Assessment of Partially Premixed Flame by In-Situ Adaptive Reduced Mechanisms in OpenFOAM

The partially premixed flame was modelled using an open-source software based on finite volume method (FVM) of computational fluid dynamics (CFD), called OpenFOAM. The assessment of the tabulation dynamics adaptive chemistry (TDAC) algorithms for facilitating the computation was of interest. A total of seven models were performed, consisting of six models of the TDAC framework application and a direct computation model without TDAC. Simulation results were validated by comparing against the thermal flame height (HT) of Irandoost et al. [28]. The heat released rate was established from simulation results to identify the flame front and HT. This is a novel technique to illustrate the flame front, which agreed well with the experiment. Subsequently, it was found that all but one of the reduced mechanism methods agreed well in predicting the HT. The exception was DRGEP. Particularly, the CFD results were optimal. It was discovered that the TDAC based on the mechanism reduction called element flux analysis (EFA) was the second-fastest but optimal choice to solve the partially premixed flame model.

Reduced Combustion Mechanism for Fire with Light Alcohols

The need for sustainable energy has incentivized the use of alternative fuels such as light alcohols. In this work, reduced chemistry mechanisms for the prediction of fires (pool fire, tank fire, and flash fire) for two primary alcohols—methanol and ethanol—were developed, aiming to integrate the detailed kinetic model into the computational fluid dynamics (CFD) model. The model accommodates either the pure reactants and products or other intermediates, including soot precursors (C2H2, C2H4, and C3H3), which were identified via sensitivity and reaction path analyses. The developed reduced mechanism was adopted to predict the burning behavior in a 3D domain and for the estimation of the product distribution. The agreement between the experimental data from the literature and estimations resulting from the analysis performed in this work demonstrates the successful application of this method for the integration of kinetic mechanisms and CFD models, opening to an accurate evaluation of safety scenarios and allowing for the proper design of storage and transportation systems involving light alcohols.

Analysis of Autoignition Chemistry in Aeroderivative Premixers At Engine Conditions

The minimization of autoignition risk is critical to premixer design. Safety factors based on ignition delays of homogeneous mixtures, are generally used to guide the choice of a residence time for a given premixer. However, autoignition chemistry at aeroderivative conditions is fast (0.5-2 milliseconds) and can be initiated within typical premixer residence times. The analysis of what takes place in this short period involves the study of low-temperature precursor chemistry. By coupling the evolution of the Chemical Explosive Modes to turbulence, it is possible to obtain a measure of spatial autoignition risk where both chemical (e.g. ignition delay) and aerodynamic (e.g. local residence time) influences are unified. In this article, we describe a method that couples Large Eddy Simulation to newly developed, reduced autoignition chemical kinetics to study autoignition precursors in an example premixer representative of real life geometric complexity. A blend of pure methane and dimethyl ether (DME), a common fuel used for experimental autoignition studies, was transported using the reduced mechanism (38 species / 238 reactions) at engine conditions at increasing levels of DME concentration until exothermic autoignition kernels were formed. The Chemical Explosive Mode analysis closely follows the large thermochemical changes in the premixer as a function of DME concentration and identifies where the premixer is sensitive and flame anchoring is likely to occur.

Large Eddy Simulation of a Turbulent Spray Burner Using Thickened Flame Model and Adaptive Mesh Refinement

The accurate simulation of two-phase flow combustion is crucial for the design of aeronautical combustion chambers. In order to gain insight into complex interactions between a flame, a flow, and a liquid phase, the present work addresses the combustion modeling for the large eddy simulation (LES) of a turbulent spray jet flame. The Eulerian–Lagrangian framework is selected to represent the gaseous and liquid phases, respectively. Chemical processes are described by a reduced mechanism, and turbulent combustion is modeled by the thickened flame model (TFM) coupled to the adaptive mesh refinement (AMR). The TFM-AMR extension on the dispersed phase is successfully validated on a laminar spray flame configuration. Then, the modeling approach is evaluated on the academic turbulent spray burner, providing a good agreement with the experimental data.

Implementation of kinetic mechanisms of methane combustion by example of expanding functionality of physicochemical libraries in conjunction with reactingPimpleCentralFoam solver

The possibility of using reduced combustion mechanisms for hydrocarbon fuels in solvers developed and used at ISP RAS is investigated. These mechanisms contain smaller number of stages and substances appearing in them, but they allow obtaining results in a good agreement with experimental data in a much shorter calculation time. The comparison is made with the results obtained with using the Moscow Aviation Institute solvers. A modified mechanism of methane combustion is considered. It can be extended to describe the chemical reaction processes in other hydrocarbon-oxygen mixtures. The choice of methane is due to the prospects of this fuel at the present time. As the first test problem, a standard chemFoam is used. This solver was designed to demonstrate the occurrence of chemical reactions in a computational domain consists of one cell only. The ignition delay and the parameter values of the thermodynamic equilibrium state reached are taken as the comparison criteria. The second test problem is the flow modeling in a shock tube after the shock wave has been reflected from the wall. This problem is considered in a three-dimensional domain using the ISP RAS reactingPimpleCentralFoam solver. Results were compared with ones obtained by grid-characteristic and Godunov's methods in one-dimensional nonstationary calculations. The effects of viscosity, thermal conductivity and diffusion are not taken into account. The distributions of the flow parameters behind the reflected shock wave are obtained. Results are analyzed depending on the value of the falling shock wave Mach number. Estimates of the possible application of this reduced mechanism are given.