Search

The complex composition of pyrolysis oils makes it challenging to develop detailed reaction mechanisms to model the fuel’s gasification chemistry. As a solution, surrogate fuels with a few chemical components with similar behavior to pyrolysis oils in terms of fundamental combustion properties and major physical properties can be used to model the fuel’s gasification chemistry. In the present work, ethylene glycol is selected as a single-component surrogate for the pyrolysis oil because of its similar chemical and physical properties to pyrolysis oil. However, even with this simplification, the detailed chemical kinetic mechanism for ethylene glycol available in literature is still too large to allow its efficient use in two-dimensional simulations. Therefore, in the present work, a reduced reaction mechanism has been developed for describing the gasification chemistry of ethylene glycol. This mechanism was first validated by computing ignition delay times and laminar flame speeds of several relevant species and by comparing the calculated values against published experimental data. Furthermore, the developed reduced reaction mechanism was used to perform a CFD simulation of the Research Entrained Flow GAsifier operated at the Karlsruhe Institute of Technology. The mechanism was further validated by comparing the simulation results with published experimental data from the REGA experiments. In all validation computations, the developed reduced chemical kinetic reaction mechanism showed very good agreement with the experimental data. Also, the validated reduced reaction model was used to perform a parameter study for typical REGA conditions, by investigating its performance with respect to equivalence ratio, fuel preheat temperature, and operating pressure. From this parameter study, it has been found that both the fuel preheat temperature and the operating pressure have a marginal influence on the composition of the syngas produced. The equivalence ratio had the strongest effect on the syngas composition, with an almost linear variation in the investigated equivalence ratio range.

Energy densification is the overall objective of the ongoing bioliqproject. Bioslurry, which is obtained via the fast pyrolysis of low-grade biogenic resources, is converted to high-quality syngas in a high-pressure entrained-flow gasifier. The modeling of this three-phase system, involving high-pressure and high-temperature subprocesses, is very challenging. The detailed representation of the chemical subprocesses goes along with an increase of the computational cost. In this work, a novel approach is developed to achieve fast and accurate computational fluid dynamics (CFD) simulations of the gasification of a slurry fuel in a laboratory-entrained flow gasifier under atmospheric pressure. The method investigated relies on a sectional approach to describe the char gasification. An Euler–Euler approach is used for the modeling of the slurry/gas phase system. Ethylene glycol is used to represent the liquid part of the slurry. Experimental data for validation are taken from various experiments (S. Fleck et al. Fuel2018, 217, 306–319 and S. Fleck et al. VDI-Berichte2015, 2267, 207–217) conducted at the Research Entrained flow GAsifier (REGA) at the Karlsruhe Institute of Technology (KIT).

Almost the complete amount of jet fuel available on the global market is produced from fossil crude oil being an exhaustible raw material. Furthermore its use is inherently connected with emissions of the greenhouse gas CO2. To cope with this, several processes for the production of alternative aviation fuels were developed including the use of biomass as a renewable feedstock. Since biomass from cultivation farming is in competition with food and fodder production, the preferred raw material would be residues from agriculture and forestry or municipal waste, also microalgae can be used. Independent of the raw material, the conversion of biogenic feedstock into alternative jet fuel is based on microbial, thermal and/or chemical breakdown of larger (bio)-molecules into smaller ones, followed by the catalytic formation of fuel molecules and hydrogenation. An overview on the production of different alternative bio-based jet fuels is given including a survey about producers and capacities, focusing on already certificated bio-based jet fuels. In addition to that, a comparison of fundamental combustion properties between Jet A-1 and different alternative jet fuels is presented: Laminar burning velocities and ignition delay times, each measured for two synthetic jet fuels based on fossil resources (coal-to-liquid—CtL and gas-to-liquid—GtL) as well as for two biofuels (farnesane and an Alcohol-to-Jet fuel—AtJ). Measurements of the burning velocities were performed at a preheat temperature of 473 K and pressures of 1 and 3 bar by variation of the fuel–air-equivalence ratios φ. Ignition delay times were determined for φ-values of 0.5, 1.0, and 2.0, at an initial pressure of about 16 bar and temperatures ranging between 800 and 1700 K. It turns out that with respect to the characteristic combustion properties tested the considered alternative fuels have a combustion behavior similar to Jet A-1.

