@misc{13670, abstract = {{The aging of biodiesel proceeds via multiple pathways, with oligomerization playing a central role. In this study, we investigated an epoxide-dependent oligomerization pathway, which had previously only been postulated. Using methyl oleate (C18:1) as a model monounsaturated fatty acid and acetic acid as a representative, reactive nucleophile and known biodiesel aging product with a suitable boiling point, oligomeric products were identified by size-exclusion chromatography (SEC) coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). The concentration of 20 wt% was chosen to ensure a measurable kinetic effect while maintaining stable reaction conditions. Furthermore, the role of methyl oleate during biodiesel aging was addressed. Time-resolved analysis confirmed the proposed sequential order of reactions. It was pointed out that elimination reactions may occur. The data support the formation of epoxides, despite the isobaric overlap with ketones, and show that hydroxyl intermediates undergo esterification and etherification. Moreover, experiments with pure C18:1 demonstrated that acetic acid–derived oligomers are generated. Under Rancimat conditions, addition of 20 wt% acetic acid resulted in an approximately 1.1 – 2.6 increase in product yield. Kinetic analysis revealed structure-dependent formation and decay behavior of the aging products, with slightly faster epoxidation and shifted product distributions toward higher oligomeric species in the presence of acetic acid. Reactive intermediates were consumed more rapidly than oligomeric species and all decay processes followed apparent second-order kinetics. These findings provide direct experimental evidence for the involvement of epoxide-dependent pathways in biodiesel aging.}}, author = {{Türck, Julian and Funke, Carsten and Schmitt, Fabian and Schneider, Jan and Danneel, Hans-Jürgen and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}}, booktitle = {{Fuel}}, issn = {{1873-7153}}, publisher = {{Elsevier BV}}, title = {{{Kinetic study and confirmation of epoxide-dependent oligomerization of methyl oleate}}}, doi = {{10.1016/j.fuel.2026.139339}}, volume = {{424}}, year = {{2026}}, } @misc{13671, abstract = {{The aging of biodiesel proceeds via multiple pathways, with oligomerization playing a central role. In this study, we investigated an epoxide-dependent oligomerization pathway, which had previously only been postulated. Using methyl oleate (C18:1) as a model monounsaturated fatty acid and acetic acid as a representative, reactive nucleophile and known biodiesel aging product with a suitable boiling point, oligomeric products were identified by size-exclusion chromatography (SEC) coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). The concentration of 20 wt% was chosen to ensure a measurable kinetic effect while maintaining stable reaction conditions. Furthermore, the role of methyl oleate during biodiesel aging was addressed. Time-resolved analysis confirmed the proposed sequential order of reactions. It was pointed out that elimination reactions may occur. The data support the formation of epoxides, despite the isobaric overlap with ketones, and show that hydroxyl intermediates undergo esterification and etherification. Moreover, experiments with pure C18:1 demonstrated that acetic acid–derived oligomers are generated. Under Rancimat conditions, addition of 20 wt% acetic acid resulted in an approximately 1.1 – 2.6 increase in product yield. Kinetic analysis revealed structure-dependent formation and decay behavior of the aging products, with slightly faster epoxidation and shifted product distributions toward higher oligomeric species in the presence of acetic acid. Reactive intermediates were consumed more rapidly than oligomeric species and all decay processes followed apparent second-order kinetics. These findings provide direct experimental evidence for the involvement of epoxide-dependent pathways in biodiesel aging.