We present and assess a method to reduce the computational cost of performing ensemble-based data assimilation (DA) for reacting flows in multiple-query scenarios, i.e. scenarios where multiple simulations are performed on systems with similar underlying dynamics. The accuracy of the DA, which depends on the accuracy of the sample covariance, improves with the ensemble size, but results in a commensurate

A new rotational flamelet model with inward swirling flow through a stretched vortex tube is developed for sub-grid modelling to be coupled with the resolved flow for turbulent combustion. The model has critical new features compared to existing models. (i) Non-premixed flames, premixed flames, or multi-branched flame structures are determined rather than prescribed. (ii) The effects of vorticity and

The effect of hydrogen (H2) addition on the flame dynamics of premixed methane/air mixtures in a microchannel was investigated through two-dimensional numerical computations using a detailed chemistry model. Detailed numerical simulations were performed in a 2 mm diameter tube with 120 mm length and a hyperbolic wall temperature gradient condition. All numerical computations were performed at stoichiometric

Through the use of carefully designed numerical experiments on an explosive system, that use predictive models for subcomponents and multi-material simulation, we demonstrate enhanced reactivity by energy trapping in regions of the reactive flow that were previously shocked. Particles and inclusions are placed in designed patterns in an explosive matrix. New capabilities in additive manufacture make

Phosphorus-based chemical compounds such as trimethylphosphate (TMP) and dimethylmethylphosphonate (DMMP) are widely used as fire suppressants. The detailed chemical kinetic mechanism by Jayaweera et al. [1] is frequently used to describe the flame inhibition process. The elementary reaction steps can be categorised into inhibitor molecule decomposition steps and radical recombination steps. The present

This study presents an algebraic combustion closure for Large eddy simulation (LES) exhibiting attributes of simplicity and simultaneous accuracy under realistic combustion conditions. The model makes use of the interlink between the reaction and dissipation rates in premixed turbulent combustion but relaxes the thin flame assumption by considering finite-rate chemistry effects in the small-scale turbulence

Ignition delay time (IDT) is an important global combustion property that affects the thermal efficiency of the engine and emissions (particularly NO X). IDT is generally measured by performing experiments using Shock-tube and Rapid Compression Machine (RCM). The numerical calculation of IDT is a computationally expensive and time-consuming process. Arrhenius type empirical correlations offer an inexpensive

Critical slowing down phenomena occur during the transition process of various dynamical states, such as bifurcations. The eigenvalues of dynamical systems can be regarded as an indicator of critical slowing down of impending bifurcation. Adaptive, locally linear models can extract local eigenvalues of the nonlinear dynamical system by segmenting a full-time series into multi-windows, and eigenvalue

To build a set of complete kinetic parameters of oxygenated fuels kinetic model on Pt catalyst, methanol was used as an example to carry out the catalytic oxidation kinetics experiment of oxygenated fuels on Pt/ZSM-5 catalyst. The Power law model and Langmuir–Hinshelwood (L–H) model were established to characterise the catalytic oxidation reaction of methanol. Then the oxidation kinetics of methanol

The modelling of soot formation is investigated for two turbulent flames, at atmospheric and 3 atm pressure conditions. For the first time, a semi-empirical soot formulation that accounts for soot inception, coagulation, surface growth, and oxidation processes is coupled with the turbulent combustion model, Conditional Source-term Estimation (CSE) using Reynolds-Averaged Navier–Stokes equations. Detailed

The reaction progress variable is a crucial concept in the advanced flamelet combustion models. As a controlling variable, a well-defined progress variable must consider the essential features of the combustion process. It is usually a heuristically defined linear combination of some major chemical species mass fractions. However, such a simple definition could lead to inaccurate results for the fuel-rich

Smouldering combustion plays a key role in wildfires in forests, grasslands, and peatlands due to its common occurrence in porous fuels like peat and duff. As a consequence, understanding smouldering behaviour in these fuels is crucial. Such fuels are generally composed of cellulose, hemicellulose, and lignin. Here we present an updated computational model for simulating smouldering combustion in cellulose

