© 2005-2016 Nira Control AB 14
2
Combustion, Lambda and
Measurement Principles
For combustion to take place, oxygen needs to be available. The oxygen
content of the air changes with air temperature and pressure. In an engine
there are different ways of measuring the amount of air entering the engine,
but regardless of the technique used, some way of converting the
measurements into an absolute air mass is needed.
Once the air mass has been calculated, it’s possible to meter the amount of
fuel needed. The optimal air to fuel ratio, as measured in weight, depends on
the type of fuel.
For instance, 1 gram of standard gasoline should be mixed with 14.6 grams
of air to achieve complete combustion. This air/fuel ratio is known as the
stoichiometric ratio and is also referred to as lambda 1.0. A richer mixture
(more fuel) results in lambda < 1.0. A leaner mixture results in lambda > 1.0.
Lambda is central to the calibration of NIRA i7x and it’s important to
understand what it represents and how it’s used.
2.1 Relationship Between A/F and Lambda
A/F means Air-Fuel ratio. It’s always given as a ratio of masses. The
stoichiometric A/F is different for different types of fuel.
Example of stoichiometric A/F ratios:
Air/98 Octane Gasoline = 14.6
Air/Methanol = 6.8
Air/Ethanol = 9.0
Air/E85 = 11
To Next Page
Loading...