Patent ID: 7487766

Claim:
A method of operating an internal combustion engine for use with arbitrary fuel mixtures that contain relative proportions (ratios) of gasoline and at least one alternative fuel, the engine having an exhaust gas recirculation system, an engine control unit, and a fuel mixture sensor, comprising: for each value of a number of the ratios, determining a recirculated exhaust gas value, based at least in part on knock characteristics of the engine when operating with that relative proportion; storing a set of fuel-responsive recirculated exhaust gas values, each value associated with a ratio; using the fuel mixture sensor to deliver a signal to the engine control unit that represents the ratio in the fuel mixture currently being supplied to the engine; determining whether the ratio in the fuel mixture currently being supplied to the engine has changed; if the ratio has changed, using the engine control unit to access fuel-responsive recirculated exhaust gas values and to use these values to control the amount of recirculated exhaust gas to deliver to the engine; and maintaining the current amount of fuel-responsive recirculated exhaust gas until the ratio again changes; determining whether the ratio reveals that the proportion of alternative fuel is below a predetermined minimum proportion; and if the proportion of alternative fuel is below the predetermined minimum proportion, adjusting the valve timing to reduce cylinder temperature.