Low-pressure Flames Research Articles

The influence of i-butanol addition to the chemistry of premixed 1,3-butadiene flames

Chemical structures of three low-pressure premixed flames of 1,3-butadiene/i-butanol mixtures with different ratios of 1,3-butadiene and i-butanol were investigated experimentally with flame-sampling molecular-beam mass spectrometry and numerically by chemically detailed modeling. Partially isomer-resolved mole fraction profiles of approximately 70 components per flame were determined using the well-established single-photon ionization technique via easily tunable synchrotron-generated vacuum-ultraviolet photons. The used chemical-kinetic reaction model is based on the work of Hansen et al. [Proc. Combust. Inst. 35 (2015) 771-778] of complementary 1,3-butadiene/n-butanol mixture flames. Within the present study, the reaction model has been significantly updated and simultaneously extended, to include the high-temperature oxidation chemistry of i-butanol. It is shown, by referring to both experimental and modeling results, that the concentration of benzene depends on the amount of 1,3-butadiene in the fuel mixture, indicating that i-butanol chemistry is not adding significantly towards aromatic ring formation. Trends in the concentration of other intermediates can also be largely predicted based on the established oxidation of 1,3-butadiene and i-butanol, thus revealing no detectible cross-linkages between the intermediate pools of the individual fuel components.

Experimental and kinetic modeling study of diethyl ether flames

Diethyl ether (DEE, C4H10O) is being considered as a promising biofuel. However, its combustion chemistry has not been well studied. Particularly lacking are quantitative intermediate species profiles in flames that provide a stringent test for kinetic models, and flame speed data at elevated pressures. In the present paper, we obtain species distributions in low-pressure flames and measure flame speeds at elevated pressure to gain insights into high-temperature combustion chemistry of DEE. Specifically, a fuel-rich DEE flame (ϕ∼1.8) with 25% argon dilution at 4kPa was investigated by using a dedicated combination of electron ionization (EI) molecular-beam mass spectrometry (MBMS) with gas chromatography (GC) and tunable synchrotron vacuum ultraviolet (VUV) photoionization (PI) MBMS. High-pressure flame speeds of DEE were measured in a constant-volume cylindrical chamber at an initial temperature of 298K at an equivalence ratio of ϕ=1.4 and pressure up to 507kPa. Moreover, a new detailed kinetic model for DEE combustion was developed, with the most noticeable advances over the solely existing model by Yasunaga et al., 2010 being a more complete description of the reactions of DEE radicals and the use of accurate theoretical methods, i.e. CBS-QB3, to determine the rate constants for important primary reactions. In contrast to the previously published one, the present model includes reactions of DEE radicals that directly involve the formation of ethyl vinyl ether (EVE), an addition supported by identification and quantification of EVE by PI-MBMS in the flame experiment. Finally, the results showed that DEE flames yield low concentrations of aromatic species. However, high acetaldehyde emission was observed, originating from the dominant pathways of DEE consumption via H-abstractions from C-α positions followed by β-scissions.

Ramifications of including non-equilibrium effects for HCO in flame chemistry

The formation and destruction pathways of the formyl radical (HCO) occupy a pivotal role in the conversion of fuel molecules (and their intermediates) to eventual products CO and CO2, and therefore, HCO has been a prescient indicator for heat release in combustion. In this work, we have characterized the impact of including non-equilibrium effects for HCO, i.e. “prompt” dissociation of HCO to H+CO, in simulations of laminar flame speeds for archetypal hydrocarbon and oxygenated molecules relevant to combustion. Prompt dissociation probabilities for HCO were systematically applied to all elementary reactions that included this radical (as either a product or reactant) in literature combustion kinetics models. Simulations with the prompt HCO dissociation corrected models predicted a 7–13% increase in laminar flame speeds at 1atm for the fuels characterized here (CH4, n-C7H16, CH3OH, CH3OCH3) relative to the predictions using the original models. It is evident that simulations of other fuel-air flames at 1atm will be similarly impacted, suggesting the indispensability of incorporating these non-equilibrium effects for predictive flame modeling. Simulations of higher pressure (10atm) heptane-air flames predicted a more modest effect (<5%) of incorporating these non-equilibrium effects. Additionally, species profiles in low-pressure (0.03atm) flames of CH2O and auto-ignition delay simulations (1.4atm) for CH2OO2Ar mixtures were also impacted to a noticeable extent. Lastly, it is also worth noting that prompt dissociations are a ubiquitous feature of all weakly-bound radicals; the kinetics of many of which (C2H3, C2H5, CH3O, CH2OH, etc.) are central to our current understanding of combustion chemistry. Theory/modeling studies are in progress to address the relevance of prompt dissociations in these weakly-bound radicals to combustion modeling.

