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: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Introduction to stochastic programming

Electrofuels (also called power-to-gas/liquids/fuels or synthetic fuels) are potential future carbon-based fuels produced from carbon dioxide (CO2) and water using electricity as the primary source of energy. This article assesses the production cost of electrofuels through: (i) a literature review, focusing on which steps that have the largest impact as well as the greatest uncertainty; (ii) a more comprehensive review, including the costs and efficiencies for the separate production steps, and (iii) calculations to compare the production costs of the different fuel options in a harmonized way, including a sensitivity analysis of the parameters with the greatest impact on the total electrofuel production cost. The assessment covers: methane, methanol, dimethyl ether, diesel, and gasoline. The literature review showed large differences among the studies and a broad range of production cost estimates (10–3500 €2015/MWhfuel), which is first and foremost as a result of how authors have handled technology matureness, installation costs, and external factors. Our calculations result in productions costs in the range of 200–280 €2015/MWhfuel in 2015 and 160–210 €2015/MWhfuel in 2030 using base cost assumptions from the literature review. Compared to biofuels, these estimates are in the upper range or above. Our results also show that the choice of energy carrier is not as critical for the electrofuels production cost as technological choices and external factors. Instead the two most important factors affecting the production cost of all electrofuels are the capital cost of the electrolyser and the electricity price, i.e., the hydrogen production cost. The capacity factor of the unit and the life span of the electrolyser are also important parameters affecting that production cost. In order to determine if electrofuels are a cost-effective future transport fuel relative to alternatives other than biofuels, the costs for distribution, propulsion, and storage systems need to be considered.

Electrofuels for the transport sector: A review of production costs

A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at I and 10 atm, 0.2 < 0 < 2.5, and 800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 1.0 and 650 :5 T :5 1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates and products pertinent to the oxidation of DME. These data test the Idnetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g. the primary reference fuels, n-heptane and iso- octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.

/pdf/wide-range-modeling-study-of-dimethyl-ether-oxidation-pnag57ojwu.pdf

Wide range modeling study of dimethyl ether oxidation

Increasing carbon dioxide accumulation in earth’s atmosphere and the depletion of fossil resources pose huge challenges for our society and, in particular, for all stakeholders in the transportatio...

/pdf/tailor-made-fuels-for-future-engine-concepts-1rvz5hzdgy.pdf

Tailor-made fuels for future engine concepts

The assessment of the ignition quality of a wide range of oxygenated hydrocarbons is one key challenge in the identification of novel molecular entities qualifying as biofuels or biofuel blend components derived from oxygen-rich lignocellulosic feedstocks. The present contribution summarizes the results from a comprehensive experimental screening campaign targeting a diverse set of pure-component oxygenated hydrocarbon fuels and their ignition characteristics in an ASTM D6890 Ignition Quality Tester (IQT). This constant-volume combustion chamber experiment has been chosen because of its rapid screening potential. The unique collection of data is utilized for group contribution modeling with the aim of unraveling relationships between the ignition delay observed in IQT experiments and the fuel’s molecular structure. We propose a simple, yet predictive, estimator for the derived cetane number of pure oxygenated hydrocarbons covering acyclic and cyclic, branched and straight, saturated and unsaturated hydroc...

A Novel Group Contribution Method for the Prediction of the Derived Cetane Number of Oxygenated Hydrocarbons

Prediction of combustion-related properties of (oxygenated) hydrocarbons is an important and challenging task for which quantitative structure–property relationship (QSPR) models are frequently emp...

Graph neural networks for prediction of fuel ignition quality

Oxygenates derived through the selective catalytic refunctionalization of carbohydrates of lignocellulosic biomass can be tailored to exhibit desired physicochemical fuel properties that unlock the full potential of advanced internal combustion engines. Considering the fuel’s molecular structure to be a design degree of freedom, we present a framework for model-based fuel design that is envisioned to guide experimental investigation toward the most promising molecular entities. Following a generate-and-test approach to computer-aided molecular design, a novel rule-based generator of molecular structures is introduced to refunctionalize and join molecular graphs of predefined biobased intermediates in an attempt to resemble carbon- and energy-efficient biofuel synthesis. Computational property prediction is employed to virtually screen the generated structures with regard to key physicochemical fuel properties, e.g., the derived cetane number or fuel volatility. Two case studies are dedicated to the identi...

Model-Based Design of Tailor-Made Biofuels

Oxygenated species obtained from the selective chemo-catalytic refunctionalization of lignocellulosic materials and rationally formulated mixtures thereof can be tailored to the needs of advanced internal combustion engine concepts like low temperature compression-ignition or highly boosted spark-ignition combustion. In the present contribution, we present a framework for model-based formulation of biofuel blends with tailored properties by considering the fuel’s molecular composition as the fundamental design degree of freedom. To this end, optimization-based reaction pathway screening is combined with mathematical fuel property prediction by means of structural group contribution and quantitative structure–property relationship modeling in order to formulate and solve an integrated product and pathway design problem. The model-based approach is envisioned (i) to guide fundamental experimental investigations of the combustion behavior of blended biofuels toward the most favorable mixtures and (ii) to ide...

http://pubs.acs.org/doi/pdf/10.1021/acs.energyfuels.7b00118

Manuel Dahmen

Papers

Tailor-made fuels for future engine concepts

A Novel Group Contribution Method for the Prediction of the Derived Cetane Number of Oxygenated Hydrocarbons

Graph neural networks for prediction of fuel ignition quality

Model-Based Design of Tailor-Made Biofuels

Model-based formulation of biofuel blends by simultaneous product and pathway design