for Journals by Title or ISSN
for Articles by Keywords
help
Followed Journals
Journal you Follow: 0
 
Sign Up to follow journals, search in your chosen journals and, optionally, receive Email Alerts when new issues of your Followed Journals are published.
Already have an account? Sign In to see the journals you follow.
Journal Cover Combustion and Flame
  [SJR: 3.12]   [H-I: 124]   [116 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0010-2180
   Published by Elsevier Homepage  [3043 journals]
  • Influence of flame-holder temperature on the acoustic flame transfer
           functions of a laminar flame
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Daniel Mejia, Maxence Miguel-Brebion, Abdula Ghani, Thomas Kaiser, Florent Duchaine, Laurent Selle, Thierry Poinsot
      The occurrence of combustion instabilities in high-performance engines such as gas turbines is often affected by the thermal state of the engine. For example, strong bursts of pressure fluctuations may occur at cold start for operating conditions that are stable once the engine reaches thermal equilibrium. This observation raises the question of the influence of material temperature on the response of flames to acoustic perturbations. In this study, we assess the influence of the temperature of the flame holder for a laminar flame. Both experiments and numerical simulations show that the Flame Transfer Function (FTF) is strongly affected by the flame-holder temperature. The key factors driving the evolution of the FTF are the flame-root location as well as the modification of the flow, which affects its stability. In the case of the cooled flame-holder, the formation of a recirculation zone is identified as the main impact on the FTF.

      PubDate: 2017-10-11T09:13:47Z
       
  • Evolution of turbulence through a broadened preheat zone in a premixed
           piloted Bunsen flame from conditionally-averaged velocity measurements
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Timothy M. Wabel, Aaron W. Skiba, James F. Driscoll
      This work assesses two hypotheses that predict how turbulence properties vary within premixed turbulent flames that lie in the regime of Broadened Preheat-Thin Reaction layers. There have been few prior measurements describing flames in this regime. The authors previously found that very broad preheat layers were achieved for turbulence levels (u′/SL ) up to 243. Surprisingly, the reaction layer thickness did not increase, despite having Kolmogorov scales smaller than the laminar reaction layer thickness. A first hypothesis is that the turbulence decays in the preheat layer (as the temperature rises and viscous forces increase), so that the reaction layer sees only a small fraction of the initial turbulence. It follows that this turbulence decay might be responsible for the observed non-linear bending of the curve of turbulent burning velocity versus turbulence level. A second hypothesis is that the total turbulent kinetic energy does not decrease significantly in the preheat zone; instead, the small eddies decay and cause the integral scale to increase. Conditional averages are required to assess these two hypotheses. Fluorescence imaging identified the reaction zone boundary and particle image velocimetry diagnostics were applied simultaneously. The velocity measurements were conditioned on η, the distance to the upstream boundary of the reaction zone in each image. Conditioned measurements of turbulent kinetic energy, average eddy rotational velocity, strain rate, enstrophy, and integral length scale were computed through the flame. Results indicate that the turbulence level does not decrease within the broad preheat layers, and therefore the first hypothesis is not valid. In fact, the turbulence level within the entire burner core does not vary appreciably. However, the second hypothesis was supported by the measurements, since the integral scale increased by 50% across the preheat layer. The total turbulent kinetic energy did not decrease significantly. One explanation for this result is that small eddies are dissipated in the preheat zone.

      PubDate: 2017-10-11T09:13:47Z
       
  • Scalar dissipation rates in a turbulent partially-premixed dimethyl
           ether/air jet flame
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Frederik Fuest, Robert S. Barlow, Gaetano Magnotti, Jeffrey A. Sutton
      This paper presents the gradient structure of a turbulent partially premixed dimethyl ether (DME)/air jet flame operating at a jet Reynolds number of 29,300. Temperature and mixture fraction profiles from Raman/Rayleigh/CO-LIF line measurements are used to determine one-dimensional scalar dissipation rates at six axial locations. A major focus of the current work is to assess the effects of experimental artifacts, including spatial resolution, noise, and dimensionality, on the accuracy of the derived scalar dissipation rate. Two-dimensional probability density functions (PDFs) of the mixture fraction gradients are used to determine possible clipping effects due to insufficient spatial resolution. This resolution limit is compared to values determined from one-dimensional dissipation spectra and scaling laws. Spatial resolution also is investigated using laminar flame calculations in conjunction with optical-blur filters representing the experimental setup. The impact of noise is treated by error propagation methods. Monte Carlo simulations and experimental data from laminar flames are used to verify and validate the models used to predict noise propagation for the measurements of the absolute gradients, squared gradients, and scalar dissipation rates. Gradient and scalar dissipation rate detection limits and contribution from apparent dissipation (due to noise effects) are presented as functions of measurement signal-to-noise ratios. A noised lognormal function is introduced to investigate the impact of noise on derived PDFs and corresponding statistical moments of the measured scalar gradients and the scalar dissipation rate within the turbulent flame. Results from the turbulent flame measurements are presented in the form of scatter plots and conditional statistics to examine turbulence-chemistry interaction and develop a database for model assessment. Specifically, the results are compared to laminar flame calculations over a broad range of strain rates with multi-component and unity Lewis number transport assumptions. This comparison is used to assess the relevance of differential diffusion effects on scalar dissipation rates in the turbulent flame.

      PubDate: 2017-10-11T09:13:47Z
       
  • Influence of flash boiling spray on the combustion characteristics of a
           spark-ignition direct-injection optical engine under cold start
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Jie Yang, Xue Dong, Qiang Wu, Min Xu
      Flash boiling occurs when liquid fuel is injected into an ambient environment below its saturation pressure. Compared to non-flash-boiling (liquid) spray, flash-boiling spray features a two-phase flow that constantly generates vapor bubbles inside the liquid spray thus results in much smaller drop size and faster evaporation, which are favorable for direct-injection gasoline engine combustion. In this study, the combustion characteristics of flash boiling spray was investigated under cold start condition in a spark-ignition direct-injection (SIDI) optical gasoline engine. Three spray conditions, including liquid, transitional flash boiling, and flare flash boiling spray were studied for comparison. Optical access into the combustion chamber was realized by a quartz insert on the piston. The crank angle resolved color flame images as well as in-cylinder pressure of 150 consecutive cycles were recorded simultaneously. From the color images, the blue flame generated by excited molecules and the yellow flame resulted from soot radiation was identified and analyzed separately alongside with the cylinder pressure. Results show an improvement of indicated mean effective pressure-gross (IMEPg) and a reduction of soot formation with the introduction of flash boiling spray under cold start condition. The emission measurement shows that the formation of soot is positively related to particulate number (PN) emissions. Further study on the transient development of in-cylinder flames shows that flash boiling spray leads to higher propagation rate of the blue flame, and a subsequent statistical analysis shows a positive correlation between IMEP and the propagation rate of the blue flame.

      PubDate: 2017-10-11T09:13:47Z
       
  • Effect of Lewis number on ball-like lean limit flames
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Zhen Zhou, Yuriy Shoshin, Francisco E. Hernández-Pérez, Jeroen A. van Oijen, Laurentius P.H. de Goey
      The lean limit flames for three different fuel compositions premixed with air, representing three different mixture Lewis numbers, stabilized inside a tube in a downward flow are examined by experiments and numerical simulations. The CH* chemiluminescence distribution in CH4–air and CH4–H2–air flames and the OH* chemiluminescence distribution in H2–air flames are recorded in the experiments. Cell-like flames are observed for the CH4–air mixture for all tested equivalence ratios. However, for CH4–H2–air and H2–air flames, ball-like lean limit flames are observed. Flame temperature fields are measured using Rayleigh scattering. The experimentally observed lean limit flames are predicted qualitatively by numerical simulation with the mixture-averaged transport model and skeletal mechanism of CH4. The results of the simulations show that the entire lean limit flames of CH4–H2–air and H2–air mixtures are located inside a recirculation zone. However, for the lean limit CH4–air flame, only the leading edge is located inside the recirculation zone. A flame structure with negative flame displacement speed is observed for the leading edges of the predicted lean limit flames with all three different fuel compositions. As compared with 1D planar flames, the fuel transport caused by convection is less significant in the present 2D lean limit flames for the three different fuel compositions. For the trailing edges of the three predicted lean limit flames, a diffusion dominated flame structure is observed.

      PubDate: 2017-10-11T09:13:47Z
       
  • Experimental observation of pulsating instability under acoustic field in
           downward-propagating flames at large Lewis number
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Sung Hwan Yoon, Longhua Hu, Osamu Fujita
      According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1 + 3 ) ≈ 11), where β represents the Zel'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e., flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.