Investigation of the chemical structures of laminar premixed flames fueled by acetaldehyde

Acetaldehyde is a key intermediate formed during the combustion of hydrocarbon and oxygenated fuels, and its role as an air pollution is concern-arousing. A better understanding of its combustion characteristics is of significance in developing core mechanisms and reducing the associated emissions. In this work, chemical structures of low-pressure laminar premixed acetaldehyde flames with equivalence ratios of 1.7 and 1.0 were measured by employing molecular-beam mass spectrometry with synchrotron vacuum ultraviolet light for ionization. Totally, about 40 species were identified and their mole fraction profiles are reported with well estimated uncertainty. To our knowledge, some oxygenated species, such as ethenol and butanal, were measured for the first time in acetaldehyde flames. Experimental species mole fraction profiles were compared with modeling results using several available kinetic mechanisms. These mechanisms well reproduce the mole fraction profiles of the major species and the C1/C2 hydrocarbon intermediates, however, their unsatisfactory predictive capability for some fuel-related oxygenated intermediates, such as C2H3O isomers, suggests that the acetaldehyde sub-mechanism needs further investigation. Our experimental results provide valuable information for future mechanism development.

Speciation and the laminar burning velocities of poly(oxymethylene) dimethyl ether 3 (POMDME3) flames: An experimental and modeling study

Poly(oxymethylene) dimethyl ethers (POMDMEs) with the general chemical formula of CH3O (CH2O)nCH3 (n>1) are promising oxygenated alternative fuels with substantial soot-reduction potential. Combustion kinetics of the compound with n = 3, POMDME3 [CH3O(CH2O)3CH3], was investigated in the present study with combined experimental and modeling efforts. Twenty-six species, including some radicals and reactive intermediates, were identified and quantified in a low-pressure laminar premixed POMDME3 flame with a synchrotron vacuum ultraviolet photoionization mass spectrometry. Laminar burning velocities of POMDME3/air mixtures were measured in a spherical bomb at atmospheric pressure with the equivalence ratio ranging from 0.7 to 1.6. A kinetic model aimed at interpreting the high-temperature combustion chemistry of POMDME3 was constructed and tested by all the measurements with uncertainties of both experiments and model predictions taken into consideration. In addition, model analysis of the reaction pathways was performed to reveal the consumption processes of POMDME3 and the formation mechanisms of some crucial intermediates. The absence of carbon-carbon (C-C) bonds in the (C-O) chain structure results in significant soot-reduction potential. Relevant reaction patterns could also apply to larger POMDME compounds.

New insights into methane-oxygen ion chemistry

External electric fields may reduce emissions and improve combustion efficiency by active control of combustion processes. In-depth, quantitative understanding of ion chemistry in flames enables predictive models to describe the effect of external electric fields on combustion plasma. This study presents detailed cation profile measurements in low-pressure, burner-stabilized, methane/oxygen/argon flames. A quadrupole molecular beam mass spectrometer (MBMS) coupled to a low-pressure (P=30Torr) combustion chamber was utilized to measure ion signals as a function of height above the burner. Lean, stoichiometric and rich flames were examined to evaluate the dependence of ion chemistry on flame stoichiometry. Additionally, for the first time, cataloging of flame cations is performed using a high mass resolution time-of-flight mass spectrometer (TOF-MS) to distinguish ions with the same nominal mass. In the lean and stoichiometric flames, the dominant ions were H3O+, CH3O2+, C2H7O+, C2H3O+ and CH5O+, whereas large signals were measured for H3O+, C3H3+ and C2H3O+ in the rich flame. The spatial distribution of cations was compared with results from numerical simulations constrained by thermocouple-measured flame temperatures. Across all flames, the predicted H3O+ decay rate was noticeably faster than observed experimentally. Sensitivity analysis showed that the mole fraction of H3O+ is most sensitive to the rate of chemi-ionization CH+O↔CHO++E−. To our knowledge, this work represents the first detailed measurements of positive ions in canonical low-pressure methane flames.

