Simulations and experiments on the ignition probability in turbulent premixed bluff-body flames

Abstract

The ignition characteristics of a premixed bluff-body burner under lean conditions were investigated experimentally and numerically with a physical model focusing on ignition probability. Visualisation of the flame with a 5 kHz OH* chemiluminescence camera confirmed that successful ignitions were those associated with the movement of the kernel upstream, consistent with previous work on non-premixed systems. Performing many separate ignition trials at the same spark position and flow conditions resulted in a quantification of the ignition probability P ign , which was found to decrease with increasing distance downstream of the bluff body and a decrease in equivalence ratio. Flows corresponding to flames close to the blow-off limit could not be ignited, although such flames were stable if reached from a richer already ignited condition. A detailed comparison with the local Karlovitz number and the mean velocity showed that regions of high P ign are associated with low Ka and negative bulk velocity (i.e. towards the bluff body), although a direct correlation was not possible. A modelling effort that takes convection and localised flame quenching into account by tracking stochastic virtual flame particles, previously validated for non-premixed and spray ignition, was used to estimate the ignition probability. The applicability of this approach to premixed flows was first evaluated by investigating the model's flame propagation mechanism in a uniform turbulence field, which showed that the model reproduces the bending behaviour of the S T -versus-u curve. Then ignition simulations of the bluff-body burner were carried out. The ignition probability map was computed and it was found that the model reproduces all main trends found in the experimental study.

Polydispersity Effects in Low-order Ignition Modeling of Jet Fuel Sprays

“…The low-order ignition model called Stochastic Particle Integrator for High-Altitude Relight (SPINTHIR), developed by Neophytou, Richardson, and Mastorakos (2012), simulates the stochastic motion of virtual "flame particles" to predict the ignition probability map in a combustor. The model is based on a time-averaged cold-flow field and a Karlovitz number extinction criterion (Abdel-Gayed and Bradley 1985), and has been tested for non-premixed and spray flames (Neophytou, Richardson, Mastorakos 2012;Soworka et al 2014) and premixed flames (Sitte et al 2016). Nevertheless, previous experimental evidence suggests that spray flames can extinguish at global Damköhler numbers that differ from those verified by Abdel-Gayed and Bradley (1985) in gaseous premixed flames (Bradley et al 2014;Cavaliere, Kariuki, Mastorakos 2013;Yuan, Kariuki, Mastorakos 2018).…”

Large Eddy Simulation of Bluff-Body Flame Approaching Blow-Off: A Sensitivity Study

“…19 and reported and discussed in the experimental study by Kariuki et al (2015). An alternative view is discussed by Sitte et al (2016) which focuses on the ignition of the current burner under identical conditions and discusses the quenching and ignition in terms of Karlovitz number (Ka). Sitte et al (2016) argues that, since neither the u rms nor the length scales L t differ significantly between the cases, the Ka fields only differ by the factor 1/S 2 l .…”

Combustion Simulation of Propane/Oxygen (With Nitrogen/Argon) Mixtures Using Rate-Controlled Constrained-Equilibrium

“…The most accurate way to simulate the combustion process is using the detailed kinetic model (DKM), which includes all possible species, reactions, corresponding thermodynamic data, and transport properties. It has been used for zerodimensional, one-dimensional combustion simulations [1][2][3][4][5][6]. Such model often involves hundreds of species and thousands or even more reactions.…”