      PubDate: 2017-10-11T09:13:47Z
       
  • Transition condition and control mechanism of subatmospheric flame spread
           rate over horizontal thin paper sample
    • Abstract: Publication date: February 2018
      Source:Combustion and Flame, Volume 188
      Author(s): Jun Fang, Xuan-ze He, Kai-yuan Li, Jing-wu Wang, Yong-ming Zhang
      The horizontal flame spread over paper samples was investigated using a subatmospheric cabin with varied O2 concentration. The 25 kPa is found to be a clear turning point for the flame illumination and structure, radiative heat flux and flame spread rate (FSR), which leads to the transition boundary between the extinction limits and power law regions. In the extinction limits (non-linear) region below 25 kPa, the oxygen partial pressure is low with a small Da number. Consequently, the flame spread is gas phase kinetics controlled, resulting in low burning rate, low radiative heat loss and weak buoyancy, and thus the FSR is more sensitive to the oxygen concentration while less sensitive to the ambient pressure. In the power law (linear) region above 25 kPa, in contrast, the oxygen partial pressure is high and the Da number is large, and the flame spread is heat transfer controlled, which weakens the dependence of FSR on oxygen concentration and enhances the dependence on air pressure.

      PubDate: 2017-10-11T09:13:47Z
       
  • Effects of oxygen-enrichment and fuel unsaturation on soot and NOx
           emissions in ethylene, propane, and propene flames
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Krishna C. Kalvakala, Viswanath R. Katta, Suresh K. Aggarwal
      We have performed a computational study on the effects of oxygen enrichment 1 1 In this paper, the term oxygen enrichment (or oxygenation) is used to indicate simultaneous O2 enhancement of the oxidizer stream and N2 dilution of the fuel stream. and fuel unsaturation on the flame structure, PAHs, soot, and NO x emissions. Counterflow flames burning ethylene, propane, and propene are simulated with CHEMKIN-Pro, using a validated mechanism with 197 species and around 5000 reactions. The stoichiometric mixture fraction (ζ st) is varied by simultaneously using O2-enriched airstream and N2-diluted fuel stream such that the adiabatic flame temperature is nearly constant. Dominant reaction paths are analyzed to examine the relative roles of hydrodynamics and changes in flame structure on PAHs and soot emissions. As ζ st is increased, results indicate a significant reduction in acetylene and PAHs formation, and with additional soot oxidation in the post flame region, it leads to a nearly non-sooting flame. The drastic reduction in PAHs and soot formation can be attributed to both the hydrodynamic and the flame structure effects. At moderate oxygenation levels, changes in flame structure seems to play a more prominent role, while at higher oxygenation levels, the hydrodynamic effect seems to be more important. With the increase in ζ st, the O, OH, and H radical pool is enhanced, and, consequently, the intermediate species (propargyl, allene, and propyne) are reduced to smaller hydrocarbons, decreasing the formation of PAHs and soot. With further increase in ζ st, the flame location shifts from oxidizer to fuel side, and, consequently, PAH species and soot get oxidized in the oxygen rich region, leading to nearly soot free flames. However, as ζ st is increased, NO emissions increase monotonically. At low ζ st values, the prompt route contributes more to NO formation, while at high ζ st values, the thermal route contributes more. The rate of production analysis indicates that the presence of double bond promotes reactions which produce higher amounts of allyl and propargyl species, and thus higher amounts of soot precursors; benzene and pyrene. Consequently, propene and ethylene flames produce significantly higher amount of soot compared to propane flames.

      PubDate: 2017-10-11T09:13:47Z
       
  • Propagation speeds for interacting triple flames
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Stephen W. Grib, Michael W. Renfro
      Triple (or tribrachial) flames propagate through mixtures faster than the premixed laminar flame speed due to streamline divergence ahead of the flame base that decelerates the flow into the leading edge of the flame. When multiple triple flames are in close proximity, the bulk propagation speed of the structure can be even faster due to additional streamline divergence. Turbulent flames in partially-premixed conditions can encounter these situations, where multiple stoichiometric crossing are in close proximity, leading to multiple interacting triple flames being formed. Propagation speeds of the flame structure with respect the bulk flow for individual triple flames have been well characterized in previous studies, and the local flame speed of interacting triple flames have been reported; however, characterization of the propagation speed for the overall flame structure of interacting triple flame speeds has not been reported. The present work utilizes a laminar five slot burner, which allows both the concentration gradients and stoichiometric separation distance of two interacting triple flames to be varied. The bulk propagation speed of the multiple edge flames has been characterized as a function of the distance between the flame bases (or stoichiometric locations) and the local flame curvatures in order to better understand the conditions which lead to larger streamline divergence and faster propagation speeds. Interaction between multiple edge flames has been found to play an essential role in this propagation speed. Interacting edge flame speeds were modeled by modifying the relationship for single triple flame propagation speed with an added term for the interaction between the two flames to account for the increased effective divergence.

      PubDate: 2017-10-11T09:13:47Z
       
  • Spark ignition probability and minimum ignition energy transition of the
           lean iso-octane/air mixture in premixed turbulent combustion
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Long Jie Jiang, Shenqyang (Steven) Shy, Minh Tien Nguyen, Shih Yao Huang, De Wei Yu
      This paper measures turbulent spark ignition probability and minimum ignition energy (MIE) of the pre-vaporized iso-octane/air mixture at an equivalence ratio ϕ = 0.8 at 373 K with Le ≈ 2.98 over a wide range of turbulent intensities (u′/S L), where Le is the mixture's effective Lewis number and S L is the laminar burning velocity. Ignition experiments using a fixed 2-mm electrode gap are conducted in a large dual-chamber, constant-temperature/pressure, fan-stirred 3D cruciform burner capable of generating near-isotropic turbulence. Spark discharges having nearly square voltage and current waveforms are created for accurate determination of the ignition energy (E ig) across the electrodes. MIE E ig(50%) that is determined statistically from many repeated experiments at a given condition using a range of E ig to identify an overlapping energy band within which ignition and non-ignition coexist even at the “same discharge E ig”, where the subscript “ig(50%)” indicates 50% ignitability. Results show that the increasing slopes of MIET/MIEL = Г versus u′/S L change drastically from linearly to exponentially when u′/S L is greater than a critical value of 4.8, which is much smaller than previous rich methane data (Le > 1) at ϕ  = 1.2 with (u′/S L)c ≈ 16 and at ϕ = 1.3 with (u′/S L)c ≈ 24, revealing MIE transition. The subscripts T and L represent turbulent and laminar properties. When a reaction zone Péclet number Pe RZ =u′η k/α RZ is used for scaling, it is found that both present lean iso-octane and previous methane data can be collapsed onto a general correlation of Г1 = 1 + 0.4Pe RZ in the pre-transition and Г2 ∼ Pe RZ 4 in the post-transition with the transition occurring at (Pe RZ)c ≈ 4.2, showing similarity on MIE transition. η k is the Kolmogorov length scale of turbulence and α RZ is the reaction zone thermal diffusivity estimated at the instant of kernel formation.

      PubDate: 2017-10-04T08:42:09Z
       
  • A systematic method to estimate and validate enthalpies of formation using
           error-cancelling balanced reactions
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Philipp Buerger, Jethro Akroyd, Sebastian Mosbach, Markus Kraft
      This paper presents an automated framework that uses overlapping subsets of reference data to systematically derive an informed estimate of the standard enthalpy of formation of chemical species and assess the consistency of the reference data. The theory of error-cancelling balanced reactions (EBRs) is used to calculate estimates of the standard enthalpy of formation. Individual EBRs are identified using linear programming. The first part of the framework recursively identifies multiple EBRs for specified target species. A distribution of estimates can then be determined for each species from which an informed estimate of the enthalpy is derived. The second part of the framework iteratively isolates inconsistent reference data and improves the prediction accuracy by excluding such data. The application of the framework is demonstrated for test cases from organic and inorganic chemistry, including transition metal complexes. Its application to a set of 920 carbon, hydrogen and oxygen containing species resulted in a rapid decrease of the mean absolute error for estimates of the enthalpy of formation of each species due to the identification and exclusion of inconsistent reference data. Its application to titanium-containing species identified that the available reference values of TiOCl and TiO(OH)2 are inconsistent and need further attention. Revised values are calculated for both species. A comparison with popular high-level quantum chemistry methods shows that the framework is able to use affordable density functional theory (DFT) calculations to deliver highly accurate estimates of the standard enthalpy of formation, comparable to high-level quantum chemistry methods for both hydrocarbons and transition metal complexes.