The oxidation of the novel lignocellulosic biofuel γ-valerolactone in a low pressure flame

A first oxidation study of the novel lignocellulosic biofuel γ-valerolactone (GVL) has been performed in a low pressure premixed flat flame. A stoichiometric GVL/methane flame was investigated experimentally and numerically at a pressure of 50 Torr. The measurements include flame temperatures and species concentrations. Species profiles from online gas chromatography measurements are presented for about 40 species including oxygen, hydrogen, argon, carbon monoxide, carbon dioxide, water, hydrocarbon, and oxygenated species with separated isomers. The recent kinetic model for GVL pyrolysis of De Bruycker et al. (2016) was extended for oxidation and the resulting model shows good agreement with the experimental flame data. A reaction pathway analysis was performed, which elucidates the fuel specific oxidation pathways of GVL at the investigated conditions. Additionally, an enthalpy analysis of the flame was performed highlighting the consistency of the different measurement techniques.

Contributions to improving small ester combustion chemistry: Theory, model and experiments

Biodiesel combustion models demand detailed understanding of the reactions undertaken by the ester functional group in the molecule. Investigations of the chemistry of small methyl esters can contribute to this goal. We have thus chosen methyl propanonate (MP) as a representative ester molecule in a study combining theory, model, and experiments. As an advantage, its reactions are also amenable to high-level theoretical calculations. Based on recent theoretical calculations (Tan et al., 2015), a new kinetics model for small ester combustion was developed and validated. New experimental results were obtained here in an extensive range of conditions, including full speciation in laminar low-pressure flames at two different stoichiometries (ϕ = 0.8 and 1.5) using electron ionization (EI) molecular-beam mass spectrometry (MBMS) and flame speed measurements in a spherical confined chamber (1–6atm). Comparison of the experimental data to the present model shows overall improved performance. Some specific new reaction pathways to form methanol, methylketene, methyl acetate, and acetic acid from the fuel radicals were identified and will permit more detailed insights into the combustion properties of methyl propanoate.

Pyrolysis and oxidation of methyl acetate in a shock tube: A multi-species time-history study

High-temperature methyl acetate (MA) pyrolysis and oxidation were studied behind reflected shock waves using laser-absorption species time-history measurements of CO, CO2, OH and H2O. The shock tube experiments with very dilute fuel mixtures covered a temperature range of 1401–1605K for MA pyrolysis (0.2% MA/Ar) and 1423–1674K for MA oxidation (0.4% O2, ϕ=1), and pressures around 1.5atm. The dominant sensitivity of CO2 concentration to MA unimolecular decomposition reactions enabled accurate determination of the rate coefficient and dissociation branching ratio by monitoring the CO2 time-history during MA pyrolysis. A recent kinetic mechanism developed by Yang et al. [13] originally for interpreting flow reactor and low-pressure flame data was adopted to simulate and compare with the current shock tube data. The measured CO and CO2 time-histories during MA pyrolysis were both well-predicted by the modified Yang et al. [13] mechanism. A relatively complete description of MA oxidation behavior was given by measuring CO, CO2, OH and H2O time-histories at the same temperature and pressure (1480K, 1.5atm). A unique two-stage CO2 formation during MA oxidation was clearly observed in the measured CO2 time-histories over the entire temperature range, with the rapid pre-ignition CO2 formation analyzed to be associated with the initial MA dissociation. Despite the overprediction of MA ignition delay times by 18–40% between 1623 and 1423K, the kinetic model successfully captures the plateau levels and the peak values of all the measured species profiles, as well as simulates the characteristic two-stage formation of CO2 observed experimentally.

