Experimental and modeling study of burning velocities for alkyl aromatic components relevant to diesel fuels (original) (raw)
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Laminar flame speeds and extinction stretch rates of selected aromatic hydrocarbons
Fuel, 2012
The laminar flame speeds and premixed extinction limits of n-propylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and toluene have been studied experimentally to assess the effects of different alkyl substitutions to the benzene ring on flame propagation and extinction. The experiments were carried out in a twin-flame counterflow setup under atmospheric pressure. The laminar flame speeds of fuel/ air mixtures at two unburned mixture temperatures of 400 K and 470 K were determined over an equivalence ratio range of / = 0.7-1.4. Additionally, the extinction stretch rates of fuel/O 2 /N 2 mixtures at an unburned mixture temperature of 400 K were measured over an equivalence ratio range of / = 0.8-1.6, with an oxidizer composition of 16% O 2 and 84% N 2 by mole. The experimental laminar flame speeds and extinction stretch rate values were compared to simulated results, for each fuel, using detailed kinetic models available in the literature. The simulation results were found to be in reasonable agreement with the current experimental data, except for 1,2,4-trimethylbenzene, where the model under-predicts the extinction limits significantly. Sensitivity and flux analyses were conducted to identify reactions and species to which the computed results were most sensitive.
Physical Chemistry Chemical Physics, 2002
Kinetic modeling is becoming a powerful tool for the quantitative description of combustion processes covering different fuels and large ranges of temperature, pressure and equivalence ratio. In the present work, a reaction mechanism which was developed initially for benzene oxidation, and included the formation of polycyclic aromatic hydrocarbons was extended and tested for the combustion of acetylene and ethylene. Thermodynamic and kinetic property data were updated. If available, data were taken from the recent literature. In addition, density functional theory as well as ab initio computations on a CBS-Q and CBS-RAD level, partially published previously, were carried out. Quantum Rice-Ramsperger-Kassel analysis was conducted in order to determine pressure-dependent rate constants of chemically activated reactions. The model was developed and tested using species concentration profiles reported in the literature from molecular beam mass-spectrometry measurements in four unidimensional laminar premixed low-pressure ethylene, acetylene and benzene flames at equivalence ratios (f) of 0.75 and 1.9 (C 2 H 4 ), 2.4 (C 2 H 2 ) and 1.8 (C 6 H 6 ). Predictive capabilities of the model were found to be at least fair and often good to excellent for the consumption of the reactants, the formation of the main combustion products as well as the formation and depletion of major intermediates including radicals. Selfcombination of propargyl (C 3 H 3 ) followed by ring closure and rearrangement was the dominant benzene formation pathway in both rich acetylene and ethylene flames. In addition, reaction between vinylacetylene (C 4 H 4 ) and vinyl radical (C 2 H 3 ) contributed to benzene formation in the f ¼ 1.9 ethylene flame. Propargyl formation and consumption pathways which involve reactions between acetylene, allene, propyne and singlet and triplet methylene were assessed. Significant overpredictions of phenoxy radicals indicate the necessity of further investigation of the pressure and temperature dependence and the product distribution of phenyl oxidation. The possible formation of benzoquinones, the ratio of the ortho and para isomers and their degradation pathways are of particular interest.
Some Observations Regarding Benzene Oxidation and Combustion
The pyrolysis and oxidation of benzene occupies a pivotal role in the combustion chemistry of practical fuels. Despite numerous experimental and numerical investigations, significant uncertainties exist regarding even major benzene combustion features, particularly under lean and stoichiometric conditions. Novel benzene premixed flame datasets that have recently appeared in the literature offer a unique possibility for the judicious evaluation of mechanisms developed solely on the basis of a single flame (Bittner and Howard). In this context, a detailed kinetic mechanism for benzene oxidation and combustion has been further developed and validated against available premixed flame data (a total of six flames) and data from shock tubes, stirred and flow reactors. A significant re-evaluation of phenyl radical oxidation, phenol/phenoxy chemistry and the cyclopentadiene sub-mechanism is proposed in view of both new rate data and validation targets. Benzene chemistry is shown to be largel...
