Method for determining the ethanol content of the fuel in a motor vehicle

1. A method for determining an Ethanol content of fuel of a motor vehicle having multiple cylinders, comprising:

progressively reducing an amount of fuel injected into a first cylinder;

during the reduction of the quantity of fuel injected into the first cylinder, progressively increasing an amount of fuel injected into the other cylinders of the motor vehicle to compensate for the reduced fuel injection into the first cylinder;

monitoring a coefficient of variance for the first cylinder during the reduction of fuel injected into the first cylinder;

identifying a limit point at which the coefficient of variance for the first cylinder reaches a predetermined lean-running limit;

determining an amount of the fuel injection reduction at the identified limit point;

determining the Ethanol content of the fuel based on the determined amount of fuel reduction at the identified limit point.

2. The method according to claim 1 , wherein, during the reduction of the quantity of fuel injected into the first cylinder, the amount of fuel injected into the other cylinders is progressively increased so that an excess-air factor is kept at a constant value.

3. The method according to claim 1 , wherein the Ethanol content of the fuel is obtained from an engine map in which the Ethanol content is plotted against the reduction of the injected fuel required to reach the lean-running limit.

4. The method according to claim 3 , wherein the Ethanol content in the engine map is plotted as a function of a speed and load of the internal combustion engine.

5. The method according to claim 1 , wherein the lean-running limit is determined for an operation of the internal combustion engine at a stationary load point.

6. The method according to claim 1 , wherein the Ethanol content of the fuel is used for validation of the Ethanol content obtained using another method.

7. A system for determining an Ethanol content of fuel of a motor vehicle having multiple cylinders, comprising:

means for progressively reducing an amount of fuel injected into a first cylinder;

means for progressively increasing an amount of fuel injected into the other cylinders of the motor vehicle during the reduction of the quantity of fuel injected into the first cylinder to compensate for the reduced fuel injection into the first cylinder;

means for monitoring a coefficient of variance for the first cylinder during the reduction of fuel injected into the first cylinder;

means for identifying a limit point at which the coefficient of variance for the first cylinder reaches a predetermined lean-running limit;

means for determining an amount of the fuel injection reduction at the identified limit point;

means for determining the Ethanol content of the fuel based on the determined amount of fuel reduction at the identified limit point.

8. The system according to claim 7 , wherein, during the reduction of the quantity of fuel injected into the first cylinder, the system is operable to increase the amount of fuel injected into the other cylinders progressively so that an excess-air factor is kept at a constant value.

9. The system according to claim 7 , wherein the Ethanol content of the fuel is obtained from an engine map in which the Ethanol content is plotted against the reduction of the injected fuel required to reach the lean-running limit.

10. The system according to claim 9 , wherein the Ethanol content in the engine map is plotted as a function of a speed and load of the internal combustion engine.

11. The system according to claim 7 , wherein the system is operable to determine lean-running limit for an operation of the internal combustion engine at a stationary load point.