On the validity of quasi-steady assumption in transient droplet combustion

Thermal-drag and Transition from Quasi-steady to Highly-unsteady Combustion of a Fuel Droplet in the Presence of Upstream Velocity Oscillations

“…Since our simulations are close to infinitely-fast kinetics and, therefore, insensitive to the reaction parameters (it will be discussed in the next section), to save run-time on supercomputer we have used A = 3.35 × 10 12 s −1 (m 3 /kmol) a+b −1 , E a = 153 kJ/mole and a = b = 1. These parameters guaranty that the extinction due to forced convection does not occur for the Re < 150 which are consistent with experimental observation in references [15][16][17].…”

“…These distances; however, are too small to be considered as an inlet boundary condition described by (20). It has been also reported by Jangi et al [16] that flame sometimes, especially at low velocity, reached to the inlet of the nozzle during the experiments. Therefore, in order to find the nearest distance between the droplet and the nozzle in which the inlet boundary condition could be applicable for that, several distances from the droplet to the nozzle were examined.…”

“…1 a domain with a size of sixty times the initial droplet radius is employed. In the experiments of references [15][16][17] the distance from the nozzle to the droplet was varied between 4 mm to 7 mm. These distances; however, are too small to be considered as an inlet boundary condition described by (20).…”

“…The experimental data available in the literature [15][16][17] are the base for verification of the validity of the numerical results. The main proposes of this study are to demonstrate and characterize the role of a new mechanism that is responsible for the enhancement of the burning rate and deviation from those behaviors which are predicted by quasi-steady model.…”

“…Figure 1 shows a schematic of their model. Several experiments under microgravity conditions were performed later in the same research team as Mitsuya et al in order to observe the behavior of 1-butanol fuel droplets in the presence of upstream velocity oscillations [15][16][17]. Based on the results of the experimental data, Jangi et al [16] have shown the classical quasi-steady model [18], which is film-theory based, [19] cannot predict the hysteresis and drastical enhancement of the burning rate during the combustion of a 1-butanol fuel droplet when upstream velocity oscillates.…”