Adiabatic Peak Research Articles

Effect of Initial Temperature and Pressure on the Explosion Characteristics and Intermediate Reaction Products of Formic Acid Mixtures: A Theoretical Study

Formic acid is a promising candidate fuel that can be produced by reacting renewable hydrogen with carbon dioxide. However, the burning safety characteristics of formic acid–air mixtures have not been fully studied. This paper presents an extensive theoretical study of the adiabatic explosion pressure of formic acid–air premixed laminar flames at various initial conditions (composition of formic acid: 17–38% volume; initial pressure: 0.1–1.5 bar; initial temperature: 333–500 K), using the GASEQ software package. GASEQ software calculates chemical equilibria based on ideal gas behavior and is based on the hypothesis of adiabatic expansion inside a closed containment that allows ideal expansion. The influence of the initial conditions (pressure, temperature, and concentration) of formic acid–air mixtures on the adiabatic explosion pressures, maximum flame temperature, and peak concentrations of the main reaction intermediates is investigated and discussed. It is found that the adiabatic peak explosion pressure (calculated equilibrium pressure) of the studied concentrations decreases with increasing initial temperature and increases linearly with increasing initial pressure.

Smart-Factory: Optimization and Process Control of Composite Centrifuged Pipes

Process optimization strategies and intelligent control algorithms for an industrial centrifugal pipe production are presented. The chemo-rheological and thermo-kinetic features of the polymerization of unsaturated polyester based composites are analyzed by means of a mathematical model that uses the heat transfer and generation properties of polymerizable systems. The evolution of the system temperature, viscosity and degree of cure profiles in a composite centrifuged pipe wall have been identified and mathematically described. The temperature profiles were calculated according to an appropriate kinetic and heat transfer modeling and then the corresponding viscosity profiles were evaluated. The viscosity and kinetic parameters to use in the model were measured in calorimetric and rheological tests. A commercial polyester system, which is used for centrifugal forming, has been catalyzed with two different types of peroxide (Methyl-Ethyl-Ketone and Acetyl-Acetone peroxides) and characterized by Differential Scanning Calorimetry (DSC) and adiabatic peak temperature measurements (gel time tests). The problem of incomplete cure in sections of the pipe wall has been discussed with respect to the processing conditions and creep behavior. Experimentally verification of thermal theoretical modeling and creep tests have been carried out on a system catalyzed with AA peroxide and processed in two different ways. The thermo-kinetic process modeling and control adequately predicts the thermal behavior at the internal surface of pipes that has been used to optimize by simulation of two different centrifugal pipe processing thermal cycles.

Spectroscopic and thermochemical properties of the c-C6H7 radical: A high-level theoretical study

The electronic ground state (X(2)B(1)) of the cyclohexadienyl radical (c-C(6)H(7)) has been studied by explicitly correlated coupled cluster theory at the RCCSD(T)-F12x (x = a, b) level, partly in combination with the double-hybrid density functional method B2PLYP. An accurate equilibrium structure has been established and the ground-state rotational constants are predicted to be A(0) = 5347.3 MHz, B(0) = 5249.7 MHz, and C(0) = 2692.5 MHz. The calculated vibrational wavenumbers agree well with the recent p-H(2) matrix IR data [M. Bahou, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012)] and several predictions have been made. A low value of 6.803 ± 0.005 eV is predicted for the adiabatic ionization energy of c-C(6)H(7). Owing to a moderately large change in the equilibrium structure upon ionization, the first band of the photoelectron spectrum is dominated by the adiabatic peak (100%) and only the peaks corresponding to excitation of the two lowest totally symmetric vibrations (ν(12) and ν(11)) by one vibrational quantum have relative intensities of more than 15%. The C(6)H(6)-H dissociation energy is calculated to be D(0) = 85.7 kJ mol(-1), with an estimated error of ~2 kJ mol(-1).

Calculated photoelectron spectra of isotopomers of the propargyl radical (H 2C 3H): An explicitly correlated coupled cluster study

Explicitly correlated coupled cluster theory at the (U)CCSD(T∗)-F12a level has been employed to study the vibrational structure of the first two bands of the low-temperature photoelectron spectra of four different isotopomers of the propargyl radical with C 2v symmetry (H 2C 3H, H 2C 3D, D 2C 3H, and D 2C 3D). A five-dimensional anharmonic model is employed to calculate the peak positions and relative intensities. While the first band of the PE spectra of all four isotopomers is dominated by the adiabatic peak, the second band shows a progression in the pseudoantisymmetric CC stretching vibration v 3 with relative intensities of 100:68:23:5:1 for n = 0–4 in the case of the most abundant isotopomer.

