Luc-Sy Tran

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part I: Furan

Fuels of the furan family, i.e. furan itself, 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) are being proposed as alternatives to hydrocarbon fuels and are potentially accessible from cellulosic biomass. While some experiments and modeling results are becoming available for each of these fuels, a comprehensive experimental and modeling analysis of the three fuels under the same conditions, simulated using the same chemical reaction model, has - to the best of our knowledge - not been attempted before. The present series of three papers, detailing the results obtained in flat flames for each of the three fuels separately, reports experimental data and explores their combustion chemistry using kinetic modeling. The first part of this series focuses on the chemistry of low-pressure furan flames. Two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of furan were studied at two equivalence ratios (φ=1.0 and 1.7) using an analytical combination of high-resolution electron-ionization molecular-beam mass spectrometry (EI-MBMS) in Bielefeld and gas chromatography (GC) in Nancy. The time-of-flight MBMS with its high mass resolution enables the detection of both stable and reactive species, while the gas chromatograph permits the separation of isomers. Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. A single kinetic model was used to predict the flame structure of the three fuels: furan (in this paper), 2-methylfuran (in Part II), and 2,5-dimethylfuran (in Part III). A refined sub-mechanism for furan combustion, based on the work of Tian et al. [Combustion and Flame 158 (2011) 756-773] was developed which was then compared to the present experimental results. Overall, the agreement is encouraging. The main reaction pathways involved in furan combustion were delineated computing the rates of formation and consumption of all species. It is seen that the predominant furan consumption pathway is initiated by H-addition on the carbon atom neighboring the O-atom with acetylene as one of the dominant products.

Experimental study of the structure of laminar premixed flames of ethanol/methane/oxygen/argon

The structures of three laminar premixed stoichiometric flames at low pressure (6.7 kPa): a pure methane flame, a pure ethanol flame, and a methane flame doped by 30% of ethanol, have been investigated and compared. The results consist of mole fraction profiles of CH4, C2H5OH, O2, Ar, CO, CO2, H2O, H2, C2H6, C2H4, C2H2, C3H8, C3H6, CH3-C CH (propyne), CH2 C CH2 (allene), CH2O, and CH3HCO, measured as a function of the height above the burner by probe sampling followed by on-line gas chromatography analyses. Flame temperature profiles have been also obtained by using a PtRh thermocouple. The similarities and differences between the three flames have been analyzed. The results show that, in these three flames, the mole fraction of the intermediates with two carbon atoms is much larger than that of the species with three carbon atoms. In general, the mole fraction of all intermediate species in the pure ethanol flame is the largest, followed by the doped flame, and finally the pure methane flame.

Progress in Fixed-Photon-Energy Time-Efficient Double Imaging Photoelectron/Photoion Coincidence Measurements in Quantitative Flame Analysis

Abstract Photoelectron photoion coincidence (PEPICO) spectroscopy as an attractive new technique for combustion analysis was used in a fixed-photon-energy configuration to provide quantitative species profiles in laminar premixed flames. While such measurements are conventionally performed with molecular-beam mass spectrometry (MBMS) using electron ionization (EI) or vacuum ultraviolet (VUV) photoionization (PI) with synchrotron radiation, these techniques have some limitations. The possibility to record photoelectron spectra (PES) simultaneously with photoionization data, providing fingerprint information for reliable species identification, presents a significant advantage of PEPICO spectroscopy especially in complex reactive mixtures. The multiplex approach presented here, enhanced by the imaging capabilities of the electron and ion detection in the so-called double-imaging PEPICO scheme (i2PEPICO), provides, in different experimental situations, an unprecedentedly detailed combustion analysis regarding both species identification and quantification. Problems and perspectives of the present fixed-photon-energy PEPICO approach will be discussed.