      PubDate: 2017-10-04T08:42:09Z
       
  • Order reduction in models of spray ignition and combustion
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Sergei S. Sazhin, Elena Shchepakina, Vladimir Sobolev
      In most papers focused on the system order reduction models, describing processes of heating, evaporation and ignition in fuel sprays, it is assumed that all functions in corresponding differential equations are sufficiently smooth and consequently Lipschitzian. In many cases, however, these functions are non-Lipschitzian. This means that the conventional approach to system order reduction, based on the theory of integral manifolds, cannot be applied. It is pointed out that the order reduction of systems with non-Lipschitzian non-linearities can be performed, using a concept of positively invariant manifolds. This concept is discussed and applied to the analysis of spray ignition based on five ODEs (for gas temperature, fuel vapour and oxygen concentrations, and droplet temperatures and radii). This system is reduced to single ordinary differential equations for the gas temperature or fuel concentrations. It is shown that the equation for gas temperature predicts an increase in gas temperature up to its limiting value during finite time. The reaching of this temperature is accompanied by the complete depletion of either fuel vapour or oxygen depending on their initial concentrations, as follows from the analysis of the equations for gas temperature and fuel concentration.

      PubDate: 2017-10-04T08:42:09Z
       
  • Reaction mechanism, rate constants, and product yields for the oxidation
           of Cyclopentadienyl and embedded five-member ring radicals with hydroxyl
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): G.R. Galimova, V.N. Azyazov, A.M. Mebel
      Potential energy surfaces for the C5H5 + OH and C15H9 + OH reactions have been studied by ab initio calculations at the CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G(d,p) and G3(MP2,CC)//B3LYP/6-311G(d,p) levels of theory, respectively, in order to unravel the mechanism of oxidation of the cyclopentadienyl radical and five-member-ring radicals embedded in a sheet of six-member rings with OH. The VRC-TST approach has been employed to compute high-pressure-limit rate constants for barrierless entrance and exit reaction steps and multichannel/multiwell RRKM-ME calculations have been utilized to produce phenomenological pressure- and temperature-dependent absolute and individual-channel reaction rate constants. The calculations allowed us to quantify relative yields of various products in a broad range of conditions relevant to combustion and to generate rate expressions applicable for kinetic models of oxidation of aromatics. The C5H5 + OH reaction is shown to proceed either by well-skipping pathways without stabilization of C5H6O intermediates leading to the bimolecular products ortho-C5H5O + H, C5H4OH (hydroxycyclopentadienyl) + H, and C4H6 (1,3-butadiene) + CO, or via stabilization of the C5H6O intermediates, which then undergo unimolecular thermal decomposition to ortho-C5H5O + H and C4H6 + CO. The well-skipping and stabilization/dissociation pathways compete depending on the reaction conditions; higher pressures favor the stabilization/dissociation and higher temperature favor the well-skipping channels. For the C15H9 + OH reactions, the results demonstrate that embedding decreases the oxidation rate constants and hinder the decarbonylation process; the removal of CO grows less likely as the number of common edges of the five-member ring with the surrounding six-member rings increases.

      PubDate: 2017-10-04T08:42:09Z
       
  • The effect of the flame phase on thermoacoustic instabilities
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Giulio Ghirardo, Matthew P. Juniper, Mirko R. Bothien
      This paper concerns the influence of the phase of the heat release response on thermoacoustic systems. We focus on one pair of degenerate azimuthal acoustic modes, with frequency ω 0. The same results apply for an axial acoustic mode. We show how the value ϕ 0 and the slope − τ of the flame phase at the frequency ω 0 affects the boundary of stability, the frequency and amplitude of oscillation, and the phase ϕqp between heat release rate and acoustic pressure. This effect depends on ϕ 0 and on the nondimensional number τω 0, which can be quickly calculated. We find for example that systems with large values of τω 0 are more prone to oscillate, i.e. they are more likely to have larger growth rates, and that at very large values of τω 0 the value ϕ 0 of the flame phase at ω 0 does not play a role in determining the system’s stability. Moreover for a fixed flame gain, a flame whose phase changes rapidly with frequency is more likely to excite an acoustic mode. We propose ranges for typical values of nondimensional acoustic damping rates, frequency shifts and growth rates based on a literature review. We study the system in the nonlinear regime by applying the method of averaging and of multiple scales. We show how to account in the time domain for a varying frequency of oscillation as a function of amplitude, and validate these results with extensive numerical simulations for the parameters in the proposed ranges. We show that the frequency of oscillation ωB and the flame phase ϕqp at the limit cycle match the respective values on the boundary of stability. We find good agreement between the model and thermoacoustic experiments, both in terms of the ratio ωB /ω 0 and of the phase ϕqp , and provide an interpretation of the transition between different thermoacoustic states of an experiment. We discuss the effect of neglecting the component of heat release rate not in phase with the pressure p as assumed in previous studies. We show that this component should not be neglected when making a prediction of the system’s stability and amplitudes, but we present some evidence that it may be neglected when identifying a system that is unstable and is already oscillating

      PubDate: 2017-10-04T08:42:09Z
       
  • Experimental and numerical study of the laminar burning velocity of
           CH4–NH3–air premixed flames
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Ekenechukwu C. Okafor, Yuji Naito, Sophie Colson, Akinori Ichikawa, Taku Kudo, Akihiro Hayakawa, Hideaki Kobayashi
      With the renewed interest in ammonia as a carbon-neutral fuel, mixtures of ammonia and methane are also being considered as fuel. In order to develop gas turbine combustors for the fuels, development of reaction mechanisms that accurately model the burning velocity and emissions from the flames is important. In this study, the laminar burning velocity of premixed methane–ammonia–air mixtures were studied experimentally and numerically over a wide range of equivalence ratios and ammonia concentrations. Ammonia concentration in the fuel, expressed in terms of the heat fraction of NH3 in the fuel, was varied from 0 to 0.3 while the equivalence ratio was varied from 0.8 to 1.3. The experiments were conducted using a constant volume chamber, at 298 K and 0.10 MPa. The burning velocity decreased with an increase in ammonia concentration. The numerical results showed that the kinetic mechanism by Tian et al. largely underestimates the unstretched laminar burning velocity owing mainly to the dominance of HCO (+H, OH, O2) = CO (+H2, H2O, HO2) over HCO = CO + H in the conversion of HCO to CO. GRI Mech 3.0 predicts the burning velocity of the mixture closely however some reactions relevant to the burning velocity and NO reduction in methane–ammonia flames are missing in the mechanism. A detailed reaction mechanism was developed based on GRI Mech 3.0 and the mechanism by Tian et al. and validated with the experimental results. The temperature and species profiles computed with the present model agree with that of GRI Mech 3.0 for methane–air flames. On the other hand, the NO profile computed with the present model agrees with Tian et al.’s mechanism for methane–ammonia flames with high ammonia concentration. Furthermore, the burned gas Markstein length was measured and was found to increase with equivalence ratio and ammonia concentration.

      PubDate: 2017-10-04T08:42:09Z
       
  • n-Heptane cool flame chemistry: Unraveling intermediate species measured
           in a stirred reactor and motored engine
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Zhandong Wang, Bingjie Chen, Kai Moshammer, Denisia M. Popolan-Vaida, Salim Sioud, Vijai Shankar Bhavani Shankar, David Vuilleumier, Tao Tao, Lena Ruwe, Eike Bräuer, Nils Hansen, Philippe Dagaut, Katharina Kohse-Höinghaus, Misjudeen A. Raji, S. Mani Sarathy
      This work identifies classes of cool flame intermediates from n-heptane low-temperature oxidation in a jet-stirred reactor (JSR) and a motored cooperative fuel research (CFR) engine. The sampled species from the JSR oxidation of a mixture of n-heptane/O2/Ar (0.01/0.11/0.88) were analyzed using a synchrotron vacuum ultraviolet radiation photoionization (SVUV-PI) time-of-flight molecular-beam mass spectrometer (MBMS) and an atmospheric pressure chemical ionization (APCI) Orbitrap mass spectrometer (OTMS). The OTMS was also used to analyze the sampled species from a CFR engine exhaust. Approximately 70 intermediates were detected by the SVUV-PI-MBMS, and their assigned molecular formulae are in good agreement with those detected by the APCI-OTMS, which has ultra-high mass resolving power and provides an accurate elemental C/H/O composition of the intermediate species. Furthermore, the results show that the species formed during the partial oxidation of n-heptane in the CFR engine are very similar to those produced in an ideal reactor, i.e., a JSR. The products can be classified by species with molecular formulae of C7H14O x (x = 0–5), C7H12O x (x = 0–4), C7H10O x (x = 0–4), C n H2 n (n = 2–6), C n H2 n −2 (n = 4–6), C n H2 n +2O (n = 1–4), C n H2 n O (n = 1–6), C n H2 n −2O (n = 2–6), C n H2 n −4O (n = 4–6), C n H2 n +2O2 (n = 0–4, 7), C n H2 n O2 (n = 1–6), C n H2 n −2O2 (n = 2–6), C n H2 n −4O2 (n = 4–6), and C n H2 n O3 (n = 3–6). The identified intermediate species include alkenes, dienes, aldehyde/keto compounds, olefinic aldehyde/keto compounds, diones, cyclic ethers, peroxides, acids, and alcohols/ethers. Reaction pathways forming these intermediates are proposed and discussed herein. These experimental results are important in the development of more accurate kinetic models for n-heptane and longer-chain alkanes.

