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At least 199 records · Page 11

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NASA NTRS1990

High energy-density liquid rocket fuel performance

A fuel performance database of liquid hydrocarbons and aluminum-hydrocarbon fuels was compiled using engine parametrics from the Space Transportation Engine Program as a baseline. Propellant performance parameters are introduced. General hydrocarbon fuel performance trends are discussed with respect to hydrogen-to-carbon ratio and heat of formation. Aluminum-hydrocarbon fuel performance is discussed with respect to aluminum metal loading. Hydrocarbon and aluminum-hydrocarbon fuel performance is presented with respect to fuel density, specific impulse, and propellant density specific impulse.

Rapp, Douglas C.↗

NASA NTRS1990

High energy-density liquid rocket fuel performance

Rapp, Douglas C.↗

NASA NTRS1992

Lattice parameters of fcc binary alloys using a new semiempirical method

A new method is presented for the calculation of heats of formation, lattice parameters and cohesive energies of binary alloys. The method is applied to some fcc alloys and compared with experimental data, as well as other semiempirical results.

Bozzolo, Guillermo↗

NASA NTRS1992

The effect of H2O gas on volatilities of planet-forming major elements. I - Experimental determination of thermodynamic properties of Ca-, Al-, and Si-hydroxide gas molecules and its application to the solar nebula

The vapor pressures of Ca(OH)2(g), Al(OH)3(g), and Si(OH)4(g) molecules in equilibrium with solid calcium-, aluminum, and silicon-oxides, respectively, were determined, and were used to derive the heats of formation and entropies of these species, which are expected to be abundant under the currently postulated physical conditions in the primordial solar nebula. These data, in conjunction with thermodynamic data from literature, were used to calculate the relative abundances of M, MO(x), and M(OH)n gas species and relative volatilities of Fe, Mg, Si, Ca, and Al for ranges of temperature, total pressure, and H/O abundance ratio corresponding to the plausible ranges of physical conditions in the solar nebula. The results are used to explain how Ca and Al could have evaporated from Ca,Al-rich inclusions in carbonaceous chondrites, while Si, Mg, and Fe condensed onto them during the preaccretion alteration of CAIs.

Hashimoto, Akihiko↗

NASA NTRS1992

Lattice parameters of fcc binary alloys using a new semiempirical method

A new semiempirical method has been developed to predict the concentration dependence of the heats of formation and lattice parameters of binary alloys consistent with equivalent crystal theory. This method accurately predicts the composition dependence of the lattice parameters both qualitatively and quantitatively. A simple formulation is provided of the algorithm for performing defect calculations.

Bozzolo, Guillermo↗

NASA NTRS1992

Determination of parameters of a new method for predicting alloy properties

Recently, a semiempirical method for alloys based on equivalent crystal theory was introduced. The method successfully predicts the concentration dependence of the heat of formation and lattice parameter of binary alloys. A study of the parameters of the method is presented, along with new results for (gamma)Fe-Pd and (gamma)Fe-Ni alloys.

Bozzolo, Guillermo↗

NASA NTRS1992

Computer program for calculating and fitting thermodynamic functions

A computer program is described which (1) calculates thermodynamic functions (heat capacity, enthalpy, entropy, and free energy) for several optional forms of the partition function, (2) fits these functions to empirical equations by means of a least-squares fit, and (3) calculates, as a function of temperture, heats of formation and equilibrium constants. The program provides several methods for calculating ideal gas properties. For monatomic gases, three methods are given which differ in the technique used for truncating the partition function. For diatomic and polyatomic molecules, five methods are given which differ in the corrections to the rigid-rotator harmonic-oscillator approximation. A method for estimating thermodynamic functions for some species is also given.

Mcbride, Bonnie J.↗

NASA NTRS1992

An extensive ab initio study of the structures, vibrational spectra, quadratic force fields, and relative energetics of three isomers of Cl2O2

Quantum mechanical computational methods are employed for an ab initio investigation of: (1) the molecular properties of the lowest isomers of the ClO dimer; and (2) predicted molecular and thermochemical properties. Techniques employed include electron correlation and particularly singles and doubles coupled-cluster (CCSD) theory with or without perturbational estimates of the effects of connected triple excitations. The isomers ClOClO and ClClO2 are found to have higher energies than the ClOOCl isomer, and the theoretical vibrational frequencies of the isomers are well correlated with experimental data. Experimental values of the heat of formation for the isomers are also compared with calculations based on an isodesmic reaction with Cl2O, H2O, and HOOH.

