Predicting the ignition delay of turbulent methane jets using Conditional Source-term Estimation

Abstract

A predictive simulation of the autoignition process of non-premixed methane in a turbulent jet configuration was performed. Closure for the chemical source-term was obtained using Conditional Sourceterm Estimation with Laminar Flamelet Decomposition (CSE-LFD). The ambient oxidizer conditions -the high pressure and moderate temperatures characteristic of compression ignition engines -were chosen with the intent to validate the combustion model used under engine-relevant conditions. Validation was obtained by comparison of the predicted ignition delay to experimental results obtained from a shock-tube facility at several initial temperatures. Overall, the combination of full chemistry that has been carefully tuned to predict autoignition of premixed methane-air mixtures under similar temperature/pressure conditions with the CSE-LFD model is able to successfully predict the autoignition delay time of methane-air jets well within the scatter in the experimental data.

Conditional Source-Term Estimation as a Method for Chemical Closure in Premixed Turbulent Reacting Flow

“…Steiner and Bushe [18] used CSE in their LES of the Sandia Flame D [19] using a two-step mechanism for methane. Grout et al [20] combined CSE and the Laminar Flamelet Decomposition (LFD) [21] method to study the ignition delay of methane jets. Huang and Bushe [22] combined CSE with a Trajectory Generated Low-Dimensional Manifold (TGLDM) method to study the same auto-igniting methane jets.…”

Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

“…Flamelet-like asymptotic chemistry solutions are also used in the inversion process to combat the ill-conditioned nature of the problem. As noted by the CSE developers, however, the use of these flamelet solutions allows a somewhat more general chemistry/flow interaction to be considered than with purely steady flamelets [38]. The unsteadiness that can be accounted for may be helpful in partially premixed settings.…”

“…An approach that is closely related to CMC is Conditional Source term Estimation (CSE) [38,39]. In this approach, independent variables are not added to the problem's dimensionality or to the computational mesh.…”

“…In this approach, independent variables are not added to the problem's dimensionality or to the computational mesh. Rather, functions describing the conditional scalar profiles are determined by inverting a system of equations relating the conditional profiles to filtered or mean values of a set of scalars [38,39]. This approach requires solving transport equations for several reactive quantities, so that there are an adequate number of mean or filtered scalar values to accomplish the inversion at a given mesh point.…”

“…Conditional Moment Closure (CMC) approaches [34][35][36][37][38][39][40] attempt to describe chemistry by solving for values of chemical species that have been conditioned on a particularly relevant scalar. A mixture fraction or progress variable is typically used for this purpose.…”