      PubDate: 2017-10-04T08:42:09Z
       
  • Combustion of aluminum nanoparticles and exfoliated 2D molybdenum trioxide
           composites
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Naadaa Zakiyyan, Anqi Wang, Rajagopalan Thiruvengadathan, Clay Staley, Joseph Mathai, Keshab Gangopadhyay, Matthew R. Maschmann, Shubhra Gangopadhyay
      Exfoliated two-dimensional (2D) molybdenum trioxide (MoO3) of approximately 3-4 monolayers in thickness was produced from sonicating bulk MoO3 powder, and then mixed with 80 nm diameter Al nanoparticles to prepare nanoenergetic composites with high interfacial contacts between the fuel and oxidizer. Combustion measurements demonstrated peak pressures as high as 42.05 ± 1.86 MPa, pressurization rates up to 3.49 ± 0.31 MPa/µs, and linear combustion rates up to 1,730 ± 98.1 m/s, the highest values reported to date for Al/MoO3 composites. TGA/DSC measurements indicate energetic reactions between the Al and 2D MoO3 sheets occur prior to the melting temperature of Al. SEM and TEM analysis of the composites prior to combustion suggests high interfacial contact area between the Al and MoO3. After reaction, we observe that the 2D MoO3 sheets are converted to extended alumina flakes during reaction in a process attributed to Al adsorption and diffusion processes. These alumina features act as a physical barrier against Al NP sintering while also provide separation for reaction gases to flow and preheat unreacted materials.

      PubDate: 2017-09-26T12:19:30Z
       
  • New insights into the shock tube ignition of H2/O2 at low to moderate
           temperatures using high-speed end-wall imaging
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Erik Ninnemann, Batikan Koroglu, Owen Pryor, Samuel Barak, Leigh Nash, Zachary Loparo, Jonathan Sosa, Kareem Ahmed, Subith Vasu
      In this work, the effects of pre-ignition energy releases on H2 O2 mixtures were explored in a shock tube with the aid of high-speed imaging and conventional pressure and emission diagnostics. Ignition delay times and time-resolved camera image sequences were taken behind the reflected shockwaves for two hydrogen mixtures. High concentration experiments spanned temperatures between 858 and 1035 K and pressures between 2.74 and 3.91 atm for a 15% H2\18% O2\Ar mixture. Low concentration data were also taken at temperatures between 960 and 1131 K and pressures between 3.09 and 5.44 atm for a 4% H2\2% O2\Ar mixture. These two model mixtures were chosen as they were the focus of recent shock tube work conducted in the literature (Pang et al., 2009). Experiments were performed in both a clean and dirty shock tube facility; however, no deviations in ignition delay times between the two types of tests were apparent. The high-concentration mixture (15%H2\18%O2\Ar) experienced energy releases in the form of deflagration flames followed by local detonations at temperatures < 1000 K. Measured ignition delay times were compared to predictions by three chemical kinetic mechanisms: GRI-Mech 3.0 (Smith et al.), AramcoMech 2.0 (Li et al., 2017), and Burke's et al. (2012) mechanisms. It was found that when proper thermodynamic assumptions are used, all mechanisms were able to accurately predict the experiments with superior performance from the well-validated AramcoMech 2.0 and Burke et al. mechanisms. Current work provides better guidance in using available literature hydrogen shock tube measurements, which spanned more than 50 years but were conducted without the aid of high-speed visualization of the ignition process, and their modeling using combustion kinetic mechanisms.

      PubDate: 2017-09-26T12:19:30Z
       
  • Structure and extinction of spherical burner-stabilized diffusion flames
           that are attached to the burner surface
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Melvin K. Rodenhurst, Beei-Huan Chao, Peter B. Sunderland, Richard L. Axelbaum
      The structure and extinction of a diffusion flame stabilized by a spherical porous burner, and attached to the burner, was analyzed by activation energy asymptotics. The extinction state was identified by the smallest Damköhler number, representing the weakest burning intensity, at which a flame exists. Four limiting flames, based on a fuel/air flame, but with different flow direction and inert distribution, were used to study the effects of various controlling parameters. For the attached flame, the burning characteristics and extinction state were controlled by the mass fraction of the reactant supplied from the burner (lean reactant), and the flame behaves like a premixed flame with a lean reactant. This is consistent with the premixed flame regime introduced by Liñán. With reduced Damköhler number (Da), or mass flow rate (m), the reaction becomes weaker, the leakage of the burner reactant increases, and there exists a minimum Da or m below which the flame extinguishes. Comparison of the four flames reveals that all four flames extinguish at the same fuel consumption rate when other conditions are the same. As to the effects of Lewis numbers, the flame is stronger and more difficult to extinguish when either the Lewis number of the reactant supplied from the burner is increased or the Lewis number of the reactant in the ambient is decreased. When the size of the burner is reduced, the flame reaches the burner at a smaller mass flow rate with extinction occurring also at a smaller flow rate. There exists a smallest burner size below which the flame will extinguish before reaching the burner.

      PubDate: 2017-09-26T12:19:30Z
       
  • Principal component analysis coupled with nonlinear regression for
           chemistry reduction
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Mohammad Rafi Malik, Benjamin J. Isaac, Axel Coussement, Philip J. Smith, Alessandro Parente
      Large kinetic mechanisms are required in order to accurately model combustion systems. If no parameterization of the thermo-chemical state-space is used, solution of the species transport equations can become computationally prohibitive as the resulting system involves a wide range of time and length scales. Parameterization of the thermo-chemical state-space with an a priori prescription of the dimension of the underlying manifold would lead to a reduced yet accurate description. To this end, the potential offered by Principal Component Analysis (PCA) in identifying low-dimensional manifolds is very appealing. The present work seeks to advance the understanding and application of the PC-transport approach by analyzing the ability to parameterize the thermo-chemical state with the PCA basis using nonlinear regression. In order to demonstrate the accuracy of the method within a numerical solver, unsteady perfectly stirred reactor (PSR) calculations are shown using the PC-transport approach. The PSR analysis extends previous investigations to more complex fuels (methane and propane), showing the ability of the approach to deal with relatively large kinetic mechanisms. The ability to achieve highly accurate mapping through Gaussian Process based nonlinear regression is also shown. In addition, a novel method based on local regression of the PC source terms is also investigated which leads to improved results.

      PubDate: 2017-09-26T12:19:30Z
       
  • The effect of exit Reynolds number on soot volume fraction in turbulent
           non-premixed jet flames
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): S.M. Mahmoud, G.J. Nathan, Z.T. Alwahabi, Z.W. Sun, P.R. Medwell, B.B. Dally
      Soot volume fraction (SVF) was measured in five attached turbulent non-premixed jet flames of a C2H4 H2 N2 fuel mixture using the Laser-Induced Incandescence (LII) technique. The five flames comprise two sets with exit strain rates of 4100 and 7500 s−1, respectively. Within each set, the exit Reynolds number was changed both by varying the jet diameter and the fuel exit velocity of the flames. Measurements of the mean, instantaneous and integrated SVF reveal a weak inverse dependence on the exit Reynolds number. A minor dependence of the axial and radial profiles of soot intermittency on the exit Reynolds number is also observed. The total soot yield is found to scale linearly with both the jet exit diameter and the fuel flow rate for the two flame sets of different exit strain. The total soot yield is also found to be a strong function of both the exit strain and the flame volume, but to be almost independent of the exit Reynolds number. A non-negligible effect of buoyancy on SVF is also deduced from the global correlations.

      PubDate: 2017-09-26T12:19:30Z
       
  • Direct numerical simulation of turbulent channel-flow catalytic
           combustion: Effects of Reynolds number and catalytic reactivity
    • Abstract: Publication date: January 2018
      Source:Combustion and Flame, Volume 187
      Author(s): Behrooz O. Arani, Christos E. Frouzakis, John Mantzaras, Fransesco Lucci, Konstantinos Boulouchos
      Three-dimensional direct numerical simulations of fuel-lean (equivalence ratio ϕ = 0.24 ) hydrogen/air turbulent catalytic combustion were carried out in a platinum-coated planar channel with isothermal walls and an incoming fully-developed turbulent flow, at two inlet bulk Reynolds numbers ( R e H = 5700 and 12,360 based on the channel height H) and four global catalytic reaction rates. The turbulent flow laminarization due to heat transfer from the hot catalytic walls was appreciable, with turbulent intensities dropping by 37% and 25% at the channel outlet for the low and high ReH , respectively. The ratio of the local average turbulent hydrogen conversion rate to the corresponding local laminar conversion rate ( 〈 s ˙ T 〉 / s ˙ L ) was found to be a monotonically increasing function of streamwise distance, Reynolds number ReH , and catalytic reactivity. Despite the turbulent flow laminarization, 〈 s ˙ T 〉 / s ˙ L ratios at the channel outlet reached values up to 170% for the highest ReH = 12,360 and for infinitely-fast catalytic chemistry. A correlation was further established for the ratio of the turbulent hydrogen conversion rate at finite-rate chemistry to the corresponding turbulent conversion rate at infinitely-fast chemistry. The instantaneous local catalytic reaction rates exhibited large fluctuations, which were up to 300% and 500% for the low and high ReH , respectively. Fourier analysis indicated that a diminishing catalytic reactivity acted as a low-pass frequency filter for the overlying fluctuations of the turbulent flow.

