This study presents the development of the HyMAm-Flex burner manufactured by powder bed fusion of metals using a laser beam (PBF-LB/M). The burner was conceived to demonstrate the potential of additive manufacturing for highly integrated combustion systems, enabling fuel-flexible operation. The concept targets the reduction of carbon dioxide emissions by allowing the use of carbon-free fuels (ammonia and hydrogen) as well as carbon-based fuels (methanol) with distinctly different combustion characteristics. To ensure high corrosion resistance and high-temperature strength, the burner prototype is manufactured from the nickel-based alloy IN718. Additive manufacturing enables the integration of multiple functions into a single, monolithic burner design, including micro-channels for hydrogen injection, internal air distribution networks, and the integration of an ultrasonic atomizer for methanol atomization. These features are essential for achieving stable combustion conditions and would only be manufacturable using conventional techniques with significant additional effort. Large-eddy simulations (LES) of the multiphase flow are employed to analyze the hydrogen distribution within the burner geometry and to support the design process. The burner developed in this work is intended for experimental validation in a dedicated combustion test rig.

In this work, spray flamelet structures subject to curvature are systematically studied, emphasizing the ways in which this quantity modifies the budgets of the corresponding flamelet equations and their stretch-induced extinction limit. More specifically, a theoretical extension of the tubular counterflow configuration is first proposed, which allows the injection of droplets from the inner cylinder. After appropriate mathematical descriptions for this new configuration in physical and composition space are introduced, several ethanol/air tubular counterflow flames are studied. It is found that increasing curvature leads to major modifications of the resulting flamelet structures, which is attributable to its influence on the evaporation profiles. Further, it is found that increasing curvature considerably reduces the stretch-induced extinction limit, which can be directly related to a corresponding reduction of the maximum mixture fraction within the flamelet. Finally, it is concluded that extinction in tubular counterflow spray flames occurs through a mechanism significantly different from what has been previously observed for gas flamelets.Novelty and Significance StatementA theoretical extension of the classical gas tubular counterflow configuration is proposed, which allowed systematically studying curvature effects on spray flamelet structures for the first time. Mathematical models currently available in the literature, both in physical and mixture fraction space, are extended accordingly and used to analyze different flamelet structures. It was found that spray flamelet structures are considerably more sensitive to curvature than their gaseous counterpart, which can be attributed to the explicit effect of this quantity on the evaporation profiles. Additionally, a new extinction mechanism is identified, which considerably differs from what has been previously observed for gas flamelets.

Solutions of the spray flamelet equations reported in the literature during the last decade have been limited to very specific situations presenting steady evaporation profiles. Implicitly, this corresponds to the adoption of a continuous droplet injection strategy. In this work, it is shown how a relaxation of this restrictive assumption allows obtaining an entire spectrum of new solutions of the spray flamelet equations. For this, a Lagrangian description of the liquid phase in mixture fraction space is introduced, which is obtained by assuming that droplets travel along mixture fraction gradient trajectories. The resulting formulation is then employed to analyze ethanol/air non-premixed gas flamelets perturbed by mono-disperse sprays generated with continuous and discontinuous droplet injection strategies. It is observed that the latter leads to periodically oscillating solutions of the spray flamelet equations exhibiting time-averaged maximum temperatures up to 46 K higher than the ones obtained adopting the former. Additionally, a discontinuous injection strategy leads to an important extension of the ranges of initial droplet radii and velocities leading to burning flamelet structures (16% and 25%, respectively). Finally, it is illustrated how the developed approach also allows obtaining solutions of the spray flamelet equations for extinction/re-ignition phenomena, which have received no attention in the spray flamelet literature so far. The introduced formalism provides an appropriate basis for the future improvement of flamelet-based models for the simulation of turbulent spray flames. Novelty and significance This work presents the first unsteady solutions of the spray flamelet equations reported in the literature. These can be classified in two different groups: (i) Periodically oscillating unsteady flamelet structures and (ii) flamelets experiencing extinction/re-ignition phenomena. Until now, none of these had received any attention in the spray flamelet literature and, therefore, this study represents an important contribution towards the goal of bringing spray flamelet theory to the same level of development of its classical formulation for gas flames.

