EFFECT OF OXYGENATES ON WATER-UPTAKE IN HYDROCARBON FUELS

The addition of water to gasoline can boost octane number and decrease NO, emissions. Oxygenates-which are already used in gasoline for boos ting octane quality (EU) and reducing CO (U.S.)-can boost water uptake in hydrocarbon fuel. At 20% butanol concentration in a paraffinic PRF 60 fuel, up to 1% water can be absorbed, leading to a boost of 1-3 oc tane points. However, at a more realistic oxygenates (10%) concentrati on, only about 0.2% water can be absorbed and this is insufficient for significant octane boosting. The effects are independent of the paraf finic or aromatic nature of the base fuel. We compared a range of oxyg enates (alcohols and ethers) in a paraffinic refinery base stream by r anking their ability to absorb water. The best oxygenate species for a bsorbing water have a thin polar tail and a bulky covalent head with a spatially intermediate polarizable element. The relatively low levels of water uptake suggest that surfactants should still be used, althou gh at lower concentrations as the oxygenate can serve as a cosolvent.