Solid(catalyst)-solid(soot) contact is a crucial factor in diesel soot catalytic combustion, and rationally optimizing solid(catalyst)-solid(soot) contact is a promising yet challenging pathway for improving catalytic diesel soot combustion performance. Here, we report a micrometer scaled sheet-type CeO2-ZrO2 soot oxidation catalyst. The nitrogen adsorption-desorption result indicates that soot particulates

The current work assesses the impact of turbulence on flame surface characteristics and scalar dissipation rates (χC) of piloted premixed methane-air flames. This assessment is facilitated via the application of planar Rayleigh scattering (PRS) to a subset of the flames considered in Part I (13 in total), which possess turbulent Karlovitz, Damköhler, and Reynolds numbers in the range of 1.1 ≤KaT,P≤ 144

The characteristics of the flame structure, stabilization, and extinction of counterflow nonpremixed flames of CH4/He versus air at low strain rates are investigated by performing a series of experiments and two-dimensional (2-D) numerical simulations. By adopting an experimental methodology using He curtain flow, we can locate the flames near the center of the counterflow burner and measure the critical

Data obtained in recent direct numerical simulations (Lee et al.) of statistically one-dimensional and planar, lean complex-chemistry hydrogen-air flames characterized by three different Karlovitz numbers Ka ranging from 3 to 33 are further analyzed in order to explore local characteristics and structure of (i) extreme points characterized by the peak (over the computational domain) Fuel Consumption

The mechanism of evolution of polycyclic aromatic hydrocarbons (PAHs) into carbonaceous particles in combustion, atmosphere, and interstellar space has been the subject of intense debate. Recently, there has been emerging evidence supporting resonantly-stabilized radicals as key players in PAH growth. In this work, we build on this hypothesis and propose that, beyond a critical size, PAH reactivity

A novel functional form for approximating the conditional scalars in turbulent reacting flows is introduced based on the Bernstein polynomial. Multi-scalar measurement data of turbulent premixed and non-premixed flames are used to demonstrate that the new functional form provides an excellent reduced-order model for the conditional scalars. This model order reduction technique can be used to improve

The overall impact of CO2 on the coal char combustion is complicated due to the interplay between the CO2 thermal effect and chemical effect (including the gasification endothermicity, and its direct additional carbon consumption). To assess the impact of these factors on the carbon consumption process, we conduct a quantitative study on the separate physicochemical effects of CO2 through experimental

Previous studies have shown that addition of potassium chloride (KCl) reduces soot concentration and primary particle size. To improve the understanding of this phenomenon, this work focuses on investigating the influence of KCl addition on formation of polycyclic aromatic hydrocarbons (PAHs), assumed to be precursors of soot. The method used is laser-induced fluorescence (LIF), for which different

A three-dimensional numerical study is performed to investigate concurrent-flow flame spread over thin solid fuels in microgravity. The model considers the burning scenarios of a recently concluded ISS microgravity experiment, Confined Combustion. Cellulose based thin samples are burned in a small flow duct. The height of the flow duct and the radiation reflectance of the duct wall are varied. Flame

In biomass thermal conversion processes, the release of potassium in high temperature environments crucially influences the operating efficiency and safety. The dominant potassium species can be potassium hydroxide (KOH) and/or potassium chloride (KCl). We report a species-specified quantitative measurement of potassium hydroxide (KOH) in combustion environments using laser-induced photofragmentation

A Direct Numerical Simulation (DNS) study of statistically one-dimensional and planar, lean complex-chemistry hydrogen-air flames characterized by a low Lewis number Le and three different Karlovitz numbersKa ranging from 3 to 33 is performed, with the same complex-chemistry flames being also simulated by setting molecular diffusivities of all species equal to the heat diffusivity of the mixture. The

The present study analyses the flame extinction of timber under different levels of external heating and oxygen contents in the surrounding atmosphere. An existing theoretical framework conceived initially for the analysis of a counter-flow diffusion flame established above the surface of a condensed fuel is extended for charring materials to deliver a fundamental understanding of the self-extinction

