The effect of methyl pentanoate addition on the structure of a non-premixed counterflow n‑heptane/O2 flame

The influence of methyl pentanoate (MP) addition to n-heptane on the species pool in a nonpremixed counterflow flame fueled with n-heptane at atmospheric pressure has been investigated experimentally and numerically. Two non-premixed flames in counterflow configuration have been examined: (1) n-heptane/Ar (5.3%/94.7%) vs O2/Ar (24.1%/75.9%) and (2) n-heptane/MP/Ar (2.5%/2.5%/95%) vs O2/Ar (19.6%/80.4%). Both flames had similar strain rates and stoichiometric mixture fractions to allow an adequate comparison of their structures. The mole fraction profiles of the reactants, major products, and intermediates in both flames were measured using flame sampling molecular beam mass spectrometry. These experimental data were used for validation of a detailed chemical kinetic mechanism, which was proposed earlier for prediction of combustion characteristics of n-heptane/iso-octane/toluene/MP mixtures. The addition of MP to n-heptane reduced the flame temperature and the peak mole fractions of many flame intermediates, responsible for the formation of polycyclic aromatic hydrocarbons, specifically, of benzene, cyclopentadienyl, acetylene, propargyl, and vinylacetylene. Significant discrepancies between the calculated and measured mole fractions of cyclopentadienyl and benzene were found. A kinetic analysis of the reaction pathways resulting in formation of these intermediates in both flames and a sensitivity analysis of cyclopentadienyl and benzene were carried out to understand the origins of the observed discrepancies. The peak mole fractions of the major flame radicals (H, O, OH, CH3) were found to decrease with MP addition. The influence of MP addition on the relative contributions of the primary stages of n-heptane consumption is discussed

Laminar flame structure of ethyl pentanoate at low and atmospheric-pressure: Experimental and kinetic modeling study

Ethyl pentanoate (EPE) or ethyl valerate is considered a surrogate for biodiesel fuels and a potential fuel for spark ignition engines. Knowledge of its combustion chemistry is of great importance for the development of high-performance and environmentally friendly combustion devices fueled with biofuels. In this work, a detailed chemical kinetic mechanism for the combustion of EPE is developed on the basis of a well-validated kinetic model proposed earlier for short ethyl esters up to ethyl propionate (by Sun et al.). The Sun et al. mechanism was augmented with primary oxidation reactions of ethyl butanoate and ethyl pentanoate and specific intermediates involved in these reactions. The proposed kinetic mechanism was validated against the new experimental data reported in this work on the chemical speciation of laminar premixed flames of stoichiometric EPE/O2/Ar mixtures at low (50 Torr) and atmospheric pressures. The mechanism provided a good predictive capability for experimental mole fraction profiles of many flame intermediates. The new mechanism was also shown to predict well literature experimental data on laminar flame speeds of EPE/air mixtures in a range of equivalence ratios and pressures. The reported flame data can be used for validation of kinetic models for ethyl ester-based biofuels

Flame Structure at Elevated Pressure Values and Reduced Reaction Mechanisms for the Combustion of CH₄/H₂ Mixtures

Understanding and controlling the combustion of clean and efficient fuel blends, like methane + hydrogen, is essential for optimizing energy production processes and minimizing environmental impacts. To extend the available experimental database on CH4 + H2 flame speciation, this paper reports novel measurement data on the chemical structure of laminar premixed burner-stabilized CH4/H2/O2/Ar flames. The experiments cover various equivalence ratios (φ = 0.8 and φ = 1.2), hydrogen content amounts in the CH4/H2 blend (XH2 = 25%, 50% and 75%), and different pressures (1, 3 and 5 atm). The flame-sampling molecular-beam mass spectrometry (MBMS) technique was used to detect reactants, major products, and several combustion intermediates, including major flame radicals. Starting with the detailed model AramcoMech 2.0, two reduced kinetic mechanisms with different levels of detail for the combustion of CH4/H2 blends are reported: RMech1 (30 species and 70 reactions) and RMech2 (21 species and 31 reactions). Validated against the literature data for laminar burning velocity and ignition delays, these mechanisms were demonstrated to reasonably predict the effect of pressure and hydrogen content in the mixture on the peak mole fractions of intermediates and adequately describe the new data for the structure of fuel-lean flames, which are relevant to gas turbine conditions

The Effect of Methyl Pentanoate Addition on the Structure of a Non-Premixed Counterflow <i>n</i>‑Heptane/O₂ Flame

The influence of methyl pentanoate (MP) addition to <i>n</i>-heptane on the species pool in a nonpremixed counterflow flame fueled with <i>n</i>-heptane at atmospheric pressure has been investigated experimentally and numerically. Two non-premixed flames in counterflow configuration have been examined: (1) <i>n</i>-heptane/Ar (5.3%/94.7%) vs O₂/Ar (24.1%/75.9%) and (2) <i>n</i>-heptane/MP/Ar (2.5%/2.5%/95%) vs O₂/Ar (19.6%/80.4%). Both flames had similar strain rates and stoichiometric mixture fractions to allow an adequate comparison of their structures. The mole fraction profiles of the reactants, major products, and intermediates in both flames were measured using flame sampling molecular beam mass spectrometry. These experimental data were used for validation of a detailed chemical kinetic mechanism, which was proposed earlier for prediction of combustion characteristics of <i>n</i>-heptane/iso-octane/toluene/MP mixtures. The addition of MP to <i>n</i>-heptane reduced the flame temperature and the peak mole fractions of many flame intermediates, responsible for the formation of polycyclic aromatic hydrocarbons, specifically, of benzene, cyclopentadienyl, acetylene, propargyl, and vinylacetylene. Significant discrepancies between the calculated and measured mole fractions of cyclopentadienyl and benzene were found. A kinetic analysis of the reaction pathways resulting in formation of these intermediates in both flames and a sensitivity analysis of cyclopentadienyl and benzene were carried out to understand the origins of the observed discrepancies. The peak mole fractions of the major flame radicals (H, O, OH, CH₃) were found to decrease with MP addition. The influence of MP addition on the relative contributions of the primary stages of <i>n</i>-heptane consumption is discussed