The current research work focused on the effect of the heterogeneous distribution of elements on the ash melting behavior of Zhundong coal at the sub-particle scale by using a high temperature stage microscope (HTSM) and scanning electron microscope (SEM) equipped with energy dispersive spectrometry (EDS). Experimental results showed that both molten and unmolten areas existed in the residual ash sample

This contribution experimentally investigates the heat transfer and the consequent auto-ignition of thermally thick PMMA (polymethyl methacrylate) exposed to linearly declining heat flux (HF) coupling with a theoretically derived model. Thermal decomposition in solid was ignored and critical temperature was utilized. Both scenarios neglecting and considering surface heat loss were studied in the proposed

The oxidation of CH4/diethyl ether mixtures was studied with laser absorption-based time-resolved temperature and CO concentration measurements behind reflected shock waves. Fuel-rich (equivalence ratio ϕ = 2.0) mixtures were studied because of their relevance for mechanism development for partial oxidation reactions in the context of polygeneration processes and measurements at ϕ = 0.5 and 1.0 were

A knock intensity mitigation effect resulting from the application of dielectric barrier discharge (DBD) was experimentally demonstrated. The DBD was utilized to reform fuel–air premixtures. A rapid compression and expansion machine (RCEM) was used for the demonstration experiment. A rectangular combustion channel was installed in the RCEM's cylinder to observe flame propagation and end-gas auto-ignition

Turbulent flames are highly three-dimensional and while planar measurement techniques for studying these flames are widely used, the interpretation of two-dimensional flame data can suffer from three-dimensional, out-of-plane effects. In this study, a methodology to statistically estimate three-dimensional effects on flame propagation measured from planar high-speed measurements is presented. This

The structural evolution of SF-soot (derived from the rapid pyrolysis of ShenFu bituminous coal) and a carbon black (Printex) was performed for air oxidation at 1273 and 1473 K. The morphology and nanostructure transformations were examined at conversion fractions ~0.2, 0.4, 0.6, and 0.8. Three modes of behavior were evident. The behavior of SF-soot followed an internal oxidation model (IOM) at 1273 K

Numerical simulation of soot formation in a laminar premixed burner-stabilized ethylene stagnation flame was performed with a detailed population balance model (DPBM) capable of tracking full structural details of aggregates as well as their chemical composition. A thorough parametric sensitivity study was carried out to understand the influence of individual sooting processes on the computed primary

In order to have a deep insight into the NO formation mechanism during oxy-fuel combustion, density functional theory (DFT) was used to investigate the interaction between char(N) and CO2 at molecular level. The geometric structures, orbital electron distribution properties and reaction paths were calculated and optimized. The outer orbital electron properties of char(N) and CO2 indicate that CO2 acts

The three-dimensional structure of an accelerating flame front makes it very difficult to visualize. Most experimental studies that provided a visualization of flame acceleration and deflagration-to-detonation transition (DDT) events were done in rectangular tubes using the shadow technique. Qualitative information obtained by these optical methods has been two-dimensional and line-of-sight integrated

This work presents a novel application of multi-wavelength, multi-species laser absorption methods in the pyrolysis of JP-10 fuel. Two different multi wavelength approaches are used to measure the species from JP-10 pyrolysis in a shock tube at pressures of 2.5–3 atm and temperatures of 1166–1522 K. A five wavelength (5λ) analysis combination produces species time histories for ethylene, cyclopentadiene

Combustion chemistry models have been developed with inherent uncertainties in them. Whether a model that is developed using fundamental combustion experiments is capable to reproduce practical combustion processes within typical levels of measurement uncertainty is an open question. This paper quantifies the uncertainty of engine autoignition simulation using the uncertainties in the selected chemical

An experimental work is carried out to investigate the influence of pressure on morphological parameters of soot in counterflow flames of N2-diluted methane and air. Flames are stabilized at 3, 5, 7 and 10 atm in a pressure vessel and a global strain rate of 30 s−1 is maintained at all pressures by adjusting the inlet mass flux. The mole fraction of methane is maintained at 0.7. The entire soot zone

