Ethylene Flames Research Articles

Soot Formation and Growth in Toluene/Ethylene Combustion Catalyzed by Ruthenium Acetylacetonate

ABSTRACT Ruthenium-based compounds are efficient catalysts to enhance combustion performance and suppress soot emission. However, systematic mechanism and in-situ research on reducing soot are rarely addressed. In this study, ruthenium acetylacetonate (Ru(C5H7O2)3, Ru(acac)3) was utilized as the catalyst precursor in different concentration conditions to investigate its impacts on the size, volume, and morphology of the soot particles in the ethylene flames with central toluene injection. The soot particles were detected by in-situ small-angle X-ray scattering (SAXS) and ex-situ transmission electron microscopy (TEM). This study confirms that Ru(acac)3 can suppress the surface growth for the primary soot particles, but no significant change of the morphology has been discovered for the aggregates. Compared with the undoped flame, the volume of the soot particles in the Ru(acac)3-doped flames is lower and the particle size is smaller, indicating a valid inhibition effect of Ru(acac)3 on the soot emission by affecting its surface growth and oxidation process. Despite the remarkable distinction between the undoped and doped flames, no obvious difference is found between the flames with different catalyst concentrations.

Chemical effects of carbon dioxide in ethylene, ethanol and DME counter-flow diffusion flames: An experimental reference for the fictitious CO2 flame

The chemical effects of carbon dioxide on flame chemistry were investigated numerically and experimentally in ethylene, ethanol, and dimethyl-ether (DME) counter-flow diffusion flames. In this work, a method that could add an experimental reference flame for the fictitious CO2 flame (FCO2) was proposed. The fuel/oxidant carrier gas (FCO2+argon+helium) in the FCO2 flames was replaced by an inert gas mixture (nitrogen+argon+helium) whose composition was optimized to maintain approximately the same thermal and dilution effects as FCO2 addition. The differences in the flame temperatures and the measured species concentration between CO2 flame and the inert gas mixture flame could then be attributed to the pure chemical effects. The new experimental strategy was applied to ethylene, ethanol, and dimethyl-ether (DME) counter-flow diffusion flames. Good agreement was found between the experimental and the computational results. The chemical effects of CO2 addition, indicated by both the numerical FCO2 flame and the experimental inert gas mixture flame, both decreased the peak flame temperatures and the concentration of CH4, H2, and C2H2 except CO. The effects of CO2 addition on the production pathways of CO and C2H2 were very similar in ethylene, ethanol, and DME flames. Decreased CO oxidation rate through CO+OH = CO2+H was a significant feature of the chemical effects identified by both the FCO2 flame and the inert gas mixture flame. Thermal effects of CO2 addition decreased the formation rate of C2H2 through C2H3(+M) = H+C2H2(+M) while the chemical effects on this pathway were weaker.

Chemical and Sooting Structures of Counterflow Diffusion Flames of Butanol Isomers: An Experimental and Modeling Study

ABSTRACT This work reports an experimental and numerical analysis on the sooting characteristics of butanol isomers. Light extinction and gas chromatography were used to measure soot and gas-phase species, respectively. Kinetic analysis of the tested flames was performed with detailed gas-phase mechanism and a sectional soot model. The present work aims to provide an understanding on the effects of butanol isomeric structures on sooting tendencies. For a comprehensive analysis, flames of both neat butanol fuels and butanol/hydrocarbon mixtures were studied. The results showed that the relative ranking of sooting tendencies among the butanol isomers were similar in neat butanol flames and in butanol-doped ethylene flames. In addition, we show that a small amount of butanol addition in ethylene flame enhanced soot formation. It was found that different isomeric structures mainly affected the formation of C3H3, which led to the different concentrations of important aromatic soot precursors. In the butanol-doped ethylene flames, the blending of the four butanol isomers increased the number of C3H3 formation pathways, which in turn significantly increased the production of benzene. Structural effects explaining for the differences in the sooting tendencies of the four butanol isomers in neat butanol flames and ethylene/butanol flames were found to be the same.

