Turbulence effects on the combustion of single hydrocarbon droplets

Abstract

An experimental facility was developed to study the effect of isotropic turbulence on single-droplet burning. The facility allows the generation of a zero mean velocity, isotropic, and homogeneous turbulence with variable turbulent kinetic energy. The turbulent field was characterized using laser Doppler anemometry. Turbulent integral length scale was determined directly using two-point velocity measurements. It was found to be constant and independent of the turbulence kinetic energy level. The study was conducted at normal ambient room temperature and pressure conditions by systematically varying the turbulence kinetic energy and the fuel type for mono- and bicomponent hydrocarbon ( n -alkane) droplets. The suspended droplet technique was used in this investigation with a quartz fiber of 0.2 mm diameter. Monocomponent hydrocarbon droplet burning was found to obey the D 2 law, as well as bicomponent droplet burning of n -heptane and n -decane mixtures, where only one sequence was observed. This is not surprising since at high temperature conditions the bicomponent droplet burning is controlled by the least volatile component. Furthermore, the study of isolated single mono- and bicomponent hydrocarbon droplet burning under isotropic turbulence and zero mean velocity conditions showed that a spatially fluctuating flame envelopes the droplet and its extinction takes place for a turbulent velocity of the order of the propagation velocity of the associated hydrocarbon/air laminar premixed flame. The turbulence effect on the monocomponent and bicomponent droplet combustion rates before extinction was found to be negligible compared with the stagnant case.