Nonadiabatic combustion waves in a two-step competitive exothermic-reaction model

We consider travelling front solutions of a one-dimensional reaction-diffusion system corresponding to two-stage competitively exothermic reactions. We suppose all reactions occurring during the combustion may be lumped together as two different paths. Both exothermic reactions compete for the same reactant. Properties of travelling wave fronts, particularly flame speed, are determined numerically by solving the governing partial differential equations. The flame speed is analysed for different values of the heat loss parameter. It is demonstrated that, as the heat loss coefficient increases, the flame speed decays gradually until the front ceases to exist due to insufficient energy being available to sustain the flame front. Earlier studies for the adiabatic case showed the existence of bi-stability (fast and slow waves co-exist for the same parameter values). We study how heat loss affects the size of the bi-stable region. Furthermore, we investigate how the extinction limit depends on the heat loss parameter as well as the parameter representing the ratio of the activation energy to the heat release of the second reaction. Numerical solutions show that there is no travelling front when these parameters are above threshold values. The dependence of flame speed on the temperature profile is also investigated. The bi-stability phenomenon is demonstrated by perturbing the temperature profile. References W. Choi, S. Hong, J. T. Abrahamson, J.-H. Han, C. Song, N. Nair, S. Baik and M. S. Strano. Chemically driven carbon-nanotube-guided thermopower waves. Nat. Mater. 9:423–429, 2010. doi:10.1038/nmat2714 A. G. Merzhanov. Combustion and explosion processes in physical chemistry and technology of inorganic materials. Russ. Chem. Rev. 72:289–310, 2003. doi:10.1070/rc2003v072n04abeh000766 J. K. Bechtold and C. K. Law. The structure of premixed methane-air flames with large activation energy. Combust. Flame 97:317–338, 1994. doi:10.1016/0010-2180(94)90024-8 K. Seshadri, N. Peters and F. A. Williams. Asymptotic analysis of stoichiometric and lean hydrogen-air flames. Combust. Flame 96:407–427, 1994. doi:10.1016/0010-2180(94)90108-2 A. L. Sanchez, A. Lepinette, M. Bollig, A. Linan and B. Lazaro. The reduced kinetic description of lean premixed combustion. Combust. Flame 123:436–464, 2000. doi:10.1016/S0010-2180(00)00177-2 A. L. Sanchez, G. Balakrishnan, A. Linan and F. A. Williams. Relationships between bifurcation and numerical analyses for ignition of hydrogen-air diffusion flames. Combust. Flame 105:569–590, 1996. doi:10.1016/0010-2180(95)00241-3 V. V. Gubernov, A. V. Kolobov, A. A. Polezhaev and H. S. Sidhu. Analysing the stability of premixed rich hydrogen-air flame with the use of two-step models. Combust. Flame 160:1060–1069, 2013. doi:10.1016/j.combustflame.2013.01.021 R. Ball, A. McIntosh and J. Brindley. Thermokinetic models for simultaneous reactions: a comparative study. Combust. Theor. Model. 3:447–468, 1999. doi:10.1088/1364-7830/3/3/302 N. A. Martirosyan, S. K. Dolukhanyan and A. G. Merzhanov. Nonuniqueness of stationary states in combustion of mixtures of zirconium and soot powders in hydrogen. Combust. Explo. Shock 19:569–571, 1983. doi:10.1007/BF00750423 H. S. Sidhu, I. N. Towers, V. V. Gubernov, A. V. Kolobov and A. V. Polezhaev. Investigation of flame propagation in a model with competing exothermic reactions. Chemeca 2013 , Brisbane, Australia, 29 September–2 October, 2013. http://www.conference.net.au/chemeca2013/papers/29350.pdf I. N. Towers, V. V. Gubernov, A. V. Kolobov, A. V. Polezhaev and H. S. Sidhu. Bistability of flame propagation in a model with competing exothermic reactions. Proc. R. Soc. Lond. A 469:20130315, 2013. doi:10.1098/rspa.2013.0315 L. K. Forbes and W. Derrick. A combustion wave of permanent form in a compressible gas. Anziam J. 43:35–58, 2001. doi:10.1017/S144618110001141X Z. Huang, H. S. Sidhu, I. N. Towers, Z. Jovanoski and V. V. Gubernov. Investigating flame fronts in competitive exothermic reactions. MODSIM2015 , 21st International congress on Modelling and simulation, Gold coast, Australia, 29 November–4 December, 2015. http://www.mssanz.org.au/modsim2015/A1/huang.pdf F. A. Williams. Combustion theory . Westview Press, 1985. https://westviewpress.com/?s=Combustion+theory FlexPDE\(^TM\), PDE Solutions Inc. http://www.pdesolutions.com W. E. Schiesser. The numerical method of lines: integration of partial differential equations . Academic Press, San Diego, 1991. http://store.elsevier.com/The-Numerical-Method-of-Lines/isbn-9780128015513/ A. C. McIntosh, R. O. Weber and G. N. Mercer. Non-adiabatic combustion waves for general Lewis numbers: wave speed and extinction conditions. Anziam J. 46:1–16, 2004. doi:10.1017/S1446181100013638 A. R. Hall and H. G. Wolfhard. Multiple reaction zones in low pressure flames with ethyl and methyl nitrate, methyl nitrite and nitromethane. Proc. Combust. Inst , 6:190–199, 1957. doi:10.1016/S0082-0784(57)80029-0

