The Role of Fuel-Spray Oscillations in the Formation of Multiple Flames

摘要

The sensitivity to the vaporization Damkohler number of the behavior of a co-flowrnlaminar spray diffusion flame in an oscillating flow field is investigated. Dropletrngrouping induced by the host gas flow oscillations is accounted for. The spray isrnmodeled using the sectional approach and a perturbation analysis using a smallrnsectional Stokes number is utilized for solving the liquid phase governing equations.rnThe effect of droplet grouping is described through a specially constructed model forrnthe vaporization Damkohler number that responds to the proximity of the droplets asrnthey cluster due to the spray-flow oscillations. A formal analytical solution isrndeveloped for Schwab-Zeldovitch parameters through which the dynamics of thernspray flame front shapes and thermal fields are deduced. Computed results based onrnthe solutions demonstrate how strongly the vaporization Damkohler number includingrndroplet grouping effects impacts on the type of primary homogeneous flame formedrnand on the possible existence of multiple flame sheets as a result of dynamic changesrnfrom under- to over-ventilated flames as the flow field oscillates. A further subtle,rnallied phenomenon that produces isolated regions of high fuel vapor concentrations isrnfuel droplet enrichment that stems from the combination of droplet grouping and thernoscillating droplet and host gas flow fields. Such regions also lead to the formation ofrnmultiple flames under certain operating conditions.