This paper studies premixed flame dynamics in half-open tubes by solving the two-dimensional, fully compressible, reactive Navier-Stokes equations on a dynamically adapting mesh using a high-order algorithm. A simplified chemical-diffusive model was used to describe the chemical reaction and diffusive transports in a stoichiometric hydrogen-air mixture. The influence of the length scale was examined

Combustion of a porous solid fuel is considered. An exothermic reaction takes place between the fuel and a gaseous oxidiser which is delivered to the reaction zone by filtration through the pores in the sample from an open end toward which the combustion wave propagates (counterflow filtration). The gas reacts with the solid fuel to form a solid product. The gas filtration is due to the pressure difference

Diffusive transport of mass occurs at small scales in turbulent premixed flames. As a result, multicomponent mass diffusion, which is often neglected in direct numerical simulations (DNS) of premixed combustion, has the potential to impact both turbulence and flame characteristics at small scales. In this study, we evaluate these impacts by examining enstrophy dynamics and the internal structure of

The effects of body force on the statistical behaviour of turbulent scalar flux and its closure in the context of Reynolds Averaged Navier–Stokes simulations have been studied using Direct Numerical Simulations (DNS) of statistically planar turbulent premixed flames under different turbulence intensities and Froude numbers. An increase in body force magnitude in the case of unstable density stratification

We present an investigation of the stabilisation of premixed laminar flames by means of an isolated highly conductive bluff-body, a circular cylinder, placed in a uniform flow of a combustible mixture. It is shown that the problem has non-unique steady-state solutions for certain values of the parameters. Moreover, we solve the time-dependent equations to check the stability of the solutions and demonstrate

The main objective of this article is to investigate the capability of the flamelet progress variable (FPV) model to capture the extinction processes observed in under-ventilated fire scenarios. To this end, large eddy simulation (LES) of the methane line fire plumes in oxygen-reduced environments down to global extinction, investigated experimentally at the University of Maryland (UMD), is performed

In the context of the large thermal-expansion approximation, we derive an equation describing flame front dynamics under conditions of Darrieus-Landau instability. We show that the second-order theory leads to system of two evolution equations for the flame front perturbations and for the potential of the unburned mixture flow. In the limiting case of long evolution, the system of equations can be

This paper addresses the aerodynamics of a new type of Tsuji burner involving a cylindrical porous fuel injector of radius a placed at the centre of a planar air counterflow configuration with strain rate A∞, with specific attention given to flows with large values of the Reynolds number A∞a2/ν, where ν represents the air kinematic viscosity. For cases in which the fuel-injection velocity Ui is comparable

Spontaneous ignition of isolated n-heptane droplets with initial diameters of 20–100  μm is simulated using air at 4 atm and 700–1200 K, which includes the typical operating conditions of recuperated microturbines. Because some fuel droplets in a combustor may be sprayed or carried to near the recirculation zone, the simulations use a mixture of pure air and hot combustion products as the oxidiser

Due to the specific prediction requirements in combustion simulations, the reduced chemical mechanism developed focusing on particular applications is usually needed. A systematic method for chemical mechanism reduction orientated toward specific applications is proposed in this work. The reduction process is divided into two parts for large-molecule fuels, including the reduction of the fuel-specific

In this study, we investigate the effect of different split injection strategies on ignition delay time (IDT) and heat release rate (HRR) characteristics in Reactivity Controlled Compression Ignition conditions via large-eddy simulation and finite-rate chemistry. A diesel surrogate (n-dodecane) is injected into a domain with premixed methane and oxidiser in two separate injection pulses. Three different

We investigate the calibration of an instrument model for a high-pressure chemical reactor and vacuum ultraviolet photoionisation mass spectrometry apparatus, using a collection of ‘static’ mass spectrometry data (i.e. from unreactive samples). A Bayesian calibration method is applied to characterise the uncertainty of the model parameters, the associated model error, and the predicted mass spectrum