In the last years, several alternative aviation jet fuels have been approved as a response to worldwide concerns on adverse environmental effects of greenhouse gas emissions. However, comprehensive emissions studies are not part of the approval process. When burning a jet fuel, the exhaust gases are a mixture of gaseous specious including aromatics and non-gaseous species, particles, and soot. In addition, these species may affect the growth and lifetime of contrails known to be of influence on the climate due to their radiative forcing. Within this context, the use of synthetic aviation fuels may offer several advantages, going beyond reduced CO2emissions. These issues were addressed by studying the combustion of synthetic jet fuels taking into account their individual composition. An overview of what is known on their emission pattern was presented. Mostly, the same general trends were reported for the emissions of interest, for the fuels considered and at the power settings selected, with no adverse emissions effects. In particular, less soot particle emissions were reported, in mass and in number concentration, for GtL, HEFA, and farnesane. Moreover, a strong link between the amount and type of aromatics content of a jet fuel and soot emissions was observed.

Since the last decade, the aviation sector is looking for alternatives to kerosene derived from crude oil triggered also by commitments and policy packages, such as the ‘Flightpath 2050’ initiative and the comprehensive alternative fuels strategy, both released by the European Commission. An aircraft need with regard to a fuel is very strict, with severe constraints to ensure a safe and reliable operation for the whole flight envelope. When synthesizing a jet fuel from scratch, two important aspects need to be addressed: First, the safety aspect—the new fuel candidate must be certified, qualifying through several well-defined cost and time expensive tests, according to the approval protocol; secondly, the environmental aspect. Alternative aviation fuels alike Jet A-1 are composed of hydrocarbons; however, the amount and type of hydrocarbons (chemical family) differ considerably. The question is how the composition of the fuel will affect its suitability and performance: (i) thermo-physical and thermo-chemical properties of the new components to exclude any shortcomings with respect to performance and safety issues, and (ii) the new fuel combustion characteristics, i.e., ignition, flame speed, and emission pattern (pollutants), in particular. These issues are addressed in the present study. Thus, the road will be paved for developing a generalize science-based tool to investigate in an efficient way if a new fuel candidate may meet the fuel specifications.

Sustainably produced synthetic fuels offer great potential for a fast reduction of the greenhouse gas emissions of the transport sector. For an immediate application within the existing infrastructure and vehicle fleet, synthetic fuels need to comply with existing standards such as the EN 228 for gasoline. Beyond these standards and with optimized fuel design, certain properties can be improved compared to conventional fuels. For this purpose, methods for evaluating the properties are needed.

During the last years, the aviation sector has been looking into alternatives to kerosene from crude oil, to combat climate change by reduction of greenhouse gas (GHG) emissions and to ensure security of supply at affordable prices. The efforts are also a reaction to commitments and policy packages. Currently, a wide range of possible fuel candidates and fuel blends are discussed in the triple feedstock, process, and product. Any (synthetic) aviation fuel must be certified; hence, a profound knowledge on its properties, in particular thermophysical and chemical, is inevitable. In the present paper, an overview is given on alternative jet fuels, looking into the short-term and long-term perspective. Examples focusing on experimental and modeling work of combustion properties of existing—coal to liquid, gas to liquid (GtL)—and possible alternative fuels—GtL + 20 % 1-hexanol, GtL + 50 % naphthenic cut—are presented. Ignition delay times and laminar flame speeds were measured for different alternative aviation fuels over a range of temperatures, pressures, and fuel–air ratios. The data are used for the validation of a detailed chemical reaction mechanism following the concept of a surrogate. Such validated reaction models able to describe and to predict reliably important combustion properties of jet fuels are needed to further promote the development of even more sophisticated jet engines and to optimize synthetic jet fuel mixtures in practical combustors.

An existing two-equation soot model is extended by nucleation of soot particles from phenyl to improve the model´s results for aromatic fuels. The model describes the soot formation processes by rate equations for the soot concentration and the soot volume fraction. These two equations are solved fully coupled with the rate equations of the gas-phase species resulting from a detailed chemical kinetics model.The soot model is tested under shock-tube conditions for the oxidation of n-heptane and toluene. The maximum volume fraction needed as input to the two-equation model is derived from simulations with a detailed soot model, when no experimental values are given. Therefore a bell-shaped curve is fit to the detailed simulation´s results and the so determined fit parameters are passed to the two-equation model.Two sets of parameters for the simplified model are found, one representing the former version of the model with nucleation solely depending on propargyl and another one additionally including phenyl in the nucleation process. Both parameter sets show good agreement to the experimental values and nearly equal results for the time evolution and temperature dependence during the oxidation of n-heptane. However, during the oxidation of toluene additionally considering particle nucleation from phenyl improves the results compared to the former version of the two-equation model as the soot yield is predicted much better for lower temperatures.