Laminar burning velocity of acetic acid + air flames

Laminar burning velocities of acetic acid + air flames at 1 atm and initial gas temperatures of 338 K, 348 K, and 358 K were determined using the heat flux method. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions. Due to experimental problems related to the corrosiveness of acetic acid towards the burner material, the uncertainty of the burning velocities was relatively high up to ± 2 cm/s. Seventy reactions pertinent to acetic acid and ketene have been reviewed and detailed reaction mechanism for acetic acid combustion was developed. The model over-predicts measured burning velocities by about 3 cm/s. The mechanism was also tested comparing with flame structure of the low-pressure flame of acetic acid (Leplat and Vandooren, 2012). Good agreement with the concentration profiles of major products was found, however several minor intermediates were over- or under-predicted by the model. To elucidate reactions responsible for the differences observed, the sensitivity analysis was performed. It was found that the calculated burning velocities are insensitive to the reactions of acetic acid and mostly governed by C1 chemistry typical for all hydrocarbons and by reactions of ketene. Possible modifications of the rate constants within the evaluated uncertainty factors were discussed.

Isomer discrimination of PAHs formed in sooting flames by jet-cooled laser-induced fluorescence: application to the measurement of pyrene and fluoranthene

Jet-cooled laser-induced fluorescence is a spectroscopic method, specifically developed for the study of PAHs formed in flames. This technique has already been used to measure different aromatic species in sooting low-pressure methane flames such as benzene, naphthalene, and pyrene. The use of the LIF technique to excite PAHs drastically cooled down inside a supersonic jet offers the possibility to get selective and quantitative profiles of PAHs sampled from sooting flames. In this paper, we demonstrate the ability of this experimental method to separate the contribution of two mass isomers generated in sooting flames which are the pyrene and the fluoranthene. The selectivity of the method is demonstrated by studying the spectral properties of these species. The method is then applied to the measurement of both these species in two sooting flames with different equivalence ratios and stabilized at 200 torr (26.65 kPa). The sensitivity of the technique has been found to reach a few ppb in the case of fluoranthene measurements.

Temperature imaging in low-pressure flames using diode laser two-line atomic fluorescence employing a novel indium seeding technique

The use of diode lasers for spatially resolved temperature imaging is demonstrated in low-pressure premixed methane–air flames using two-line atomic fluorescence of seeded indium atoms. This work features the advantages of using compact diode lasers as the excitation sources with the benefits of two-dimensional planar imaging, which is normally only performed with high-power pulsed lasers. A versatile and reliable seeding technique with minimal impact on flame properties is used to introduce indium atoms into the combustion environment for a wide range of flame equivalence ratios. A spatial resolution of around 210 µm for this calibration-free thermometry technique is achieved for three equivalence ratios at a pressure of 50 mbar in a laminar flat flame.