      PubDate: 2017-09-26T12:19:30Z
       
  • Raman/LIPF data of temperature and species concentrations in swirling
           hydrogen jet diffusion flames: Conditional analysis and comparison to
           laminar flamelets
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): T.S. Cheng, J.-Y. Chen, R.W. Pitz
      Simultaneous point measurements of temperature, mixture fraction, major species (H2, H2O, O2, N2) concentrations from KrF laser-induced spontaneous Raman scattering and minor species (OH) concentrations from KrF laser-induced predissociative fluorescence (LIPF) in unswirled (Sg  = 0), low swirl (Sg  = 0.12), and high swirl (Sg  = 0.5) lifted turbulent hydrogen jet diffusion flames into still air are reprocessed to obtain profiles of the Favre-averaged scalars and conditional moments. Large discrepancies between the Favre-averaged and ensemble-averaged temperature, H2O, and OH mole fractions are found at the lifted flame region, due to density weighting of fairly large samples of unreacted mixtures. Conditional statistics are used to reveal the reaction zone structure in mixture fraction coordinates. The cross-stream dependence of conditional means of temperature and species concentration is found to be significant in the lifted flame region of the swirled flames and decreases to negligible levels with increasing streamwise position. Comparison of the measured conditional mean variation of OH vs. H2O with a series of stretched laminar partially premixed flame and diffusion flame calculations reveals that for the unswirled flame, the differential molecular diffusion and radial dependence of conditional means are minor at x/D = 6.4 for stretch rates from a = 14,000 to 400 s-1. For the low and high swirling flames, however, the measured OH vs. H2O conditional means at the lifted flame region are not consistent with stretched laminar flame calculations. The level of partial premixing and the stretch rate decrease with increasing downstream locations. The estimated stretch rate at x/D = 53.5 is about 50–10 s-1, while at x/D = 107 the stretch rate is about 10 s-1 with some measurements at adiabatic equilibrium.

      PubDate: 2017-09-26T12:19:30Z
       
  • Measurement of the size distribution, volume fraction and optical
           properties of soot in an 80 kW propane flame
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Daniel Bäckström, Adrian Gunnarsson, Dan Gall, Xiangyu Pei, Robert Johansson, Klas Andersson, Ravi Kant Pathak, Jan B.C. Pettersson
      This work presents measurements of the size distribution, volume fraction, absorption and scattering coefficients of soot in an 80 kW swirling propane-fired flame. Extractive measurements were performed in the flame using an oil-cooled particle extraction probe. The particle size distribution was measured with a Scanning Mobility Particle Sizer (SMPS) and the optical properties were measured using a Photo Acoustic Soot Spectrometer (PASS-3). A detailed radiation model was used to examine the influence of the soot volume fraction on the particle radiation intensity. The properties of the gas were calculated with a statistical narrow-band model and the particle properties were calculated using Rayleigh theory with four different complex indices of refraction for soot particles. The modelled radiation was compared with measured total radiative intensity, the latter which was measured with a narrow angle radiometer. The results show that the measured soot volume fraction yields particle radiation that corresponds well with the determined difference between gas and total radiation. This indicates that the presented methodology is capable of quantifying both the particle and gaseous radiation in a flame of technical size.

      PubDate: 2017-09-26T12:19:30Z
       
  • Shock tube study and RRKM calculations on thermal decomposition of
           2-chloroethyl methyl ether
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Parandaman A., Rajakumar B.
      The thermal decomposition of 2-chloroethyl methyl ether (2-CEME) was studied in the temperatures between 1175 and 1467 K. The decomposition of 2-CEME happens predominantly via molecular elimination reactions than via CC and CO bond fission channels. The major decomposition products are methane, ethylene and methanol. The minor are acetaldehyde and ethane. The Arrhenius expression for the overall decomposition of 2-CEME was obtained to be k t o t a l e x p ( 1175 − 1467 K ) = ( 4.12 ± 0.42 ) × 10 11 exp ( − ( 52.2 kcal mo l − 1 ± 2.6 ) / RT ) s − 1 . To simulate the distribution of reactant and products over the experimentally studied temperatures between 1175 and 1467 K, a reaction scheme was constructed with 45 species and 71 elementary reactions. The pressure and temperature dependent rate coefficients were calculated for various unimolecular dissociation pathways in 2-CEME using RRKM theory. The high pressure limit temperature dependent rate coefficient for the total decomposition of 2-CEME was obtained to be k total CCSDT / / M 06 − 2 X (500–2000 K) = (2.55 ± 0.21) × 1014 exp (−(67.6 kcal mol−1  ± 3.0)/RT) s−1.
      Graphical abstract image

      PubDate: 2017-09-13T13:21:59Z
       
  • An investigation of a turbulent spray flame using Large Eddy Simulation
           with a stochastic breakup model
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): William P. Jones, Andrew J. Marquis, Dongwon Noh
      A computational investigation of a turbulent methanol/air spray flame in which a poly-dispersed droplet distribution is achieved through the use of a pressure-swirl atomiser (also known as a simplex atomiser) is presented. A previously formulated stochastic approach towards the modelling of the breakup of droplets in the context of Large Eddy Simulation (LES) is extended to simulate methanol/air flames arising from simplex atomisers. Such atomisers are frequently used to deliver fine droplet distributions in both industrial and laboratory configurations where they often operate under low-pressure drop conditions. The paper describes improvements to the breakup model that are necessary to correctly represent spray formation from simplex atomisers operated under low-pressure drop conditions. The revised breakup model, when used together with the existing stochastic models for droplet dispersion and evaporation, is shown to yield simulated results for a non-reacting spray that agree well with the experimentally measured droplet distribution, spray dynamics and size-velocity correlation. The sub-grid scale (sgs) probability density function (pdf) approach in conjunction with the Eulerian stochastic field method are employed to represent the unknown interaction between turbulence and chemistry at the sub-filter level while a comprehensive kinetics model for methanol oxidation with 18 chemical species and 84 elementary steps is used to account for the gas-phase reaction. A qualitative comparison of the simulated OH images to those obtained from planar laser-induced fluorescence (PLIF) confirms that the essential features of this turbulent spray flame are well captured using the pdf approach. They include the location of the leading-edge combustion (or lift-off height) and the formation of a double reaction zone due to the polydisperse spray. In addition, the influence of the spray flame on the structure of the reacting spray in respect of the mean droplet diameters and spray velocities is reproduced to a good level of accuracy.

      PubDate: 2017-09-13T13:21:59Z
       
  • Numerical analysis of laminar methane–air side-wall-quenching
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Sebastian Ganter, Arne Heinrich, Thorsten Meier, Guido Kuenne, Christopher Jainski, Martin C. Rißmann, Andreas Dreizler, Johannes Janicka
      Flame-wall-interaction (FWI) is investigated numerically using a premixed stoichiometric Side-Wall-Quenching configuration. Within the 2D fully resolving laminar simulation, detailed chemistry is used to study the stationary quenching of a methane–air (CH4) flame at an isothermal inert wall of 300 K. The investigation is related to a recent experimental study that revealed that the carbon-monoxide distribution substantially differs in the near-wall region when compared to an undisturbed flame. Simulations are carried out using different reaction mechanisms (GRI and Smooke) as well as diffusion treatments (unity Lewis and mixture averaged transport) and the results are compared to the measured temperature and CO concentrations. Specifically regarding the latter, being an important pollutant, recent attempts based on tabulated chemistry failed in predicting its near-wall accumulation. Accordingly, within this work the detailed chemistry simulations are used to investigate the origin of CO near the wall. Therefore, a Lagrangian analysis is applied to quantify the contribution of chemical production and consumption as well as diffusion to understand the root mechanism of the high CO concentrations measured. The analysis revealed that the high CO concentrations near the wall results from a transport originating from CO produced at larger wall distances. In that region being not submitted to large heat losses, a high chemical activity and corresponding CO production is found. Accordingly, a diffusion process is initiated towards the wall where the chemical sources itself were actually found to be negative.