Lee, Timothy J.↗

NASA NTRS1993

Structure and thermochemistry of ClO2 radicals

The structure of ClO2 has been calculated for the X 2A-double prime ground state using unrestricted Hartree-Fock (UHF), unrestricted second-order Moller-Plesset perturbation (UMP2), configuration interaction employing single and double excitation (CISD), and quadratic configuration interaction (QCI) ab initio molecular orbital methods. Calculations using UMP2 and CISD wave functions predict a ClO bond length of 1.728 +/- 0.01 A. The single-configuration-based QCI in the singles and doubles space with perturbation inclusion of triple substitutions, denoted QCISD(T), yield a ClO bond length of 2.205 A. The QCI results are consistent with results of Jensen (1990) who showed that the ClO bond length is 2.181 A using annihilated self-consistent methods (AUMP2). The thermochemistry of ClO2 radical has been calculated using MP2 and QCI methods employing an isodesmic scheme. Our scheme predicts the heat of formation for ClO2 at 0 K to be 24.6 +/- 2 kcal/mol.

Francisco, J. S.↗

NASA NTRS1993

Theoretical characterization of the reaction NH2 + O yields products

The potential energy surface for NH2+O has been characterized using complete active space self-consistent field (CASSCF)/derivative calculations to determine stationary point geometries and frequencies followed by internally contracted configuration interaction (ICCI) calculations to determine the energetics. The calculations predict a NO bond strength of 85.8 kcal/mol for NH2O. The barrier for isomerization of NH2O to trans-HNOH is predicted to be 48.0 kcal/mol and the barriers for H+HNO forming NH2O and NHOH are predicted to be 2.1 and 8.3 kcal/mol, respectively (all corrected for zero-point energy). The computed heats of formation for NH2O and cis- and trans-HNOH are in good agreement with the present results. The barrier for H + HNO yields H2 + NO is computed to be about 0.3 kcal/mol.

Walch, Stephen P.↗

NASA NTRS1993

Coefficients for calculating thermodynamic and transport properties of individual species

Libraries of thermodynamic data and transport properties are given for individual species in the form of least-squares coefficients. Values of C(sup 0)(sub p)(T), H(sup 0)(T), and S(sup 0)(T) are available for 1130 solid, liquid, and gaseous species. Viscosity and thermal conductivity data are given for 155 gases. The original C(sup 0)(sub p)(T) values were fit to a fourth-order polynomial with integration constants for H(sup 0)(T) and S(sup 0)(T). For each species the integration constant for H(sup 0)(T) includes the heat of formation. Transport properties have a different functional form. The temperature range for most of the data is 300 to 5000 K, although some of the newer thermodynamic data have a range of 200 to 6000 K. Because the species are mainly possible products of reaction, the data are useful for chemical equilibrium and kinetics computer codes. Much of the data has been distributed for several years with the NASA Lewis equilibrium program CET89. The thermodynamic properties of the reference elements were updated along with about 175 species that involve the elements carbon, hydrogen, oxygen, and nitrogen. These sets of data will be distributed with the NASA Lewis personal computer program for calculating chemical equilibria, CETPC.

Mcbride, Bonnie J.↗

NASA NTRS1995

Analysis of the Defect Structure of B2 Feal Alloys

The Bozzolo, Ferrante and Smith (BFS) method for alloys is applied to the study of the defect structure of B2 FeAI alloys. First-principles Linear Muffin Tin Orbital calculations are used to determine the input parameters to the BFS method used in this work. The calculations successfully determine the phase field of the B2 structure, as well as the dependence with composition of the lattice parameter. Finally, the method is used to perform 'static' simulations where instead of determining the ground state configuration of the alloy with a certain concentration of vacancies, a large number of candidate ordered structures are studied and compared, in order to determine not only the lowest energy configurations but other possible metastable states as well. The results provide a description of the defect structure consistent with available experimental data. The simplicity of the BFS method also allows for a simple explanation of some of the essential features found in the concentration dependence of the heat of formation, lattice parameter and the defect structure.

Bozzolo, Guillermo↗

NASA NTRS1995

Bulk Properties of Ni3Al(gamma') With Cu and Au Additions

The BFS method for alloys is applied to the study of 200 alloys obtained from adding Cu and Au impurities to a Ni3Al matrix. We analyze the trends in the bulk properties of these alloys (heat of formation, lattice parameter, and bulk modulus) and detect specific alloy compositions for which these quantities have particular values. A detailed analysis of the atomic interactions that lead to the preferred ordering patterns is presented.