In direct-injection engines, the formation of fuel wall film on piston surface and liner wall is a primary cause for emissions of unburnt hydrocarbons and particulate matter. It is therefore important to investigate the behavior and effect of a wall fuel film under typical engine conditions. Following our previous study of wall film effects on flame propagation and quenching under constant thermodynamic

The focus of the present work is to investigate a new methodology for the rapid generation of laminar flame speed lookup tables, to be used replacing correlation laws in internal combustion engine simulations. Current production engines run mostly under the thickened wrinkled flame combustion regime, which allows the application of a flamelet modelling approach, which requires the a-priori evaluation

It remains a long-standing challenge to predict the reaction kinetics of large complex hydrocarbon system from first principles. Exo-tricyclo[5.2.1.02,6]decane, which is further called tricyclodecane and which is the major component in JP-10 aviation fuel, and therefore its reaction with hydroxyl radical is very significant. We report high-level theoretical calculations of the rate constants of tricyclodecane + OH

Soret or thermal diffusion is known to impact combustion mixtures by diffusion of species along a temperature gradient. In this numerical modelling study we show that Soret diffusion can cause considerable local changes in the stabilization of H2 enriched premixed flames. First we validate two reduced Soret diffusion models with a more complete multi-component model. One model is able to capture the

Theoretically predicted rate coefficient parameters play an increasing role in combustion kinetic models. Understanding the uncertainty propagation during RRKM/master equation modeling and quantitatively evaluating the uncertainties of the phenomenological rate coefficients would be a great boon to chemical modeling. In the present work, the global uncertainty and sensitivity analysis were performed

Short-carbon-chain ketones are known for their high octane numbers, their knock resistance, and their low soot emission. However, studies on the combustion behavior of ketones, particularly in the low temperature regime, are sparse, and small ketones as acetone and butanone show limited low temperature chemistry (LTC). Therefore, saturated linear five-carbon ketones are good candidates to better understand

In turbulent premixed flames at low Karlovitz number, combustion heat release can have a significant impact on turbulence. Thermal expansion in flame induces dilatation, and the corresponding pressure–dilatation correlation acts as a primary source of turbulent kinetic energy (TKE). As a consequence, the flame-normal component of the normal Reynolds stresses significantly increases. Additionally, for

In an attempt to make a step forward towards predictive fire modelling, the application of turbulence modelling approaches, calculating the sub-grid scale viscosity, kinetic energy, turbulent Prandtl and Schmidt numbers based on a dynamic procedure, has been tested on a wide range of pool fire scenarios (i.e., MaCFP workshop test cases). Through the use of Large Eddy Simulations, it is investigated

This study reports experimental data regarding the effects of the addition of propene and propane in the fuel stream on soot formation in acetylene counterflow diffusion flames. Compared to the baseline acetylene flame, a continuous reduction of soot volume fraction was observed as more propene was mixed in the fuel. However, the addition of 1% propane resulted in an enhancement of soot formation,

Features of the flame transfer function (FTF) are characterized for turbulent, non-swirled, bluff body stabilized “M” flames for different hydrogen and methane blends including pure hydrogen flames. An increase in the cut-off frequency of the FTF is observed for increasing hydrogen concentration. Modulations in the form of peaks and troughs in the gain and the phase were also observed and are shown

Recent experiments have revealed the propagation of a sustained single-head detonation propagation through an obstructed channel. In this study, new experiments and analysis of the complex three-dimensional behaviour of such a single-headed wave in stoichiometric hydrogen-oxygen mixtures is presented. An optically accessible channel of square cross-section containing obstacles with 50% area blockage

The deflagration-to-detonation transition (DDT) in hot, thermally damaged HMX (δ-phase) and HMX-based polymer-bonded explosives (PBX 9501, LX-14, LX-10 and PBX 9012) differs in some respects from what has been observed in similar tests (DDT tube experiments) with room temperature granular explosives. We provide streak images with other observations and demonstrate the behavior can be binned according

A universal cookoff model (UCM) is applied to the melt cast explosive Comp-B composed of RDX and TNT. The UCM uses a simple kinetic mechanism with rates and thermophysical properties determined specifically for Comp-B. The success of the UCM is primarily attributed to the flexible form of the rate expression as well as accurate thermophysical properties obtained from small-scale experiments. The rate