      PubDate: 2017-09-13T13:21:59Z
       
  • Direct estimation of edge flame speeds of lifted laminar jet flames and a
           modified stabilization mechanism
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Min-Kyu Jeon, Nam Il Kim
      The flame stabilization mechanism of a lifted flame in a laminar fuel jet has been explained based on the edge flame concept. Previous studies have employed a similarity solution between velocity and fuel concentration, and showed that a lifted flame can be stabilized when the Schmidt number, Sc, is within a range of either Sc > 1 or Sc < 0.5. However, two unsolved problems remained, and they were mainly answered in this study. First, the edge flame speed could not be determined from the similarity solution using the experimental results of stable lifted flames. To resolve this, the experimental relationship between the fuel flow rate and the liftoff height was measured with a higher resolution, and a new method employing an effective Schmidt number was suggested. As a result, the relationship between the edge flame speed and the fuel concentration gradient could then be directly estimated from the simple experimental values for flow rate and the liftoff height. This new method was validated for various experimental parameters including the tube diameter, air-premixing ratio, and nitrogen-dilution ratio. Second, the reason why a stable lifted flame was not obtained when Sc < 0.5 could not be explained theoretically. Here, the existence of a unique criterion of Sc > 1, for a stable lifted flame was clarified theoretically. This study will advance understanding of the characteristics and stabilization mechanism of lifted edge flames in laminar non-premixed fuel jets.

      PubDate: 2017-09-07T17:47:35Z
       
  • Simultaneous imaging of fuel, OH, and three component velocity fields in
           high pressure, liquid fueled, swirl stabilized flames at 5 kHz
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Ianko Chterev, Nicholas Rock, Hanna Ek, Benjamin Emerson, Jerry Seitzman, Naibo Jiang, Sukesh Roy, Tonghun Lee, James Gord, Tim Lieuwen
      This paper describes implementation of simultaneous, high speed (5 kHz) stereo PIV, OH and fuel-PLIF in a pressurized, liquid fueled, swirl stabilized flame. The experiments were performed to characterize the flow field, qualitative heat release and fuel spray distributions, and flame dynamics. Acquiring high speed OH-PLIF in pressurized, liquid fuel systems is difficult due to the strong overlap of the fuel's absorption and emission spectra with the OH fluorescence spectrum. To overcome difficulties associated with the overlap, the OH and fuel fluorescence signals were partially separated by using two cameras with differing spectral filters and data acquisition timing. Upon data reduction, regions containing fuel, OH and a mixture of fuel and OH are identified. Instantaneous and time-averaged results are discussed showing the flow field, flame position and dynamics, and spray distribution from the fuel signal for two multi-component liquid fuels, at two inlet temperatures and three pressures. These results are used to infer several important observations on coupled flow and flame physics. Specifically, the flame is “M-shaped” at higher preheat temperature and higher fuel/air ratio, as opposed to no visible reaction on the inside of the annular fuel/air jet at low temperature and fuel/air ratio conditions. While such fundamentally different flame topologies in gaseous, premixed flames are well known, these results show that there are also different families of flame shapes and heat release distributions in spray flames. In addition, the flame position with respect to the flow is different for the liquid-fueled flame than for gaseous, premixed flames—in premixed flames with this geometry, the flame lies in the low velocity shear layer separating the reactants and the recirculating products. In contrast, the flame location is controlled by the spray location in this spray flame, as opposed to the shear layer. For example, reactions are observed near the nozzle outlet in the core of the high velocity annular jet, something which would not be observed in the premixed flame configuration. Also of interest is the near invariance of the key flow features—such as jet core trajectory or shear layer locations—to the operating condition changes for this study, even as the spray penetration and distribution, and flame position change appreciably.

      PubDate: 2017-09-07T17:47:35Z
       
  • A comprehensive experimental and kinetic modeling study of n-propylbenzene
           combustion
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Wenhao Yuan, Yuyang Li, Philippe Dagaut, Yizun Wang, Zhandong Wang, Fei Qi
      This work presents a comprehensive experimental and kinetic modeling study on the combustion of n-propylbenzene. Flow reactor pyrolysis of n-propylbenzene at 0.04, 0.2 and 1 atm and laminar premixed flames of n-propylbenzene at 0.04 atm with equivalence ratios of 0.75 and 1.00 were investigated with synchrotron vacuum ultraviolet photoionization mass spectrometry. Jet stirred reactor (JSR) oxidation of n-propylbenzene at 10 atm with equivalence ratios of 0.5, 1.0, 1.5 and 2.0 was investigated with gas chromatography. A detailed kinetic model for n-propylbenzene combustion with 340 species and 2069 reactions was developed and validated against the data measured in this work. Model analyses such as rate of production analysis and sensitivity analysis were also performed to reveal the key pathways in the consumption of fuel and formation of polycyclic aromatic hydrocarbons (PAHs). The analysis results demonstrate that the benzylic CC bond dissociation reaction is crucial for the decomposition of n-propylbenzene in the pyrolysis and rich flame. Low temperature oxidation reactions play important roles in the high pressure JSR oxidation of n-propylbenzene. In addition, the formation pathways of PAHs are strongly related to the fuel structure, especially for the formation of bicyclic PAHs such as indene and naphthalene. Furthermore, the present model was also validated against previous experimental data of n-propylbenzene combustion under a wide range of conditions, including ignition delay times, laminar flame speeds, extinction strain rates, speciation profiles in atmospheric pressure JSR oxidation, flow reactor oxidation and high pressure shock tube pyrolysis and oxidation.

      PubDate: 2017-09-07T17:47:35Z
       
  • Approximate analytical solutions for temperature based transient mass flux
           and ignition time of a translucent solid at high radiant heat flux
           considering in-depth absorption
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Junhui Gong, Yabo Li, Jinghong Wang, Jing Li, Yixuan Chen, Juncheng Jiang, Zhirong Wang
      Most studies, employing ignition temperature as the ignition criterion, utilized surface absorption of radiant incident heat flux in analytical models when investigating the ignition mechanism of solid combustibles. However, in-depth absorption exerts its influence on ignition time significantly for translucent solid, especially at high radiant heat flux. In this work, we extend the previous researches from surface absorption to in-depth absorption to develop an approximate analytical ignition model using critical mass flux instead of critical temperature. An approximation methodology is proposed during derivation to study the in-depth absorption scenario. The comparison among this model, available experimental data of black PMMA in the literature and previous numerical simulations indicates that the proposed model provides relatively high accuracy in predicting ignition time. Furthermore, the pure surface absorption circumstance is also reexamined and compared with the classical ignition theory. The results show that surface absorption hypothesis accelerates the total mass flux, which consequently shortens the ignition time. However, in-depth absorption assumption eliminates the heat accumulation on surface and results in good prediction for ignition time at high heat flux. For in-depth absorption, the absorption coefficient affects the heat penetration depth and temperature distribution in this layer which consequently affects the thermal degradation reaction rate, mass flux and finally ignition time. Meanwhile, the ignition time considering both surface and in-depth absorption is discussed, and the relationship with pure surface and in-depth absorption conditions is obtained.

      PubDate: 2017-09-07T17:47:35Z
       
  • Lagrangian analysis of high-speed turbulent premixed reacting flows:
           Thermochemical trajectories in hydrogen–air flames
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Peter E. Hamlington, Ryan Darragh, Clarissa A. Briner, Colin A.Z. Towery, Brian D. Taylor, Alexei Y. Poludnenko
      A Lagrangian analysis approach is used to examine the effects of high-speed turbulence on thermochemical trajectories in unconfined, stoichiometric hydrogen–air (H2–air) premixed flames. Two different intensities of turbulence in the unburnt reactants are considered, giving premixed flames with Karlovitz numbers of roughly 150 and 450. These two cases are modeled using direct numerical simulations (DNS) with both multi- and single-step H2–air reaction kinetics. In each of the four resulting simulations, trajectories of fluid parcels are calculated using a high-order Runge–Kutta method, and time series of temperature and chemical composition within each parcel are recorded. The resulting thermochemical trajectories are used to examine the evolution of thermodynamic quantities and chemical composition, as well as measure fluid parcel residence times and path lengths during different phases of the combustion process. Fuel mass fraction and temperature within fluid parcels are shown to be frequently non-monotonic along fluid trajectories in both single- and multi-step H2–air simulations, and the prevalence of non-monotonic trajectories increases with increasing turbulence intensity. Using results from single-step simulations, it is shown that this non-monotonicity can be caused solely by molecular transport processes resulting from large gradients in temperature and species concentrations created by turbulent advection. As a related consequence of advection, fluid parcel residence times are found to be smaller than in a laminar flame and the ratio of turbulent to laminar residence times decreases from roughly 0.8 to 0.6 as the turbulence intensity increases. By contrast, fluid parcel path lengths in the present high-speed turbulent flames are found to be substantially greater than laminar path lengths, resulting in fluid parcels that travel 4 and 7 times further than in a laminar flame for the two different turbulence intensities considered here.

