Patent ID: 8733158

Claim:
A method for determining the composition of a fuel mixture consisting of a first fuel and a second fuel to operate an internal combustion engine having at least one cylinder pressure sensor for determining a cylinder pressure ( 40 ) in at least one cylinder of the internal combustion engine, comprising determining a calorific value ( 11 ) of the fuel mixture or a characteristic variable correlating to said calorific value ( 11 ) from the cylinder pressure ( 40 ), and determining the composition of the fuel mixture from said calorific value ( 11 ) or the correlating characteristic value; wherein an indicated mean effective pressure p mi is determined from a course of the cylinder pressure ( 40 ), in that a mean indicated work W i is determined from the indicated mean effective pressure p mi , in that the calorific value ( 11 ) or the characteristic variable correlating to said calorific value ( 11 ) is determined from the mean indicated work W i and a fuel quantity injected in the respective combustion cycle, and the composition of the fuel mixture is determined from said calorific value or the characteristic variable correlating thereto.