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A laminar stagnation flow flame stabilized at a plane wall is theoretically analyzed, coupled with a thermo‐elasticity model in the wall. Mathematical models for both the flame and the wall will be proposed, and corresponding analytical solutions based on their dimensionless forms will be obtained. The mathematical analysis of this flame‐solid interaction primarily focuses on the effect of the flame on combustion‐induced thermo‐mechanical stresses and the influence of wall material on flame properties such as flame temperature and stability against extinction. A sensitivity analysis is further performed to examine how thermo‐mechanical stress inside the wall is affected by changes in other combustion conditions (e.g., mixture composition, flame stretch rate). This study offers valuable insights into understanding the interaction between flames and solids, a relationship crucial in engineering applications such as the interaction between combustion processes and blades within gas turbine machinery. [ABSTRACT FROM AUTHOR]

Polyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a promising alternative fuel to diesel with higher reactivity and low soot formation tendency. In this study, PODE3-4 is used as a pilot ignition fuel for methane (CH4) and the combustion characteristics of PODE3-4/CH4 mixtures are investigated numerically using an updated PODE3-4 mechanism. The ignition delay time (IDT) and laminar burning velocity (LBV) of PODE3-4/CH4 blends were calculated at high temperature and high pressure relevant to engine conditions. It is discovered that addition of a small amount of PODE3-4 has a dramatic promotive effect on IDT and LBV of CH4, whereas such a promoting effect decays at higher PODE3-4 addition. Kinetic analysis was performed to gain more insight into the reaction process of PODE3-4/CH4 mixtures at different conditions. In general, the promoting effect originates from the high reactivity of PODE3-4 at low temperatures and it is further confirmed in simulations using a perfectly stirred reactor (PSR) model. The addition of PODE3-4 significantly extends the extinction limit of CH4 from a residence time of ~0.5 ms to that of ~0.08 ms, indicating that the flame stability is enhanced as well by PODE3-4 addition. It is also found that NO formation is reduced in lean or rich flames; moreover, NO formation is inhibited by too short a residence time. [ABSTRACT FROM AUTHOR]

Partially-premixed flames (PPFs) incorporate effects of both premixed and non-premixed types of reaction zones. The modelling of PPFs using manifold-based model reduction methods faces some inherent difficulties due to the underlying assumptions of a-priori identification of the type of combustion system. In this work, the reaction–diffusion manifold (REDIM) model reduction method is applied to study PPFs. The REDIM method requires minimal prior knowledge about the type of combustion system, which makes it a suitable method for studying PPFs. It allows incorporating system-specific diffusion (gradients) terms in a generic way so that the manifold can evolve according to the diffusion related information provided by the combustion system. In this way, a prior identification of the type of combustion system is no longer needed. This work utilises an iterative methodology to generate REDIM chemistry tables so that the reduced manifold can be iteratively converged very close to the detailed manifold according to the gradients of the reduced coordinates provided by the physical combustion system in each iteration step. In addition, a new method is proposed to provide the gradient estimates of the reduced coordinates during the generation of REDIM from the scattered gradient data in REDIM reduced CFD calculations. Laminar triple flames, a special case of PPFs, with two types of mixture fraction gradients are selected as the target cases to assess the presented iterative methodology. REDIM reduced calculations are compared with simulations based on detailed finite-rate kinetics. It is found that in the final iteration steps, temperature and all considered major and minor species mass fraction profiles are very well predicted by the REDIM reduced calculations. [ABSTRACT FROM AUTHOR]

Ignition processes in laminar counterflow configuration using both detailed and reduced chemistry based on the Reaction-Diffusion Manifolds (REDIM) method are investigated. We choose in this work: (i) ignition by hot gas and (ii) spark ignition. The temporal development of thermo-kinetic quantities (e.g. temperatures and species concentrations) are compared. It is demonstrated that the two-dimensional REDIM reduced chemistry is accurate enough to predict the time evolution of different thermo-kinetic quantities compared with the detailed solutions for flows perturbed by different strain rates. Furthermore, the two-dimensional REDIM model for the spark ignition process can reproduce values of the minimal ignition energy very well. This confirms the concept and quality of the REDIM reduced model, which can be then further applied for turbulent flame simulations. [ABSTRACT FROM AUTHOR]