      PubDate: 2017-09-07T17:47:35Z
       
  • The critical conditions for thermal explosion in a system heated at a
           constant rate
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Daniel Sánchez-Rodriguez, Jordi Farjas, Pera Roura
      We have analyzed the condition needed for thermal explosion to occur in a solid sample when the temperature of the vessel walls is raised at a constant rate. We have developed a dimensionless model that allows its direct comparison with an isoperibolic system (constant vessel wall temperature). We have obtained an analytical expression for the critical condition as a function of the system parameters. Our solution takes into account reactant consumption and covers different geometries: thin film, finite and infinite cylinder. The critical condition has been validated with numerical simulations and experiments. We show that, compared to the isoperibolic system, thermal explosion is a little bit more difficult to achieve under constant heating conditions. Besides, we show that thermal explosion on submicrometric films is nearly impossible.

      PubDate: 2017-09-07T17:47:35Z
       
  • Flamelet regime characterization for non-premixed turbulent combustion
           simulations
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Wai Lee Chan, Matthias Ihme
      Regime characterization has been shown to be an insightful technique in the study of turbulent combustion, providing useful information about the relation between fundamental combustion modes and physical scales that require consideration. Regime diagrams can guide the appropriate utilization of combustion models, which is critical for the accuracy of numerical simulations of turbulent reacting flows. In the present study, a flamelet regime diagram is developed to assess the applicability of various diffusion flamelet models with respect to the local grid resolution and underlying flow/flame structure. The flamelet regime parameter is defined such that it can be unambiguously determined with fully resolved data, as in the case of direct numerical simulations (DNS), and adequately estimated from filtered information of large-eddy simulations (LES). To this end, the flamelet regime diagram is studied through an a priori analysis of a DNS dataset of a turbulent lifted hydrogen jet flame in a heated coflow. Findings from this analysis verify the length-scale arguments that are based on the concepts of inner-reaction zone thickness and dissipation element, upon which the regime diagram is constructed on. In addition, the relevance of the regime diagram to the numerical grid size enables it to act as a guiding tool for model selection in non-premixed combustion LES.

      PubDate: 2017-09-07T17:47:35Z
       
  • Ignition of a hydrogen–air mixture by low voltage electrical contact
           arcs
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Rajiv Shekhar, Lorenz R. Boeck, Carsten Uber, Udo Gerlach
      This article presents an experimental and computational study of ignition caused by a low voltage electrical contact arc. The contact arc is a transient electrical discharge which occurs due to movement of electrical contacts, for example, when two energised electrodes are separated. The physical properties of this discharge are significantly different from the more conventional high voltage spark. Its potential to cause ignition is an important consideration in international explosion protection standards. As these standards are based on unreliable empirical methods, a more fundamental investigation is warranted. This study uses a specially designed apparatus and electrical circuit to create the contact arc in a hydrogen–air mixture. The transient development of the resulting flame kernel is observed using Mach–Zehnder interferometry with high spatial and temporal resolution. These experimental results are compared to simulations of a 3-D reactive flow model with detailed chemical kinetics and molecular transport. A quantitative comparison is effected by the generation of synthetic optical phase plots from the simulation output. This comparison showed reasonable correspondence between the simulated and measured flame shape. Ignition delays and thresholds were, however, under-predicted by the model. The comparison was complicated by significant statistical scattering in the experimental results. Additional investigations into the sensitivity of the model showed good robustness to grid size variations, and that inclusion of a simplified consideration of heat transfer through the electrodes produces small differences in flame shape and ignition delay.

      PubDate: 2017-09-07T17:47:35Z
       
  • Effects of the equivalence ratio on turbulent flame–shock
           interactions in a confined space
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Haiqiao Wei, Jianfu Zhao, Lei Zhou, Dongzhi Gao, Zailong Xu
      In this work, the influences of the equivalence ratio on flame front propagation velocity, shock wave velocity and pressure oscillation as well as flame–shock interactions with different combustion phenomena were comprehensively studied experimentally in a newly designed constant volume combustion bomb (CVCB). And a hydrogen–air mixture was chosen as the test fuel. In the CVCB, an orifice plate was used to obtain flame acceleration and promote turbulent flame formation. High-speed Schlieren photography was employed to capture the turbulent flame front and shock wave in the present work. The evolution of the flame and shock wave together with influences of the equivalence ratio on the flame tip velocity, shock wave velocity and pressure oscillation were clearly presented. The results showed that, after the laminar flame passed through the orifice plate, wrinkled turbulent flame gradually formed, and the shock wave ahead of flame front could be seen at a certain condition. The shock wave formation and enhancement process induced by flame acceleration was clearly captured by the Schlieren photography. It was found that the mean turbulent flame tip velocity reached a maximum value at an equivalence ratio of 1.25. In addition, an increase in the initial ambient pressure resulted in an increase of the turbulent flame tip velocity. Forced by the flame–shock/acoustic interactions, the flame would reverse and the backward flame velocity was positively related to that of the forward flame. The forward shock wave showed little differences among different equivalence ratios, while the reflected shock decayed fastest for the fastest flame, and the turbulent flame was pushed back more apparently. And the effect of the equivalence ratio on the pressure oscillation caused by flame acceleration and flame–shock interactions in the end gas region of confined space was determined.

      PubDate: 2017-09-07T17:47:35Z
       
  • Development of a two-part n-heptane oxidation mechanism for two stage
           combustion process in internal combustion engines
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Fadila Maroteaux
      This paper presents an attempt to build a very reduced kinetics mechanism of n-heptane to simulate the two stage ignition process in terms of ignition delay time and in-cylinder pressure profiles over the whole range of engine operations. Starting from the previous 26 reactions and 25 species mechanism, two reduced schemes have been developed, one with 18 reactions and 19 species and the other with 13 reactions and 14 species. The reduction step shows that when the reactions describing the first stage are reduced as in the 18-step model, the accuracy is poor. The second 13-step model, where the reaction path describing the low temperature period has been kept, is more reliable when the window of engine operations is restricted. From this reduction step, a two-part reaction mechanism linked with a temperature criterion has been developed, while maintaining a wide range of engine operating conditions. This mechanism includes a low temperature reaction group and a high temperature reaction group, linked with a transition temperature correlation. Ignition delay times calculated with the two-part model are compared to those from the detailed mechanism. In addition, the comparison of the Indicated Mean Effective Pressure (IMEP) with the results of the previous 26-step mechanism has been done. The results obtained with the present model are in good agreement with the 26-step one. Moreover, this model has a very short computational time and thus could be used in CFD simulations as well as single zone or multi-zone engine models, and also model-based design.

      PubDate: 2017-09-01T22:30:00Z
       
  • Large eddy simulation of explosion deflagrating flames using a dynamic
           wrinkling formulation
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Pedro S. Volpiani, Thomas Schmitt, Olivier Vermorel, Pierre Quillatre, Denis Veynante
      Reliable predictions of flames propagating in a semi-confined environment are vital for safety reasons, once they are representative of accidental explosion configurations. Large eddy simulations of deflagrating flames are carried out using a dynamic flame wrinkling factor model. This model, validated from a posteriori analysis, is able to capture both laminar and turbulent flame regimes. At early stages of the flame development, a laminar flame propagates in a flow essentially at rest and the model parameter is close to zero, corresponding to a unity-wrinkling factor. Transition to turbulence occurs when the flame interacts with the flow motions generated by thermal expansion and obstacles. The model parameter and wrinkling factor take higher values at these stages. Three configurations investigated experimentally by Masri et al. 2012, corresponding to different scenarios of flame acceleration are simulated. The first case (OOBS) is characterized by a long laminar phase. In the second one (BBBS) the flame is the most turbulent and the highest overpressure is observed in the vessel. For the last case (BOOS), the flame front is relaminarized after crossing the first row of obstacles. In all configurations, large eddy simulations (LES) predict the flow dynamics and maximum overpressure with good accuracy.

      PubDate: 2017-09-01T22:30:00Z
       
  • Laser-diagnostic mapping of temperature and soot statistics in a 2-m
           diameter turbulent pool fire
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Sean P. Kearney, Thomas W. Grasser
      We present spatial profiles of temperature and soot-volume-fraction statistics from a sooting, 2-m base diameter turbulent pool fire, burning a 10%-toluene/90%-methanol fuel mixture. Dual-pump coherent anti-Stokes Raman scattering and laser-induced incandescence are utilized for simultaneous point measurements of temperature and soot. The research fuel-blend used here results in a lower soot loading than real transportation fuels, but allows us to apply high-fidelity laser diagnostics for spatially resolved measurements in a fully turbulent, buoyant fire of meter-scale base size. Profiles of mean and rms fluctuations are radially resolved across the fire plume, both within the hydrocarbon-rich vapor-dome region near fuel pool, and higher within the actively burning region of the fire. The spatial evolution of the soot and temperature probability density functions is discussed. Soot fluctuations display significant intermittency across the full extent of the fire plume for the research fuel blend used. Simultaneous, spatially overlapped temperature/soot measurements permit us to obtain estimates of joint statistics that are presented as spatially resolved conditional averages across the fire plume, and in terms of a joint pdf obtained by including measurements from multiple spatial locations. Within the actively burning region of the fire, soot is observed to occupy a limited temperature range between ∼1000 and 2000 K, with peak soot concentration occurring at 1600–1700 K across the full radial extent of the fire plume, despite marked changes in the local temperature pdf across the same spatial extent. A wider range of soot temperatures is observed in the fuel vapor-dome region low in the pool fire, with detectable cold soot persisting into conditionally averaged statistics. The results yield insight into soot temperature across a wide spatial extent of a fully turbulent pool fire of meaningful size, which are valuable for development of soot radiative-emission models and for validation of fire fluid-dynamics codes.

