Sinéad M. Burke

Critical Evaluation of Thermochemical Properties of C1–C4 Species: Updated Group-Contributions to Estimate Thermochemical Properties

A review of literature on enthalpies of formation and molar entropies for alkanes, alkenes, alcohols, hydroperoxides, and their associated radicals has been compiled and critically evaluated. By comparing literature values, the overall uncertainty in thermochemical properties of small hydrocarbons and oxygenated hydrocarbons can be highlighted. In general, there is good agreement between heat of formation values in the literature for stable species; however, there is greater uncertainty in the values for radical species and for molar entropy values. Updated values for a group-additivity method for the estimation of thermochemical properties based on the evaluated literature data are proposed. The new values can be used to estimate thermochemical data for larger, combustion-relevant species for which no calculations or measurements currently exist, with increased confidence.

LAMINAR FLAME SPEED MEASUREMENTS AND MODELING OF ALKANE BLENDS AT ELEVATED PRESSURES WITH VARIOUS DILUENTS

Laminar flame speeds at elevated pressure for methane-based fuel blends are important for refining the chemical kinetics that are relevant at engine conditions. The present paper builds on earlier measurements and modeling by the authors by extending the validity of a chemical kinetics mechanism to laminar flame speed measurements obtained in mixtures containing significant levels of helium. Such mixtures increase the stability of the experimental flames at elevated pressures and extend the range of laminar flame speeds. Two experimental techniques were utilized, namely a Bunsen burner method and an expanding spherical flame method. Pressures up to 10 atm were studied, and the mixtures ranged from pure methane to binary blends of CH4 /C2 H6 and CH4 /C3 H8 . In the Bunsen flames, the data include elevated initial temperatures up to 650 K. There is generally good agreement between model and experiment, although some discrepancies still exist with respect to equivalence ratio for certain cases. A significant result of the present study is that the effect of mixture composition on flame speed is well captured by the mechanism over the extreme ranges of initial pressure and temperature covered herein. Similarly, the mechanism does an excellent job at modeling the effect of initial temperature for methane-based mixtures up to at least 650 K.Copyright

Laminar Flame Speeds of Hydrocarbons with Helium Dilution at Raised Pressures and Temperatures

Difficulties with flame stability arise when hydrocarbon fuels are burned with air at elevated pressures. The use of helium dilution abates these instabilities to allow the measurement of flame speeds at these elevated pressures. This study inspects the effects of said helium dilution at elevated temperatures and pressures to construct a reliable database for hydrocarbon mixtures at these conditions and to validate a chemical kinetics model. Seven different fuel and oxidizer mixtures were studied at 5 atm and 473 K including pure methane and both 80/20 and 60/40 blends of each methane/propane and methane/ethane. The model accurately predicts the flame speed data at each condition with high accuracy. Furthermore, the Lewis numbers and Markstein lengths explain the stable flames seen in this study.