An experimental and theoretical study of toluene pyrolysis with tunable synchrotron VUV photoionization and molecular-beam mass spectrometry

An experimental study of toluene pyrolysis (1.24 vol.% toluene in argon) was performed at low pressure (1.33 kPa) in the temperature range of 1200–1800 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species up to m/z = 202 (C₁₆H₁₀), containing many radicals (CH₃, C₃H₃, C₅H₃, C₅H₅, C₇H₅, C₇H₇, C₉H₇, C₁₁H₇ and C₁₃H₉) and isomers, such as C₃H₄ (propyne and allene), C₄H₄ (vinylacetylene and 1,2,3-butatriene), C₅H₅ (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C₆H₄ (3-hexene-1,5-diyne and benzyne), C₆H₆ (benzene and fulvene), C₇H₈ (toluene and 5-methylene-1,3-cyclohexadiene) and so on, were identified from near-threshold measurements of photoionization mass spectra, and the mole fraction profiles of the pyrolysis products were evaluated from measurements of temperature scan. Experimental results indicate that the reaction C₇H₈ → C₇H₇ and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C₇H₈ → C₆H₅ and subsequent reactions gradually become competitive and important with increasing temperature. Furthermore the barriers of the decomposition pathways of toluene and benzyl radical determined by quantum mechanical calculation are in good agreement with the initial formation temperatures of the species. Based on the mole fractions and formation temperatures of the detected pyrolysis species, a simple reaction network is deduced. At relatively high temperatures, H-abstraction is prevalent and the mole fraction of C₂H₂ is so high that many aromatics are formed through the hydrogen-abstraction/C₂H₂-addition (HACA) mechanism. Moreover the reactions of benzyl with toluene/benzyl/phenyl/propargyl radicals to directly produce larger aromatics should play an influential role in PAH formation. Meanwhile the five-member-ring recombination mechanism also plays an indispensable role in the aromatics growth, as cyclopentadienyl radical (C₅H₅) was determined to be a major product of the decomposition of toluene.     

Interior acoustics of a truck cabin with hard and impedance surfaces

Interior acoustics of a truck cabin is determined and the consequences of an attempt, which was performed with acoustic linings in order to improve the interior comfort, are presented. Acoustic field generated from the harmonic vibrations of the cabin floor panel was expressed by the Helmholtz integral equations. Numerical results were obtained by a computer code which was developed in Visual Basic programming language in order to solve the integral equations by using boundary element method. The effects of the linings on the levels and distributions of the sound pressure in the cabin are presented by means of the comparison of the results calculated from two different boundary conditions: hard wall and impedance wall.     

Short term motion analysis of icebergs in linear waves

The need for the analysis of the motion of icebergs in waves is presented and the possible interaction effects between the iceberg and waves as well as its interaction with offshore structures is briefly discussed along with the hydrodynamic aspects involved in the analysis of wave induced motions of icebergs. A combined theoretical and experimental study for the estimation of the first order wave induced motions in surge and heave of a free floating iceberg in a regular wave field is presented. The theoretical model is based on the mathematical formulations of Garrison (1979) and Standing (1979) which employ a three dimensional source distribution technique. The computed model results have been compared with the previous analytical model and good agreement has been found. The computed results are then compared with the measured heave and surge motions of the model icebergs which agree quite well, within the limits of experimental error. The computational and experimental models are not meant to address in detail all the hydrodynamic aspects of wave interaction with a free floating iceberg. Only the oscillatory motions of icebergs have been computed and measured. The results indicate that the surge and heave velocity of model icebergs, with a draft to water depth ratio of less than 0.1 can be greater than 0.8 times the water particle velocity when the iceberg horizontal dimension is less than 0.3 times the wavelength. Additional computational and experimental model studies showed that the surge motion is reduced to less than 0.1 times the particle velocity when the draft to depth ratio is about 0.9 and the horizontal dimensions of the iceberg are increased to 0.5 times the wavelength. The heave motion for the same situation is reduced to about 0.5 times the particle velocity.     

Contour integration on the graphics screen and its application in CADCAM

A method for evaluating contour integrals over arbitrary boundaries normally not expressed by an explicit mathematical function is developed. Neither spline nor other approximation techniques are required in this approach. The computational strategy for implementing the algorithm is presented in detail along with a listing of the developed set of Fortran subroutines. An illustrative example is presented to establish the high degree of accuracy of the method. Applications to several other engineering problems are also discussed.     

