Lean-Blow-Out Simulation of Natural Gas Fueled, Premixed Turbulent Jet Flame Arrays With LES and FGM-Modeling

To ensure compliance with stricter regulations on exhaust gas emissions, new industrial burner concepts are being investigated. One of these concepts is the matrix burner, consisting of an array of premixed, non-swirling jet flames. For the design of such burners, the prediction of fundamental burner properties is mandatory. One of these essential quantities is the lean blowout limit (LBO), which has already been investigated experimentally. This study investigates the possibility of numerical LBO prediction using a tabulated chemistry approach in combination with Large-Eddy-Simulation turbulence modeling. In contrast to conventional swirl burners, the numerical description of blowout events of multi jet flames has not yet been studied in detail. Lean blowout simulations have therefore been conducted for multiple nozzle variants, varying in their diameter and global dump ratio for a variety of operating conditions, showing their general applicability. A procedure to induce LBO is introduced where a stepwise increase in total mass flow is applied. LBO is determined based on the temporal progress of the mean reaction rate. A comparison with measurements shows good agreement and demonstrates that the procedure developed here is an efficient way to predict LBO values. Further investigations focused on the flame behavior when approaching LBO. The flame shape shows a drastic change from single jet flames (stable conditions) to a joint conical flame approaching LBO, which increases in length for increasing inlet velocity, showing the importance of jet interaction at LBO

Determination of a correlation for predicting lean blow off limits of gaseous fueled, premixed turbulent jet flame arrays enclosed in a hexagonal dump combustor

Combustion of natural gas with air in gas turbines is a key technology for efficient provision of electric energy and heat. More stringent regulations regarding the emission of pollutants, such as NOx emissions, are necessitating research on technologies to reduce NOx formation during the combustion process. One technical approach onto the reduction of NOx-formation during combustion is fuel-lean premixed combustion. Current lean combustion concepts applied in stationary gas turbine combustors rely on flame stabilization through recirculation of hot flue gas using swirling flows. Swirl stabilized flames may be prone to combustion instabilities especially in lean premixed arrangements. Therefore, another approach is followed in the present study. In this concept, a matrix of turbulent lean premixed jet flames in a dump combustor is applied. The matrix burner consists of a nozzle with an array of circular channels in a hexagonal arrangement and a combustion chamber with a hexagonal cross section. In order to develop an appropriate burner design based on this concept, the experimental determination and theoretical evaluation of the lean blow out limit using different nozzles and operating conditions were conducted in this work in order to quantify the influence of different parameters on the flame stability. The varied geometric parameters are the diameter of the circular channels in the burner matrix as well as the ratio of the free cross section area of the nozzle to the cross section are of the combustion chamber, the combustor area dump ratio. The lean blow limit was determined at different preheating temperatures and flow velocities. The results show that the velocity at the LBO limit increases with increasing channel diameter, area combustor dump ratio and preheating temperature. The experimental results of three matrix burner are correlated in terms of a critical Damkoehler number and it is shown through experimental validation, that the Damkoehler number correlation derived is capable of predicting the LBO of a scaled matrix burner

Ubiquitin-phosphonamidates and -phosphonothiolates for DUB targeting and protein ubiquitination

