A well-resolved database of a small-scale heptane pool fire is analyzed to assess the assumptions of flamelet models in fire simulations. The pool fire database features well-resolved turbulence fields, finite-rate chemistry for heptane using a 33-species skeletal mechanism, and a coupled Monte Carlo ray-tracing radiation solver with a line-by-line spectral model. A budget analysis of the flamelet

Ignition delay times (IDTs) and laminar flame speeds (SL) of C9H20 (nonane) isomers are systematically investigated. IDTs of normal nonane (n-C9), 2-methyloctane (2mC8), 2,4-dimethylheptane (24mC7), and 2,2,4,4-tetramethylpentane (2244mC5) are experimetally obtained by a shock tube facility and numerically simulated by a chemkin 0-D reactor model. Further, laminar flame speeds (SL) of n-C9 and 2244mC5

The ignition delay times (IDTs) of n-alcohol/diesel blends were measured in a heated shock tube (ST) and a heated rapid compression machine (RCM). Three sets of blends were formulated to investigate the effect of n-alcohol (the volume ratio of n-alcohol/diesel being 20%/80% for four blends), cetane number (CN = 43, the volume ratio of n-alcohol/diesel being 20%/80% ethanol/diesel, 20.5%/79.5% n-propanol/diesel

Energy transfer in a pulsed-microwave enhanced flame is investigated using hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) to monitor both vibrational and rotational temperatures of nitrogen in an atmospheric pressure laminar premixed natural gas/air stagnation flame. Temperatures were measured throughout the laminar flame structure following a 30-kW peak power, 2 μs duration, 3 GHz microwave

While the sooting tendencies of regular hydrocarbons, oxygenates, and complex fuel mixtures have been well-studied, far less research has been devoted to analyzing the influence of fuel-nitrogen on soot formation. The effect of nitrogen on soot formation becomes relevant for diesel fuels with nitrogen-containing additives, as well as biomass or biomass-derived fuels, which can contain up to 30% nitrogen-containing

Laser-induced incandescence (LII) was used to quantify the soot volume fraction in five piloted turbulent non-premixed C2H4-N2 jet flames at elevated pressures. In one series of flames, the bulk jet velocity was held constant as the pressure was increased from 1 bar (Re = 10,000) to 3 bar (Re = 30,000), and then 5 bar (Re = 50,000). In the other series, a Reynolds number of 10,000 was held constant

One of the major concerns in high pressure combustion is its high soot yield. An exact and comprehensive mechanism behind this phenomenon, from a chemical kinetics perspective, is still elusive. In this study, a series of pressurized (1–16 atm) co-flow ethylene diffusion sooting flames are simulated with detailed finite-rate chemistry and molecular transport. The experimental maximum soot volume fraction

The enhanced mixing and combustion mechanism of pulsed sonic jet with optimal frequency in supersonic crossflow with a 10° ramp has been investigated using Large Eddy Simulation (LES). The results show that the energetic structures from the barrel shock and shear vortex are further enlarged at the phase of 1/4T0 periodically due to the swing forward and backward effect of the bow shock. There coexists

Alkylbenzenes constitute a significant portion of middle-distillate transportation fuels, and they are judged as the key contributors to the extent of soot production and consequent exhaust particulate emissions in combustion engines. Because of the uncertainties involved in engine experiments due to boundary condition variation among test platforms and the difficulties involved in controlling engine

In a flow reactor, the pyrolysis process of n-pentane in the 450–750 °C temperature range was investigated at 760 Torr. The pyrolysis products, particularly free radicals and isomers, were identified using synchrotron radiation vacuum ultraviolet photoionization mass spectrometry, and their mole fractions were determined. In this study, the existing n-pentane pyrolysis kinetic model was updated according

Although C5H4 isomers are detected in flames, they are not thoroughly incorporated into detailed chemical kinetics models (DCKMs). Here we use RRKM/ME modelling to simulate C5H4 + H reactions on a C5H5 potential energy surface. Kinetic studies indicate that C3H3 + C2H2 is the main fate but fall-off from the initial adduct isomer back to C5H4 + H cannot be ignored at relevant combustion temperatures

