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 argondiluted (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.

Complex reactive processes in the gas phase often proceed via numerous reaction steps and intermediate species that must be identified and quantified to develop an understanding of the reaction pathways and establish suitable reaction mechanisms. Here, photoelectron-photoion coincidence (PEPICO) spectroscopy has been applied to analyse combustion intermediates present in a premixed fuel-rich (ϕ = 1.7) ethene-oxygen flame diluted with 25% argon, burning at a reduced pressure of 40 mbar. For the first time, multiplexing fixed-photon-energy PEPICO measurements were demonstrated in a chemically complex reactive system such as a flame in comparison with the scanning "threshold" TPEPICO approach used in recent pioneering combustion investigations. The technique presented here is capable of detecting and identifying multiple species by their cations' vibronic fingerprints, including radicals and pairs or triplets of isomers, from a single time-efficient measurement at a selected fixed photon energy. Vibrational structures for these species have been obtained in very good agreement with scanning-mode threshold photoelectron spectra taken under the same conditions. From such spectra, the temperature in the ionisation volume was determined. Exemplary analysis of species profiles and mole fraction ratios for isomers shows favourable agreement with results obtained by more common electron ionisation and photoionisation mass spectrometry experiments. It is expected that the multiplexing fixed-photon-energy PEPICO technique can contribute effectively to the analysis of chemical reactivity and kinetics in and beyond combustion.

Electron ionization, photoionization and photoelectron/photoion coincidence spectroscopy in mass-spectrometric investigations of a low-pressure ethylene/oxygen flame, Proc. Combust. Inst. 35 (2015) 779-786.

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and nondestructive, are an ideal choice for many flame applications. While many important radicals such as OH and CH have strong absorption bands in the UV/Vis and can easily be detected using techniques such as LIF or CRDS, electronic transitions of stable molecules like CO and CO 2 lie in the deep UV. Detection schemes like twophoton LIF [1] are possible, but quantification is prone to errors. For these molecules, rovibrational transitions in the infrared provide an alternative detection method. Due to the availability of cheap tunable diode lasers in the nearinfrared (NIR), this spectral region has already been widely used for combustion diagnostics in the past [2][3][4][5].The strong fundamental bands in the mid-infrared (MIR) have the potential for a more sensitive detection compared to the weaker overtone bands in the NIR. The development of quantitative detection schemes in the MIR was, however, hindered by the lack of laser sources with adequate qualities. Most lasers available required cryogenic cooling and output powers were low [2, 6]. Wondraczek et al. used difference frequency generation (DFG) as an alternative method to generate MIR radiation. They detected CO is around 5 µm even though the output power of their laser system was only 30 nW [7]. In this work, tomography has been applied to visualize CO in a flat flame.In recent years, quantum cascade lasers (QCL) have proven to be reliable light sources in the MIR. Even though the operating principle for this type of laser has already been proposed in 1971 by Kazarinov and Suris [8], the first working quantum cascade laser has been presented more than twenty years later [9]. QCLs provide high output powers (several milliwatts) and narrow-band output with operation at room temperature which simplifies the experimental setup. This enables QCLs to compete with conventional techniques like Fourier transform spectrometer for highresolution molecular spectroscopy in the infrared [10].Abstract An experimental setup for the simultaneous detection of CO and CO 2 and the temperature in lowpressure flames using a pulsed quantum cascade laser at 4.48 μm is presented. This comparatively new type of laser offers good output energies and beam quality in the mid-infrared, where the strong fundamental transitions of many molecules of interest can be accessed. A single-pass absorption setup was sufficient to obtain good accuracy for the stable species investigated here. Due to the high repetition rate of the laser and the speed of the data acquisition, measurement of two-dimensional absorption spectra and subsequent tomographic reconstruction was feasible. As demonstration of this technique, two-dimensional CO and CO 2 concentrations have been measured in two fuel-rich methane flames with different coflow gases (nitrogen and air). The influence of the coflow gas on the flame center concentration profiles was investigated and compared with one-dimensional model simulations.