Liquid Fuel Property Effects on Lean Blowout in an Aircraft Relevant Combustor

Abstract

This paper describes results from an experimental study on influences of liquid fuel properties on lean blowout (LBO) limits in an aero-type combustor. In particular, this work aimed to elucidate the roles of fuel chemical and physical properties on LBO. Fuel chemical properties stem from the fuel chemical structure, thus governing chemical kinetic behaviors of oxidation characteristics (e.g., ignition or extinction time scales) and others (e.g., fuel thermal stability or sooting tendencies). Fuel physical properties affect the spray characteristics (e.g., atomization and evaporation rates). Eighteen different fuels, with a wide range of physical and chemical fuel properties, were tested. Several of these fuels were custom blends, developed to break intercorrelations between various physical and chemical properties. Fuel physical and chemical property effects were further separated by measuring blowout boundaries at three air inlet temperatures between 300 and 550 K, enabling variation in vaporization rates. The condition at 300 K corresponds to a temperature that is less than the flash point for most of the studied fuels and, therefore, forming a flammable mixture was challenging in this regime. The opposite scenario occurred at 550 K, where fuel droplets evaporate quickly, and the temperature actually exceeds the auto-ignition temperatures of some of the fuels. At 300 K, the data suggest that blowout is controlled by fuel physical properties, as a correlation is found between the blowout boundaries and the fuel vaporization temperature. At 450 and 550 K, the blowout boundaries correlated well with the derived cetane number (DCN), related to the global chemical kinetic reactivity.