Numerical Investigations of Reignition in Vortex-Perturbed n-Heptane Nonpremixed Flames

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

“…Sripakagorn et al 18 reported that when the excursions of over e are relatively large, reignition is likely to occur through edge-flame propagation and engulfment scenarios. This trend was confirmed in our recent flamevortex interaction studies with both single-step 15 and multistep n-heptane chemistries, 20 where reignition was found to occur through edge-flame interactions governed by vortexinduced curvature. In particular, it was shown that while the extinction phase is dominated by unsteady effects, the reignition phase is controlled by both unsteady and curvature effects.…”

“…Similarly, the choice of the higher pressure ͑=40 bars͒ to emulate diesel engine conditions primarily affects the Damkohler number through the chemical time scale. As discussed in our recent studies under diesel conditions, 20 the ideal gas equation of state is adequate even at these high pressures ͑=40 bars͒ due to the predominant presence of diluents such as N 2 in the flame zone. The choice of simple chemistry precludes the resolution of kinetic effects due to the higher temperatures and pressures.…”

“…In addition, the domain sizes chosen are at least eight times larger than the simulated vortices in either direction to minimize boundary effects. Our recent studies 20 show that the chosen resolution is sufficient to adequately describe the physical mechanisms governing extinction/reignition for the conditions employed here. An initially flat diffusion flame is established between pure n-heptane at 1000 K one side, and diluted air ͑15% O 2 +85% N 2 molar composition͒ on the other side.…”

“…15,19,20 The direct-numerical-simulation ͑DNS͒ study of Sripakagorn et al 18 in reacting isotropic turbulence employing a singlestep kinetic model revealed three modes of reignition: an independent-flamelet scenario, where the extinguished flamelets reignite through autoignition, an edge-flame propagation scenario, where reignition occurs through propagation of edge flames, which are extremities of diffusion flame holes, 21 and an engulfment scenario, where turbulent convection of hot products from neighboring burning regions leads to reignition. Sripakagorn et al 18 reported that when the excursions of over e are relatively large, reignition is likely to occur through edge-flame propagation and engulfment scenarios.…”

“…The flame-vortex studies are performed with the twodimensional ͑2D͒ version of the flow, large-eddy, and direct simulation ͑FLEDS͒ code, 15,20 which has been developed inhouse and used in several prior studies of nonreacting 24 and reacting shear layers, 15,20,25 and large eddy simulation ͑LES͒ of nonreacting jets. 26 A detailed discussion of the numerical formulation, including the governing equations, implementation of numerical schemes and boundary conditions may be found in a recent publication.…”