Method and control device for operating an internal combustion engine

1. A method for operating an internal combustion engine, that is operative for rotating an output shaft of the engine, to enable selective operation of the engine in a normal operating mode for generating a desired output power by introducing a suitable quantity of operating fuel into the engine, comprising the steps of:

operating the engine in the normal operating mode at least at a defined rotational speed and at zero load to determine an initial output power to operating fuel quantity relationship;

storing the initial output power to operating fuel quantity relationship;

operating the engine in a calibration mode by operating the engine so that the engine output shaft rotates at the defined rotational speed and at zero load;

determining, in the calibration mode operation of the engine, a calibrating fuel quantity comprising the quantity of fuel being introduced into the engine to operate the engine at the defined rotational speed during the calibration mode at zero load;

determining a fuel quantity calibration offset based on the calibrating fuel quantity;

determining, in the normal operating mode of the engine, the output power being generated by the engine as a function of:

the determined calibrating fuel quantity at the defined rotational speed and at zero load and

the quantity of operating fuel being introduced into the engine in the normal operating mode at the defined rotational speed and at zero load; and

operating the internal combustion engine at a modified output power to operating fuel quantity relationship comprising the initial output power to operating fuel quantity relationship and the calibration offset.

2. A method in accordance with claim 1 , wherein said determining of the output power in the normal operating mode of the engine comprises determining the output power using a characteristic curve dependent on the operating fuel quantity introduced into the engine, the characteristic curve being calibrated using the determined calibrating fuel quantity.

3. A method in accordance with claim 2 , wherein said determining of the output power in the normal operating mode of the engine comprises determining the output power based on a linear dependency of the operating fuel quantity introduced into the engine and the output power.

4. A method in accordance with claim 3 , wherein the linear dependency comprises:

P=a+b*E,

wherein P is the output power of the engine, E is the operating fuel quantity and a and b are constants of the linear dependency, and wherein the constant a is determined based on the determined calibrating fuel quantity.

5. A method in accordance with claim 1 , wherein in the calibrating mode of the engine the engine is operated in an output shaft rotational speed-controlled manner.

6. A method in accordance with claim 1 , wherein the engine is operated in the calibration mode immediately after start-up of the engine.

7. A method in accordance with claim 1 , further comprising the step of correcting the determined calibrating fuel quantity based on at least one of a measured fuel viscosity, a calculated fuel viscosity, a measured fuel temperature, and a calculated fuel temperature.

8. A control device of an internal combustion engine, comprising an automated controller for carrying out the method of claim 1 .