Method for controlling an internal combustion engine

Process for controlling an internal combustion engine, especially with lean operation, to achieve pre-determined nitrogen oxide emission values comprises determining, preferably directly, the actual value of the lambda value or the calorific value of a fuel/air mixture to be burnt in the engine or a nitrogen oxide emission value and controlling the value according to a variable characteristic of the quality and/or quantity of the fuel or according to the output (P) of the engine. Independent claims are also included for: (1) Control device for carrying out the above process; and (2) Internal combustion engine comprising the above control device. Preferred Features: The fuel is a combustible gas e.g. methane.