In the present work, the ignition of lean laminar premixed methane-air flames in a counterflow configuration is investigated using detailed numerical simulations. The dependence of the minimum energy necessary for a successful ignition on various parameters (spark geometry, spark duration, mixture composition, flow strain rates) is studied. A one-dimensional numerical calculation is performed using detailed chemical kinetics for the methane-air combustion system. Depending on various parameters, the system can be either successfully ignited (stable flame as stationary solution) or quenched (quenched flame as stationary solution). Furthermore, different detailed chemical mechanisms have been tested. A sensitivity analysis with respect to the Arrhenius parameters shows the key elementary reactions in the prediction of the minimal energy necessary for a successful ignition, which provides important information in the development of detailed chemical mechanisms. [ABSTRACT FROM AUTHOR]

A new model to couple the multiple mapping conditioning (MMC) mixing model with manifold based simplified chemistry is proposed. The concept is based on the fact that the system state can be locally confined to a manifold with lower dimension, which is embedded in the manifold with higher dimension. Therefore, in the framework of the MMC mixing model, particles to be mixed must be selected such that they are localized in the reference variable space with the dimension which corresponds to the minimum number of the progress variables describing the thermo-kinetic states locally. This can be achieved by comparing the physical mixing time-scale with the chemical time-scales describing the movement on the slow manifold, and the dimension of the necessary reference variables can be determined automatically. The present work uses an IEM-based MMC mixing model and Reaction-Diffusion Manifolds (REDIMs) as the simplified chemistry, but it can be extended easily to other mixing models. The proposed methodology is validated by testing the well-known non-premixed Sandia Flame D and F, and the results show good agreement with experimental results and those obtained using the detailed chemistry. [ABSTRACT FROM AUTHOR]

The accurate prediction of the NOx formation has gained great attention in view of clean combustion. In this direction, a reliable reduction technique for the chemical kinetics is important to capture the NOx formation accurately with reduced computational costs for the practical turbulent combustion processes. This work focuses on the hierarchical construction of Reaction-Diffusion Manifolds (REDIM) to include the NOx chemistry, which is well-known to be governed by very slow chemical reactions. Based on the hierarchical structure of the REDIM method, a two-dimensional (2D) and a three-dimensional (3D) REDIM model are generated, without any principle extension of the REDIM method. Sample calculations of NOx formation in methane/air non-premixed counterflow flames verify the REDIM method for both steady and transient processes. [ABSTRACT FROM AUTHOR]

In this work, the influence of H2 addition on the auto-ignition and combustion properties of CH4 is investigated experimentally and numerically. Experimental ignition delay times (IDT) are compared with simulations and laminar burning velocities (LBVs), and extinction limits/extinction strain rates (ESRs) are compared with data from the literature. A wide variety of literature data are collected and reviewed, and experimental data points are extracted for IDT, LBV and ESR. The results are used for the validation of existing reaction mechanisms. The reaction mechanisms and models used are able to reproduce the influence of H2 addition to CH4 (e.g., shortening IDTs, increasing ESRs and increasing LBVs). IDTs are investigated in a range from 6 to 15 bar and temperatures from 929 to 1165 K with H2 addition from 10 to 100 mol%. We show that LBV and ESR are predicted in a wide range by the numerical simulations. Moreover, the numerical simulations using detailed Aramco Mech 3.0 (581 species) are compared with the derived reduced reaction mechanism UCB Chen (49 species). The results show that the reduced chemistry obtained by considering only the IDT is also valid for LBV and ESR. [ABSTRACT FROM AUTHOR]