Chemical Conversion of SO2 in Low-Temperature Low-Pressure Oxyhydrogen Flames. 2. Mechanism of Formation of Elemental Sulfur

Chemical Conversion of SO2 in Low-Temperature Low-Pressure Oxyhydrogen Flames. 2. Mechanism of Formation of Elemental Sulfur

An experimental and kinetic modeling study on dimethyl carbonate (DMC) pyrolysis and combustion

Dimethyl carbonate (DMC) is a promising oxygenated additive or substitute for hydrocarbon fuels, because of the absence of C–C bonds and the large oxygen content in its molecular structure. To better understand its chemical oxidation and combustion kinetics, flow reactor pyrolysis at different pressures (40, 200 and 1040 mbar) and low-pressure laminar premixed flames with different equivalence ratios (1.0 and 1.5) were investigated. Mole fraction profiles of many reaction intermediates and products were obtained within estimated experimental uncertainties. From theoretical calculations and estimations, a detailed kinetic model for DMC pyrolysis and high-temperature combustion consisting of 257 species and 1563 reactions was developed. The performance of the kinetic model was then analyzed using detailed chemical composition information, primarily from the present measurements. In addition, it was examined against the chemical structure of an opposed-flow diffusion flame, relying on global combustion properties such as the ignition delay times and laminar burning velocities. These extended comparisons yielded overall satisfactory agreement, demonstrating the applicability of the present model over a wide range of high-temperature conditions.

Modeling of NO formation in low pressure premixed flames

In this paper a detailed sub-mechanism NOMecha2.0 for NOx chemistry at high temperature is validated on a large experimental database obtained in flames, a jet-stirred reactor (JSR) and a plug-flow reactor under sub-atmospheric and atmospheric conditions. This sub-mechanism mainly based on the one implemented in the GDFkin®3.0_NCN model for prompt-NO formation has been thoroughly updated. Prompt-NO formation results from the reaction between CH and N2 yielding NCN and H. Then, NCN radicals react with H and O-atoms yielding HCN + N and CN + NO, respectively. Care was taken in the choice of the enthalpy of formation of the N-species, especially for NCN radicals for which the enthalpy values reported in the literature differ by more than 10 kJ mol−1. Critical rate constant values for the two main reactions (CH + N2 → NCN + H and NCN + H → HCN + N) and the branching ratio of the reactions NCN + H → products are discussed. Validation focuses mainly on prompt-NO formation in low pressure flames stabilized with different fuels (CH4, C2H6, C3H8 and C2H2) using data from the literature. It draws in particularly on the extended experimental database, including species profiles (CH, NCN, CN, HCN, NCO and NO) previously obtained in Lille in CH4 and C2H2 flames, which was extended in this work. Validation also considers experiments dedicated to HCN oxidation in a JSR or in flames, and to HNCO oxidation performed in a plug-flow reactor. In order to improve the prediction of HNCO, HCN/HNC isomerization has been implemented in NOMecha2.0. Finally the NOMecha2.0 sub-mechanism was satisfactorily coupled to a detailed chemical mechanism from the literature dedicated to the oxidation of acetylene at high temperature to predict NO formation.

Detailed influences of ethanol as fuel additive on combustion chemistry of premixed fuel-rich ethylene flames

To better understand potential pollutant formations during combustion of conventional hydrocarbon fuels blended with oxygenated fuels, detailed influences of ethanol as fuel additive on small polycyclic aromatic hydrocarbons (PAHs) precursors, aldehydes, ketene and other important intermediate species in premixed fuel-rich low-pressure ethylene flames are distinguished among dilution, thermal and chemical effects of additives. Dominant effects of ethanol addition on each species are underlined respectively. Ethylene oxidation process is delayed when ethylene is substituted by ethanol. The influence of ethanol dilution and thermal effects on ethylene consumption are larger than chemical effects. CO mole fractions slightly decrease mainly as a result of dilution and thermal effects of added ethanol. The reductions in small PAHs precursors (acetylene and propargyl) are attributed to dilution and thermal effects of ethanol addition instead of chemical effects. The ethanol chemical effects promote formations of hazardous pollutants formaldehyde and acetaldehyde, and especially are responsible for the significant increase of acetaldehyde. C2H6, C4H2 and C4H4 mole fractions decrease in a similar way with acetylene and propargyl as ethanol is added. Ethanol used here only serves as a prototype of oxygenated additive, and identification method in this work is more universal which can be easily extended for analyzing other fuel blends of hydrocarbon and oxygenated fuels.