The tangent linear approximation (TLA) developed in Almohammadi et al. (Combust. Flame 230, 111426) is extended to estimate the sensitivity of the ignition delay time with respect to species enthalpies and entropies. The proposed method relies on integrating the linearized system of equations governing the evolution of the state vector’s partial derivatives with respect to variations in thermodynamic

This paper presents numerical simulations of the evolution of premixed flames in channels with obstacles using the Chemical-Diffusive Model (CDM) coupled to a compressible Navier-Stokes solver. The CDM is a parametric model for chemical reaction and diffusive transport, and it is calibrated to reproduce a set of properties of one-dimensional laminar flame and the Zel’dovich-Neumann-Döring (ZND) detonation

The kinetics of the reactions H2NO + O2(3Σg−) → HNO(X˜1A′) + HO2 and NH2 + HO2 → NH3 + O2(3Σg−), which are, respectively, very sensitive chain-propagation and chain-termination reactions in ammonia kinetic models, have been revisited by means of high-level electronic structure and variational transition state theory calculations with the goal of improving former predictions and the performance of ammonia

This study focuses on exploring the thermochemistry in flame-wall interaction (FWI) for fully premixed side-wall quenching of a laminar, atmospheric-pressure dimethyl ether flame at equivalence ratio Φ=0.83 by simultaneous measurement of CO2 and CO mole fractions and gas phase temperature T. The applied laser diagnostics are dual-pump coherent anti-Stokes Raman spectroscopy (DP-CARS) targeting N2 and

Novel design of one-layer porous burner for experimental studies of the flame front dynamics at pore scale level is proposed. Results of the experimental and numerical studies of non-stationary flame front behavior at pore scale are discussed and compared at a qualitative level. The results demonstrate that upstream propagation of the combustion wave can be accompanied by the oscillations of two different

Modeling turbulent non-premixed combustion remains a challenge in the context of Large Eddy Simulation (LES) in complex geometries and for realistic conditions, taking into account all physical phenomena impacting the flame such as heat loss, dilution, or liquid fuel atomization and evaporation. In this work, the Thickened Flame concept, which allows to resolve the flame front on the LES grid while

The impact of confinement on a turbulent lean premixed swirl flame is investigated using a finite-volume large-eddy simulation method to solve the compressible Navier-Stokes equations and a combined G-equation progress variable approach to model the flame. The geometry is an experimentally investigated burner by Moeck et al. [Combust. Flame, 159, 2650-2668 (2012)] in which a precessing vortex core

Ammonia (NH3) is a promising carbon-free fuel and a hydrogen carrier. In recent years, there has been a large number of experimental and numerical studies to understand the chemical kinetics of NH3 in moderate to extremely complex systems. This study focused on understanding the chemical kinetics of NH3 in a simple system (pyrolysis). Shock-tube experiments were performed to monitor the NH3 time history

Strict regulations on fuel economy are driving modern gasoline engines to adopt more advanced technologies to improve thermal efficiency. Some of the technologies, for example ultra-high compression ratio and spark assisted compression ignition, will elevate the thermodynamic condition near top dead center (TDC) to a considerably high level, even up to or beyond the negative temperature coefficient

Applying the Bray-Moss-Libby (BML) bi-modal asymptotic limit to a progress variable signal in a premixed turbulent flame, a relation is established between the variation rate of the mean turbulent flame brush thickness, the flame surface wrinkling and the turbulent burning velocity. This scaling suggests that the link between the amplification of the flame surface by turbulence and the increase of

Thermally dissipated energy from periodic mechanical action can lead to the creation of areas of intense, localized heating in heterogeneous composite materials, called hot spots. Measurements of hot spots have been performed in shock, impact, and friction studies of energetic materials, amongst others. In this work, high-frequency contact loading allows for the controlled development of hot spots