Here, a finite-rate chemistry large-eddy simulation (LES) solver is utilized to investigate dual-fuel (DF) ignition process of n-dodecane spray injection into a methane–air mixture at engine-relevant ambient temperatures. The investigated configurations correspond to single-fuel (SF) ϕCH4= 0 and DF ϕCH4= 0.5 conditions for a range of temperatures. The simulation setup is a continuation of the work

Diisopropyl-methylphosphonate (DIMP) is a common surrogate of Sarin for which a detailed kinetics mechanism was developed in 2002 (Glaude et al.— [12]). In the present paper, ignition delay times and laminar flame speeds of DIMP-based mixtures were studied around atmospheric pressure for the first time. Methane and hydrogen were used as baseline fuels, and mixtures of these fuels were doped with DIMP

Composite powders combining boron with BiF3 and Bi in different amounts were prepared by high energy milling. Thermal analysis in an argon-oxygen mixture showed significant oxidation starting about 200 K lower than for pure boron. Selective oxidation of metallic Bi at low temperatures was observed. Composites containing either Bi or BiF3 ignited more readily than pure boron when heated by a CO2 laser

The use of Al-based nano-energetic materials has been limited in part due to difficulties in fabrication of high-density composites. In this paper, free-standing energetic composites with loading of up to 90 wt% Al-CuO were fabricated by 3D printing. A polymer hybrid of 3 wt% hydroxy propyl methyl cellulose (HPMC), 3.5 wt% nitrocellulose (NC) and 3.5 wt% polystyrene (PS), enables fabrication of mechanically

The propellant synthesis community is constantly looking for green alternative monopropellants. Energetic ionic liquids have several attractive properties such as high energy content, high bulk density, low vapor pressure, high thermal stability, wide liquidus range, low corrosiveness, low toxicity, and ease of handling. The combustion characteristics of an energetic ionic liquid hydroxyethylhydrazinium

In this work, we achieve a sub-breakdown electric field measurement in a premixed stagnation flame by electric-field-induced second-harmonic generation (ESHG) using a nanosecond laser. Under the application of a DC voltage, the premixed flame can transit from a flat substrate-stabilized mode to a conical nozzle-stabilized mode due to the two-way interaction between the electric and hydrodynamic responses

Non-premixed laminar or turbulent flames can undergo extinction when scalar dissipation rates exceed a critical value. When local extinction occurs, negative edge flames that act to expand the region of extinction are initially present. Steady negative edge flames have been previously studied in a combustor designed to support the negative propagation velocity of the flame edge, but unsteady negative

Unsteady flame propagation within a narrow channel, namely a Hele-Shaw burner, exhibits complicated phenomena. Recently, a new narrow-gap-disk-burner (NGDB) was developed, of which the disk-gap could be varied continuously and precisely. Although various complicated flame structures have been observed successfully, their dependency on the initial ignition has not been clarified. In this study, the

Measurements of autoignition delay times of NH3 and NH3/H2 mixtures in a rapid compression machine are reported at pressures from 20–75 bar and temperatures in the range 1040–1210 K. The equivalence ratio, using O2/N2/Ar mixtures as oxidizer, varied for pure NH3 from 0.5 to 3.0; NH3/H2 mixtures with H2 fraction between 0 and 10% were examined at equivalence ratios 0.5 and 1.0. In contrast to many hydrocarbon

Building on previous experiments conducted in an obstructed narrow rectangular channel, new details of the three-dimensional propagation behaviour of supersonic combustion waves have been revealed. In this study, a square channel equipped with 50% blockage ratio obstacles was used. Average velocity measurements coupled with high-speed schlieren photography and sooted glass sheets were used to simultaneously

Partially premixed combustion (PPC) often adopts the early fuel-injection strategy that could result in spray-wall interaction involved with piston top-land crevice. This interaction may produce a significant impact on engine combustion and unburned hydrocarbons (UHC) emission, which is still not well understood. In this study, we investigated the detailed spray-wall interaction and its effects on

