the power output is controlled by the amount of the fuel-air mixture.
Under full load, it may be necessary to enrich the fuel mixture to a lambda value of approximately 0.8 in order to avoid excessive exhaust gas temperatures.

See also:
Lambda regulation, additive and multiplicative adjustment factors