A framework is proposed to investigate the behavior of LES flame surface density models for simple academic cases, here the development of a statistically one-dimensional flame in an homogenous and isotropic turbulence, by comparison with a prescribed reference solution. First, a set of zero-dimensional equations is derived to reproduce a fractal flame surface evolving from an initially planar shape

NOx emissions remain a primary concern for modern and future gas turbines, particularly as we progress towards a net-zero carbon future. It is critical to identify novel strategies to mitigate environmental pollutants for both modern turbines operated on natural gas and future turbines projected to use carbon-free fuels (such as hydrogen). In the current study, NOx emissions of a reacting methane-air

Deep neural network (DNN) is applied to mean reaction rate modelling. Two DNN structures, species-dependent (SD) and species-independent (SI), are considered.1 Due to the explicit inclusion of all species variables in the input layer for SD-DNN, this model may consider relationships of different chemical species. However, the prediction can be performed only for simulations with chemical mechanisms

Thermochemical states of a turbulent, lean premixed dimethyl ether/air flame were assessed for the first time using simultaneous measurements of gas temperature T, CO2 and CO mole fractions with locations as close as 120 μm above the quenching wall. This is realized by combined dual-pump coherent anti-Stokes Raman spectroscopy (DP-CARS) and two-photon laser-induced fluorescence (LIF) of CO. In addition

Understanding the parameters that affect firebrand burning conditions is needed to quantify and model heat transfer from firebrands to combustible surfaces. In this research, an experimental and analytical effort was conducted to determine the variable relationships that control firebrand burning. A series of experiments were performed to quantify the mass loss rate, temperature, and char diameter

We have recently shown that premixed CH4/air flames anchored behind flame holders can stabilize in two flame stabilization regimes characterised by the presence or absence of a recirculation vortex [1]. Focus of the present work is on the underlying mechanisms governing flames anchored without the presence of a vortex for methane-air flames. We revisit the definition of the flame anchoring location

The interaction between ammonia and NO under combustion conditions is analyzed in the present work, from both experimental and kinetic modelling points of view. An experimental systematic study of the influence of the main variables for the NH3NO interaction is made using a laboratory tubular flow reactor installation. Experiments are performed at atmospheric pressure and variables analyzed include:

The homogeneous ignition and volatile combustion of pulverized solid fuel in single-particle and particle group configurations were studied numerically in a laminar flat flame burner. Simulations with increasing particle streams were performed to investigate the influence of the interactions in particle groups on homogeneous ignition and combustion. An extensive set of simulations are conducted considering

Ammonia combustion, owing to its zero greenhouse gas CO2 emission, is attracting attention for energy utilization. However, the thermal radiation of NH3 has not been reported and involved in the numerical simulations of ammonia flames, which may cause serious errors in estimating the laminar flame speeds. In this study, the effects of radiation reabsorption on the laminar flame speed at different equivalence

This paper presents particle size distributions and chemical compositions of soot measured using a Scanning Mobility Particle Sizer (SMPS) and a Fourier-Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS), respectively, in flames of ethylene-oxygen and ethylene-oxygen doped with ammonia. The inhibitory effect of ammonia addition on soot formation in ethylene flames, as well as the influence

Ammonia is a compelling carbon-free fuel, and co-firing ammonia with conventional hydrocarbon fuels receives growing interest as a feasible solution to mitigate CO2 emission. This study experimentally and numerically investigated the soot formation characteristics of n-heptane co-flow laminar diffusion flames with different contents of ammonia (up to 40% by volume, balanced using argon). The soot volume

An experimental and kinetic study on the pyrolysis and oxidation of isopentane (2-methylbutane) were conducted in this work. The experiments were performed in a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of oxygen, hydrogen, CO, CO2, C1C6 hydrocarbons and methanol were measured

A detailed description is given of double burner fire whirls that are similar in structure to the type of combined whirls seen in nature. The whirls are generated using the fixed frame method, and two burners are placed symmetrically about the center of the fixed frame. The flame from each burner sweeps along the ground until it reaches the point midway between the burners, where the two flames wrap