Zastosowanie warstw pośrednich nanoszonych różnymi metodami natryskiwania cieplnego do lutowania miękkiego aluminium z miedzią

The manuscript presents a possibility for application of coatings deposited by thermal spraying methods and working as interlayers in soldering process. Crucial problems occurring in aluminium-copper soldering process with potential solving are presented. Results of wettability and propagation of filler zinc with 4% wt. Al addition on sprayed Al, Zn, Ni95Al5 and Ni85Al15 coatings by Low Pressure Cold Spraying, flame and arc spraying methods and working as interlayers are shown. Finally an assessment of solder-ability of interlayers was conducted and metallographic analysis of dissimilar Al-Cu lap joints with deposited by LPCS method aluminium coating onto copper substrate is presented. A possibility for application of coatings deposited by thermal spraying methods and working as interlayers in soldering process

Effect of the Methyl Substitution on the Combustion of Two Methylheptane Isomers: Flame Chemistry Using Vacuum-Ultraviolet (VUV) Photoionization Mass Spectrometry

Alkanes with one or more methyl substitutions are commonly found in liquid transportation fuels, so a fundamental investigation of their combustion chemistry is warranted. In the present work, stoichiometric low-pressure (20 Torr) burner-stabilized flat flames of 2-methylheptane and 3-methylheptane were investigated. Flame species were measured via time-of-flight molecular-beam mass spectrometry, with vacuum-ultraviolet (VUV) synchrotron radiation as the ionization source. Mole fractions of major end-products and intermediate species (e.g., alkanes, alkenes, alkynes, aldehydes, and dienes) were quantified axially above the burner surface. Mole fractions of several free radicals were also measured (e.g., CH3, HCO, C2H3, C3H3, and C3H5). Isomers of different species were identified within the reaction pool by an energy scan between 8 and 12 eV at a distance of 2.5 mm away from the burner surface. The role of methyl substitution location on the alkane chain was determined via comparisons of similar species trends obtained from both flames. The results revealed that the change in CH3 position imposed major differences on the combustion of both fuels. Comparison with numerical simulations was performed for kinetic model testing. The results provide a comprehensive set of data about the combustion of both flames, which can enhance the erudition of both fuels combustion chemistry and also improve their chemical kinetic reaction mechanisms.

An experimental and modeling study of the combustion of tetrahydrofuran

Tetrahydrofuran (THF) is a well suited starting point fuel to study the combustion chemistry of saturated cyclic esters that are being considered as promising bio-fuels. To better understand the combustion chemistry of THF, laminar low-pressure premixed flame structure, atmospheric adiabatic laminar burning velocities, and high-pressure ignition delay times were investigated. The structure of laminar premixed low-pressure (6.7kPa) argon-diluted (78%) flames of THF were studied at three equivalence ratios (0.7, 1.0 and 1.3) using on-line gas chromatography analyses. The results consist of temperature and mole fraction profiles (about 40 species) measured as a function of the height above the burner. Ethylene, propene, formaldehyde, acetaldehyde, and dihydrofurans were observed as important intermediates. Aromatic species were detected in very low amounts. The adiabatic laminar burning velocities of THF–air mixtures were measured using the heat flux burner method at atmospheric pressure (initial temperatures from 298 to 398K, at equivalence ratios from 0.55 to 1.60). The maximum burning velocity of THF was comparable to that of ethanol and diethyl ether. The ignition delay times of THF–oxygen–argon mixtures were measured behind reflected shock waves (temperatures from 1300 to 1700K, pressures around 8.5atm, mixtures containing 0.25–1% of fuel for equivalence ratios of 0.5–2.0). A new detailed kinetic model for THF combustion was developed using a combination of automatic generation (EXGAS), Evans–Polanyi correlations (for H-abstraction kinetic data), and CBS-QB3 theoretical calculations (for unimolecular initiation, H-abstraction and β-scission kinetic data). An overall good agreement between simulations and the present experimental results has been found. The main THF reaction pathways under flame conditions have been identified from flow rate analyses.