Comprehensive mechanisms for combustion chemistry: An experimental and numerical study with emphasis on applied sensitivity analysis

This research program is an integrated effort to determine the reaction mechanisms responsible for the oxidation of small molecule hydrocarbon structures under conditions representative of combustion environments. The experimental aspects of the work are conducted in an atmospheric pressure flow reactor (APFR) as well as in a new variable pressure flow reactor (VPFR) facility which extends the ranges of parameters available in the APFR, particularly the pressure, (1--15 atm.), the temperature (600 K to 1200 K), and the observation time (10 to 5000 milli-seconds). Gas sampling of stable reactant, intermediate, and product species concentrations provide substantial definition of not only the phenomenology of reaction mechanisms, but a much more constrained set of pure kinetic information than can be derived in flames, or shock tubes. Analytical techniques used for detecting hydrocarbons and carbon oxides include gas chromatography, gas chromatography/mass spectrometry for off-time analyses. Non-dispersive infrared and Fourier transform. Infrared methods are utilized for continuous on-line sample detection of light hydrocarbons, carbon oxides, and oxygenated species. The modeling aspects of the program emphasize the use of hierarchical mechanistic construction along with path and elemental gradient sensitivity analyses in developing detailed kinetic mechanisms. Modeling using a well defined and validated mechanism for the CO/H{sub 2}/Oxidant systems and perturbations of experimental oxidations by small amounts of additives are also used to derive absolute reaction rates and to investigate the compatibility of elementary kinetic rate information

Fundamental and semi-global kinetic mechanisms of hydrocarbon combustion. Annual report, October 1, 1977--September 30, 1978

Aimed at understanding practical combustion environments, present modeling efforts have been hampered by difficulties related to coupling combustion chemistry to the complex fluid mechanics present. In an attempt to circumvent such difficulties the present research program is aimed at the development of simplified chemical kinetic models (usually termed global models) to represent the combustion chemistry. Initially aimed at simple hydrocarbon fuels the program is progressing to studies of more complex aliphatics as well as important alternative fuels. The objective of this research is multifold: (a) to determine mechanistic oxidation routes of hydrocarbons derived from crudes and alternate sources, so that efficient and environmentally clean power plants based on internal and external combustion processes can be designed; (b) to develop and validate actual simplified (global) reaction rates for these hydrocarbons so that these power plants can be modelled; and (c) to develop an understanding of particulate (soot) formation to permit the rapid and successful introduction of the inexpensive, heavy, highly aromatic fuels. Studies of paraffin, olefin and alcohol hydrocarbons are reviewed. Appropriate global models are presented and compared with experimental data. The results clearly demonstrate that the turbulent flow reactor facility can be used to develop accurate global models for a variety of important fuels

Inhibition of moist carbon monoxide oxidation by trace amounts of hydrocarbons

The moist carbon monoxide oxidation reaction perturbed by small quantities of hydrocarbons is studied over the temperature range 1026--1140 K at 1 atm to yield information on the reactions of OH, H, and O radicals with hydrocarbons (RH) and on general mechanistic inhibition behavior. The inhibiting action of hydrocarbons below the second explosion limit of Co/H{sub 2}O/O{sub 2} mixtures is used for obtaining rate parameters for RH + OH in the case of methane and propene. Considering all the hydrocarbons studied, the general ranking of effectiveness as an inhibitor was found to follow the order: propene > propane > methane > ethane > ethene > acetylene. In fact, acetylene was observed to always promote the oxidation of moist CO, thus emphasizing the importance of O-atom radical attack rather than OH attack on acetylene. The kinetics of these mixtures are shown to complement mechanistic studies on RH/O{sub 2} mixtures for the development and validation of hierarchical hydrocarbon oxidation reaction mechanisms

Comprehensive mechanisms for combustion chemistry: An experimental and numerical study with emphasis on applied sensitivity analysis

Over the last three years, this program has made significant progress on a number of problems: development of a data base for oxidation of the CO/H[sub 2]/O[sub 2] system; development and refinement of a comprehensive kinetic mechanism for the CO/H[sub 2]/O[sub 2] system; additional experiments on formaldehyde oxidation in the, comprehensive mechanistic studies inclusive of flow reactor results and literature results from static reactors, shock tubes, and flames, and identification of elementary reactions needing further study; mechanistic study of previously acquired APFR flow reactor data on ethanol oxidation, including an estimation of the branching ratios for C[sub 2]H[sub 5]0H + X, X= OH,H and identification of elementary reactions needing additional study; completion and mechanistic evaluation of the first insitu optical diapostic measurements of OH in the APFR; determinations of uni-molecular decomposition rate for 1,3,5-Trioxane at 700 to 800 K; seeded perturbation experiments on moist CO oxidation in flow reactors as a means to determine elementary rate constants for specific reactions; determination of elementary rates for CH[sub 4] + OH [yields] CH[sub 3] + H[sub 2]0 at 1026 and 1140 K, and C[sub 3]H[sub 6] + OH [yields] products at 1020 K; First experimental studies of the H[sub 2]/O[sub 2] reaction system in the VPFR at conditions between the extended second and third explosion limits

A modelling study of the combustion of n-heptane and iso-octane in a high pressure turbulent flow reactor

The primary reference fuels n-heptane and iso-octane and their mixtures are used as a measure of the tendency of a given automotive fuel to cause knocking or pre-ignition in an internal combustion engine. Consequently, many experimental studies have been performed on these hydrocarbons in an attempt to better understand their oxidation. Shock tube studies at high temperature and pressure have been performed. Low temperature studies, in which species concentration profiles of primary, intermediate and final products, have been carried out using jet stirred flow reactors. In addition, experiments have been performed in CFR engines and fundamental features of n-heptane autoignition have been observed using a rapid compression machine. A detailed chemical kinetic reaction mechanism is employed here to study the oxidation of both fuels. Computed results are compared with experimental data obtained in the High Pressure Turbulent Flow Reactor at Princeton University

A wide-ranging kinetic modeling study of methyl butanoate combustion

International audienceA detailed chemical kinetic model has been used to study methyl butanoate (a model compound for biodiesel fuels) oxidation over a wide range of conditions. New experimental results obtained in a jet stirred reactor (JSR) at 0.101 MPa, Φ = 1.13 and 800 < T (K) < 1350 were obtained and used to test and modify an earlier model. In addition, new experimental data generated in an opposed-flow diffusion flame at 0.101 MPa and in the Princeton variable pressure flow reactor (VPFR) at 1.266 MPa, 0.35 < Φ < 1.5 and 500 < T (K) < 900 are presented and compared against the revised model. The numerical model consists of 295 chemical species and 1498 chemical reactions and gives a good description of the data. Experimentally, the oxidation of methyl butanoate shows very little low temperature and negative temperature coefficient behaviour, with hot ignition occurring at about 800 K. Modeling results show similar diminished low temperature oxidation character, but reasonably reproduce hot ignition behaviour found in the VPFR. At higher temperature conditions, the model well describes the intermediate species found in the jet stirred reactor and in opposed flow diffusion flame experiments