In a method for identifying a fuel type or a fuel mixture for a combustion chamber of an internal combustion engine having (i) a first intake opening connected to a first intake manifold inside which a first fuel injector is located, and (ii) a second intake opening connected to a second intake manifold inside which a second fuel injector is located, in a first method step, the first fuel injector remains closed, and in a second method step the first fuel injector is opened again and a first test fuel quantity is injected into the combustion chamber in the second method step via the first intake opening, and a second test fuel quantity is injected via the second intake opening, the first test fuel quantity and the second test fuel quantity being made up to form a predefined fuel quantity.

A system includes an internal combustion engine having an air intake, a fuel inlet, and exhaust outlet. The system further includes a NO.sub.x sensor operably coupled to the exhaust outlet and structured to provide an exhaust O.sub.2 value, and a controller structured to functionally execute operations for determining a tank biofuel value. The controller includes an operation conditions module that interprets an intake O.sub.2 value, the exhaust O.sub.2 value, and a biofuel O.sub.2 correlation, an O.sub.2 fuel determination module that determines an O.sub.2 biofuel value in response to the intake O.sub.2 value, the exhaust O.sub.2 value, and the biofuel O.sub.2 correlation, and a fuel composition module that determines a tank biofuel value in response to the O.sub.2 biofuel value. The controller further includes a biofuel reporting module that provides the tank biofuel value.

In an apparatus for controlling an air/fuel ratio of a general-purpose internal combustion engine using mixed fuel containing alcohol and gasoline and operated at a desired engine speed inputted by the operator while a throttle opening is regulated such that a detected engine speed converges to the inputted desired engine speed, a fuel injection amount for mixed fuel determined based on fuel injection amount characteristics is increased/decreased when a load is kept constant and the output air/fuel ratio (at which an output of the engine becomes maximum) is estimated. And the fuel injection amount is corrected based on the estimated air/fuel ratio, thereby enabling to estimate the output air/fuel ratio without using an expensive air/fuel ratio sensor and to feedback-control the fuel injection amount such that the engine is operated at the output air/fuel ratio.

Method for operating an internal combustion engine, wherein the internal combustion engine is operated by an air-fuel mixture comprising a fuel mixture and air, wherein the fuel mixture comprises a first fuel, preferably natural gas, and hydrogen as a second fuel different from the first fuel, wherein a hydrogen content of the fuel mixture is determined, and at least an ignition timing is adapted as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine,
wherein the higher the amount of hydrogen in the fuel mixture the later the ignition timing is set for at least partially compensating a shift of a center of combustion due to higher flame speed of hydrogen compared to the first fuel.

Method for operating an internal combustion engine, wherein the internal combustion engine is operated by an air-fuel mixture comprising a fuel mixture and air, wherein the fuel mixture comprises a first fuel, preferably natural gas, and hydrogen as a second fuel different from the first fuel, wherein a hydrogen content of the fuel mixture is determined, and at least an ignition timing is adapted as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine,
wherein the higher the amount of hydrogen in the fuel mixture the later the ignition timing is set for at least partially compensating a shift of a center of combustion due to higher flame speed of hydrogen compared to the first fuel.