Development and verification of simplified methane/dimethyl ether mechanism for micro-combustion

In this work, a simplified mechanism for simulating methane/dimethyl ether micro-flames is developed by validating the flame speed and ignition delay time. Towards this goal, DRGEPSA is used to simplify the pure dimethyl ether mechanism proposed by Zhao. Then the simplified mechanism is coupled with the existing pure methane mechanism (kee-58 mechanism) to obtain the blended fuel mechanism. The sensitivity analysis indicates that the chemical reaction HCOOH = HCO + OH is most beneficial to the optimization of the blended fuel mechanism. By adjusting this reactions reaction rate, the dynamic characteristics and applicability of the blended fuel mechanism in the numerical simulation are adjusted, resulting in a simplified mechanism containing 25 species and 96 chemical reactions. The predicted ignition delay time and laminar flame speed are well matched with the experimental results under certain conditions, showing the capability of this simplified mechanism in describing the combustion characteristics. Finally, this mechanism is applied to predict the transition rules of flame structure, flame location, and blowout limit of methane/dimethyl ether flames under micro-scale conditions using a three-dimensional model. A good agreement between calculations and experimental measurements is achieved, demonstrating the reliability of the simplified mechanism developed in the present work.

Experimental study on the effect of hydrogen addition on methane/ethylene diffusion flame soot formation based on light extinction measurement

In this study, the mixed diffusion flame soot of methane, ethylene and hydrogen were studied, and the two-dimensional light extinction measurement was applied to investigate the distribution characteristics of the ethylene flame soot concentration with different methane and hydrogen ratios. The soot concentration distribution was analyzed, and the effect of hydrogen addition and methane addition on the soot distribution of a laminar ethylene diffusion flame was investigated. The experiments showed that the flame soot of pure ethylene was mainly distributed in both sides of the flame, which increased first and then decreased in the height direction, and the distribution in the radial direction moved toward the center of the flame as the height increased. The low methane addition in pure ethylene flame will produce a synergistic effect to promote soot formation, and its effect disappeared with the increase of methane addition, and the adding of hydrogen in pure ethylene flame will inhibit soot formation, and the inhibiting effect increased with the increase of hydrogen. When the three gases were blended together, the inhibition effect of hydrogen on soot formation was greater than the promotion effect of methane on soot formation at this ratio.

PAHs and fullerenes as structural and compositional motifs tracing and distinguishing organic carbon from soot

Examining the features distinguishing organic carbon from soot is crucial for understanding the source, the effect on the environment and their respective role in aerosol chemistry and soot formation. Beside to the obvious PAH picking-out in the low-mass mode (C number < 40), the challenging identification of PAHs in the high-mass mode (C number > 40) of organic carbon, separated by carbon particulate matter extraction from young and mature soot thermophoretically sampled in premixed flames, was done by laser-desorption-time-of-flight mass spectrometry, exploiting the laser power increase. The perusal of organic carbon mass spectra through mathematical tools in comparison to aromatic and alkyl-substituted PAH-laden samples and the persistence of high-mass mode at high laser power led to exclude the contribution of dimers and alkyl-bridged PAHs attributing the second mode to both fully-benzenoid and cyclopenta-PAHs.Profound differences between mass spectra of organic carbon and soot were noticed as neither molecules nor radicals of PAHs could be drawn out from soot, even at high laser power, and only small radicals and carbon clusters like fullerenes were observed, especially for young soot. These inferences evidenced the importance of analysing separately organic carbon and soot especially if insights into soot particles nucleation are to be obtained. In the case of benzene flame, already at the inception, soot consists of strongly tangled aromatic motifs crosslinked each other, presumably deriving from reactive coagulation/clustering of relatively small aromatic hydrocarbons/radicals early formed. In methane and ethylene flames, coalesced liquid-like material composed of soot and PAHs is formed and transformed later on undergoing some carbonization and molecular growth, respectively.

