Mechanisms of flame propagation in jet fuel sprays as revealed by OH/fuel planar laser-induced fluorescence and OH* chemiluminescence

On the Dynamics of Atomization and Combustion in Turbulent Spray Flows

“…Detailed measurements in turbulent spray flames remain difficult but are gradually evolving to reveal the flame propagation rates and burning modes in the presence of droplets and fluid fragments of various sizes and shapes. The group of Mastorakos [42,43] have focused on the effects of droplet size distributions on the flame structure and have identified three propagation modes demarcated with respect to Group number and overall equivalence ratio. The propagation modes are: (i) droplet (ii) inter-droplet and (iii) gaseous-like propagation modes, as shown in Fig.…”

“…The interdroplet spacing is calculated by assuming a uniform distribution of N number of droplets in a vapour cloud having the size similar to the ring-combustion size presented by Singh et al [30]. Notwithstanding the uncertainties in the estimates used to determine the Group number, G, it is worth noting that the flames stabilized on the Sydney needle burner fall in the gaseous-like and inter-droplet propagation regimes presented by Mastorakos [42,43].…”

“…Fig. 6: (a) Regime diagram illustrating plotting Group number versus overall equivalence ratio, φ highlighting the various flame propagation modes in turbulent spray flames[43]. (b) Results from Singh et al[30] plotted on the same diagram at x/D=5 in ethanol spray flames: cases EF2 (φ=3.3), EF6 (φ=2.0),, EF7 (φ=2.0), and EF8 (φ=1.5).…”

Low-order modeling of high-altitude relight of jet engine combustors

“…In fact, as a result of the contribution of droplets to stretch due to strain and curvature at the dropletscale, 23 it has been expected 24 and recently verified 21,[25][26][27] that the global Karlovitz number of spray flames at which extinction is observed differs significantly from those of premixed flames. 18 In recent experiments with spherically propagating flames, 1 local flame extinction in polydisperse kerosene sprays was observed to be led mainly by large droplets approaching the reaction zone. It is worth noting that these experiments were carried out at flow conditions not necessarily close to those of stable spray flames commonly seen in the literature, thus exhibiting three distinct spray-flame propagation modes.…”

“…In aeronautical engines, the fuel is typically injected in the form of a liquid spray. Compared to gaseous flames, the presence of liquid droplets increases the complexity of the ignition process which is strongly affected by the size and location of the droplets as well as the volatility of the liquid, 1,2 among all the other factors. The sub-atmospheric conditions associated to high-altitude relight, characterized by low pressure and low temperature, make the ignition process even more challenging.…”