THERM: Thermodynamic property estimation for gas phase radicals and molecules

Abstract

We have developed a computer code for an IBM PC/XT/AT or compatible which can be used to estimate, edit, or enter thermodynamic property data for gas phase radicals and molecules using Benson's group additivity method. The computer code is called THERM (THermo Estimation for Radicals and Molecules). All group contributions considered for a species are recorded and thermodynamic properties are generated in old NASA polynomial format for compatibility with the CHEMKIN reaction modeling code. In addition, listings are created in a format more convenient for thermodynamic, kinetic, and equilibrium calculations. Polynomial coefficients are valid from 300-5000 K using extrapolation methods based upon the harmonic oscillator model, an exponential function, or the Wilhoit polynomials. Properties for radical and biradical species are calculated by applying bond dissociation increments to a stable parent molecule to reflect loss of H atom. THERM contains a chemical reaction interpreter to calculate thermodynamic property changes for chemical reactions as functions of temperature. These include equilibrium constant, heat release (required heat, AHr), entropy change (ASr), Gibbs free energy change (AG,), and the ratio of forward to reverse Arrhenius A-factors (for elementary reactions). This interpreter can also process CHEMKIN input files. A recalculation procedure is incorporated for rapid updating of a database of chemical species to reflect changes in estimated bond dissociation energies, heats of formation, or other group values. All input and output files are in ASCII so that they can be easily edited, expanded, or updated.

Autoignition behavior of unsaturated hydrocarbons in the low and high temperature regions

“…The incident shock velocity at the endwall was used to calculate the temperature and pressure of the mixtures behind the reflected shock wave using the equilibrium program Gaseq [19]. The thermodynamic data needed for the program of the pentene and hexene isomers were calculated using the THERM program of Ritter and Bozzelli [20], based on group additivity methods developed by Benson [21]. These data are in agreement with estimates in the NIST WebBook [22].…”

Kinetic modeling of gasoline surrogate components and mixtures under engine conditions

“…The thermodynamic properties of all the species included in the mechanism were evaluated using the THERM program developed by Ritter and Bozzelli, implementing Benson's group additivity method [9]. The kinetic model here discussed is available upon request and will be soon available on the LLNL website [14].…”

“…octane) [9][10][11][12][13][14], toluene [15][16] and 1-hexene [17] in a wide range of operating conditions. Data collected in shock tube and rapid compression machine at stoichiometric conditions in air.…”

Chemical Kinetic Modeling Study of the Effects of Oxygenated Hydrocarbons on Soot Emissions from Diesel Engines

“…As in our previous mechanism developments 47 , thermodynamic parameters were estimated using quantum chemistry methods and group additivity [49][50][51] . For most species the enthalpy of formation was computed using CBS-Q methods with geometries optimized at the B3LYP/6-31G9(d,p) level following Bozzelli 52 , and other details of the techniques are described by Glaude et al 47 .…”