Method for detecting fuel blending ratio

A fuel blending ratio detecting device for an internal combustion engine comprising:

• a blending ratio sensor disposed in a fuel path for feeding fuel to the internal combustion engine to detect a first blending ratio of methanol;
• an O.sub.2 sensor for generating information of an air/fuel ratio in exhaust gases from the internal combustion engine, said O.sub.2 sensor output being increased or decreased with time relative to a rich/lean decision voltage;
• fuel control means for computing an air/fuel ratio feedback compensation coefficient from an integral control of the output of said O.sub.2 sensor to regulate the quantity of supplied fuel so that an air/furl ratio of the fuel mixture supplied to the internal combustion engine corresponds to a predetermined target value;
• a first computing means for computing a feedback learned value at intervals of a first predetermined period as a result of said integral control on the basis of the factor of the feedback compensation coefficient and multiplying the current blending ratio compensation coefficient by said feedback learned value to compute the next blending ratio compensation coefficient so as to compute a second blending ratio on the basis of said next blending ratio compensation coefficient;
• second computing means for computing a peak mean value of the current and preceding peak values of said feedback compensation coefficient each time peak values appear and multiplying the current blending ratio compensation coefficient by said peak mean value to compute the next blending ratio compensation coefficient so as to compute a third blending ratio on the basis of said next blending ratio compensation coefficient;
• and
• selecting means for selecting one of said first, second and third blending ratios according to the operating conditions of the internal combustion engine.