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.

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Wall temperatures were measured with thermographic phosphors on the quartz walls of a model combustor in ethylene/air swirl ames at 3 bar. Three operating conditions were investigated with dierent stoichiometries and with or without additional injection of oxidation air downstream of the primary combustion zone. YAG:Eu and YAG:Dy were used to cover a total temperature range of 10001800 K. Measurements were challenging due to the high thermal background from soot and window degradation at high temperatures. The heat ux through the windows was estimated from the temperature gradient between the in-and outside of the windows. Dierences in temperature and heat ux density proles for the investigated cases can be explained very well with the previously measured dierences in ame temperatures and ame shapes. The heat loss relative to thermal load is quite similar for all investigated ames (1516 %). The results complement previous measurements in these ames to investigate soot formation and oxidation. It is expected, that the data set is a valuable input for numerical simulations of these ames. 1 Introduction Because of the increasingly stringent regulations for particle emissions, i.e. mainly soot, continuing eort is needed for the development and improvement of gas turbines for propulsion and power generation. Soot formation and oxidation in high-pressure turbulent ames are complex processes that are still not completely understood. Numerical simulation is an important tool for the development of gas turbine combustors. However, to evaluate and improve the reliability of numerical predictions, comprehensive experimental data sets are needed from technically-relevant sooting ames under elevated pressures with well-dened boundary conditions. An important parameter in this respect is the temperature of the combustor walls. Due to the lack of accurate measure

Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high time resolution. To study the feasibility of this technique for full-scale gas turbine applications, a high momentum confined jet combustor at 8 bar was used. Successful measurements up to 1700 K on a ceramic surface are shown with good accuracy. In the same combustor, temperatures on the combustor quartz walls were measured, which can be used as boundary conditions for numerical simulations. An atmospheric swirl-stabilized flame was used to study transient temperature changes on the bluff body. For this purpose, a high-speed setup (1 kHz) was used to measure the wall temperatures at an operating condition where the flame switches between being attached (M-flame) and being lifted (V-flame) (bistable). The influence of a precessing vortex core (PVC) present during M-flame periods is identified on the bluff body tip, but not at positions further inside the nozzle.

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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.

Wall temperature measurements with fiber coupled online phosphor thermometry were, for the first time, successfully performed in a full scale H-class Siemens gas turbine combustor. Online wall temperatures were obtained during high-pressure combustion tests up to 8 bar at the Siemens CEC test facility. Since optical access to the combustion chamber with fibers being able to provide high laser energies is extremely challenging, we developed a custom-built measurement system, consisting of a water-cooled fiber optic probe and a mobile measurement container. A suitable combination of chemical binder and thermographic phosphor was identified for temperatures up to 1800 K on combustor walls coated with a thermal barrier coating (TBC). To our knowledge these are the first measurements reported with fiber coupled online phosphor thermometry in a full scale highpressure gas turbine combustor. Details of the setup and the measurement procedures will be presented. The measured signals were influenced by strong background emissions, probably from CO*2 chemiluminescence. Strategies for correcting backgroundemissions and data evaluation procedures are discussed. The presented measurement technique enables detailed study of combustor wall temperatures and using this information an optimization of the gas turbine cooling design.

Absolute concentrations of all important chemiluminescent species, OH-A, CH-A, CH-B, and C 2 -d have been measured for the first time in methane-oxygen flames at low pressure. The optical detection system for chemiluminescence measurements has been calibrated with Rayleigh and Raman scattering of a cw laser, with the latter approach yielding superior results.The measured ratio between the concentration of CH-B and CH-A suggests that the electronically excited CH* is formed close to thermal equilibrium. Introduction of different rate constants for reactions leading to CH-A and CH-B were not necessary to explain the experimental results. Results are compared with a recent numerical model. Deviations in profile shape and peak positions are relatively small for stoichiometric flames, but become more pronounced in richer mixtures. Larger discrepancies are observed for the absolute concentrations, depending on the chemiluminescent species and the stoichiometry.In an attempt to find an alternative method for the quantification of chemiluminescent species, MIR-CRDS has been performed around 3.9 μm. While H 2 O and OH-X could be measured, the sensitivity was not high enough to detect the low sub-ppb concentration of OH-A-in part due to the limited reflectivity of mirrors in the MIR, in part due to a significant background of hot H 2 O lines.