Droplet-combustion experiments with normal-alkane fuels, carried out onboard the International Space Station, have shown that, after radiative extinction of a droplet burning with an ordinary hot flame, often quasi-steady burning is initiated and sustained by a chemical-kinetic mechanism associated with cool flames. This second, cool-flame combustion stage occurs in a partial-burning regime in which

Ammonia is regarded as a potential carbon-free alternative fuel. To have a better understanding of its combustion characteristics, development of feasible techniques for ammonia detection in combustion environments is essential. In the present work, planar laser-induced photofragmentation fluorescence (LIPF) was developed for quantitative measurements of ammonia in hot gas flows. A 193 nm ArF excimer

Skeletal model reduction based on local sensitivity analysis of time dependent systems is presented in which sensitivities are modeled by forced optimally time dependent (f-OTD) modes. The f-OTD factorizes the sensitivity coefficient matrix into a compressed format as the product of two skinny matrices, i.e. f-OTD modes and f-OTD coefficients. The modes create a low-dimensional, time dependent, orthonormal

Thermoacoustic interactions in a circumferential network of lean-premixed combustors have a substantial impact on engine-level dynamics in a can-annular gas turbine combustion system. Previous experimental and numerical studies have focused on identifying the formation of large-scale interaction patterns and the modal dynamics of multiple eigenmodes. Since those investigations were primarily concerned

Direct numerical simulation (DNS) results are analysed to investigate the effect of flame–flame interaction on the scalar distribution in a large eddy simulation context. The DNS data consist of turbulent premixed planar flame, V-flame and swirl flame cases with different turbulence and equivalence ratio, and relatively large Damköhler number conditions are considered for the three DNS cases. The volumetric

Low-temperature oxidation of cyclohexane is investigated in two jet-stirred reactors (JSRs) at 1.04 bar and the equivalence ratio of 0.25. Reactive hydroperoxides and highly oxygenated molecules are detected using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The isomers of C6H10O (5-hexenal, cyclic ethers and cyclohexanone) are separated using gas chromatography combined

Singly Conditional Source-term Estimation (CSE) is extended to Doubly Conditional Source-term Estimation (DCSE) to simulate three turbulent ethanol spray flames (EtF1, EtF3 and EtF4) for the first time. Reynolds-Averaged Navier Stokes equations are solved with a two-way coupling Eulerian-Lagrangian method to account for the gas-spray interactions. The objective of this work is to compare the performance

The inclusion of molecular diffusion into the joint-probability density function (JPDF) method requires terms for molecular transport in physical space and mixing in composition space. The former is typically neglected for high Reynolds number flows but becomes important in flows close to surfaces and for flamelet related reaction-diffusion structures associated with high Damköhler numbers. McDermott

Propagation of smoldering combustion and its blow-off phenomena are of practical importance in evaluating the fire dynamics of solid fuels, but the scientific understanding is still limited. In this work, we quantify the smoldering propagation rates on consolidated biomass and the blow-off limits under concurrent and opposed external airflows up to 50 m/s. The incense cylinders with different diameters

Pressurized oxy-fuel combustion is deemed an advanced oxy-fuel combustion technique due to the lower cost and little decrease in the generating efficiency compared to conventional PC system without CO2 capture. Butane is an important composition of petroleum and natural gas. In this work, the ignition delay times (IDTs) for n-butane and i-butane under O2/CO2 atmospheres were measured in a shock tube

The paper first reviews the mode of generation of fire whirls, their properties, and operational regimes, under well-controlled experimental conditions. The situation is different with wildfires. These are uncontrolled and less well understood. A modified analytical approach is described for these conditions. This is based on global energy levels, per unit ground area, for different fuels, and their

The flowability of nano-aluminum (nAl) particles is poorly characterized or tailored but must be improved for their manufacturing or application of interest. In this work, a strategy was proposed to improve the fluidity of nAl particles and increase the active aluminum content of nAl particles to be higher than that of naturally passivated nAl with similar size by 14%. The main method was introducing

