Patent ID: 8387445

Claim:
A method for determining an ethanol proportion of a fuel for an internal combustion engine of a motor vehicle, wherein a dependency of a lean-burn running limit of the internal combustion engine of the motor vehicle on the ethanol proportion of the fuel is used for determining the ethanol proportions, the method comprising: for the purpose of determining the lean-burn running limit, injecting a first fuel quantity into a cylinder of the internal combustion engine in an operating range of an overrun fuel cutoff of the internal combustion engine, the first fuel quantity insufficient to allow combustion of the air/fuel mixture, increasing the fuel quantity progressively until combustion occurs, monitoring a smooth running of the internal combustion engine during this activity for this cylinder, and recognizing the lean-burn running limit as having been reached when the smooth running exceeds a predefined threshold value, wherein the ethanol proportion of the fuel is then deduced from the increase in the injected fuel quantity which is required to reach the lean-burn running limit.