Public concern about the environmental situation creates strong restrictions on the purity of exhaust gases in various polluting industrial enterprises. A promising method of gas cleaning is the use of pulsed corona discharges. In these devices, short pulses at high frequency allow one to increase the energy input and radical production for subsequent transformation of toxic pollutants (NOx, SO2, CxHy, etc).For a better understanding and optimization of the possible applications of this technique it is necessary to develop models for the underlying physical and chemical processes which are responsible for the removal of pollutants.In this work, we have theoretically investigated the removal of NO and the effect of ethane and propene on NO removal by non-thermal plasma discharges at low temperature (373 K) and at atmospheric pressure.The model takes into account the production of radicals after every discharge and the subsequent removal of NO and HC by radicals. Reaction flow analysis reveals the characteristic differences of NO reactions in the presence of unburned alkanes and alkenes. The results of our numerical simulations show good agreement with experimental data published in the literature.

A universally applicable model is presented for the calculation of the transport properties of ionized species in CFD simulations. A multicomponent mixture formulation and simple mixing rules are used to compute the transport coefficients of dissociated and ionized air from room temperature up to 30000 K at different pressures. Both formulations share little input data, which simplifies the handling of the transport model. The calculated binary diffusion coefficients are similar to the results of Levin et al.1-3and Capitelli et al.4The computed transport coefficients of the mixture are compared to the results of Gupta et al.5A good agreement is found in the temperature range below 10000 K. At higher temperatures the results differ, because of the differences in the collision integrals of neutral-ion and Coulomb interactions and because of the use of higher approximations of transport properties of electrons in the present model.

Es wird ein Verfahren vorgestellt, mit dem sich die Schwingungen und die Stabilität von Zentrifugen berechnen lassen, deren zylindrische Trommel mit einer schwach viskosen Flüssigkeit teilweise gefüllt ist. Dabei wird die zu untersuchende Maschine als ein ungedämpftes, diskretisiertes System aufgefaßt.

The thermochemical conversion of biomass, through gasification and consecutive fuel synthesis, can produce high-quality fuels. Entrained-flow gasification is regarded as the forthcoming technology providing syngas of sufficient quality, though the technology readiness level needs to be raised to allow its wide use. To this end, investigations within the bioliq project have been conducted on the gasification of fast pyrolysis products: pyrolysis oil and biochar, forming together a so-called bioslurry. This article will present the parametrization and results of numerical simulations of entrained-flow gasification. A first set of simulations on the gasification of a liquid fuel on two well-referenced experimental data sets is presented. Here, the liquid is monoethylene glycol, a surrogate for pyrolysis oil. Then, simulations of slurry fuels are considered, where the conversion of the biochar particles is numerically solved with a sectional approach. The simulations prove to retrieve the experimental results with a high accuracy, thus making CFD simulations based on the proposed approaches an adapted tool to investigate further operating conditions or for scaling-up. Particular attention is drawn on the parametrization of the approach. It will be shown that the majority of the model’s parameters, such as the pseudospecies size distribution, composition, and thermodynamic properties, can be derived from regular analytical chemistry techniques. The parameter with the highest sensitivity was identified to be the gasification reaction rate of the secondary char. The proposed model is sensitive to the properties of different types of biochar as well as to the amount of solid in the slurry fuel. By presenting a methodology, which can be quickly adapted to further solid fuels, the present work will allow for tackling the variability of biomass-derived fuels and find suitable operating conditions adapted to specific biomass conditions.

The pathway of methylidyne (CH) oxidation on Rh{211} was studied using plane wave density functional theory (DFT) slab calculations and microkinetic simulations. We present ample evidence that the direct decomposition and oxidation mechanism is not the main reaction route to sythesis gas especially during light-off of catalysts. We characterize the transition state for the surface oxidation of CH to oxomethylidyne (CHO) species and subsequent decomposition to CO and H as products to establish the minimum energy pathway.