Im ersten Teil dieser Arbeit wurde die Staudinger-Phosphonit-Reaktion auf Azidohomoalanin-haltiges Ubiquitin angewendet, um ortsspezifisch modifizierte Alkinphosphonamidat-Ubiquitine zu erzeugen. Diese Ubiquitin-basierten Sonden wurden bei neutralem pH-Wert in selektiven Konjugationen mit DUBs, die ein Cystein im aktiven Zentrum beinhalten, eingesetzt, auch in Anwesenheit anderer Thiole. Dabei beobachteten wir DUB-Spezifitäten in Abhängigkeit von der Phosphonamidat-Position innerhalb der Sonde. Die DUB-Selektivität konnte auch an Pull-Down-Experimenten aus Zelllysaten gezeigt werden. Zusätzlich konnte die Cystein-Selektivität der Sonde an ausgewählten konjugierten DUBs mittels MS/MS-Analyse nachgewiesen werden. Wir beobachteten auch unterschiedliche Ausmaße der DUB-Inhibition bei der Inkubation mit den verschiedenen Phosphonamidat-Sonden. Im Hinblick auf das DUB-Targeting in lebenden Zellen untersuchten wir auch Bedingungen für zellpenetrierende Peptid-konjugierte Ubiquitine für einen Transport der Sonde in das Zytosol der Zellen. Im zweiten Teil der Arbeit haben wir die neuartige, chemisch induzierte Phosphonothiolat Elektrophile für Thiol-Konjugation angewendet, um unhydrolysierbare ubiquitinierte Substrate herzustellen. Es gelang uns, ein hoch elektrophiles Ubiquitin-Vinylphosphonothiolat mit guter Ausbeute zu erzeugen. Wir konnten die frisch hergestellte Sonde in Konjugationen mit Cysteinen an ausgewählten Proteinen einsetzen. Um unser Konzept zu etablieren, generierten wir ein monoubiquitiniertes α-Synuclein und demonstrierten dessen strukturelle Integrität in einer enzymatischen Ubiquitinierung des Konjugats. Außerdem stellten wir ein künstlich K48-verknüpftes Diubiquitin her, das von spezifischen Antikörpern ähnlich erkannt wurde wie das native K48-verknüpfte Diubiquitin, aber in Gegenwart von DUBs sich als stabil erwies. Das Ubiquitin-Vinylphosphonothiolat zeigte ebenfalls eine selektive DUB-Konjugation, wenn nur kurze Inkubationszeiten verwendet wurden.In the first part of this thesis a Staudinger-phosphonite reaction was applied on azidohomoalanine-containing ubiquitin to generate site-specifically modified alkynephosphonamidate ubiquitins. These ubiquitin-based probes were utilized in selective conjugations of active site cysteine-containing DUBs at neutral pH, even in the presence of other thiols. Furthermore, we observed DUB specificities depending on the phosphonamidate position within the probe. The selectivity could also be demonstrated in pull-down experiments from cell lysates. Moreover, the probe’s cysteine selectivity within chosen conjugated DUBs could be determined using MS/MS analysis. Consequently, we observed varying extents of DUB inhibition upon incubation with the different phosphonamidate probes. For DUB targeting in living cells we also investigated conditions of cell penetrating peptide conjugated ubiquitin in order to successfully deliver them to the cytosol. In the second part of this thesis, we applied the novel chemically induced phosphonothiolate electrophiles for thiol conjugation to produce unhydrolyzable ubiquitinated substrates. Starting from a disulfide-activated cysteine ubiquitin mutant, we managed to generate a highly electrophilic ubiquitin vinylphosphonothiolate in satisfactory yield. We could apply the freshly prepared probe in conjugations with cysteines on selected proteins, in which the conjugation product showed to be remarkably stable. To establish our concept, we prepared monoubiquitinated α-synuclein and demonstrated its structural integrity in the performance of an enzymatical ubiquitination of the conjugate. Furthermore, we produced an artificially K48-linked diubiquitin, which was similarly recognized by specific antibodies as the native K48-linked diubiquitin and was not hydrolyzed in the presence of DUBs. The ubiquitin vinylphosphonothiolate displayed also selective DUB conjugation, when only short incubations were used

Functional expression of the epithelial sodium channel ?-subunit in human respiratory epithelial cells

THESIS 10085Mammalian amiloride-sensitive epithelial Na+ channel (ENaC) can be composed by different combinations of four homologous subunits, ?, ?, ? and ?. The canonical ???- ENaC, abundantly expressed in Na+ absorbing epithelia, is thoroughly investigated and well known for its crucial role in Na+ homoeostasis. Via aldosterone-controlled Na+ reuptake in the kidney, ENaC regulates blood volume and pressure. In the lung, it facilitates the maintenance of alveolar lining fluid layer and efficient gas exchange. Delta-ENaC, mainly expressed in non-epithelial tissues, has recently been described in human airway epithelia. Its physiological role, however, remains largely hypothetical and is primarily based on the expression data as well as the biophysical characteristics of the heterologously expressed protein

Numerische Untersuchung der Flammenform eines vorgemischten, unverdrallten Multijetbrenners

