Publications (7)0 Total impact
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ABSTRACT: Chemical kinetic modeling of hydrocarbon ignition is discussed with reference to a range of experimental configurations, including shock tubes, detonations, pulse combustors, static reactors, stirred reactors and internal combustion engines. Important conditions of temperature, pressure or other factors are examined to determine the main chemical reaction sequences responsible for chain branching and ignition, and kinetic factors which can alter the rate of ignition are identified. Hydrocarbon ignition usually involves complex interactions between physical and chemical factors, and it therefore is a suitable and often productive subject for computer simulations. In most of the studies to be discussed below, the focus of the attention is placed on the chemical features of the system. The other physical parts of each application are generally included in the form of initial or boundary conditions to the chemical kinetic parts of the problem, as appropriate for each type of application being addressed.
08/1995
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ABSTRACT: Autoignition of the five distinct isomers of hexane is studied experimentally under motored engine conditions and computationally using a detailed chemical kinetic reaction mechanism. Computed and experimental results are compared and used to help understand the chemical factors leading to engine knock in spark-ignited engines and the molecular structure factors contributing to octane rating for hydrocarbon fuels. The kinetic model reproduces observed variations in critical compression ratio with fuel structure, and it also provides intermediate and final product species concentrations in very dose agreement with observed results. In addition, the computed results provide insights into the kinetic origins of fuel octane sensitive.
05/1995;
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ABSTRACT: 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.
04/1995
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ABSTRACT: A detailed chemical kinetic reaction mechanism is used to study the oxidation of n-heptane under several classes of conditions. Experimental results from ignition behind reflected shock waves and in a rapid compression machine were used to develop and validate the reaction mechanism at relatively high temperatures, while data from a continuously stirred tank reactor (cstr) were used to refine the low temperature portions of the reaction mechanism. In addition to the detailed kinetic modeling, a global or lumped kinetic mechanism was used to study the same experimental results. The lumped model was able to identify key reactions and reaction paths that were most sensitive in each experimental regime and provide important guidance for the detailed modeling effort. In each set of experiments, a region of negative temperature coefficient (NTC) was observed. Variation in pressure from 5 to 40 bars were found to change the temperature range over which the NTC region occurred. Both the lumped and detailed kinetic models reproduced the measured results in each type of experiments, including the features of the NTC region, and the specific elementary reactions and reaction paths responsible for this behavior were identified and rate expressions for these reactions were determined.
04/1995
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ABSTRACT: A detailed chemical kinetic model has been developed that accurately describes pyrolysis, ignition and oxidation of many small hydrocarbon fuels over a wide range of experimental conditions. Fuels include carbon monoxide and hydrogen methane, and other alkane species up to n-butane, ethylene, propene, acetylene, and oxygenated species such as methanol, acetaldehyde, and ethanol. Formation of some larger intermediate and product species including benzene, butadiene, large olefins, and cyclopentadiene has been treated in a semiempirical manner. The reaction mechanism has been tested for conditions that do not involve transport and diffusional processes, including plug flow and stirred reactors, batch reactors and shock tubes. The present kinetic model and its validation differ from previous comprehensive detailed reaction mechanisms in two important ways. First, in addition to conventional combustion data, experiments more commonly associated with chemical engineering problems such as oxidative coupling, oxidative pyrolysis and steam cracking are use to test the reaction mechanisms, making it even more general than previous models. In addition, H-atom abstraction and some other reaction rates, even for the smaller C[sub 2], C[sub 3], and C[sub 4] species, are treated using approximations that facilitate future extensions to larger fuels in a convenient manner. The construction of the reaction mechanisms and selected comparisons with experimental data are described that illustrate the generality of the model.
10/1994
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ABSTRACT: A detailed chemical kinetic mechanism has been developed and used to study the oxidation of iso-octane in a jet-stirred reactor, flow reactors, shock tubes and in a motored engine. Over the series of experiments investigated, the initial pressure ranged from 1 to 45 atm, the temperature from 550 K to 1700 K, the equivalence ratio from 0.3 to 1.5, with nitrogen-argon dilution from 70% to 99%. This range of physical conditions, together with the measurements of ignition delay time and concentrations, provide a broad-ranging test of the chemical kinetic mechanism. This mechanism was based on our previous modeling of alkane combustion and, in particular, on our study of the oxidation of n-heptane. Experimental results of ignition behind reflected shock waves were used to develop and validate the predictive capability of the reaction mechanism at both low and high temperatures. Moreover, species’ concentrations from flow reactors and a jet-stirred reactor were used to help complement and refine the low and intermediate temperature portions of the reaction mechanism, leading to good predictions of intermediate products in most cases. In addition, a sensitivity analysis was performed for each of the combustion environments in an attempt to identify the most important reactions under the relevant conditions of study.
Combustion and Flame.
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ABSTRACT: A detailed chemical kinetic mechanism has been developed and used to study the oxidation of n-heptane in flow reactors, shock tubes, and rapid compression machines. Over the series of experiments numerically investigated, the initial pressure ranged from 1–42 atm, the temperature from 550–1700 K, the equivalence ratio from 0.3–1.5, and nitrogen-argon dilution from 70–99%. The combination of ignition delay time and species composition data provide for a stringent test of the chemical kinetic mechanism. The reactions are classed into various types, and the reaction rate constants are given together with an explanation of how the rate constants were obtained. Experimental results from the literature of ignition behind reflected shock waves and in a rapid compression machine were used to develop and validate the reaction mechanism at both low and high temperatures. Additionally, species composition data from a variable pressure flow reactor and a jet-stirred reactor were used to help complement and refine the low-temperature portions of the reaction mechanism. A sensitivity analysis was performed for each of the combustion environments. This analysis showed that the low-temperature chemistry is very sensitive to the formation of stable olefin species from hydroperoxy-alkyl radicals and to the chain-branching steps involving ketohydroperoxide molecules.
Combustion and Flame.
