Reaction zone characteristics of iso-pentanol swirl spray flames using OH-PLIF and 2C-LII

Abstract

This paper focuses on the reaction zone and soot emission characteristics of swirl spray flames of iso-pentanol and blends. OH planar laser induced fluorescence (PLIF) measurements were used to study the lift-off and local extinction features. Soot emission was investigated using the planar time-resolved two-colour laser induced incandescence (2C-LII) diagnostic technique. Fuels used in this study were n-heptane, iso-pentanol, ethanol and blends of n-heptane/iso-pentanol and n-heptane/ethanol. Different operating conditions were tested and categorized into three flame types including stable, near blow-off, and far away from blow-off. A clear double flame sheet structure appeared in most flames, referred to as the inner and outer regions in this study. Also, all flames other than pure iso-pentanol displayed an open-up spray in a cone-like “V” shape. Results of stable and near blow-off conditions showed that the addition of iso-pentanol to an n-heptane flame caused the flame to become more attached to the bluff-body. In stable flames, the addition of iso-pentanol to n-heptane increased the occurrence of local extinctions. Whereas the addition of ethanol to n-heptane decreased occurrences of local extinction. Across near blow-off conditions, the impact on lift-off height caused by the addition of ethanol to n-heptane was less than that of the addition of iso-pentanol to n-heptane. In the far from blow-off conditions, less local extinction in pure iso-pentanol was found compared to the n-heptane/iso-pentanol mixture. Soot volume fraction of the iso-pentanol flame was less than the n-heptane flame, and the addition of iso-pentanol to the n-heptane flame reduced the soot volume fractions to a lower level than in the pure n-heptane flame.