Detailed chemistry simulations of turbulent reacting flows involving combustion of hydrocarbons can easily exceed the available computational resources, depending on the dimensions of the chemical system. Previous work of the authors showed how the combination of the Eulerian Stochastic Fields (ESF) model with tabulated chemistry based on 2-dimensional Reaction-Diffusion Manifolds (REDIM) provided

In this work, a mathematical formulation for the calculation of the sensitivity of manifold-based simplified chemistry with respect to the scalar gradient is derived. This methodology allows to answer how important the scalar gradient is for the Reaction–Diffusion Manifolds (REDIM) reduced chemistry and how sensitive the reduced scheme is with respect to the gradient estimate. Based on the governing

In this paper, a computational framework for modelling the thermochemical conversion of powdered solid fuels in a MILD reactor is presented. Specific fuels of interest are high ash coals and lignocellulosic biomass. The novelty of the current framework lies in recognising that the devolatilisation process of charring fuels like biomass and coal is surface heat transfer limited at heating rates relevant

This work presents a series of simulations of the light-round process in a premixed annular combustor, consisting of 18 individual swirl bluff body burners, using improvements to the previously published stochastic low-order model SPINTHIR that mimics flame propagation with a Langevin particle model and continuous new particle generation. The improvements presented include the effect of dilatation

Considerable research studies have been reported on developing effective active control means to mitigate combustion instability. In this work, a neural network PID (NN-PID) controller is proposed and demonstrated to suppress the oscillating pressure in a cylindrical Rijke tube, for which the combustion instability is modelled by a 1D acoustic network model together with linear and nonlinear flame

The laminar burning velocity (SL) was measured at sub-atmospheric pressure (0.84 atm) and an environmental temperature of 295 ± 2 K for two high C2H6 content fuel mixtures, 75% CH4 – 25% C2H6 (mixture M1), and 50% CH4 – 50% C2H6 (mixture M2), as well as the pure constituent fuels. The equivalence ratios for the experiments ranged between 0.8 and 1.4. Numerical calculations predicting SL were performed

In this work, to further optimise the porous media combustion model and explore the combustion characteristics of low-concentration methane in porous media, a thermal non-equilibrium model of porous media combustion is established with modified effective thermal conductivity of the porous media based on the volume average method. The effects of foam ceramics pore density, inlet velocity and wall heat

To reduce the injury caused by hydrogen explosion accident, numerical simulation study is carried out to study the characteristics of hydrogen explosion in confined space under different venting conditions. The results show that in the process of the flame passing through the side vent, the position of the side vent can affect the leading role of the side venting on the flame front distortion. When

The homogeneous, isochoric and adiabatic autoignition of rich methanol mixtures is analysed using algorithmic tools of Computational Singular Perturbation. It is shown that ignition delay decreases as the equivalence ratio ϕ increases, due to the faster production of OH radicals via the reactions CH 3OH + HO 2 → CH 2OH + H 2O 2 and H 2O 2 (+M) → OH + OH (+M). After ignition and for sufficiently rich

An accurate prediction of the probability density function (PDF) of the mixture fraction is crucial to the prediction of combustion since mixing plays an important role in turbulent non-premixed and partially premixed flames. This work provides an assessment of the large-eddy simulation (LES)/filtered density function (FDF) method for the prediction of the PDF of the mixture fraction. The advantage

The study of combustion-thermoacoustic instabilities is a topic of interest in the development of engines. However, the modelling of these systems involves a high computational burden. This paper focuses on a simpler class of systems that still features such instabilities: inverted conical flames anchored on a central bluff-body. Here these flames are modelled by solving species mass, momentum and

