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As ketene is a crucial intermediate for the high-temperature combustion of oxygenated hydrocarbons in general, an in-depth understanding of its chemistry is a fundamental requirement for the kinetic modeling of bio-based fuels. To gain a profound insight into the decomposition of ketene and subsequent reaction pathways high level ab initio methods were used. DSD-PBEP86/cc-pVTZ level of theory was applied for the geometries and frequencies, while single-point energies were determined at the CCSDT-1a level of theory extrapolated to the basis set limit. The reaction rate parameters for 38 reactions involved in the ketene chemistry including C1 to C4 species like acetylene, ethylene, propyne and allene were computed. For a total of 16 species, the thermochemistry were updated. The calculated rate parameters and the two new species cyclopropenone and 1,4-dioxo-1,3-butadiene were used to update the AramcoMech 3.0 base mechanism, which was then validated against speciation measurements during ketene pyrolysis. A reaction pathway analysis was performed to find the most prominent reactions at the investigated conditions and to discuss the simulation results. A significant improvement in the model's prediction capability was found when applying the newly calculated reaction rate parameter and thermochemical data. [ABSTRACT FROM AUTHOR]

Cyclic ethers are important intermediates in the oxidation of hydrocarbons and biofuels. Studying the oxidation and pyrolysis of cyclic ethers will help in improving our understanding of this functional group and provide consistency to the base mechanism where they play an important role. In this aspect, propylene oxide has been investigated in this study by obtaining ignition delay time measurements in the rapid compression machine and shock tube. The experiments were performed in a range of pressures varying from 10 to 40 bar at different equivalence ratios (0.5–2.0) and dilution percentages. Additionally, speciation measurements in the shock tube at pyrolysis conditions have been performed at a pressure of 40 bar to explore the isomerization pathways. A detailed kinetic mechanism was developed to describe both the oxidation and pyrolysis chemistry of propylene oxide. The mechanism is not only able to predict the data obtained from this study but also reproduces the data from the literature in a consistent trend. For a better understanding of the oxidation and pyrolysis chemistry of propylene oxide, the kinetic analyses were performed using the developed mechanism to comprehend the important reaction pathways and sensitive reactions. At the investigated regime, the consumption of propylene oxide through its isomerization channels is the critical pathway that controls the reactivity of the fuel. [ABSTRACT FROM AUTHOR]

The pyrolysis and oxidation of acetone were studied using three complementary experimental setups. Jet-stirred reactor experiments were performed at four equivalence ratios (ϕ = 0.5, 1, 2, and ∞), at pressure of 1.067 bar (800 Torr) and over the temperature range of 700–1200 K for pyrolysis and 600–1150 K for oxidation. The decomposition of acetone starts around 800 K with a conversion rate of 50% obtained around 1000 K in both pyrolysis and oxidation studies. The main stable products detected in both conditions are small hydrocarbons (methane, ethane, and ethylene), with also acetaldehyde, CO and CO 2 for oxidation. Oscillation behavior was detected beyond 1000 K under oxidation conditions and the products were followed with on-line mass spectrometry. Ignition delay times were measured using a rapid compression machine at pressures of 20 and 40 bar under non-diluted stoichiometric conditions over the temperature range 850–1100 K. The ignition delay times measured in the present study, combined with shock tube data of literature, exhibit a slight inflexion to the Arrhenius behavior, but no negative temperature coefficient. Laminar burning velocities were measured using a flat flame burner at atmospheric pressure for three fresh gas temperatures: ambient temperature, 358 and 398 K. A detailed kinetic model of the combustion of acetone including 852 species and 3265 reactions was developed. This new kinetic mechanism predicts relatively well the experimental measurements of ignition delay times, the mole fraction of the products in the jet-stirred reactor including oscillations and laminar burning velocities. Related flow rate and sensitivity analysis are also presented providing new insights into the acetone reaction network. [ABSTRACT FROM AUTHOR]

The application of oxymethylene ethers as an alternative fuel (additive) produced via carbon capture and utilization can lead to lower CO 2 and particulate matter emissions compared to fossil fuels. To improve the understanding of the pyrolysis and oxidation chemistry of oxymethylene ether-2 (OME-2), a combined experimental and kinetic modeling study has been carried out. Pyrolysis experiments were performed using a quartz reactor over a broad temperature range, from 373 to 1150 K, to elucidate both the primary and secondary pyrolysis chemistry. The thermal decomposition of OME-2 is initiated via a dominant formaldehyde elimination reaction. Radical chemistry becomes only significant at higher temperatures (>800 K) and competes with unimolecular decomposition. Radicals originate mainly from the decomposition of carbenes. Important intermediate products formed during pyrolysis are dimethoxymethane, formaldehyde, methane and methyl formate. The formation of products with carbon-carbon bonds is minor since only carbon-oxygen bonds are present in OME-2. The oxidation chemistry was investigated between 600 and 715 K by ignition delay time measurements in a rapid compression machine for OME-2/air mixtures with an equivalence ratio ϕ of 0.5. No negative temperature coefficient region is observed. An elementary step kinetic model is constructed with the automatic kinetic model generator Genesys starting from the base mechanism AramcoMech 1.3. Important thermodynamic parameters and reaction rate coefficients to describe the low- and high-temperature decomposition chemistry are obtained from quantum chemical calculations. The new kinetic model satisfactorily reproduces the measured ignition delay times, as well as major product mole fractions from the pyrolysis experiments within the experimental error margin of 10% on average, without fitting thermodynamic or kinetic parameters. Finally, rate of production analyses reveal the important decomposition pathways to methyl formate, formaldehyde and others under pyrolysis and low-temperature oxidation conditions. [ABSTRACT FROM AUTHOR]