This paper introduces a conservative criterion for thermo-acoustic stability. By subdividing a thermo-acoustic system into a passive subsystem – containing no source of acoustic energy – and an active subsystem containing all sources, the criterion can be formulated as follows: For positive or zero growth rates, the passive subsystem cannot feed acoustic energy into the active part. If for a given

The explosion characteristics of diethyl ether-Al mixtures under different ambient pressure (57.4–101.3 kPa), temperature (263–333 K), and relative humidity (48.3–90%) were investigated in a 20 L explosion vessel. The explosion pressures and lower flammability mass concentration limits of diethyl ether-Al mixture under different ambient conditions were obtained after a series of experiments. The components

This investigation outlines a data-assisted approach that employs random forest classifiers for local and dynamic submodel assignment in turbulent-combustion simulations. This method is demonstrated in simulations of a single-element GOX/GCH4 rocket combustor; a priori as well as a posteriori assessments are conducted to (i) evaluate the accuracy and adjustability of the classifier for targeting different

The pyrolysis of 1-heptene was studied in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry at 0.04 and 1 atm and in a jet-stirred reactor using gas chromatography at 1 atm. Flow reactor pyrolysis products, including the allyl radical, cycloalkenes and aromatics, were identified and quantified. Alkenes are found to be the dominant product family, among which ethylene

o-Xylene oxidation displays an autoignition behavior similar to alkanes at low temperatures. This paper presents a detailed investigation of the chemical kinetics of oxygen additions with the o-xylyl radical that control the ignition reactivity of o-xylene at low temperatures. High-level electronic structure calculations, transition state theory, and master equation simulations are combined to predict

The Cambridge/Sandia turbulent stratified flame (SwB5) is simulated with the LES and Flamelet-Generated Manifolds (FGM) combustion model. Three 3D FGM manifolds are adopted. With the purpose to examine the influence of transport properties, unity and non-unity Lewis numbers (Le) are included in the first two manifolds, respectively. The combined effects of non-unity Le and stretch are investigated

Autoignition delay times of ammonia/dimethyl ether (NH3/DME) mixtures were measured in a rapid compression machine with DME fractions of 0, 2 and 5 and 100% in the fuel. The measurements were performed at equivalence ratios φ=0.5, 1.0 and 2.0 and pressures in the range 10–70 bar; depending on the fuel composition, the temperatures after compression varied from 610 K to 1180 K. Admixture of DME is seen

A systematic approach is formulated for the uncertainty analysis of kinetic parameters on combustion characteristics during skeletal reduction. The active subspace method together with sensitivity analysis is first employed to identify extreme low-dimensional active subspace of input parameter space and to facilitate the construction of response surfaces with small size of samples. An intermediate

A novel diagnostic is proposed to characterize the maturity of soot particles in a laminar axisymmetric coflow ethylene diffusion flame in terms of the spectral dependence of soot absorption function. The method relies on the combination of line-of-sight attenuation (LOSA) and emission measurements at four wavelengths (500, 532, 660 and 810 nm). The analysis of the measured signals enables the determination

The stagnant plate influence on spatial distributions of polycyclic aromatic hydrocarbons (PAHs), soot and hydroxyl radical (OH) in the surrogate fuel (80% n-heptane and 20% toluene in volume) partially premixed flame on a McKenna burner were originally investigated in terms of different plate heights above the burner (Hp) and plate temperatures (Tp). Both PAHs and OH distributions were qualitatively

In this paper, a kinetic-diffusion surface combustion model is examined. The model is modified such that two effects of turbulence are included: 1) enhancement of the mass transfer due to relative velocity between particles and fluid and 2) reduction of the mass transfer due to turbulence-induced particle clustering. Details of the implementation are discussed and the influence of parameters such as

In this work, pyrolysis experiments of ethyl valerate were performed in a flow reactor over 705–1051 K at low and atmospheric pressures and in a jet-stirred reactor over 633–1013 K at near-atmospheric pressure. Products were measured with synchrotron vacuum ultraviolet photoionization mass spectrometry in the flow reactor pyrolysis and gas chromatography in the jet-stirred reactor pyrolysis. Valeric