A single droplet heating, vaporization, and detailed combustion model is developed for pure p-xylene (p-C8H10) in hot air. p-C8H10 is a combustible solvent in precursor solutions, for instance, with titanium tetraisopropoxide (TTIP) for the production of TiO2 nanoparticles. In the present one-dimensional mathematical model, a spherically symmetric p-xylene droplet in hot air is considered, resolving both the droplet (liquid phase) and the ambience (gas phase). The calculation of the vaporization rate includes the Stefan velocity at the droplet surface. In the gas phase, a detailed chemical reaction scheme is used. Elementary reactions are combined with complex reactions that account for the thermal decomposition of the p-xylene. The reaction mechanism comprises 93 chemical reactions among 25 species. Variable thermo-physical properties are used for both the gas and the liquid phase. A parameter study is conducted by varying the hot ambient gas temperature and the initial droplet size. In a hot ambience, initial expansion of the p-xylene droplet occurs due to droplet heating. After initial heating and vaporization, autoignition and combustion in the gas phase take place. In contrast to similar studies of single droplet combustion in the literature, the present simulations are not only carried to the end of the droplet lifetimes but continued until the gas flame extinguishes due to lack of combustible fuel. The vaporization rate constant, the autoignition, and the flame standoff distance are analyzed.

Solving the spray flamelet equations in composition space is very challenging, which is attributable to the fact that the maximum value of the mixture fraction, Z max , is a priori unknown in such flames. In this work, an analytical solution for this quantity is proposed, which allows its determination in spray flames subject to imposed parabolic evaporation profiles. It is then illustrated how the proposed approach allows to effectively cover the solution space of the spray flamelet equations. The employed strategy works very well for the considered cases and the generality of the evaporation profile definition provides flexibility for explorations of other parametric choices in the future.

The transition toward carbon-free combustion fuels such as hydrogen (H2) and ammonia (NH3) presents significant challenges related to flame stability and pollutant formation. Many carbon-free and low-carbon, fuel-flexible burners operate with either a gaseous or liquid-phase fuel, selecting only a single phase during stable operation. In this work, the newly developed HyMAm-Flex (v18) burner is experimentally characterized for multiphase, multi-fuel combustion at 18 distinct operating conditions, demonstrating stable flames of gaseous H2, liquid ethanol (C2H5OH), and their binary and ternary mixtures with gaseous NH3 under stoichiometric conditions. A key feature of the additively-manufactured burner is the integration of an ultrasonic atomizer, which enables the generation of sprays with a narrow size distribution and low injection velocities. The atomizer performance is evaluated in situ, demonstrating the stable operation in a combustion experiment. The primary objective of the present study is to provide an initial experimental characterization of the HyMAm-Flex (v18) burner concept and its fuel flexibility. Chemiluminescence measurements in combination with visible flame luminosity are used to qualitatively assess reaction-zone structure and discuss the flame stability. Exhaust gas measurements of ternary-fuel combinations provide a quantitative baseline of the burner’s nitrogen-containing emissions and insight into the completeness of the combustion. Exhaust gas measurements showed nitrogen oxide (NOx) ¡ 400 ppmv (wet), NH3 slip ¡ 17 ppmv (wet), and nitrous oxide (N2O) ¡ 32 ppmv (dry). The addition of NH3 is associated with reduced intensity in the central flame and increased N2O and ammonia slip, whereas alcohol addition is associated with enhanced NH3 combustion within an optimal blending range. This study demonstrates the fuel flexibility of the novel burner concept and discusses potential improvements to the burner design aimed at enhancing flame stability and overall performance.

The counterflow configuration is a well-established setting to study the structure of laminar spray flames. Typically, the similarity transformation is introduced to transfer the two-dimensional gas-phase equations into one-dimensional governing equations. The equations which describe droplet motion are two-dimensional. For spray flames in the counterflow configuration, Continillo and Sirignano suggested that more than one numerical solution of these equations may exist, which meanwhile was confirmed by several studies. Up to three different structures were found for the same boundary conditions for the combustion of fuel sprays carried by air directed against an air stream. The first structure shows two chemical reaction zones one of which resides on the fuel side and the other one on the air side of the configuration. The other two spray flame structures show single chemical reaction zones that reside on one but different side of the stagnation plane. The present paper investigates the unsteady transition mechanisms between multiple methanol/air spray flame structures in the counterflow configuration. Perturbations are introduced to key parameters including gas strain rate, initial droplet size, and the equivalence ratio, to systematically analyze the physicochemical mechanisms that underlie the transitions between the different flame structures. The transitions, in general, result from the complex interplay between the spray vaporization and motion, which includes droplet reversal and oscillation, and the chemical reactions. The timescales of the transitions between the three different spray flame structures are analyzed in detail in the present paper.