Evolution of fuel droplet evaporation zone and its interaction with propagating flame front are studied in this work. A general theory is developed to describe the evolutions of flame propagation speed, flame temperature, droplet evaporation onset and completion locations in ignition and propagation of spherical flames. The influences of liquid droplet mass loading, heat exchange coefficient (or evaporation

We have extended the computational singular perturbation (CSP) method to differential algebraic equation (DAE) systems and demonstrated its application in a heterogeneous-catalysis problem. The extended method obtains the CSP basis vectors for DAEs from a reduced Jacobian matrix that takes the algebraic constraints into account. We use a canonical problem in heterogeneous catalysis, the transient continuous

Preferential diffusion is very important in simulations of hydrogen flames. Flame stretch and curvature induce strong preferential diffusion effects in laminar premixed hydrogen flames, causing strong local deviations from the unburnt mixture fraction in the reaction zone. In tabulated chemistry methods, this necessitates the use of a partially premixed model even if the inlet mixture is purely premixed

Enhancing oil recovery using in-situ combustion (ISC) is an attractive alternative, especially for heavy crudes. During ISC, part of the hydrocarbon is pyrolysed/oxidised, which generates heat and deposits fuel in the combustion front. In this study, crude reactions during ISC are modelled after their thermogravimetry thermo-oxidative profiles using advanced machine learning systems. The model inputs

Large-eddy simulation with the thickened flame model (LES/TFM) is conducted to simulate a three-dimensional dual swirl partially premixed methane/air gas turbine model combustor. Finite-rate chemistry is described by a skeletal chemical mechanism consisting of 16 species and 41 reactions. Flame sensors based on formyl radical (HCO) and chemical explosive mode analysis (CEMA) are proposed and implemented

In this study, with the aim of deriving a temperature-based energy equation and evaluating the fractal dynamic SGS (FDSGS) combustion model under an isochoric condition, modelling of the filtered energy conservation equation in the temperature form is considered and is tested in the contexts of a priori and a posteriori, comparing with a corresponding DNS of turbulent combustion in a constant volume

In this work we perform three-dimensional simulations to study the breaking of symmetry of lean premixed isobaric flames propagating in narrow channels of circular cross-section subject to an inlet Poiseuille flow. In particular we consider the effects of the flow rate, the channel diameter, wall heat-losses for flames with the Lewis number (Le) equal or less than unity. Numerical analysis shows that

A simplified chemical-kinetic cool-flame mechanism for n-alkanes has recently been developed and applied to the description of quasi-steady droplet combustion. Chemistry of this same general type can support premixed laminar cool-flame deflagrations. The present contribution derives the structure of the associated freely propagating cool premixed flame controlled by the low-temperature chemistry and

Previous work shows that auto-ignition propagation modes for strong knocking in engines are dominated by both chemical reactivity and energy density. To clarify the unique role of energy density and chemical reactivity, hotspot auto-ignition induced reaction wave propagation was investigated using direct numerical simulations, addressing the detonation regime in the detonation peninsula. Different

The aim of several combustion experiments is the determination of the rate coefficients of important elementary reactions. The experimental conditions are usually selected on the basis of local sensitivity analysis. Shock tube and tubular flow reactor experiments are often designed in such a way that only one reaction step is important at the investigated conditions. Sheen and Manion (J. Phys. Chem

The work proposes a model for synthesising a ‘metallic matrix–reinforcing inclusions’ composite in a simplified reaction scheme. A suggested mathematical model takes into account the interdependence of thermal, chemical and mechanical phenomena. The problem includes kinetic equations for determining the composition of the synthesis products. The reactions are initiated by a thermal impulse from a surface

This paper presents a coupled thermal-hydraulic-chemical numerical model to study the temperature development and solid–gas conversion during underground coal gasification (UCG). Theoretical formulations are based on the porous medium approach, involving the gas flow, solid mass loss, and heat flow, and the chemical reactions driving the phase change and transformation of gaseous species are considered

