Patent ID: 7237539

Claim:
A method for controlling a fuel system of an internal combustion engine, the fuel system including a source of liquid fuel comprising alcohol, at least one fuel injector, a heat source, for heating the liquid fuel in the at least one fuel injector the heat source capable of heating the liquid fuel to a level sufficient to convert at least a portion thereof from the liquid state to a vapor state and a metering valve operable to achieve a range of flow rates, the range of flow rates characterized by a valve open versus valve closed duty cycle, the method comprising the steps of: (a) metering a predetermined amount of fuel based on engine operating conditions; (b) controlling power supplied to the heat source of the at least one fuel injector to achieve a target temperature; (c) determining alcohol concentration of the fuel by (i) measuring the power supplied to the heat source; and (ii) measuring the duty cycle of the metering valve; and (d) adjusting the power supplied to the heat source of the at least one fuel injector based on the determination of step (c), wherein the alcohol concentration is determined using a predetermined relationship between injector mass flow rate at a measured duty cycle for the at least one fuel injector and power supplied to the heat source to achieve a target resistance set point.