      PubDate: 2017-09-01T22:30:00Z
       
  • Turbulent jet ignition assisted combustion in a rapid compression machine
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): AbdoulAhad Validi, Harold Schock, Farhad Jaberi
      Numerical simulations of turbulent jet ignition (TJI) and combustion in a rapid compression machine (RCM) are conducted by a hybrid Eulerian–Lagrangian large eddy simulation/filtered mass density function (LES/FMDF) computational model. TJI is a novel method for initiating combustion in ultra-lean mixtures and often involves one or several hot combustion product turbulent jets, rapidly propagating from a pre-chamber (PCh) to a main chamber (MCh). An immersed boundary method is developed and used together with LES to handle complex geometries and to decrease the complexity and computational cost of the Monte Carlo (MC) particle operations, while maintaining the high accuracy of the hybrid LES/FMDF model. Analysis of numerical data suggests three main combustion phases in the RCM-TJI: (i) cold fuel jet, (ii) turbulent hot product jet, and (iii) reverse fuel-air/product jet. The effects of various parameters (e.g., the igniter location, mixture composition, and wall heat transfer) on these phases are studied numerically. It is found that the turbulent jet features and the MCh combustion are very much dependent on the PCh ignition details. Igniting the PCh at the lower locations close to the nozzle forces the PCh charge to fully participate in the PCh combustion and prevents the unburned fuel leaking to the MCh. It also leads to longer discharge of the PCh hot products into the MCh with more uniform jet velocity, enhancing the MCh combustion. The results predicted by LES/FMDF are found to be comparable with the available experimental data, both qualitatively and quantitatively.

      PubDate: 2017-09-01T22:30:00Z
       
  • CSP-based chemical kinetics mechanisms simplification strategy for
           non-premixed combustion: An application to hybrid rocket propulsion
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Pietro P. Ciottoli, Riccardo Malpica Galassi, Pasquale E. Lapenna, G. Leccese, D. Bianchi, F. Nasuti, F. Creta, M. Valorani
      A set of simplified chemical kinetics mechanisms for hybrid rocket applications using gaseous oxygen (GOX) and hydroxyl-terminated polybutadiene (HTPB) is proposed. The starting point is a 561-species, 2538-reactions, detailed chemical kinetics mechanism for hydrocarbon combustion. This mechanism is used for predictions of the oxidation of butadiene, the primary HTPB pyrolysis product. A Computational Singular Perturbation (CSP) based simplification strategy for non-premixed combustion is proposed. The simplification algorithm is fed with the steady-solutions of classical flamelet equations, these being representative of the non-premixed nature of the combustion processes characterizing a hybrid rocket combustion chamber. The adopted flamelet steady-state solutions are obtained employing pure butadiene and gaseous oxygen as fuel and oxidizer boundary conditions, respectively, for a range of imposed values of strain rate and background pressure. Three simplified chemical mechanisms, each comprising less than 20 species, are obtained for three different pressure values, 3, 17, and 36 bar, selected in accordance with an experimental test campaign of lab-scale hybrid rocket static firings. Finally, a comprehensive strategy is shown to provide simplified mechanisms capable of reproducing the main flame features in the whole pressure range considered.

      PubDate: 2017-09-01T22:30:00Z
       
  • Experimental study and analysis on the interaction between two slot-burner
           buoyant turbulent diffusion flames at various burner pitches
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Longhua Hu, Lili Huang, Qiang Wang, Kazunori Kuwana
      This paper investigated the interaction of two slot-burner buoyant turbulent diffusion flames at various burner pitches. Experiments were conducted by employing two identical slot burners (length: 142.5 mm; width: 2 mm) using propane as fuel at various fuel exit velocities. Results showed that with an increase in burner pitch, the interaction of the two flames made a transition from merging to non-merging, resulting in a complex non-monotonic evolution of flame height. An analytical model was developed to characterize the critical burner pitch for flame merging, which was found to be proportional to the free flame height, or have a 2/3 power law dependence on the fuel exit velocity. As a result of their interaction, the flame merging point height increased till the two flames separated with the increase in burner pitch. Meanwhile, the flame height was shown to first decrease, then increase and finally approach the free flame height with the increase in burner pitch. A scaling non-dimensional formula was finally proposed, based on the analysis of the change in air entrainment into the flame from the space between the two burners with burner pitch variation. This proposed formula was shown to well correlate the above transitions based on a newly defined non-dimensional heat release rate using an “effective” entrainment perimeter as a characteristic length, which includes the burner width and length as well as the additional flame base “extension” due to the change in burner pitch.

      PubDate: 2017-09-01T22:30:00Z
       
  • Autoignition characteristics of oxygenated gasolines
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Changyoul Lee, Ahfaz Ahmed, Ehson F. Nasir, Jihad Badra, Gautam Kalghatgi, S. Mani Sarathy, Henry Curran, Aamir Farooq
      Gasoline anti-knock quality, defined by the research and motor octane numbers (RON and MON), is important for increasing spark ignition (SI) engine efficiency. Gasoline knock resistance can be increased using a number of blending components. For over two decades, ethanol has become a popular anti-knock blending agent with gasoline fuels due to its production from bio-derived resources. This work explores the oxidation behavior of two oxygenated certification gasoline fuels and the variation of fuel reactivity with molecular composition. Ignition delay times of Haltermann (RON = 91) and Coryton (RON = 97.5) gasolines have been measured in a high-pressure shock tube and in a rapid compression machine at three pressures of 10, 20 and 40 bar, at equivalence ratios of φ = 0.45, 0.9 and 1.8, and in the temperature range of 650–1250 K. The results indicate that the effects of fuel octane number and fuel composition on ignition characteristics are strongest in the intermediate temperature (negative temperature coefficient) region. To simulate the reactivity of these gasolines, three kinds of surrogates, consisting of three, four and eight components, are proposed and compared with the gasoline ignition delay times. It is shown that more complex surrogate mixtures are needed to emulate the reactivity of gasoline with higher octane sensitivity (S = RON–MON). Detailed kinetic analyses are performed to illustrate the dependence of gasoline ignition delay times on fuel composition and, in particular, on ethanol content.

      PubDate: 2017-09-01T22:30:00Z
       
  • A new diagnostic for hydrocarbon fuels using 3.41-µm diode laser
           absorption
    • Abstract: Publication date: December 2017
      Source:Combustion and Flame, Volume 186
      Author(s): Shengkai Wang, Thomas Parise, Sarah E. Johnson, David F. Davidson, Ronald K. Hanson
      We report the development of a novel laser absorption diagnostic for accurate, time-resolved and in situ measurement of various hydrocarbon fuels in combustion systems. This diagnostic method utilized a wavelength-tunable interband cascade laser operated near 3.41 µm, providing improved performance in several aspects over the conventional 3.39-μm He–Ne gas laser diagnostic. First, it enabled a simplified and more compact experimental setup that significantly reduced the measurement complexity. Second, it improved the long-term stability over the 3.39-μm diagnostic by at least a factor of 2, leading to substantially reduced measurement uncertainties. Lastly, the new diagnostic also avoided a cluster of CH4 transitions that coincide with the He–Ne wavelength, and hence minimized CH4 interference in other hydrocarbon measurements. Absorption cross-sections of a variety of hydrocarbons at both 3.39 and 3.41 µm were measured in a high-purity shock tube over 531–1659 K, 0.34–3.1 atm, and reported here as functions of temperature. Example applications of this new diagnostic in shock tube pyrolysis studies of methylcyclohexane, n-heptane and iso-octane are also presented. These studies have yielded an improved value of the overall decomposition rate constant of methylcyclohexane as kd = 3.3 × 1015 exp(−38000 K/T) s− 1 + 28%/−34%, which is valid over 1260–1400 K and near 1.5 atm.

      PubDate: 2017-09-01T22:30:00Z
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
Home (Search)
Subjects A-Z
Publishers A-Z
Customise
APIs
Your IP address: 54.224.13.210
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2016