Multiphase Flows and Combustion

Droplet Evaporation and Combustion

Droplet evaporation and combustion and their interaction are fundamental to spray flow modeling. Single droplet vaporization includes droplet heating which typically causes the increase of droplet size - the modeling of this process requires consideration of variable liquid properties. Moreover, detailed modeling of the surrounding convective gas flow as well as processes at the liquid/gas interface is required.

Figure 1 displays the convective flow around a stagnant droplet. The gas flow imposes vortices inside the droplet and flow separation is visible downstream of the droplet. This separation influences the ignition location shown in Fig. 2 for a methanol droplet in air at 30 bar. Ignition does not occur on the centerline but it is displaced in radial direction. For lower gas velocities where separation does not occur, ignition occurs at the centerline, c.f. Fig. 3.

Droplet interaction during ignition is shown in Fig. 4. For a large droplet separation distance, each droplet is surrounded by an individual flame front whereas for closer droplet distance, an envelope flame comprises both droplets. It is also seen from Fig, 4 that the droplets influence each other. In single droplet ignition, ignition typically occurs downstream of the droplet whereas Fig. 4 reveals that the second droplet's ignition position located upstream.

Parameter studies are to be performed for more complex configurations which then enter into mroe complex spray flame simulations.