In this work, spray flamelet structures subject to curvature are systematically studied, emphasizing the ways in which this quantity modifies the budgets of the corresponding flamelet equations and their stretch-induced extinction limit. More specifically, a theoretical extension of the tubular counterflow configuration is first proposed, which allows the injection of droplets from the inner cylinder. After appropriate mathematical descriptions for this new configuration in physical and composition space are introduced, several ethanol/air tubular counterflow flames are studied. It is found that increasing curvature leads to major modifications of the resulting flamelet structures, which is attributable to its influence on the evaporation profiles. Further, it is found that increasing curvature considerably reduces the stretch-induced extinction limit, which can be directly related to a corresponding reduction of the maximum mixture fraction within the flamelet. Finally, it is concluded that extinction in tubular counterflow spray flames occurs through a mechanism significantly different from what has been previously observed for gas flamelets.

This work presents a numerical study of bi-component n-heptane/ethanol spray flames in a counterflow to improve the understanding of the effect of non-ideal mixtures on the flame-spray interaction. The simulations of this spray configuration allow for the detailed examination of the real fluid behavior and its influence on gas-phase combustion kinetics for a wide range of relevant parameters, i.e., droplet composition, size, and gas strain rate. The results reveal that due to the large real activity coefficient of n-heptane and the resulting selective evaporation of the heavier component, the burning characteristics of the spray with a high initial ethanol content do not differ if non-ideal mixture is considered. Conversely, the flame structure with a low ethanol content is substantially different, and displacement of the flame towards the spray side of the configuration is found. A multiple reaction zone, displaying both partially-premixed and diffusion flames, exists, which is overestimated spatially if the fluid is assumed ideal. In general, the ideal prediction of real fluid would misinterpret the composition evaporation order, prolonging the droplet lifetime and consequently, enhancing the flame-spray interaction locally, which results in a lower flame temperature. A parameter characterizing the multicomponent droplet penetration is introduced, which highlights the appreciable non-ideal effects that vary with droplet size and composition, and most importantly, further demonstrates the necessity of considering the real fluid properties in design of next-generation engines with blended fuels.

Structures of laminar non-premixed ethanol/air spray flames in the axisymmetric counterflow configuration are studied under fuel-rich conditions by means of numerical simulations. The monodisperse ethanol spray is carried by air and directed against an air stream. Both streams enter at 300 K, and the system is at atmospheric pressure. Up to three different structures of these flames for identical boundary and initial conditions are identified, and regime diagrams are presented that show their conditions of existence in terms of the gas strain rate on the spray side of the configuration, a − ∞ , starting from 55/s at an initial spray velocity of 0.44 m/s. The equivalence ratio on the spray side, E − ∞ , is varied between 1.1 and 1.6, and initial droplet radii, R 0 , from 10 to 50 μ m are considered. The most stable spray flame structure is characterized by two chemical reaction zones. For some conditions, single chemical reaction zones on either side of the counterflow configuration are found. Conditions under which these different flame structures exist are analyzed. Previous studies identified only two different structures for non-identical boundary conditions, and in this study, three different structures are presented for the first time. Moreover, the transition mechanisms of one structure to another are analyzed. The competition between the energy-consuming spray evaporation and the exothermic chemical reaction rates as well as the location of the spray determines the existence of the different flame structures. This transition of the different flame structures may explain spray flame characteristics such as flame pulsation or flame instabilities. Keywords Triple structures , fuel-rich spray flames , counterflow configuration , transition mechanisms