The evolution of species concentrations in turbulent premixed flames crossing the soot inception limit

The current study quantifies the impact of equivalence ratio and rate of strain on the spatial distribution of major species and soot precursors in premixed turbulent ethylene flames crossing the soot inception limit. A back-to-burnt (BTB) opposed jet configuration is used to provide accurate control of the turbulent and chemical timescales. The upper nozzle features fractal grid generated turbulence and premixed ethylene/air mixtures with flames stabilised against well-defined hot combustion products emerging from the lower nozzle. The study combines simultaneous PAH/CH2OPLIF and elastic light scattering (ELS) with probe sampling. Gas chromatography-mass spectrometry (GCMS) and gas chromatography-thermal conductivity detector (GC–TCD) were used to quantify concentrations of major species and poly-aromatic hydrocarbons (PAHs). The laser based diagnostics show that the rate of strain exerts a dominant impact on the growth of soot particles with low turbulent Reynolds numbers (50≤Ret≤94) used to promote soot formation. The probe measurements indicate that acetylene, 1-methylnaphthalene (1–MN), m/z = 154, m/z = 276 and benzo(a)pyrene correlate with soot formation and that the equivalence ratio is the controlling PAH growth parameter. It is further shown that the spatial extent of the PAH containing reaction zone exceeds three integral length scales.

Chemical speciation and soot measurements in laminar counterflow diffusion flames of ethylene and ammonia mixtures

Ammonia is considered as one of the most promising alternative fuels due to its carbon neutrality and the existing infrastructure for its mass production and delivery. However, burning neat ammonia has the issue of poor flame stability and high NOx emissions, making co-firing ammonia with conventional fuel a more feasible approach. The present work investigated the sooting characteristics of counterflow diffusion flames of ethylene/ammonia mixtures. Experimentally, soot volume fraction (SVF) and average soot particle diameter in the neat ethylene, ammonia- and nitrogen- doped flames were non-intrusively measured. Both SVF and average soot particles diameter were found to decrease with the addition of ammonia. Flame temperature were measured with tunable diode laser absorption spectroscopy and the results suggested that the inhibiting effect of ammonia on soot formation was chemical instead of thermal. For further kinetic insights, numerical simulation with newly-constructed reaction mechanisms were performed and the results were compared against chemical speciation data from gas chromatography (GC) measurements; the results showed that ammonia doping would lead to more significant reduction of benzene concentration than nitrogen doping. Kinetic pathways of the chemical suppressing effect of ammonia addition on soot and its precursor formation were then explained based on numerical results. The major contribution of the present work can be summarized in the following aspects: 1) New comprehensive experimental data on sooting characteristics, important intermediate species concentrations of diffusion counterflow flames of ethylene/ammonia mixtures were provided for model validation; 2) One coupled mechanism with detailed hydrocarbon-nitrogen interactions was established to predict PAHs formation and soot formation; 3) Detailed chemical kinetics insight of ammonia effect on soot formation was presented in the counterflow flame.

Modeling laser-induced incandescence of Diesel soot\u2014Implementation of an advanced parameterization procedure applied to a refined LII model accounting for shielding effect and multiple scattering within aggregates for {varvec{alpha}}_{{varvec{T}}} and {varvec{E}}left( {varvec{m}} right) assessment

An extensive set of LII signals measured in a Diesel spray flame has been simulated using a refined LII model built upon a comprehensive version of soot heat- and mass-balance equations. This latter includes terms standing for saturation of linear, single- and multi-photon absorption processes, cooling by sublimation, conduction, radiation and thermionic emission in addition to mechanisms depicting soot oxidation and annealing, non-thermal photodesorption of carbon clusters as well as corrective factors allowing considering shielding effect and multiple scattering (MS) within aggregates. A complete parameterization of the so-proposed model has been achieved by means of an advanced optimization procedure coupling design of experiments with a genetic algorithm-based solver. Doing so, the values of different factors involved in absorption and sublimation terms have been assessed for a 1064-nm laser excitation wavelength including the multi-photon absorption cross section for C2 photodesorption and the saturation coefficients for linear- and multi-photon absorption, among others. This parameterized model has then been demonstrated to effectively reproduce signals measured in different combustion media including a CH4/O2/N2 premixed flat flame and a diffusion ethylene flame. As a result of the data derived from the analysis of the Diesel flame, a thermal accommodation coefficient value of 0.49 has been assessed against 0.34 when neglecting the shielding effect. In addition, values of the soot absorption function (Eleft( m right)) comprised between 0.18 and 0.31 have been inferred depending on the particle maturation stage. On the other hand, Eleft( m right) 24% higher on average have been estimated when neglecting MS thus illustrating the importance of aggregate characteristics on soot properties derived through LII modeling. Eventually, the Eleft( m right) evolution observed herein has been compared with results issued from studies conducted with varied hydrocarbons which led to highlight the crucial role played by the soot maturity level over the nature of the burnt fuel as far as optical properties are concerned.

