Isomer-specific influences on the composition of reaction intermediates in dimethyl ether/propene and ethanol/propene flame

This work provides experimental evidence on how the molecular compositions of fuel-rich low-pressure premixed flames are influenced as the oxygenates dimethyl ether (DME) or ethanol are incrementally blended into the propene fuel. Ten different flames with a carbon-to-oxygen ratio of 0.5, ranging from 100% propene (phi = 1.5) to 100% oxygenated fuel (phi = 2.0), are analyzed with flame-sampling molecular-beam mass spectrometry employing electron- or photoionization. Absolute mole fraction profiles for flame species with masses ranging from m/z = 2 (H2) to m/z = 80 (C6H8) are analyzed with particular emphasis on the formation of harmful emissions. Fuel-specific destruction pathways, likely to be initiated by hydrogen abstraction, appear to lead to benzene from propene combustion and to formaldehyde and acetaldehyde through DME and ethanol combustion, respectively. While the concentration of acetaldehyde increases 10-fold as propene is substituted by ethanol, it decreases as propene is replaced with DME. In contrast, the formaldehyde concentration rises only slightly with ethanol replacement but increases markedly with addition of DME. Allyl and propargyl radicals, the dominant precursors for benzene formation, are likely to be produced directly from propene decomposition or via allene and propyne. Benzene formation through propargyl radicals formed via unsaturated C2 intermediates in the decomposition of DME and ethanol is negligibly small. As a consequence, DME and ethanol addition lead to similar reductions of the benzene concentration.     

Scale size of magnetic turbulence in tokamaks probed with 30-MeV electrons

Measurements of synchrotron radiation emitted by 30-MeV runaway electrons in the TEXTOR-94 tokamak show that the runaway population decays after switching on neutral beam injection (NBI). The decay starts only with a significant delay, which decreases with increasing NBI heating power. This delay provides direct evidence of the energy dependence of runaway confinement, which is expected if magnetic modes govern the loss of runaways. Application of the theory by Mynick and Strachan [Phys. Fluids 24, 695 (1981)] yields estimates for the "mode width" (delta) of magnetic perturbations: delta<0.5 cm in Ohmic discharges, increasing to delta = 4.4 cm for 0. 6 MW NBI.     

Biofuel Combustion Chemistry: From Ethanol to Biodiesel

Biofuels, such as bio‐ethanol, bio‐butanol, and biodiesel, are of increasing interest as alternatives to petroleum‐based transportation fuels because they offer the long‐term promise of fuel‐source regenerability and reduced climatic impact. Current discussions emphasize the processes to make such alternative fuels and fuel additives, the compatibility of these substances with current fuel‐delivery infrastructure and engine performance, and the competition between biofuel and food production. However, the combustion chemistry of the compounds that constitute typical biofuels, including alcohols, ethers, and esters, has not received similar public attention. Herein we highlight some characteristic aspects of the chemical pathways in the combustion of prototypical representatives of potential biofuels. The discussion focuses on the decomposition and oxidation mechanisms and the formation of undesired, harmful, or toxic emissions, with an emphasis on transportation fuels. New insights into the vastly diverse and complex chemical reaction networks of biofuel combustion are enabled by recent experimental investigations and complementary combustion modeling. Understanding key elements of this chemistry is an important step towards the intelligent selection of next‐generation alternative fuels.     

CanSAS‐IV

A two-day workshop on beamline integration and data formatting (HDF5/NeXus) of the EIGER detector was held in Baden, Switzerland, January 24–25, 2013. Its aim was to discuss the technical challenges inherent with the next generation of high-frame-rate, high-resolution X-ray imaging detectors, and specifically with the EIGER detector. EIGER is a photon-counting hybrid pixel detector developed at the Paul Scherrer Institute (PSI) and DECTRIS Ltd. With even higher spatial resolution and frame rates than its predecessor, the PILATUS detector, it will be able to continuously produce up to 3000 images per second. The corresponding extreme data rates generated by this and future detectors present a significant challenge for beamline integration of the detectors, for data handling by the users, and for data processing software. Efficient data flow, storage, and processing must be achieved to handle the huge data sets that will be produced in seconds by these devices.     

An exact solution for flow in a porous pipe

Summary An exact solution of the Navier-Stokes equations for flow in a porous pipe is presented. This solution allows the suction or injection at the wall to vary with axial distance and will provide new insight into flows through porous pipes.

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Resumé Une solution exacte d'équation de Navier-Stokes est présentée pour l'écoulement d'un liquide visqueux dans un tube perméable. Ce liquide est aspiré ou injecté avec une vélocité variable et la solution donne une nouvelle optique quant aux tubes poreuses.

     

Isomer-specific fuel destruction pathways in rich flames of methyl acetate and ethyl formate and consequences for the combustion chemistry of esters

The influences of fuel-specific destruction pathways on flame chemistry are determined for two isomeric ester fuels, methyl acetate, CH3(CO)OCH3, and ethyl formate, H(CO)OC2H5, used as model representatives for biodiesel compounds, and their potential for forming air pollutants is addressed. Measurements are presented of major and intermediate species mole fractions in premixed, laminar flat flames using molecular-beam sampling and isomer-selective VUV-photoionization mass spectrometry. The observed intermediate species concentrations depend crucially on decomposition of the different radicals formed initially from the fuels. The methyl acetate structure leads to preferential formation of formaldehyde, while the ethyl formate isomer favors the production of acetaldehyde. Ethyl formate also yields higher concentrations of the C2 species (C2H2 and C2H4) and C4 species (C4H2 and C4H4). Benzene concentrations, while larger for ethyl formate, are at least an order of magnitude smaller for both flames than seen for simple hydrocarbon fuels (ethylene, ethane, propene, and propane).