Concurrent flow flame spread experiments are conducted over thermally thin solid fuels in microgravity aboard the International Space Station (ISS) under varying levels of confinement. Samples of cotton fiberglass blended textile fabric are burned in air flows in a small flow duct. Baffles are placed parallel to the sample sheet, one on each side symmetrically. The distance between the baffles is varied

The challenges in designing high-performance aeronautical combustion systems have not changed significantly over the years, but the increase of stringent regulations and the need to tackle rising fuel prices require new sophisticated analysis processes. To address this concern, the theme of this study was cast in terms of the ability of improving the performances of advanced non-intrusive instrumentation

With the objective of recovering the values of ignition delays of reactive heterogeneous mixtures a single-step chemistry model has been developed. The corresponding model extends a recent optimization procedure introduced to describe flame propagation in heterogeneous media featuring composition variations (equivalence ratio and temperature) in the fresh reactants or containing residual burned gases

Shock tube techniques for kinetic studies are continuously evolving driven by advances in kinetic modeling and detection techniques. An innovative category of shock tubes has been recently developed for use at Synchrotron facilities. In this work, a new high-repetition-rate shock tube (HRRST) was constructed to employ synchrotron-based double imaging photoelectron/photoion coincidence spectroscopy

In spite of widely use of ethanol, mostly as a fuel extender in ground transportation engines, its sooting propensity with pressure and with ethanol content in the base fuel has not been clarified. Although, information on ethanol’s sooting and other combustion characteristics at atmospheric conditions is extensive, scaling this information to elevated pressures is problematic. Information that could

Nanosecond-gated laser-induced breakdown spectroscopy (n-LIBS) has been used to quantify fuel mole fraction (ΧC2H4) in the cavity flameholder of a model high-speed combustor. The measurement locations selected, in the vicinity of the cavity shear layer, have low fuel concentrations. Previous n-LIBS measurements showed unexpectedly high values at these locations with expected low average fuel mole fraction

Thermochemical interaction – represented by CO mole fraction and gas phase temperature measurements – between flame and cooling air is investigated in a close-to-reality effusion-cooled single sector model gas turbine combustor. To investigate the influence of effusion cooling air mass flow on the thermochemical state, a parametric study is conducted. Temperature measurements are performed using ro-vibrational

This paper investigates the simplifying assumptions used for deriving low order models of thermoacoustic instabilities and thermoacoustic intermittency in turbulent combustor. These models consists in self-sustained oscillators subject to parametric and additive stochastic forcing. The main aspects of the thermoacoustic dynamics investigated in the present work are the phase between acoustic pressure

The pyrolysis of 2-ethylfuran (EF2) in a flow reactor was studied by using synchrotron vacuum ultraviolet photoionization mass spectrometry at 846 – 1319 K and at 30 and 760 Torr. Over 20 pyrolysis products were detected and measured. A detailed kinetic model was constructed by extending the reported comprehensive 2,5-dimethylfuran model to describe the pyrolysis of EF2 and validated against the current

The modified models MLC (modified linear curvature model) and MNQ (modified nonlinear quasi-steady model) for the extrapolation of laminar flame speeds and Markstein lengths based on the expansion of the finite-structure stretched flames were derived from the mass conservation equation, which consider effects of finite flame thickness and finite species distributions on flame propagation. These modified

A new chemical reaction rate source term in the transport equation of a single progress variable is proposed and implications for premixed flame modelling are discussed. This surrogate source term approximates the Arrhenius one over a large range of activation energies and density ratios almost perfectly. An analytic, invertible flame profile and the corresponding 1D laminar flame pdf are derived.