Effects of ammonia and hydrogen on the sooting characteristics of laminar coflow flames of ethylene and methane

Hydrogen and its derivatives, including ammonia, are gaining increasing attention as carbon-neutral fuel alternatives. An intermediate step in the transition to hydrogen and ammonia is the blending of these fuels with hydrocarbons, introducing the challenge of soot formation. The impact of ammonia on soot formation has recently been the focus of several studies, but a complete understanding of its chemical effects is lacking. Hydrogen, by comparison, has received significant attention from the soot community. However, controversy remains with regards to hydrogen’s chemical impact, and the dependence of this impact on fuel and flame configuration. This work investigates the effect of both hydrogen and ammonia on soot formation in laminar coflow flames of both ethylene and methane. Hydrogen or ammonia are introduced either by addition or substitution, with parallel studies of helium and argon, in order to isolate their chemical effects. Time- and spectrally-resolved laser-induced emissions from UV and IR excitation are used to quantify differences in soot and soot precursor formation. Additionally, chemical kinetics calculations and analyses are used to elucidate the effects of ammonia introduction to ethylene flames. Ammonia is found to chemically inhibit soot when mixed with either ethylene or methane, with increasing effects on larger precursors. Calculations suggest that this suppression is due to carbon consumption in the formation of HCN and CN. Hydrogen is found to chemically enhance soot formation in both ethylene and methane flames.

Detailed assessment of the thermochemistry in a side-wall quenching burner by simultaneous quantitative measurement of CO[formula omitted], CO and temperature using laser diagnostics

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 CO2, laser-induced fluorescence of CO and OH, as well as thermographic phosphor thermometry. The extension to DP-CARS to study FWI processes is the first of its kind, previous studies only provided (CO,T) measurements. The laser diagnostics are benchmarked and calibrated to an adiabatic test case and assessed in accuracy and precision. Subsequently, the approach is used to measure the thermochemistry close to a quenching wall. The nominal flame-to-wall distances from the experiment well match the numerical simulation data with a marginal offset of 20 µm. Conditioning the thermochemical data with respect to the instantaneous quenching point, named quenching-point conditioning, enables a novel tracing of the wall-parallel chemistry evolution across the quenching location. The study provides the first comparison of experimental three-scalar measurements (CO2,CO,T) with two-dimensional (2D) fully-resolved chemistry and transport (FCT) simulations. The validation of numerical simulations can now rely on the three scalars (CO2,CO,T) instead of the two scalars (CO,T) in past studies. The evaluation reveals that this novel three-scalar measurement allows highly sensitive probing of the thermochemical states and is clearly superior to the previously applied two-scalar approach. CO2 is less affected by the quenching wall compared to CO. Differential diffusion effects are experimentally confirmed by comparison to 2D-FCT, with the (CO2,T) state space being more sensitive than (CO,T). As the experimental methodology proved feasible for laminar operation, a transfer to turbulent cases, where the numerical analysis using direct numerical simulations (DNS) including FCT is limited, appears promising.

Effects of ammonia addition on soot formation in ethylene laminar premixed flames

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 on soot particle size are discussed. The results of particle size distributions showed that doping with ammonia decreases soot particle size and the volume fraction of soot particles. In this work, the flames were carefully studied under similar temperature conditions, so all observed changes could be attributed to chemical effects. The results of FTICR-MS analysis showed that polycyclic aromatic hydrocarbons (PAHs) were the main compositions in both pure ethylene and ammonia doped ethylene flames. Nitrogen-containing PAHs (N-PAHs) did not contribute significantly to soot nucleation or mass growth processes. Chemical kinetic analysis revealed that CN species generated in ethylene-ammonia flames removed carbon from participating in soot precursor formation, thereby reducing soot formation.