Sprays of precursor solutions are used in flame spray pyrolysis (FSP) to produce functional nanoparticles with specific properties. The present study concerns the precursor titanium(IV) isopropoxide (TTIP) in p-xylene. A dilute monodisperse spray carried by an air stream is directed against an air stream to establish a counterflowing laminar spray flame. The complex thermophysical properties of the bi-component droplets are incorporated into the code as well as the detailed chemical reactions of the system with 213 chemical reactions among 52 species; the chemical reaction mechanism includes thermal decomposition of the TTIP and the combustion of p-xylene. The droplets are modeled using the multicomponent evaporation model. Drag and gravity forces are considered in the equation of droplet motion. Monodisperse spray flame structures are presented depending on the gas strain rate, the initial droplet size, the precursor mass loading as well as the equivalence ratio. The preferential evaporation of the more volatile p-xylene provides the gaseous fuel for combustion, and the thermal decomposition of the precursor TTIP considerably reduces the flame temperature.

<p>Halogen radicals can drastically alter the atmospheric chemistry. In the polar regions, this is made evident by the ozone depletion in the stratosphere (ozone hole) but also by destruction of boundary layer ozone during polar springs. These recurrent episodes of catalytic ozone depletion, better known as “ozone depletion events” (ODEs) are driven by enhanced concentrations of reactive bromine compounds. The proposed mechanism by which these compounds are released into the troposphere is known as “bromine explosion” - reactive bromine is formed autocatalytically from the condensed phase.</p> <p>In comparison to previous satellite missions, the TROPOspheric Monitoring Instrument (TROPOMI) onboard ESA’s S5-P satellite allows an improved localization and a more precise specification of these events due to its superior spatial resolution of up to 3.5 x 5.5 km<sup>2</sup>. Together with the better than daily coverage over the polar regions, this allows for investigations of the spatio-temporal variability of enhanced BrO levels and their relation to different possible bromine sources and release mechanisms.</p> <p>We present tropospheric BrO column densities retrieved from TROPOMI measurements using Differential Optical Absorption Spectroscopy (DOAS). One advantage of our retrieval is its independence from any external input data, thereby avoiding systematic biases from external datasets. We used a modified k-means clustering and methods from statistical data analysis to separate tropospheric and stratospheric partial columns, relying only on NO<sub>2</sub> and O<sub>3 </sub>columns measured by the same instrument. This ensures in particular that the derived tropospheric BrO data set keeps the same high spatial resolution as the TROPOMI instrument, because no model data with coarse resolution is used. In a second step, the retrieved tropospheric slant column densities (SCDs) are converted to vertical column densities (VCDs).</p> <p>TROPOMI’s improved spatial resolution is then utilized to study the spatial extent and shape of BrO plumes detected in the Arctic region. For this, a combination of morphological filters and connected component labeling is used to provide a statistical overview of all enhanced BrO plumes detected above certain sensitivity thresholds in the Arctic spring of 2019. This provides a lower limit for the spatial extent of enhanced BrO events (and hence also for ODEs) of around 40-60 km. Additionally, seasonal trends in size and shape of the BrO plumes as well as correlations to relevant meteorological parameters are investigated.</p>

Structures of laminar non-premixed ethanol/air spray flames in the axisymmetric counterflow configuration are studied under fuel-rich conditions by means of numerical simulations. The monodisperse ethanol spray is carried by air and directed against an air stream. Both streams enter at 300 K, and the system is at atmospheric pressure. Up to three different structures of these flames for identical boundary and initial conditions are identified, and regime diagrams are presented that show their conditions of existence in terms of the gas strain rate on the spray side of the configuration, [Formula: see text], starting from 55/s at an initial spray velocity of 0.44 m/s. The equivalence ratio on the spray side, [Formula: see text], is varied between 1.1 and 1.6, and initial droplet radii, [Formula: see text], from 10 to 50 [Formula: see text]m are considered. The most stable spray flame structure is characterized by two chemical reaction zones. For some conditions, single chemical reaction zones on either side of the counterflow configuration are found. Conditions under which these different flame structures exist are analyzed. Previous studies identified only two different structures for non-identical boundary conditions, and in this study, three different structures are presented for the first time. Moreover, the transition mechanisms of one structure to another are analyzed. The competition between the energy-consuming spray evaporation and the exothermic chemical reaction rates as well as the location of the spray determines the existence of the different flame structures. This transition of the different flame structures may explain spray flame characteristics such as flame pulsation or flame instabilities.