A detailed analysis of vibrational excitations in x-ray photoelectron spectra of adsorbed small hydrocarbons

The vibrational fine structure of x-ray photoelectron (XP) spectra of a number of different small hydrocarbon molecules and reaction intermediates adsorbed on Pt(111) and Ni(111) has been investigated in detail. The data for methyl, methylidyne, acetylene, and ethylene can consistently be analyzed within the linear coupling model. The S factor, i.e., the intensity ratio of the first vibrationally excited to the adiabatic transition, is obtained to be 0.17+/-0.02 per C-H bond; for the deuterated species a value of 0.23+/-0.02 is obtained. Therefore, the vibrational fine structure can be used for fingerprinting in the analysis of XP spectra and for identifying unknown reaction intermediates. From the data, Deltar, the change of the minimum in the potential energy curve upon core ionization, is calculated within the linear coupling model using a first order correction. For all adsorbates, including the deuterated ones, a value of Deltar=0.060+/-0.004 A is obtained. Furthermore, from the binding energy of the adiabatic peak and from the energy of the vibrational excitation in the ionic final state some information on the adsorbate/substrate bond and the adsorption site can be derived.

Theoretical investigations of free radicals and negative molecular ions and their calculated photoelectron spectra

Abstract Large-scale coupled cluster or coupled electron pair calculations have been carried out for the radicals H2CCCH, CF3 and CCl2F, the anions SiC4− and Si2C5− as well as the corresponding (N−1) electron systems. Accurate equilibrium structures are established in all cases. For the adiabatic ionization potential (IPad) of CF3, the calculations strongly favour the higher experimental value (9.05±0.01 eV). The photoelectron (PE) spectrum of CCl2F is predicted to have a very complex vibrational structure; IPad (CCl2F) is predicted to be 8.22 eV. The PE spectrum of SiC4− shows some excitation in the ν4 and ν1 stretching vibrational modes and the PE spectrum of Si2C5− is dominated by the adiabatic peak.

Franck–Condon breakdown in core-level photoelectron spectroscopy of chemisorbed CO

The photon energy dependence of the vibrational fine structure in the C1s and O1s X-ray photoelectron main lines of chemisorbed CO on Ni(100) and Ru(0001) has been measured from 6 to 150 eV above the core-level thresholds. Significant deviations from the behavior in gas-phase CO are found. A strong dominance of the adiabatic peak towards threshold is found for the C1s, but not the O1s, lines. In the C1s lines, we observe a broad maximum of vibrational excitation 5 eV above the shape resonance. At high photon energies, Franck–Condon behavior is observed in both the C1s and O1s lines. This behavior is discussed in terms of the adsorbate electronic structure and the dynamic metallic screening upon core ionization.

Coupled cluster calculations for three low-lying doublet states of linear C 10−

Making use of a large basis set of 270 contracted Gaussian-type orbitals partially restricted coupled-cluster calculations including connected triple substitutions (RCCSD(T)) have been carried out for the ground state X̃ 2Π u and two low-lying excited doublet states ( 2Σ g + and 2Π g) of linear C 10 −. The calculated T e value for the 2Π g state amounts to 10 890 cm −1, in close agreement with the T o value of 10 338 cm −1 obtained by absorption spectroscopy in a neon matrix. The observed peaks at 12 330 and 12 430 cm −1 are assigned to the 2 0 1 and 1 0 1 transitions. For the 2Σ g + state, we predict a T e value of 9 951 cm −1. Besides the adiabatic peak, the 2 0 1 transition shows up strongest in the 2Σ g +←X̃ 2Π u band.

Coupled cluster calculations for linear [formula omitted] and [formula omitted

Large-scale open-shell coupled cluster calculations have been carried out for the two lowest 2 Π states of C 8 − and the electronic ground state of linear C 8. The calculated spectrum of the 2Π u ← X ̃ 2Π g transition is in good agreement with the recent neon matrix absorption spectrum of Freivogel, Fulara, Jacobi and Maier. The calculated adiabatic electron affinity of C 8 is 4.348 eV, in close agreement with the experimental value of 4.379 ± 0.006 eV. The 4.66 eV photoelectron spectrum of C 8 − is dominated by the adiabatic peak; the 1 0 1 and 3 0 1 transitions have relative intensities of 24% and 13%, respectively.

