THE COMBUSTION OF A LIQUID FUEL DROPLET DURING FORCED-CONVECTION

A new experimental technique was used to investigate single fuel dropl et combustion during forced convection: the burning droplet was freely suspended in the controlled air stream, without any additional suppor t. Based on the photo-records of the burning process, the characterist ics of the change of square of droplet diameter with time were made an d the actual values of burning constants were determined for four hydr ocarbon fuels: benzene, n-heptane, iso-octane and toluene. The experim ents were also carried out under micro-gravity and free convection con ditions for the same set of fuels. The investigations have allowed the comparison of the burning mechanism of a single droplet for the three different external conditions and have compared quantitatively the bu rning constants. On the basis of the color pictures of the droplet bur ning under forced convection conditions and the temperature and gas co ncentration measurements within the flame, the mechanism of combustion of fuel droplet was explained. The physical and mathematical models o f the process have been proposed which included the aerodynamics of th e droplet located in the high Reynolds number air stream, the energy b alance of the evaporating droplet and the chemical reaction in the flo w. The models have made it possible to determine the quantitative depe ndence of the burning constant of different kinds of fuels on Reynolds number, the flow field parameters and the physical and chemical param eters of the liquid and its close surroundings. The calculated values of the parameters describing the burning process have been compared to the experimental data and to the results reported by other investigat ors. The model has revealed the importance of the feedback mechanism b etween physical processes involved during droplet combustion.