Fuel property estimation device

An internal combustion engine that uses a mixed fuel of three kinds of fuel, the internal combustion engine comprising:

• a fuel route including a fuel pipe that connects a fuel tank and a fuel injection valve that injects the mixed fuel into an intake passage;
• an exhaust passage;
• a first sensor provided on the fuel route for outputting a signal responsive to a physical property of the mixed fuel;
• a second sensor provided on the exhaust passage for outputting a signal responsive to an oxygen concentration of exhaust gas in the exhaust passage;
• and
• an electronic control unit (ECU) including a computer provided with memory as a storage unit and a processor for reading and executing a program stored in the storage unit, the storage unit stores simultaneous equations including a first equation that is a linear approximation of a relationship between a composition ratio of the mixed fuel and a physical property value of the mixed fuel and a second equation that is a linear approximation of a relationship between the composition ratio of the mixed fuel and a theoretical air-fuel ratio value of the mixed fuel, the ECU configured to:
• measure the physical property value of the mixed fuel used in the internal combustion engine based on the signal from the first sensor;
• correct a mixed fuel injection amount of the fuel injection valve by feedback of the signal output from the second sensor so that combustion state of the internal combustion engine is adjusted to a stoichiometric state;
• calculate an air-fuel ratio value of the mixed fuel based on an intake air amount and the mixed fuel injection amount at a time when the combustion state of the internal combustion engine is adjusted to be stoichiometric using feedback of the signal from the second sensor;
• estimate the composition ratio of the mixed fuel used in the internal combustion engine based on the physical property value of the mixed fuel measured and the air-fuel ratio value calculated by referring to the relationship between the composition ratio of the mixed fuel and the physical property value and the relationship between the composition ratio of the mixed fuel and the theoretical air-fuel ratio value, wherein estimating the composition ratio of the mixed fuel further includes solving the simultaneous equations with respect to the composition ratio of the mixed fuel using the physical property value of the mixed fuel measured and the calculated air-fuel ratio value as parameters, and determining a solution of the simultaneous equations as the composition ratio of the mixed fuel used in the internal combustion engine;
• and
• control the fuel injection valve to set the mixed fuel ignition amount and ignition timing during an air-fuel ratio control and an ignition timing control based on the determined composition ratio of the mixed fuel.