Naphthalene and alkylbenzenes are present in practical transportation fuels. This study investigates the impact of naphthalene addition to alkylbenzenes on soot formation. Naphthalene was added to two kinds of alkylbenzenes, namely, 1,2,4-trimethylbenzene and n-propylbenzene. Because they are isomers, the effect of molecular structure is isolated. The sooting characteristics of naphthalene-added alkylbenzenes

The steady burning and stabilization of the boundary layer diffusion flame over a gasifying condensed fuel surface, commonly called the Emmons flame, is an important problem in the study of boundary layer combustion. We investigate herein, theoretically and numerically, the liftoff distance and blowout limit of the Emmons flame, through the corresponding response of the controlling triple flame in

The detailed kinetic mechanism of the C2H4 + NH2 reaction, an important reaction in both combustion and atmospheric chemistry, is first theoretically reported for a wide range of conditions (T = 250 – 2000 K & P = 1 – 76,000 Torr). The accurate composite electronic structure method W1U was used to explore the potential energy surface (PES) on which the temperature-and pressure-dependent kinetic behaviors

Investigations of the turbulence-flame interaction are conducted for ethanol spray combustion with dynamic flame surface wrinkling (DFSW) models in the context of the Artificially Thickened Flame (ATF) approach. DFSW modeling strategies derived for single-phase flows are extended to improve the characterization of the mixture stratification encountered in dilute spray flames. The two-phase flow is

The mechanisms of flame blowout under pressure gradient effects are explored for a bluff-body stabilized flame. The blowout process is induced through equivalence ratio reduction from a lean stabilized flame to complete blowout. Simultaneous high-speed particle image velocimetry (PIV) and C2*/CH* chemiluminescence imaging diagnostics are used to obtain the instantaneous flame structure, vorticity field

Large eddy simulations (LES) of non reactive and reactive flows in a cavity-based scramjet combustor configuration from the U.S Air Force Research Laboratory (AFRL) are performed. These simulations feature a 22 species and 206 reactions chemical scheme for ethylene/air. The ability of LES to reproduce the main features found in the experiment is first emphasised such as the average velocity field and

This work focuses on studying the oscillating length scale of gas pipeline leakage flame restricted by parallel sidewalls with various separation distances. A series of experiments are conducted with 3, 6 and 10 mm nozzles and propane is used as fuel. Results show that reduction of the sidewall separation distance hinders the air entrainment, and provokes significant enlargement of the oscillation

For the purpose of employing laser-induced breakdown spectroscopy (LIBS), nanosecond laser pulses (6 ns FWHM) from a standard Q-switched Nd:YAG laser (2nd harmonic) are modulated or chopped—using a novel method utilizing a variable air-pressure optical cell—to limit the inverse-Bremsstrahlung photon absorption process occurring in the breakdown plasma. The resulting plasma does not ignite flammable

We present in this short communication a modification to our previous ethanol reduced combustion chemistry (Millán-Merino, 2018) that eliminates nonphysical values of the species concentrations which we discovered in applying the mechanism to the combustion of an isolated ethanol droplet. This unsteady test is reported here to check the multipurpose character of the reduced mechanism for a problem

A numerical investigation was conducted to study ignition and the initial phases of methane combustion in a two-dimensional setup consisting of a pre- (PC) and main (MC) chamber. The effect of the wall thermal boundary condition (isothermal Tw=500 K or adiabatic), initial mixture temperature (Tu=300 and 800 K) and equivalence ratio in the main chamber (ϕMC=0.5 and 1.0) was studied. A stoichiometric

Effects of CO2 on soot formation during ethylene pyrolysis were investigated in a laminar flow reactor with the addition of various amounts of CO2 (0–99.5% in mole fraction). Based on a quantitative dilution sampling technique and a scanning mobility particle sizer, soot particle size distributions and the associated global properties, including soot volume fraction, number density, and soot induction

Chemical kinetics simulations are used to explore whether detailed measurements of relevant chemical species during the oxidation of very dilute fuels (less than 1 Torr partial pressure) in a high-pressure plug flow reactor (PFR) can predict autoignition propensity. We find that for many fuels the timescale for the onset of spontaneous oxidation in dilute fuel/air mixtures in a simple PFR is similar