Cell culture scale-up is a challenging task due to the simultaneous change of multiple hydrodynamic process characteristics and their different dependencies on the bioreactor size as well as variation in the requirements of individual cell lines. Conventionally, the volumetric power input is the most common parameter to select the impeller speed for scale-up, however, it is well reported that this approach fails when there are huge differences in bioreactor scales. In this study, different scale-up criteria are evaluated. At first, different hydrodynamic characteristics are assessed using computational fluid dynamics data for four single-use bioreactors, the Mobius® CellReady 3 L, the Xcellerex™ XDR-10, the Xcellerex™ XDR-200, and the Xcellerex™ XDR-2000. On the basis of this numerical data, several potential scale-up criteria such as volumetric power input, impeller tip speed, mixing time, maximum hydrodynamic stress, and average strain rate in the impeller zone are evaluated. Out of all these criteria, the latter is found to be most appropriate, and the successful scale-up from 3 to 10 L bioreactor and to 200 L bioreactor is confirmed with cell culture experiments using Chinese Hamster Ovary cell cultivation.

Biotechnology and BioengineeringVolume 120, Issue 11 p. 3099-3103 ISSUE INFORMATIONFree Access Biotechnology and Bioengineering: Volume 120, Number 11, November 2023 First published: 13 October 2023 https://doi.org/10.1002/bit.28144AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Volume120, Issue11November 2023Pages 3099-3103 RelatedInformation

A novel matrix burner enabled the investigation of aerosol-doped laminar low-pressure flames. Iron nitrate dissolved in 1-butanol was used as a typical model system, also found in the flame spray pyrolysis for synthesis of iron oxide. The state of the aerosol entering the flame front was quantified by single-droplet evaporation calculations. Three-dimensional simulations were conducted to quantify thermal losses and the impact of buoyancy on the deviation from an ideal one-dimensional approximation. Highly resolved simulations of the burner matrix confirmed the compact, external mixing zone and the flatness of the flame in the low-pressure operation. Simulations based on the one-dimensional approximation demonstrated the suitability of the experimental setup for reaction kinetics investigations. The results were compared and validated by temperature measurements and probing mass spectrometry. Based on investigations of the particle-producing flame, a hypothesis about the origin of gas-borne nanoparticles in the spray-flame synthesis process was derived. This work demonstrates the suitability of the novel matrix burner for the investigation of reaction kinetics in aerosol doped, quasi-premixed, flat flames using one-dimensional, laminar flame simulations.

Tetrahydrofuran (THF) is a biofuel that can be added to improve the solubility of ethanol in diesel. To explore the effect of surfactants, the puffing and micro-explosion characteristics of ethanol diesel/THF (DTE) blend droplets are investigated experimentally in comparison to a counterpart blend of ethanol diesel/biodiesel (DBE). Results show that with a rise in temperature, the puffing delay time decreases rapidly opposite to the fluctuation ratio; however, the puffing delay time rises with the ethanol content, whereas the fluctuation ratio remains about constant. Moreover, the tetrahydrofuran mainly participates in the early evaporation stage resulting in more prone to the edge mode for DTE droplets, which is in contrast to the DBE droplets, which prefer the inner mode. The micro-explosion strength of DTE droplets is lower than that of DBE due to the more likely occurrence of the edge mode, but the corresponding growth rate of DTE (15.2%, 25.4%, and 56.8%) with temperatures of 573 K, 623 K, and 723 K is higher than that of DBE droplets (8.8%, 20.4%, and 48.7%). A numerical model is also established for the present blend droplets, and the simulations reveal that the THF may additionally influence the heat absorption by the liquid and hence the superheat point of ethanol, which is responsible for the bubble formation and the micro-explosion.