A comprehensive experimental and kinetic modeling study of ethylbenzene combustion
Combustion and Flame, 2016
Iso-paraffinic molecular structures larger than seven carbon atoms in chain length are commonly found in conventional petroleum, Fischer-Tropsch (FT), and other alternative hydrocarbon fuels, but little research has been done on their combustion behavior. Recent studies have focused on either mono-methylated alkanes and/or highly branched compounds (e.g., 2,2,4trimethylpentane). In order to better understand the combustion characteristics of real fuels, this study presents new experimental data for the oxidation of 2,5-dimethylhexane under a wide variety of temperature, pressure, and equivalence ratio conditions. This new dataset includes jet stirred reactor speciation, shock tube ignition delay, and rapid compression machine ignition delay, which builds upon recently published data for counterflow flame ignition, extinction, and speciation profiles. The low and high temperature oxidation of 2,5-dimethylhexane has been modeled using a comprehensive chemical kinetic model developed using established reaction rate rules. The agreement between the model and data is presented, along with suggestions for improving model predictions. The importance of propene chemistry is highlighted as critical for correct prediction of high temperature ignition delay. The oxidation behavior of 2,5dimethylhexane is also compared with oxidation behavior of other linear and branched octane isomers, in order to determine the effects of the number of methyl branches on combustion properties. Both experimental data and model predictions indicate that increasing the level of branching decreases fuel reactivity at low and intermediate temperatures. The model is used to elucidate the structural features and reaction pathways responsible for inhibiting the reactivity of 2,5-dimethylhexane.
Experimental Validation of Combustion Characteristics of Commercial Diesel Fuel
In current scenario commercially available diesel fuel becomes the primary energy resource of transportation and power production. Diffusion combustion of fuels in compression ignition engines is a very complex phenomenon. Delay period is single most important parameter which controls the performance and emission characteristics of fuels used in CI engines. Present work deals with measurement of ignition delay of commercial diesel fuel in a closed cylindrical camber and a comparison of the obtained results with the Arrhenius equation given by Wolfer and Stringer in 1959 is carried out. The comparison is done at different ambient air pressure from 10 to 25 bar and air temperature from 350 0 C to 450 0 C. It is found that, experimental results shows more consistant trends with the arrhenius equation, when fuel is injected at high injection pressure of 300bar. NOMENCLATURE í µí¼ í µí±í µí± = Ignition Delay in millisecond, P = In-cylinder pressure in Pa, í µí°¸í µí°´= Apparent activation energy in j/mol, R = Universal gas constant in j/mol-K, T = In-cylinder Temperature in Kelvin, A and n = Constants depends upon type of fuel.
The combustion of benzene in rich premixed flames at atmospheric pressure
Combustion and Flame, 1999
The structures of atmospheric-pressure, fuel-rich, premixed benzene-air flames have been described by the concentration profiles of reactants and also major and minor combustion products, as measured along the axes of two benzene/air flames with different C/O ratios (0.72 and 0.77). The main effect of the C/O ratio was on the flame temperature and on the final yields of CO, C 2 H 2 , polycyclic aromatic hydrocarbons (PAHs), and soot, whereas the relative distributions of the light hydrocarbons and PAHs did not change on increasing the C/O ratio. Large amounts of phenol and cyclopentadiene were found early on in the flames. Acetylene and methane were the dominant hydrocarbon products and had much larger concentrations later on than the C 3 -C 4 unsaturated hydrocarbons. PAHs were formed within the main reaction zone and were rapidly destroyed, while soot was formed. Some small differences in the distribution of PAHs were found with an aliphatic fuel. The concentration of PAHs as evaluated by gas chromatography takes into account a very small amount of condensed species, which are formed in significant quantities at soot inception and then consumed while soot is formed.
A wide range kinetic modelling study of laminar flame speeds of reference fuels and their mixtures
2010
Aim of this work is to further validate a general detailed mechanism of pyrolysis and oxidation for the high temperature combustion of a large variety of different fuels. The attention is first placed on the validation of the chemical mechanism in respect of the laminar flame speed of H2 and H2/CO mixtures as well as the burning velocity of small hydrocarbon fuels such as methane and C2-C4 species. Alkanes, alkenes and alkynes are considered, together with butadiene. Reference fuels for gasoline and jet fuel surrogates are also analysed. More specifically, three hydrocarbon classes are considered: alkanes (n-heptane: nC7H16 and iso-octane: iC8H18, and higher n-alkanes: nC10H22 and nC12H26), cyclo-alkanes (cyclo-hexane) and aromatics (benzene: C6H6, toluene: C7H8). Finally, burning velocity of C1-C4 alcohols are also compared with experimental data.
Laminar burning velocities of benzene + air flames at room and elevated temperatures
Fuel, 2016
h i g h l i g h t s The burning velocities of benzene + air flames at several temperatures were measured. Comparison of predictions of 3 mechanisms with the experimental data showed mixed agreement. The temperature dependence of the burning velocity was interpreted using an empirical power law. Detailed model from Politecnico di Milano performs the best over the range of conditions studied.