A bottom-up approach to assemble reduced combustion kinetics mechanisms is proposed as an alternative to conventional reduction techniques. Rather than relying on simulations using detailed mechanisms to identify the set of species and reactions to include in the reduced mechanism, the proposed “building” algorithm follows an add-as-needed approach, in which reduced mechanisms are progressively augmented

The present study aims to extend the understanding of the external group combustion for droplet clouds under two-stage autoignition conditions. First, an exemplar case has been chosen to analyze the two-stage ignition behavior and flame structure. It was found that the fuel vapor transport of the droplet cloud is mainly supported by the thin vaporization layer near the edge of the cloud, which is the

To understand the low-temperature oxidation chemistry of cyclohexane, conformational analysis and theoretical study of the first and second oxygen addition are performed using quantum chemical calculations and kinetic calculations. Pressure- and temperature-dependent rate constants and branching ratios for major reaction channels are determined with RRKM/master-equation simulations over 298–2000 K

The conditional moment closure (CMC) method with tabulated chemistry is proposed to reduce the computational load for integration of stiff reaction steps in the conventional CMC methods. It is based on the assumption that temperature and all species except CO and CO2 adjust fast enough so that they can be uniquely determined by the single reaction progress variable given as the sum of CO and CO2 mass

Femtosecond, Two-photon Absorption Laser Induced Fluorescence (fs-TALIF) corrected for collisional quenching with Raman scattering is used to capture spatially resolved atomic oxygen profiles in lean premixed, hydrogen cellular tubular flames. This method has allowed comparisons of number density and O-atom concentration distributions in flames of variable stretch rates in a manner similar to that

In the present experimental work, we investigate the thermoacoustic coupling of methane flames propagating inside 4 and 6 mm diameter tubes (slightly larger than the quenching diameter). Multiple tube’s lengths were selected (between 275 and 900 mm) so typical system’s fundamental and harmonic frequencies ranged between 190 and 600 Hz. Experimental results were obtained for stoichiometric and lean

Ammonia is a promising alternative fuel for CO2 emission mitigation. The use of ammonia blends allows for more flexibility compared to pure ammonia fuel and is often considered for immediate CO2 emission reduction in existing facilities running on natural gas. However, fundamental studies on these fuel mixtures remain scarce. This study thus focuses on ammonia/methane blend fuels. The effect of ammonia

Knock in spark-ignited (SI) engines is initiated by autoignition of the unburned gasses upstream of spark-ignited, propagating, turbulent premixed flames. Knock propensity of fuel/air mixtures is typically quantified using research octane number (RON), motor octane number (MON), or methane number (MN; for gaseous fuels), which are measured using single-cylinder, variable compression ratio engines.

Extinction of premixed flames under non-uniform, unsteady strain is a phenomenon commonly observed in turbulent combustors. To assess the role of inequity in thermal and mass diffusion, represented by a global Lewis number (Le) - defined as the ratio of the mixture’s thermal diffusivity to the mass diffusivity of the deficient species, on such extinctions, we present a study of counterflow twin-flames

To study the mechanism of the electromagnetic field influences flammable gas explosions, 9.5% methane-air explosion tests were carried out in a closed transparent pipe and the effect of the electromagnetic field on the free radicals was analyzed through COMSOL Multi-physics. The relationship between explosion pressure, explosion product composition and its concentration and movement of key free radicals

This research investigates the transient flame propagation and oscillation phenomenon in the flame speed of porous biochar dust cloud. Time-dependent mass, momentum and energy equations are solved in the spherical coordinate. The gas phase reaction includes the chemical reactions, thermodynamic properties, and multi-element transition properties. To account for the porosity effects of particles, the

The decomposing explosion behavior and characteristics of methyl nitrite (MN) were investigated by analyzing the instantaneous flame of MN decomposition explosion in this work. The lowest explosion limit of MN decreases with the addition of nitric oxide, nitrous oxide and oxygen. The ternary diagrams of the explosive range for “methyl nitrite/nitrogen/oxide gas” mixtures at 40℃ and 100 kPa were acquired