Thermo-hydrodynamic effects of the Ethylene reactive flow on convecting hot spots using LES

Combustion instability has arisen as a substantial defect for power generating systems. This is caused by the acoustic sources of the combustor, such as indirect noise, produced by accelerating hot spots, which are less explored due to their complex nature. Understanding the physics of the hot spots, therefore, is of crucial importance to reduce the noise and subsequent instabilities. Further, hot spots are a difficulty in internal combustion engines motivated auto ignition. In this study, hot spot behavior in a combustor of lean-premixed flame of Ethylene, a type of biofuel, influenced by hydrodynamic and thermal conditions, is numerically studied using the flamelet model and large eddy simulation. The impacts of inlet turbulence intensity and preheating unburnt mixture on hot spots are examined in a thermally convective and adiabatic combustor. The results show that although preheating inlet mixture improves combustion efficiency, it aids the hot spot's survival (more than 40 percent improvement in wave’s dissipation), and may cause significant instabilities. Similar to increasing the unburnt mixture temperature, decreasing the turbulence intensity and the excitation amplitude diminishes dissipation and dispersion of the wave, which makes the combustor more prone to probable instabilities. Amongst the studied parameters, the turbulence intensity and convective cooling on the walls are the most effective in decreasing the wave’s strength by approximately 85 and 95 percent, respectively. It is indicated that a hot spot in real conditions of a combustor is prone to a high level of annihilation.

Numerical Investigation on the Effect of the Oxymethylene Ether-3 (OME3) Blending Ratio in Premixed Sooting Ethylene Flames

Synthetic fuels, especially oxygenated fuels, which can be used as blending components, make it possible to modify the emission properties of conventional fossil fuels. Among oxygenated fuels, one promising candidate is oxymethylene ether-3 (OME3). In this work, the sooting propensity of ethylene (C2H4) blended with OME3 is numerically investigated on a series of laminar burner-stabilized premixed flames with increasing amounts of OME3, from pure ethylene to pure OME3. The numerical analysis is performed using the Conditional Quadrature Method of Moments combined with a detailed physico-chemical soot model. Two different equivalence ratios corresponding to a lightly and a highly sooting flame condition have been investigated. The study examines how different blending ratios of the two fuels affect soot particle formation and a correlation between OME3 blending ratio and corresponding soot reduction is established. The soot precursor species in the gas-phase are analyzed along with the soot volume fraction of small nanoparticles and large aggregates. Furthermore, the influence of the OME3 blending on the particle size distribution is studied applying the entropy maximization concept. The effect of increasing amounts of OME3 is found to be different for soot nanoparticles and larger aggregates. While OME3 blending significantly reduces the amount of larger aggregates, only large amounts of OME3, close to pure OME3, lead to a considerable suppression of nanoparticles formed throughout the flame. A linear correlation is identified between the OME3 content in the fuel and the reduction in the soot volume fraction of larger aggregates, while smaller blending ratios may lead to an increased number of nanoparticles for some positions in the flame for the richer flame condition.

An experimental multiparameter investigation on the thermochemical structures of benchmark ethylene and propane counterflow diffusion flames and implications to their numerical modeling

Counterflow diffusion flame is a canonical non-premixed flame configuration that is suitable for studying complex combustion chemistries such as soot formation. An important objective of such studies is to build predictive kinetic models. For validation of these models, complete and accurate experimental characterization of the flames are essential. Existing counterflow flame- based soot studies focused primarily on the determination of soot volume fraction, while simultaneous measurements of temperature, species concentrations and in particular flow fields were less common. Here we performed an experimental multiparameter investigation for a comprehensive characterization of the most important physical and chemical properties of four benchmark ethylene and propane counterflow flames, with the intention to provide data with sufficient details for the setup of corresponding numerical simulations and the evaluation of the resulted numerical data. Particle image velocimetry, tunable diode laser absorption spectrometry, microprobe sampling with gas chromatography, laser light extinction, laser induced incandescence are the techniques used respectively to measure flow fields, temperature, gas-phase species, and soot. Special attention was given to the effects of radial profiles of nozzle exit velocity on the quasi-one-dimensional counterflow simulation, whose results were compared against both the experiments and two-dimensional simulation. Probe effects on speciation were also quantitatively evaluated by comparing CO2 mole fraction as measured with the intrusive probe sampling as well as an independent optical technique. Our specially chosen ethylene and propane flames offered a direct experimental evidence that a flame producing higher concentration of benzene can have a significantly lower sooting tendency. It is hoped that the present comprehensive dataset can serve as a useful validation target for future high-fidelity gas-phase and soot models. It is also our intention that we provide sufficient details regarding the experimental apparatus and associated measurement techniques so that interested readers can reproduce our experimental data.