A dynamic wear rig for the scanning electron microscope

A pin-on-disk wear rig has been constructed to operate inside the scanning electron microscope to allow direct, high magnification, observation of wear as it occurs. The wear process is recorded on video tape and the variations in normal load and frictional force are measured and recorded using a data-logging system. Experiments using this rig show the formation of sheet- or flake-like debris when high purity copper pins slide on casehardened mild steel disks. The amount of debris produced over the same sliding distance (a measure of the wear rate) is found to be influenced by small variations in the surface roughness of the disks.     

Hot corrosion behavior of NdYbZr2O7 exposed to V2O5 and Na2SO4 + V2O5 molten salts

In order to evaluate the application prospects of NdYbZr₂O₇ as a novel TBC material, NdYbZr₂O₇ ceramic was synthesized via a solid-state reaction sintering method, and its hot corrosion behavior exposed to V₂O₅ and Na₂SO₄ + V₂O₅ molten salts at 900 °C, 1000 °C, and 1100 °C was comparatively investigated. For the V₂O₅ salt, the primary corrosion products were granular (Nd,Yb)VO₄ as well as cube-like m-ZrO₂. The corrosion layer consisted of two distinct layers, one of which was Zr-rich layer and another was V-rich layer. In the case of Na₂SO₄ + V₂O₅, NaVO₃, as an intermediate product, played an important role in dissolving the NdYbZr₂O₇ ceramic. Herein, the (Nd,Yb)VO₄ exhibited a rod/plate-like morphology, which could be attributed to the synergistic effect of low driving force and low nucleation rate. Since the molten salt infiltration rate was superior to the pore filling rate throughout the hot corrosion, the thickness of corrosion layer increased with the rise of temperature. The hot corrosion mechanisms of NdYbZr₂O₇ ceramic in various molten salts were discussed based on the phase diagram, Lewis acid-base rule and chemical thermodynamics. On this basis, the NdYbZr₂O₇ coating was prepared by atmospheric plasma spray (APS) and it exhibits a higher corrosion resistance compared to YSZ coating.     

Research on the rigid-flexible multibody dynamics of concrete placing boom

A method is proposed for rigid-flexible multibody dynamic modeling of concrete placing booms, to improve the calculation efficiency and ensure the accuracy. Concrete placing booms consist of four types of substructures, according to the slender rods and the mechanism features. The transfer matrixes of substructures are derived based on the discrete time transfer matrix method. Then, the manipulator's overall transfer matrix is assembled and used for the numerical calculation. An experiment based on a test rig is performed to validate the proposed method, and a model based on ADAMS (short of MSC.ADAMS) is also established to compare the calculating efficiency of the proposed method.     

Study of a hybrid modular exhaust turbocharging system and its application on an 8-cylinder marine diesel engine

Journal of Mechanical Science and Technology - For turbocharging engines, the structure of the exhaust system directly affects the flow and energy transfer process of the exhaust gas, which has a...     

An experimental and kinetic modeling study of three butene isomers pyrolysis at low pressure

Pyrolysis of three butene isomers (C₄H₈) including 1-butene (1-C₄H₈), 2-butene (2-C₄H₈) and i-butene (iC₄H₈) were studied from 900 to 1900 K at low pressure. Synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry with molecular-beam sampling technique was used for isomeric identification of products and intermediates and also for concentration measurement. Based on the experimental results, a kinetic model consisting of 76 species and 232 reactions was developed to simulate mole fractions of species. The mole fraction profiles of pyrolysis species predicted by the model are in good agreement with the experimental measurements. The decomposition pathways of C₄H₈ are illustrated according to the reaction flux analysis. Our analysis demonstrates that reaction sequences 1-C₄H₈ → aC₃H₅ → aC₃H₄ → pC₃H₄ → C₂H₂, 2-C₄H₈ → saxC₄H₇ → 1,3-C₄H₆ → C₂H₃ → C₂H₂ and iC₄H₈ → iC₄H₇ → aC₃H₄ → pC₃H₄ → C₂H₂ are the major decomposition pathways of 1-butene, 2-butene and i-butene, respectively.