In this study, the initial reaction of lignin pyrolysis was explored in depth with light gas emission combined with liquid bio-oil composition and physical-chemical structure of solid bio-char. The result reveals that lignin pyrolysis undergoes a complex initial reaction between 160 and 330 °C with significant mass loss (about 20%). Lignin molecular network begins to crack down with lignin monomer

The explosive thresholds Hcr of the composites cyclotrimethylenetrinitramine (RDX)-Al and pentaerythritol tetranitrate (PETN)-Al under the action of neodymium laser (wavelength 532 nm, pulse duration 14 ns) were experimentally determined for the first time as a function of the aluminum content. The experiments were performed using aluminum nanopowder with average diameter 100 nm. The gas-dynamic energy

This paper is a continuation of our work done in Part I, in which the a priori and budget analyses were conducted, Wen et al. (2019). In this work, we focus on addressing specific and recurring issues in flamelet modeling for pulverized coal combustion, including strong heat losses, multi-mode combustion and reaction progress variable definition. First, extended flamelet formulations are developed

This study focuses on the dynamics of compressibility-driven flames that emerge in narrow tubes, closed at their ignition end, when conductive heat losses through the walls are appreciable. A narrow gap approximation is used to reduce the governing equations to an effectively one-dimensional problem. In long channels this problem admits traveling-wave solutions which we have investigated numerically

Dimethyl methyl phosphonate (DMMP) is an organo-phosphorous compound (OPC) used as a fire suppressant and a simulant for sarin, a chemical warfare agent. There exists a critical need to gather combustion data at high heating rate and high temperatures conditions, similar to what exists during destruction process of chemical weapons. In the present work, DMMP pyrolysis and oxidation were carried out

A new multi-location soot sampling method is used to enhance the knowledge about the structural evolution of in-flame particles in a light-duty optical diesel engine. Through thermophoresis-based particle sampling performed at multiple in-bowl locations, the soot structures are shown for both early formation stage and later stage from the same combustion event. Three different jet-spacing angles of

Thermite powders with molar composition 8Al·3CuO were prepared in two stages by Arrested Reactive Milling (ARM). In the first stage, the starting materials Al and CuO were milled separately in acetonitrile. Composite powders were then prepared in the second milling stage with hexane as process control agent and in the four possible combinations of one, both, or neither starting material being premilled

In this work we experimentally investigate the onset of the diffusive-thermal instabilities for flat burner stabilized methane-air flames at normal pressure. The structure and dynamics of combustion fronts are studied by using visual imaging, including high-speed video recording, spectroscopic and acoustic measurements. Numerical simulations with a one-dimensional model for a burner stabilized flame

In this work we present a novel two-color differential absorption diagnostic near 5.6 μm using an external-cavity quantum-cascade-laser (EC-QCL) for formaldehyde (CH2O) detection in high-temperature reacting gases. This diagnostic utilizes the narrow mid-infrared absorption features of CH2O in the R branch of the C=O stretching band. Specifically, the online and offline colors were chosen as 1787.05 cm-1

Current nitromethane kinetic schemes do not fully capture the intermediate reaction states of deflagrating nitromethane, which is an explosive used in many combustion applications. There is a need for data on these transient species that can be used to validate and improve contemporary kinetic models. This work aims to analyze the evolution of identified transient species present in a nitromethane–air

The U.S. Department of Energy has a renewed interest in direct power extraction (DPE) technologies, such as a magnetohydrodynamic (MHD) generator, in conjunction with oxy-fuel combustion. As a topping cycle, this configuration can enable efficient CO2 capture, while offsetting oxygen separation penalties. In order to appropriately evaluate these cycles in the context of modern plant configurations

Pelletization of biomass increases the bulk energy density and the uniformity in size and shape with minimized mechanical degradation from transport, storage, and handling. A pellet can be burned in industrial circulating fluidized-bed or fixed-bed furnaces. This experimental study examines the combustion behavior of single pine wood and empty fruit bunch pellets in a laboratory-scale entrained-flow