Compared to conventional allothermal gasification of solid fuels (e.g., biomass, charcoal, lignite, etc.), plasma-assisted gasification offers an efficient method for applying energy to the gasification process to increase the flexibility of operation conditions and to increase the reaction kinetics. In particular, non-thermal plasmas (NTP) are promising, in which thermal equilibrium is not reached and electrons have a substantially higher mean energy than gas molecules. Thus, it is generally assumed that in NTP the supplied energy is utilized more efficiently for generating free radicals initiating gasification reactions than thermal plasma processes. In order to investigate this hypothesis, we compared purely thermal to non-thermal plasma-assisted gasification of biomass in steam in a drop tube reactor at atmospheric pressure. The NTP was provided by means of gliding arcs between two electrodes aligned in the inlet steam flow with an electric power of about 1 kW. Reaction yields and rates were evaluated using measured gas temperatures by the optical technique. The first experimental results show that the non-thermal plasma not only promotes the carbon conversion of the fuel particles, but also accelerates the reaction kinetics. The carbon conversion is increased by nearly 10% using wood powder as the fuel. With charcoal powder, more than 3% are converted into syngas.
The first results under fired internal combustion engine conditions based on a supercontinuum absorption spectrometer are presented and discussed. Temperature, pressure, and water mole fraction are inferred simultaneously from broadband HO absorbance spectra ranging from 1340 nm to 1440 nm. The auto-ignition combustion process is monitored for two premixed n-heptane/air mixtures with 10 kHz in a rapid compression machine. Pressure and temperature levels during combustion exceed 65 bar and 1900 K, respectively. To allow for combustion measurements, the robustness of the spectrometer against beam steering has been improved compared to its previous version. Additionally, the detectable wavelength range has been extended further into the infrared region to allow for the acquisition of distinct high-temperature water transitions located in the P-branch above 1410 nm. Based on a theoretical study, line-of-sight (LOS) effects introduced by temperature stratification on the broadband fitting algorithm in the complete range from 1340 nm to 1440 nm are discussed. In this context, the recorded spectra during combustion were evaluated only within a narrower spectral region exhibiting almost no interference from low-temperature molecules (here, P-branch from 1410 nm to 1440 nm). It is shown that this strategy mitigates almost all of the LOS effects introduced by cold molecules and the evaluation of the spectrum in the entirely recorded wavelength range at engine combustion conditions.
We present a novel non-invasive laser-based tool for tracer-free spatially resolved temperature measurement in superheated water vapor at atmospheric pressure. The technique exploits the temperature sensitivity of the rotational-vibrational Raman spectrum of the v stretching vibration. This Letter demonstrates the Raman sensor, its application to a steam gasification reactor, and four methods to analyze the Raman spectra in order to obtain the temperature: an equal intensity point approach, a pseudo-isosbestic point approach, and two approaches based on the reconstruction of the Raman band by Gaussian/Lorentzian profiles. The evaluated water vapor temperatures inside a reactor for plasma-assisted gasification are compared to data acquired by supercontinuum absorption spectroscopy.
1-methylnaphthalene (1-MN) is a widely used laser-induced fluorescence (LIF) tracer for planar imaging of mixture formation and temperature distributions in internal combustion (IC) engines. As the LIF measurement results can be biased by partial tracer oxidation, the conversion of 1-MN and the base fuel isooctane is analyzed in a calibration cell. First, measurements using supercontinuum laser absorption spectroscopy (SCLAS) are presented in order to quantify the conversion by detection of the produced H2O mole fraction. A single mode fiber (SMF) coupled setup is presented, with the fiber core acting as entrance slit of a Czerny-Turner spectrometer. Dependencies on residence time and global air-fuel ratio are presented at pressures up to 1.5 MPa and temperatures up to 900 K, at which distinct tracer and fuel consumption is observed. Signal loss due to intense beam steering was partially compensated using a self-stabilizing double-pass setup with a retroreflector.
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