Patent ID: 8267074

Claim:
A fuel system for an engine of a vehicle, comprising: a fuel tank configured to receive a fuel mixture, said mixture having at least some alcohol; a fuel separator configured to separate the fuel mixture received at a separator inlet passage into a first separated fuel at a first separator outlet passage and a second separated fuel at a second separator outlet passage, where the first separated fuel has a higher alcohol concentration than the second separated fuel, the separator inlet passage fluidly coupled to the fuel tank, the first separator outlet passage fluidly coupled to a first fuel injector group of the engine, the second separator outlet passage fluidly coupled to a second fuel injector group of the engine; a first fuel return passage fluidly coupling the first separator outlet passage to the fuel tank via a first valve; a second fuel return passage fluidly coupling the second separator outlet passage to the fuel tank via a second valve; and a control system configured to operate the first fuel injector group and the second fuel injector group to deliver the first separated fuel and the second separated fuel to the engine in different ratios responsive to an engine operating condition, where the control system is further configured to vary an amount of each fuel returned to the fuel tank via the first valve and the second valve in response to a separation rate of fuel and responsive to at least one of engine speed, engine load, and engine knock, and where the engine operating condition includes an indication of engine knock, and where the fuel system further includes a third fuel return passage from the fuel separator to the fuel tank, the third fuel return passage a fuel return passage for ethanol.