Patrick Nau

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.

Detection of formaldehyde in flames using UV and MIR absorption spectroscopy

Abstract Absorption spectroscopy in the ultraviolet (UV) and mid-infrared (MIR) spectral region has been used in a comparative study for the detection of formaldehyde in laminar low pressure flames of dimethyl ether (DME) and methane. Both spectral regions were tested to explore respective advantages and limitations, especially for the detection of stable molecules in flames. In the UV, cavity ring-down spectroscopy (CRDS), a highly sensitive multi-pass absorption technique, has been used for the detection of formaldehyde in the A − X410 hot band at 370 nm. For measurements in the mid-infrared, the fundamental CO-stretch vibration ν2 of formaldehyde at 5.9 μm was used. MIR laser radiation was generated with a pulsed quantum cascade laser (QCL), a novel laser type which offers high output energies and excellent beam quality in the MIR. It was shown that MIR-QCL absorption spectroscopy and UV-CRDS have a comparable sensitivity, even though only single-pass absorption was used in the MIR. Additionally, MIR-QCL is clearly superior in terms of the simplicity of the experimental setup. This shows the large potential of QCL based laser absorption spectroscopy for the sensitive detection of trace species in the MIR.

Characterization of a Single-Nozzle FLOX® Model Combustor Using kHz Laser Diagnostics

A single-nozzle FLOX® model combustor was used to produce a confined, premixed CH4-air flame with an equivalence ratio of ϕ = 0.74 and a jet exit velocity of vjet = 150m/s with a preheat temperature of T0=300°C. For the first time for this combustor, surface thermometry was performed on the chamber walls. In addition, particle imaging velocimetry (PIV) and planar laser-induced fluorescence of hydroxyl radical (OH PLIF) were acquired simultaneously in this flame at 5 kHz repetition rate. The interface between burnt and unburnt gas mixture were identified from instantaneous OH PLIF images and were compared with corresponding PIV results for flame-turbulence interaction analysis. Combustion instabilities were analyzed via proper orthogonal decomposition and phase-averaged flow field and OH distribution. A pronounced flapping motion of the jet was identified and its impact on the recirculation of hot burnt gas was characterized.Copyright

Wall temperature measurements in gas turbine combustors with thermographic phosphors

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

Development of an Infrared Absorption Spectrometer for Temperature and Species Concentration Measurements in a Gasifier

An absorption spectrometer utilizing a tunable distributed feedback diode laser at 2.3µm and an interband cascade laser at 3.1µm has been developed to measure temperature and concentrations of CO, CH4, C2H2 and H2O under gasification conditions. The setup has been tested and then applied for measurements at an atmospheric entrained flow gasifier.