Impact-parameter dependent L-K vacancy-transfer in collisions of Ni 23+ with Ge solid targets

Using a particle-photon coincidence technique, we have measured the influence of the solid target preparation and thickness on the target K-vacancy production probability ( P K( b)) in collisions of 3.6 MeV/u Ni 23+ with Ge. The probabilities were measured as a function of the impact parameter b which is calculated from the projectile scattering angle using a screened Bohr-type potential. For target thicknesses varying by more than a factor of 100, no change in the shape of the P K( b) curve was found. Even the data obtained with implanted Ge targets (≈ 1 × 10 16atoms cm −2), used for the first time in an L-K vacancy-transfer experiment, showed the typical solid target behaviour with the adiabatic peak being shifted towards smaller impact parameters.

A theoretical investigation of four electronic states of C 6− and the ground state of linear C 6

Large-scale open-shell coupled cluster calculations have been carried out for the four lowest doublet states of C 6 − and the ground state of linear C 6. They strongly support the assignment of the peaks at 607.7 and 586.5 nm observed in neon matrix isolation experiments to the 0 0 0 and 3 0 1 transitions within the electronic band C ̃ 2Π g ← X ̃ 2Π u of C 6 −. The vibrational structure of the photoelectron spectrum of C 6 − has been calculated; the 1 0 1 transition is calculated to have 42% intensity with respect to the adiabatic peak. Some misassignments of the experimental threshold photodetachment and autodetachment spectra are corrected. Excellent agreement with experiment is obtained for the electron affinity of linear C 6.

X-ray photoelectron diffraction determination of the molecular orientation of CO and methoxy adsorbed on Cu(110)

X-ray photoelectron diffraction measurements using A1 Kα radiation have been made of CO and CH 3O (methoxy) adsorbed on Cu(110). The CO species is found to have its axis perpendicular to the surface to within 10°. The angular dependence of the well-known XPS satellites seen from CO adsorbed on copper surfaces is found to be dominated by the same photoelectron diffraction process as for the main adiabatic peak. The methoxy overlayer studied gave rise to a streaked (4 × 2) LEED pattern at a coverage of 0.25 ± 0.05 monolayers. The possible influence of first order as well as zero order diffraction processes in determining the photoelectron diffraction from methoxy has been investigated, but the results are best described by a structure involving two different tilted species, one tilted 18 ± 3° in [1 1 0], the other tilted 40 ± 5° in [001]. A possible model for this adsorption structure is proposed.

Impact parameter dependence ofK-shell excitation probabilities in Ar ? Ar-collisions

The impact parameter (b) dependence of theK-shell excitation probabilities (P K (b)) in the Ar on Ar collision system at 4.5, 8, 12 and 20 MeV impact energy have been measured over a wideb range (from the kinematik peak to far outside the adiabatic peak) for different projectile charge states. In agreement with the data of Lutz et al. and Nolte et al. a very strong increase ofP K (b) towards very smallb values (corresponding to scattering angles up to 40°) has been observed. From the measuredb and projectile charge state dependences it has been derived that for the systems investigated here the 2pπ-2pσ rotational coupling mechanism gives the dominant contribution to theK-shell excitation at very smallb (kinematic peak regime) as well as at very largeb (adiabatic peak regime). The analysis of the data indicates that in disagreement with the general assumption of ab independent 2pπ vacancy probability P2pπ , the probability P2pπ increases towards smallerb. At the high projectile energy the data confirm the results of Nolte et al. of a large dynamically produced probability P 2 and of strong contributions of direct 2pσ and 1sσ excitation to the measuredP K (b) at small impact parameters.

Experimental Investigation of a New Concept of Fuel Prevaporization

The established emission standards for aircraft engines require the development of low emission combustors which incorporate new concepts of fuel prevaporization and pre-mixing systems. At MTU-Muenchen a fuel injection system was designed which greatly suppresses droplet combustion and avoids burning at stoichiometric air fuel ratios. Thereby the large quantities of NO produced at adiabatic peak temperatures are omitted and soot formation as a result of low velocity droplet combustion is avoided. Tests with a combustor incorporating the fuel injection system yielded high combustion efficiencies, improved combustor outlet temperature distributions and low pollutant emissions. Comparing the measured emission indices for CO, NO, and unburned HC with values required for civil aircraft engines showed a promising development potential of achieving the standards.