In flame spray pyrolysis, the precursor solution droplet undergoes heating and evaporation, followed by gas phase combustion and generation of nanoparticles. Depending on the precursor solution, the pre-cursor/solvent droplet may experience puffing and micro-explosion. A new one-dimensional model is developed to describe these processes in the spherically symmetric droplet interior with emphasis on the puffing and the micro-explosion. After the initial droplet heating, the preferential evaporation of the higher volatile component causes the accumulation of the lower volatile precursor at the droplet surface and thus forms a liquid shell that hinders the evaporation process. In the droplet interior away from the liquid shell, the higher volatile component accumulates and when the temperature reaches the boiling point of that liquid, puffing occurs. If the pressure inside the droplet exceeds the ambient pressure, the droplet undergoes micro-explosion. The present study concerns single precursor/solvent droplets of tita-nium(IV) isopropoxide (TTIP) in p-xylene at room temperature in hot convective air at atmospheric pres-sure. A parameter study is performed to show the dependence of the puffing and the micro-explosion on the initial precursor loading, the initial droplet size, the ambient gas temperature, and the relative velocity between the droplet and the ambience. There are situations where micro-explosion follows the puffing or puffing repeats until the end of the droplet lifetime with no micro-explosion. This is the first model to successfully describe the puffing in precursor solution droplets and the micro-explosion which may follow the puffing.(c) 2022 Elsevier Ltd. All rights reserved.

Hydrodynamic stress is an influential physical parameter for various bioprocesses, affecting the performance and viability of the living organisms. However, different approaches are in use in various computational and experimental studies to calculate this parameter (including its normal and shear subcomponents) from velocity fields without a consensus on which one is the most representative of its effect on living cells. In this letter, we investigate these different methods with clear definitions and provide our suggested approach which relies on the principal stress values providing a maximal distinction between the shear and normal components. Furthermore, a numerical comparison is presented using the computational fluid dynamics simulation of a stirred and sparged bioreactor. It is demonstrated that for this specific bioreactor, some of these methods exhibit quite similar patterns throughout the bioreactor-therefore can be considered equivalent-whereas some of them differ significantly.

Halogen radicals can drastically alter the atmospheric chemistry. In the polar regions, this is made evident by the ozone depletion in the stratosphere (ozone hole) but also by localized destruction of boundary layer ozone during polar springs. These recurrent episodes of catalytic ozone depletion, better known as “ozone depletion events” (ODEs) are caused by enhanced concentrations of reactive bromine compounds. The proposed mechanism by which these compounds are released into the troposphere is called “bromine explosion” - reactive bromine is formed autocatalytically from the condensed phase.In comparison to previous satellite missions, the TROPOspheric Monitoring Instrument (TROPOMI) onboard ESA’s S5-P satellite allows for an improved localization and a more precise specification of these events due to its superior spatial resolution of up to 3.5 x 5.5 km2. Together with the better than daily coverage over the polar regions, this allows for investigations of the spatiotemporal variability of enhanced BrO levels and their relation to different possible bromine sources and release mechanisms.We present tropospheric BrO column densities retrieved from TROPOMI measurements using Differential Optical Absorption Spectroscopy (DOAS). The advantage of our retrieval is its independence from any external input data. We used a modified k-means clustering and methods from statistical data analysis to separate tropospheric and stratospheric partial columns, thereby relying only on NO2 and O3 columns measured by the same instrument. This ensures in particular that the derived tropospheric BrO data set keeps the same spatial resolution as the TROPOMI instrument, because no model data with coarse resolution is used. In a second step, the BrO slant column densities (SCDs) are converted into vertical column densities (VCDs) by using an air mass factor (AMF). These AMFs are derived using a look-up table (LUT) generated by the McArtim radiative transfer model. From this LUT the AMF is calculated for each pixel using measured O4 SCDs and reflectance data. In a last step, satellite pixels are differentiated by their sensitivity to the lower troposphere using the determined AMF. This allows the exclusion of measurements deemed not sensitive to the troposphere from the dataset and gives a high confidence in the remaining retrieved values.Our retrieval algorithm avoids systematic biases from external data sets and climatologies and is therefore particularly well suited to compare the retrieved VCDs to additional environmental parameters suspected to alter the release and distribution of BrO during Arctic spring. We examine tropospheric BrO enhancements through case studies, with particular emphasis on the interconnection of ODEs and meteorology. We focus here on the relation of tropospheric BrO to mean sea level pressure, surface air temperature, sea ice age and wind speed and direction. In addition, the spatiotemporal extent of events is studied and compared to WRF-Chem simulations.