An experimental and numerical study of the effects of reactant temperatures on soot formation in a coflow diffusion ethylene flame

The effects of elevated reactant temperatures on soot formation in a laminar coflow ethylene flame were experimentally and numerically investigated. Ethylene flames at the reference reactant temperatures (both air and fuel), Tr, of 300K (LT), 473K (MT), 673K (HT), and 713K (UHT) were established. In the experiment, soot volume fractions (fv), primary particle diameters (dp), and soot (flame) temperatures (TF) were measured. The flames were also simulated by the CoFlame code with the Conjugate Heat Transfer (CHT) condition. The experimental results show that elevating Tr positively affects soot formation. The increase in the maximum fv is greater on the wing pathline (∼1.9 times) than on the centerline (∼1.2 times) when the adiabatic flame temperature increases by ∼100K. An analysis of the experimental and numerical data suggests that soot formation is promoted by enhanced soot surface growth. The numerical simulation reveals that PAH (polycyclic aromatic hydrocarbon) adsorption, which is a function of PAH concentration, becomes important at high Tr as its mass contribution increases from ∼50% to ∼70%. This may be attributed to early fuel pyrolysis within the fuel tube.

Evaluation of polybrominated diphenyl ether (PBDE) flame retardants from various materials in professional seating furnishing wastes from French flows.

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants that are used in polymeric materials. Due to their adverse health effects, the use of recycled wastes has been forbidden if the total PBDE content exceeds 0.1% (w/w). The objective was to estimate the proportion of PBDEs in professional seating furnishing wastes to identify the materials in which the content of PBDEs (and particularly BDE-209) could exceed the limit to eliminate them from recycling. An analytical process (microwave extraction followed by purification and chromatographic analysis) was adapted to assess with a unique methodology the amounts of eight PBDEs in materials that result from various seating wastes, such as hard plastics, foams and accompanying textiles. X-ray fluorescence (XRF) was used to rapidly predict critical PBDE concentrations via Br. From 100 samples, the total PBDE content did not exceed the current tolerated threshold. The examined materials contained only trace levels of former PBDE formulations, and BDE-209 was identified at higher amounts, mainly in hard plastics, but these amounts were less than 312mgkg-1. Since XRF was not reliable for quantitative measurements and was not specific, no direct correlation could be identified between Br and PBDE levels. Br was strongly associated with As in all the materials, but the presence of PBDEs was not clearly associated with the presence of other metals that are used in flame retardants.

Chemistry effects in the wall quenching of laminar premixed DME flames

Fundamental studies on Flame-Wall Interaction (FWI) are of the utmost importance to unravel the intricate coupling between chemistry and transport in the near-wall region, and to characterize the quenching dynamics. For this purpose, an accurate description of reaction kinetics is especially needed. In this work, the role of chemistry during the wall quenching of premixed dimethyl ether (DME) flames is numerically investigated, leveraging recently-obtained experimental data in a Side-Wall Quenching configuration (SWQ) in a variety of conditions. A detailed kinetic model describing the low-to-high temperature oxidation of DME is used as starting point. In order to accommodate it into 2D simulations, it is first reduced to a skeletal level, both accounting for (31 species and 140 reactions) and neglecting (20 species and 93 reactions) low-temperature chemistry, and successfully validated against the original model in predicting flame propagation and Head-On Quenching (HOQ). Using an established CFD framework, the SWQ features of DME are investigated in terms of flame structure, heat fluxes and thermochemical CO-T states. A good agreement with the available experimental data is observed in the operating space. In the near-wall region, the prediction of the thermochemical state is most critical, and it is found that diffusion is here the prevailing contribution in defining such state. In the same region, kinetic analysis shows that low-temperature chemistry affects the speciation of the quenching region to a good extent, which is modified with respect to a freely-propagating flame. Yet, due to the lower reactivity, SWQ thermal features are not significantly influenced. As a result, for the purposes of the wall quenching analysis, only high-temperature chemistry needs to be accounted for, and the 20-species mechanism can be safely considered as a consolidated milestone for future studies.