Um die immer strikter werdenden Vorschriften bezüglich der Abgasemissionen zu erfüllen, ist es notwendig, neue Brennerkonzepte zu erforschen und genauer zu verstehen. Eines dieser neuen Brennerkonzepte ist der Matrixbrenner, der eine Gruppe von nicht-verdrallten Strahlflammen erzeugt. Zur Auslegung solcher Brenner sind Kenntnisse über fundamentale Brennereigenschaften notwendig. Vergangene Untersuchungen berichteten bereits in Abhängigkeit der Betriebsbedingungen über eine signifikante Änderung der Flammenform, die Gegenstand der aktuellen Arbeit ist. Zu diesem Zweck werden unterschiedliche Matrixbrenner unter Änderung der Betriebsbedingungen mithilfe eines Grobstruktur- und tabellierten Chemie-Ansatzes numerisch simuliert. Zunächst werden die beiden Flammenformen genauer charakterisiert und verglichen und ein Algorithmus zur Identifikation der Flammenform vorgestellt. Weiterhin wird ein Korrelationsansatz zur Vorhersage des Flammenumschlagpunktes auf Basis des Peclet-Kriteriums vorgeschlagen

In-Cell Synthesis of Bioorthogonal Alkene Tag S-Allyl-Homocysteine and Its Coupling with Reprogrammed Translation

In this study, we report our initial results on in situ biosynthesis of S-allyl-l-homocysteine (Sahc) by simple metabolic conversion of allyl mercaptan in Escherichia coli, which served as the host organism endowed with a direct sulfhydration pathway. The intracellular synthesis we describe in this study is coupled with the direct incorporation of Sahc into proteins in response to methionine codons. Together with O-acetyl-homoserine, allyl mercaptan was added to the growth medium, followed by uptake and intracellular reaction to give Sahc. Our protocol efficiently combined the in vivo synthesis of Sahc via metabolic engineering with reprogrammed translation, without the need for a major change in the protein biosynthesis machinery. Although the system needs further optimisation to achieve greater intracellular Sahc production for complete protein labelling, we demonstrated its functional versatility for photo-induced thiol-ene coupling and the recently developed phosphonamidate conjugation reaction. Importantly, deprotection of Sahc leads to homocysteine-containing proteins—a potentially useful approach for the selective labelling of thiols with high relevance in various medical settings

Stabilization of bacterially expressed erythropoietin by single site-specific introduction of short branched PEG chains at naturally occurring glycosylation sites

The covalent attachment of polyethylene glycol (PEG) to therapeutic proteins can improve their physicochemical properties. In this work we utilized the non-natural amino acid p-azidophenylalanine (pAzF) in combination with the chemoselective Staudinger-phosphite reaction to install branched PEG chains to recombinant unglycosylated erythropoietin (EPO) at each single naturally occurring glycosylation site. PEGylation with two short 750 or 2000 Da PEG units at positions 24, 38, or 83 significantly decreased unspecific aggregation and proteolytic degradation while biological activity in vitro was preserved or even increased in comparison to full-glycosylated EPO. This site-specific bioconjugation approach permits to analyse the impact of PEGylation at single positions. These results represent an important step towards the engineering of site-specifically modified EPO variants from bacterial expression with increased therapeutic efficacy

Expression and function of the epithelial sodium channel δ-subunit in human respiratory epithelial cells in vitro.

Using human airway epithelial cell lines (i.e. NCI-H441 and Calu-3) as well as human alveolar epithelial type I-like (ATI) cells in primary culture, we studied the contribution of the epithelial sodium channel δ-subunit (δ-ENaC) to transepithelial sodium transport in human lung in vitro. Endogenous δ-ENaC protein was present in all three cell types tested; however, protein abundance was low, and no expression was detected in the apical cell membrane of these cells. Similarly, known modulators of δ-ENaC activity, such as capsazepine and icilin (activators) and Evans blue (inhibitor), did not show effects on short-circuit current (I SC), suggesting that δ-ENaC is not involved in the modulation of transcellular sodium absorption in NCI-H441 cell monolayers. Over-expression of δ-ENaC in NCI-H441 cells resulted in detectable protein expression in the apical cell membrane, as well as capsazepine and icilin-stimulated increases in I SC that were effectively blocked by Evans blue and that were consistent with δ-ENaC activation and inhibition, respectively. Consequently, these observations suggest that δ-ENaC expression is low in NCI-H441, Calu-3, and ATI cells and does not contribute to transepithelial sodium absorption