In turbulent premixed flames, the fractal dimension of flame iso-surface is argued to be D=7/3 for Damköhler’s large-scale limit (Da>>1) and D=8/3 for Damköhler’s small-scale limit (Da∼O(1)) based on heuristic scaling arguments. However, such scaling arguments do not consider the effect of the intermittent nature of turbulent kinetic energy dissipation on the flame surface. In this paper, we account

The magnesium (Mg) particle surface can be used to regulate fluorination or oxidation reactions depending on the applied heating rate and Mg particle size. Magnesium particles are surrounded by a complex hydroxide shell composed of an inner layer of magnesium oxide (MgO) and outer layer of magnesium hydroxide (Mg(OH)2). As particles approach the nanoscale, the thick oxide shell (e.g., 22 nm) becomes

The uncertainty of the rate coefficients of elementary reactions in detailed chemical kinetic mechanisms can affect the predicted species concentrations and global properties. The size of reduced mechanisms generated by reduction methods, such as directed relation graph (DRG), can also be greatly affected by the uncertainties in the rate coefficients, because these methods eliminate species by comparing

This paper presents an experimental study of turbulent non-premixed jet flames of ethylene/nitrogen where the nitrogen is substituted with different proportions of hydrogen and/or ammonia. The focus is largely on the effects of hydrogen and ammonia on soot production in turbulent flames. A combination of pointwise, laser-induced fluorescence in the visible and UV bands (LIF-UV–visible), and laser-induced

Here we present analysis of a novel reactive material system that employs dinitrogen tetroxide (N2O4) as a liquid oxidizer with metal powder fuels. The oxidizer was added to micron scale aluminum and zirconium powders by a remote injection system. When ignited with a high voltage spark, the mixtures were observed to possess reactivity comparable to nanocomposite reactive materials, with open-tube flame

The exergy loss characteristics of combustion processes under homogeneous-charge compression ignition (HCCI) and stratified-charge compression ignition (SCCI) conditions are numerically investigated by analyzing two-dimensional (2-D) direct numerical simulation (DNS) data. Two fuels, dimethyl ether and ethanol, together with the initial conditions of different mean temperatures, and levels of temperature

The relative stability of anatase and rutile in stagnation flame synthesis with stoichiometric mixtures is investigated experimentally. The measurements reveal a high sensitivity of anatase-rutile composition to the flame dilution. It is demonstrated that anatase formation is favoured in more dilute (colder) flames while rutile is favoured in less dilute (hotter) flames. A particle model with a detailed

Carbon free fuels such as hydrogen/ammonia blends show a promising potential to become sustainable and renewable fuels for gas turbines and other combustion systems. One interesting aspect about these blends is the possibility to adjust different combustion properties like the laminar burning velocity or ignition delay time by changing the ratio between H2 and NH3. Such fuel blends can be produced

Forced ignition is one of the most fundamental and important combustion problems. It is used in advanced engines and closely related to fire safety and accidental explosion. In this study, forced ignition of laminar counterflow diffusion flames with one-step chemistry is studied through two-dimensional simulations. The initial ignition kernel is simply modelled as a hot spot of unburned gas with a

Numerical simulations of one-dimensional pulsating detonation in off-stoichiometric n-heptane/air mixtures are conducted by solving the reactive Navier–Stokes equations with a skeletal chemical mechanism. The effects of mixture equivalence ratio, initial pressure and temperature on pulsating detonations are studied. The results show that the pulsating instabilities in n-heptane/air mixtures are strongly

This work investigates the reaction kinetics of the thermal decomposition of dimethoxymethane (DMM) and 1,2-dimethoxyethane (1,2-DME), which are both representative molecules of the promising clean polyether fuels. Pyrolysis experiments are carried out with helium diluted mixtures containing individual fuels in a flow tube at two different pressures of 760 Torr and 30 Torr. By varying the temperature

We develop a passive control strategy for suppressing thermoacoustic instability in a bluff-body stabilized premixed turbulent combustor. When the equivalence ratio is varied, there is a transition from combustion noise to thermoacoustic instability via intermittency in the combustor. We perform simultaneous acoustic pressure, 2D-PIV, and CH* chemiluminescence measurements to capture the pressure fluctuations

A recent analysis (Lipatnikov et al., 2020) of complex-chemistry direct numerical simulation (DNS) data obtained from lean hydrogen-air flames associated with corrugated-flame (case A), thin-reaction-zone (case B), and broken-reaction-zone (case C) regimes of turbulent burning has shown that the flamelet concept (i) can predict mean concentrations of various species in those flames if the probability

