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Knock in gasoline engines at higher loads is a significant constraint on torque and efficiency. The anti-knock property of a fuel is closely related to its research octane number (RON). Ethanol has superior RON compared to gasoline and thus has been commonly used to blend with gasoline in commercial gasolines. However, as the RON of a fuel is constant, it has not been used as needed in a vehicle. To wisely use the RON, an On-Board Separation (OBS) unit that separates commercial gasoline with ethanol content into high-octane fuel with high ethanol fraction and a lower octane remainder has been developed. Then an onboard Octane-on-demand (OOD) concept uses both fuels in varying proportion to provide to the engine a fuel blend with just enough RON to meet the ever changing octane requirement that depends on driving pattern.

HONDA has investigated On Board Separation (OBS) of high octane alcohol and aromatics from current commercial fuels such as E10, a blend of 10 volume % ethanol and 90 volume % gasoline. The high-octane components concentrated from commercial fuel can be injected when needed to suppress knock. The availability of high octane fuel enables the engine to be designed with a compression ratio and boost which gives the Octane Boost Engine (OBE) higher efficiency. 3M has developed pervaporation separation modules made with flexible organic membranes that selectively remove and concentrate ethanol and methanol from gasoline blends. The separation module profile can be circular or rectangular to best fit the available space. Organic membrane performance has been studied for up to 15% ethanol and up to 15% methanol blended with 5% ethanol added for humid condition stability. Aromatic separation capability has also been evaluated.