A comprehensive experimental study on nucleate boiling in gasoline and gasoline-ethanol blends

Abstract

Recent advances in fuel research have identified many benefits associated with heating fuels before they are injected into internal combustion engines, including improved cold starting and reduced greenhouse gas emissions. Extensive research has also been carried out into alternative, renewable biofuels. Of these, ethanol, which is normally used in ethanol-gasoline blends, is one of the most promising. However, although the characteristics and uses of heated fuel have been much discussed in the literature, it is important to improve our understanding of the fuel-heating process, which frequently involves nucleate boiling. This paper describes a comprehensive, novel experimental study of nucleate boiling in pure gasoline, ethanol and gasoline-ethanol blends. The heat transfer coefficient, critical heat flux and hysteresis effect are analyzed for each test fluid, and some considerations on the pressure effect are presented. For all the gasoline-ethanol blends, the heat transfer coefficient and critical heat flux increased with increasing pressure. Addition of ethanol to gasoline did not significantly change the heat transfer coefficient until the mole fraction exceeded 35%. The behavior of the heat transfer coefficient and critical heat flux indicates the existence of an azeotrope close to an ethanol mole fraction of 20%. Finally, gasoline exhibited partial nucleation during increasing heat flux at pressures greater than 202kPa. Addition of ethanol to pure gasoline gradually eliminated this behavior until total nucleation was achieved.