To investigate the role of five-membered rings in the growth of polycyclic aromatic hydrocarbons (PAHs) in flames, the conversion of acenaphthylene to pyrene with substituted phenalene as intermediate is studied through quantum calculations using CBS-QB3 composite method. Two pathways are considered, where one initiates with H-abstraction from the five membered ring on acenaphthylene, while the other

A new combustion regime identification methodology using the neural networks as supervised classifiers is proposed and validated. As a first proof of concept, a binary classifier is trained with labelled thermochemical states obtained as solutions of prototypical one-dimensional models representing premixed and nonpremixed regimes. The trained classifier is then used to associate the regime to any

This paper presents physics-inspired mathematical model to predict the time varying burn rate of unsteady pool fires. The model benefits from the observations on the thermal behaviour and select data from systematically and carefully designed experiments on small and large pool fires of n-heptane and small pool fires of diesel, kerosene and ethanol fuels. All modelling features are based on dimensionless

(2021). Special issue dedicated to Professor Moshe Matalon on the occasion of his 70th birthday. Combustion Theory and Modelling: Vol. 25, Special issue dedicated to Moshe Matalon on the occasion of his 70th birthday, pp. 969-969.

A theoretical analysis is developed to investigate the effects of gas expansion due to heat release on unsteady diffusion flames evolving in a pipe flow in which the mixing of reactants is controlled by Taylor's dispersion processes thereby extending a previously developed theory based on the thermo-diffusive model. It is first shown that at times larger than radial diffusion times, the pressure gradient

Underground coal gasification (UCG) is a promising option for utilising deep-seated coal for the in-situ production of syngas. In this study, we modelled and screened the chemical reactions using the previous laboratory UCG experiments to investigate the complicated chemical reaction processes to apply them to field scale UCG operations. First, we constructed 1D and 3D numerical models by matching

The prospects of 2-methylfuran (2MF) as a biofuel and gasoline blend stock are quite high. Therefore, a skeletal chemical kinetic mechanism – containing 238 species and 1156 reactions – for the simulation of premixed flames involving isooctane (representing gasoline)/2MF blends is proposed in the present work. The proposed model has been validated against a wide range of experimental data at various

In advanced propulsion systems such as scramjet engines, endothermic decomposition of onboard large hydrocarbon fuels can be used effectively for cooling and active thermal protection. During the cooling process, large hydrocarbon fuels absorb heat and decompose into small fragments. Since fuel decomposition changes the chemical and transport properties of the reactants, it is expected to affect the

An innovative kinetic mechanism reduction method, Species’ Participation in Element Fluxes (SPEF), is developed in this study. It utilises species’ participation in element fluxes to evaluate the importance of the species during the combustion process. The SPEF method has two main benefits: (1) it targets at C, H and O elements instead of pre-selected target species and has only one variable threshold

The present work describes the transition of transient one-dimensional diffusion flame into a steady two-dimensional regime in a new flow field configuration. To that end, a cylindrical burner from which fuel is ejected radially and uniformly is positioned in the middle of two impinging flows. The chosen conditions are such that the strain rate is very low. The majority of the flame is located in a

A numerical study is conducted to investigate the effects of thermal radiation on flame spread phenomenon close to limiting oxygen conditions in a low convective spacecraft environment. To understand the role of radiative heat loss from the flame, a set of simulations is performed where gas radiation is completely suppressed. The results show that radiation exerts a dual influence on flame spread rate

Different flame efficiency function (wrinkling factor) models are compared and tested for the Cambridge stratified flame using Large Eddy Simulations (LES) with an artificially thickened flame approach. Different numerical discretisations and definitions of the outer cut-off length are tested, as different practices exist that can have a strong impact on the results. The Cambridge experiment is chosen

An improved embedded-manifold/Navier–Stokes numerical methodology is developed to simulate the propagation of premixed flames within the context of the hydrodynamic theory. The method is computationally tractable, permitting calculations to not only be extended to larger physical domains but also to span a broader parametric space of physicochemical parameters. The focus of this paper is to examine