Method and apparatus for estimating an alcohol concentration in an alcohol fuel mixture supplied to an internal combustion engine

The present invention relates to a method and an apparatus for estimating an alcohol concentration in an alcohol fuel mixture supplied to an internal combustion engine, wherein the operation of the internal combustion engine supplied with the alcohol fuel mixture is operated in a stoichiometric condition, a first parameter is determined on the basis of a signal from a pressure sensor sensing the pressure inside a combustion chamber of the internal combustion engine being controlled in the stoichiometric condition, and the alcohol concentration of the alcohol fuel mixture is determined on the basis of the determined first parameter and a relation between the first parameter and the alcohol concentration of the alcohol fuel mixture.