Bozzolo, Guillermo↗

NASA NTRS1995

Characterization of the Minimum Energy Path for the Reaction of Singlet Methylene with N2: The Role of Singlet Methylene in Prompt NO

We report calculations of the minimum energy pathways connecting CH2 + N2 to diazomethane and diazirine, for the rearrangement of diazirine to diazomethane, for the dissociation of diazirine to HCN2+H, and of diazomethane to CH2N+N. The calculations use Complete Active Space Self-Consistent Field (CASSCF) derivative methods to characterize the stationary points and Internally Contracted Configuration Interaction (ICCI) to determine the energetics. The calculations suggest a potential new source of prompt NO from the reaction CH2 with N2 to give diazirine, and subsequent reaction of diazirine with hydrogen abstracters to form doublet HCN2, which leads to HCN+N(S-4) on the previously studied CH+N2 surface. The calculations also predict accurate 0 K heats of formation of 77.7 kcal/mol and 68.0 kcal/mol for diazirine and diazomethane, respectively.

Walch, Stephen P.↗

NASA NTRS1995

Characterization of the Minimum Energy Path for the Reaction of Singlet Methylene with N2: The Role of Singlet Methylene in Prompt NO

We report calculations of the minimum energy pathways connecting (1)CH2+N2 to diazomethane and diazirine, for the rearrangement of diazirine to diazomethane, for the dissociation of diazirine to HCN2+H, and of diazomethane to CH2N+N. The calculations use complete active space self-consistent field (CASSCF) derivative methods to characterize the stationary points and internally contracted configuration interaction (ICCI) to determine the energetics. The calculations suggest a potential new source of prompt NO from the reaction of (1)CH2 with N2 to give diazirine, and subsequent reaction of diazirine with hydrogen abstracters to form doublet HCN2, which leads to HCN+N(S-4) on the previously studied CH+N2 Surface. The calculations also predict accurate 0 K heats of formation of 77.7 kcal/mol and 68.0 kcal/mol for diazirine and diazomethane, respectively.

Walch, Stephen P.↗

NASA NTRS2000

Thermophysics Characterization of Kerosene Combustion

A one-formula surrogate fuel formulation and its quasi-global combustion kinetics model are developed to support the design of injectors and thrust chambers of kerosene-fueled rocket engines. This surrogate fuel model depicts a fuel blend that properly represents the general physical and chemical properties of kerosene. The accompanying gaseous-phase thermodynamics of the surrogate fuel is anchored with the heat of formation of kerosene and verified by comparing a series of one-dimensional rocket thrust chamber calculations. The quasi-global combustion kinetics model consists of several global steps for parent fuel decomposition, soot formation, and soot oxidation, and a detailed wet-CO mechanism. The final thermophysics formulations are incorporated with a computational fluid dynamics model for prediction of the combustor efficiency of an uni-element, tri-propellant combustor and the radiation of a kerosene-fueled thruster plume. The model predictions agreed reasonably well with those of the tests.

Wang, Ten-See↗

NASA NTRS1994

Achieving Chemical Accuracy with Coupled-Cluster Theory

Due to formal and computational advances in coupled-cluster theory over the past few years, it is now possible to obtain very accurate molecular geometries, vibrational frequencies, heats of formation, binding energies, and vertical electronic excitation energies. The present monograph reviews the advances that have lead to the current state-of-the art, and also summarizes selected examples from the published literature.

Lee, Timothy J.↗

NASA NTRS1999

Fourier Transform Ultraviolet Spectroscopy of the A Pi-2(3/2) Direct Current X Pi-2(3/2) Transition of BrO

The first spectra of the A (2)Pi(sub 3/2) from X (2)Pi(sub 3/2) electronic transition of BrO using Fourier transform ultraviolet spectroscopy are obtained. Broadband vibrational spectra acquired at 298 +/- 2 K and 228 +/- 5 K, as well as high-resolution rotational spectra of the A from X 7,0 and 12,0 vibrational bands are presented. Wavenumber positions for the spectra are obtained with high accuracy, and cross section assignments are made, incorporating the existing literature. With 35 cm(exp -1) (0.40 nm) resolution the absolute cross section at the peak of the 7,0 band is determined to be (1.58 +/- 0.12) x 10(exp -17) sq cm/molecule at 298 +/- 2 K and (1.97 +/- 0.15) x 10(exp -17) sq cm/molecule at 228 +/- 5 K. BrO dissociation energies are determined with a graphical Birge-Sponer technique, using Le Roy-Bernstein theory to place an upper limit on the extrapolation. From the ground-state dissociation energy, D(sub o)" = 231.0 +/- 1.7 kJ/mol, the heat of formation of BrO(g) is calculated, del(sub f)H(0 K) = 133.7 +/- 1.7 kJ/mol and del(sub f)H(298.15 K) = 126.2 +/- 1.7 kJ/mol. Cross sections for the high-resolution 7,0 and 12,0 rotational peaks are the first to be reported. The band structures are modeled, and improved band origins, rotational constants, centrifugal distortion constants, and linewidths are determined. In particular, J-dependent linewidths and lifetimes are observed for the both the 7,0 and 12,0 bands.

Wilmouth, David M.↗