Association of exposure to organophosphate flame retardants and children's behavior at a median age of 18 months

Exposure to polybrominated diphenyl ether (PBDE) flame retardants (FRs) could have adverse effects on neurodevelopment in children. Some organophosphate (OPFRs) are used as alternatives for the phased-out decabromodiphenylether such as resorcinol bis(diphenyl phosphate (PBDPP) and bisphenol A bis(diphenyl phosphate (BPA-BDPP). This study aims to investigate the relationship between indoor OPFR exposure and neurodevelopmental behavior in children. OPFRs were measured in house dust and hand wipes from 42 children, aged 8-16 months, from the LInking maternal Nutrition to Child health (LINC) study. At the median age of 18 months, the children's behavior was assessed with the Child Behavior Checklist, using three composite behavior scales: externalizing problems, internalizing problems, and total problems. Linear regression analysis was performed, adjusting for maternal education and smoking by the partner. Children with higher BPA-BDPP, PBDPP, and tris(chloroethyl) phosphate (TCEP) house dust concentrations were found to have higher scores on the behavioral problems scales. A 10-fold increase in BPA-BDPP and PBDPP concentration was associated with a 4.1 and 2.6 point increase on the internalizing problems scale (respectively p=0.004 and p=0.042). Increased BPA-BDPP concentrations were associated with elevated scores on the externalizing problems scale and total behavioral problems scale (respectively 7.6 and 16 points increase per 10-fold BPA-BDPP concentration increase, p=0.015 and p=0.007). TCEP dust concentrations were associated with the externalizing problems scale (13 point increase per 10-fold TCEP concentration increase, p=0.043). This study showed the importance of investigating the health effects of exposure to organophosphate flame retardants. Further research on neurodevelopmental health effects of OPFR exposure is warranted.

Structural effects of C3 oxygenated fuels on soot formation in ethylene coflow diffusion flames

This paper investigates how the structure of three C3 oxygenated fuels: dimethyl carbonate (DMC), dimethoxymethane (DMM) and isopropanol (IPA) influences soot formation when the fuels are blended with ethylene in laminar coflow diffusion flames. Up to 20% of the total carbon was substituted with oxygenated fuel. Colour-ratio pyrometry was used to measure the soot volume fraction (fv). IPA caused a strong increase in fv, whereas DMM and DMC both caused an initial increase followed by a progressive decrease in fv as the proportion of oxygenated fuel was increased. Differential mobility spectrometry and thermocouple probes were used to measure the particle size distribution and gas temperature in the flames at 5% blend strength. The hottest region of the 5% flames was consistently about 100 K cooler than the corresponding region of the ethylene flame, indicating a thermal effect of the doping. The 5% flames showed an increase in the maximum centre-line average particle size and fv versus the ethylene flame, with the IPA showing the largest increase. The evolution of the centre-line particle size distributions showed that the 5% flames experienced earlier particle growth compared to the ethylene flame. Consideration of the role of the chemical pathways towards benzene formation suggests that methyl radicals from the decomposition of the oxygenated fuels are responsible for the increase in fv at 5% doping. The difference in fv between the IPA versus DMM and DMC flames is thought to be due to the additional presence of C3 species originating from the carbon-carbon bonded backbone of IPA. Meanwhile, the differences between the DMC versus DMM flames are thought to arise from CO2 produced during the decomposition of DMC, and a corresponding thermal effect where the pyrolysis region of the 5% DMC flame was observed to be about 50 K cooler than the other flames.