Study of a Flame Kernel Evolution in a Turbulent Mixing Layer Using LES with a Laminar Chemistry Model

Abstract

Temporal evolution of an ignition kernel in a spark ignited turbulent hydrogen–air mixing layer is studied using the large eddy simulation approach with an implicit treatment of the reaction source terms. The applied numerical code is based on a high-order compact difference approximation combined with a weighted essentially non-oscillatory scheme, which provide an accurate resolution of the small scale phenomena. The spark is modelled by an energy deposition model coupled with the enthalpy equation. Since the fuel and oxidiser streams move in the opposite directions the flow is dominated by shear stresses and vortical structures. The ignition follows three different scenarios depending on the spark location. An interaction between the developing flame kernel and large turbulent structure is analysed starting from the energy transfer up to a fully reacting state. The size and shape of the flames are correlated with the initial ignition scenario. A 3D visualisation of the transient position of the flame kernel shows its different spatio-temporal behaviour. It is observed that the flame can stay close to the initial position and spread equally in all directions or it can move far from the initial location and follow the evolving flow field. In the latter scenario two separate sub-stages are convincingly identified. Concerning the ignition probability ($$P_{ign}$$ P ign ), when the spark is located in the immediate vicinity of the mixing layer, the $$P_{ign}$$ P ign on the fuel-rich side is higher. On the other hand, when the ignition occurs far from the mixing layer, the $$P_{ign}$$ P ign is significantly larger on the lean side. Unlike the local composition the impact of the strain rate of the velocity field was found to have very limited impact on the $$P_{ign}$$ P ign .

Numerical Study of Hydrogen Auto-Ignition Process in an Isotropic and Anisotropic Turbulent Field

“…The SAILOR code has been thoroughly verified in previous studies devoted to nonreactive flows [38,39] and number of combustion problems in jet flows [23,40,41] and mixing layers [22,42,43]. In all these cases it turned out to be very accurate.…”

A direct numerical simulation analysis of localised forced ignition in turbulent slot jets of CH4/CO2 blends

“…It is noted that future detailed chemistry and transport DNS should be conducted to confirm and refine the findings of the present work, especially during the early growth of the kernel. Additionally, future work should include shear mixing layers (similar in configuration to the LES results presented by Wawrzak and Tyliszczak 42,43 ) with various amount of shear such that its influence can be isolated.…”

“…38,39 Previous numerical studies looked at ignition of shear layers and highlighted the importance of edge flame on the kernel growth using DNS 40,41 as well as the kernel position in mixture fraction space using LES. 42,43 A recent DNS analysis by the present authors focused on the localised forced ignition of a methane fuelled turbulent planar jet 31 and analysed the effect of the energy deposition region on the kernel growth and its transition towards a fully stabilised flame.…”

Numerical Analysis of the Combustion Dynamics of Passively Controlled Jets Issuing from Polygonal Nozzles

“…The applied ILES method for the chemical source terms was proven to yield correct results for sufficiently dense meshes that ensure appropriate resolution of the scalar fields as shown in [25,26] using the SAILOR code. The chemical reaction rates are modelled using the detailed mechanism of Mueller et al [27] consisting of nine species and 21 reactions for the hydrogen oxidation.…”