In this work, the two-photon laser-induced fluorescence technique (TPLIF) was applied to measure the concentration profile of atomic hydrogen in low-pressure laminar premixed flames. Excitation of H-atoms was performed by two-photon absorption at 205 nm and collecting the fluorescence at 656.3 nm. For the first time in flames, the TPLIF signals from the H-atom have been calibrated using the TPLIF signal

Laser-based Raman spectroscopy is a powerful technique for non-intrusive measurements of chemical composition in gas, liquid, and solids. However, weak signals make it challenging to employ the technique for diagnostics under harsh conditions with various background interferences. To overcome such limitations, we have devised a method, polarization lock-in filtering (PLF) based on temporal modulation

The incorporation of aluminum (Al) into explosives represents a facility and efficient way to enhance the energy output through the secondary reaction between Al and the detonation products of explosive. The Al/O ratio and microstructure of HMX/Al play critical roles in combustion performance and energy output. Herein, a gradient structured HMX/Al composite has been designed and fabricated via 3D printing

In this paper, four kinds of guanidinium dicyanamide-based energetic salts were prepared and investigated as energetic additives to hypergolic ionic liquid 1-ethyl-3-methyl imidazolium dicyanamide ([EMIM][DCA]) for the first time. Their densities, viscosities, heat of formation, specific impulse, ignition delay time, melting point, charge distribution, decomposition temperature were tested and calculated

The pyrolysis of three-component surrogate fuel for jet fuel has been studied experimentally in flow reactor using synchrotron photoionization and molecular beam mass spectrometry techniques with temperature range of 850–1150 K. Alkenes are the most abundant products in the decomposition process. Other important intermediates such as alkanes, alkynes, polycyclic aromatic hydrocarbons were also identified

The oxidation of furfural has been studied experimentally in a jet-stirred reactor (JSR) under fuel-lean (Φ = 0.4) and fuel-rich conditions (Φ = 2.0) in the temperature range of 650–950 K; in addition, laminar burning velocity data have been measured at T = 473 K and p = 1 bar within a wide fuel-air range. From the JSR experiments, 13 species profiles have been identified and quantified by GC–MS and

Microgravity experiments are performed to study concurrent-flow flame spread over an array of thin cellulose-based fuel samples, using NASA Glenn Research Center's 5.18 s drop tower. Sample segments are distributed uniformly, separated by air gaps, on a sample holder. The exposed width of each sample segment is 5 cm. Two segment lengths, 0.5 cm and 1 cm, are tested. The gap sizes are varied in different

Autoignition delay time data are one important means to develop, quantify, and validate fundamental understanding of combustion chemistry at low temperatures (T<1200 K). However, low-temperature chemistry often has higher uncertainties and scatter in the experimental data compared with high-temperature ignition data (T>1200 K). In this study, autoignition properties of propane and oxygen mixtures were

Single pulse shock tube experiments were conducted to determine the oxidative decomposition products of F-24. Experiments were performed at 50 bar nominal pressure, 7 ms nominal reaction time, temperatures ranging from 800 K to 1300 K, initial fuel concentration of 655 ppm, and equivalence ratio of 0.93. F-24 is Jet A with additives. Experiments with Jet A were performed at similar conditions to show

Spontaneous Raman scattering from nitrogen is well-suited for temperature measurements in combustion experiments, especially at high pressure which increases the Raman signal because of the higher density in the measurement volume. In this work we investigate high density effects on the anisotropic tensor component of ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate

To improve the understanding of cyclopentadiene-based high-density liquid hydrocarbon fuels combustion chemistry, the pyrolysis experiments of 1,3-cyclopentadiene (c-C5H6), quadricyclane (QC) and ethylnorbornane (EthNB, reported in our recent work: Wang et al.,2020), were performed in a flow reactor at atmospheric and high pressure over 348–1173 K. The mole fraction profiles of products in three fuels

A model of combustion of aluminum nanopowder in water vapor has been analyzed with allowance for the formation of a condensed phase of aluminum oxide on aluminum particles. Various processes affecting the growth rate of the oxide coating have been considered including adsorption and surface diffusion of Al2O3 molecules on aluminum particles, and condensation of the molecules on the oxide coating. Model