}}, author = {{Türck, Julian and Funke, Carsten and Schmitt, Fabian and Schneider, Jan and Danneel, Hans-Jürgen and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}}, booktitle = {{Fuel : the science and technology of fuel and energy }}, issn = {{1873-7153}}, keywords = {{Biodiesel aging, Epoxide-dependent oligomerization, Acetic acid, Identification of aging products, Kinetics of aging products}}, publisher = {{Elsevier}}, title = {{{Kinetic study and confirmation of epoxide-dependent oligomerization of methyl oleate}}}, doi = {{10.1016/j.fuel.2026.139339}}, volume = {{424}}, year = {{2026}}, } @misc{12844, abstract = {{Solketal and oxymethylene ether (OME) are two promising blending candidates for regenerative fuels (e-fuels), which could contribute to a holistic solution to the energy crisis. In this study the thermo-oxidative aging of these two e-fuels in their pure form as well as in binary mixtures with different ratios (3:1, 1:1, and 1:3) (vol%) is investigated. Herein, the reaction networks of the thermo-oxidative aging process of both e-fuels and mixtures thereof is elucidated based on intermediates and decomposition products determined via GC-MS. Furthermore, changes of important fuel-specific parameters like kinematic viscosity and density as well as total acid number during aging have been determined. The 3:1 solketal:OME (vol%) mixture exhibits a higher stability to thermo-oxidative aging than the pure fuel components or mixtures with other ratios. The viscosity value of this mixture is within the DIN EN 590 norm after accelerated aging of 72 h (viscosity (72 h) = 4.25 mm(2)/s)) unlike other blends. The maximum value of the total acid number of this aged mixture reaches only similar to 29 % of the maximum value of aged pure OME and has the lowest value of all mixtures. Furthermore, the formation of a precipitate could be successfully suppressed in the 3:1 solketal:OME (vol%) mixture different from other mixtures. With these findings, this study contributes to the design of new sustainable fuels for the transport sector.}}, author = {{Lichtinger, Anne and Poller, Maximilian J. and Schröder, Olaf and Türck, Julian and Garbe, Thomas and Krahl, Jürgen and Jakob, Markus and Albert, Jakob}}, booktitle = {{Fuel : the science and technology of fuel and energy}}, issn = {{1873-7153}}, keywords = {{E -fuels, Solketal, OME, Fuel mixtures, Aging mechanism}}, publisher = {{Elsevier BV}}, title = {{{Revealing the aging mechanisms of solketal, oxymethylene ether, and mixtures thereof as promising e-fuels}}}, doi = {{10.1016/j.fuel.2025.134738}}, volume = {{390}}, year = {{2025}}, } @misc{11807, author = {{Klepp, Georg Heinrich}}, booktitle = {{Kraftstoffe Für Die Mobilität Von Morgen : 6. Tagung der Fuels Joint Research Group Am 13. und 14. Juni 2024 in Berlin}}, editor = {{Munack, Axel and Krahl, Jürgen and Bünger, Jürgen and Eilts, Peter}}, location = {{Berlin}}, pages = {{103--109}}, publisher = {{Cuvillier Verlag}}, title = {{{Digitaler Kraftstoffzwilling}}}, volume = {{35}}, year = {{2024}}, } @misc{12846, abstract = {{The decarbonization of the energy supply is one of the biggest and most important challenges of the 21st century. This paper contributes to the solution of the energy crisis by investigating the stability of alcohols as e-fuels. The focus is on the investigation of the aging mechanism of the linear alcohols 1-hexanol and 1-octanol compared to the iso-alcohol 2-hexanol. It is analysed in detail how the time-dependent aging varies depending on the chain length and the position of the hydroxy-group, both in the liquid and in the gas phase. It is shown that a variety of aging products such as aldehydes, acids, short-chain alcohols and esters are formed during the aging of the n-alcohols by oxidation, decarboxylation, oxidative C-C bond cleavage and esterification. In contrast, the decomposition of the iso-alcohol is significantly lower. The results show that the total acid number is significantly higher for aged n-alcohols than for the aged iso-alcohos, while the kinematic viscosity decreases for all alcohols during aging. Carbon mass balancing shows that after accelerated aging for 120 hours, around 80% of the iso-alcohol is still present, compared to only around 57-63% for the n-alcohols. In addition, significantly fewer acids are formed with the iso-alcohol. In this study, iso-alcohols have a higher stability against thermo-oxidative aging compared to n-alcohols, showing their potential as e-fuels. Furthermore, the chain length of the alcohols has also an influence on aging, as more different aging products can be formed with increasing chain length. This paper contributes to the solution of the energy crisis by investigating the stability of alcohols as e-fuels. The focus is on the investigation of the aging mechanism of 1-hexanol and 1-octanol compared to the 2-hexanol.}}, author = {{Lichtinger, Anne and Poller, Maximilian J. and Schröder, Olaf and Türck, Julian and Garbe, Thomas and Krahl, Jürgen and Jakob, Markus and Albert, Jakob}}, booktitle = {{ Sustainable energy & fuels : interdisciplinary research for the development of sustainable energy technologies }}, issn = {{2398-4902}}, keywords = {{OXIDATION, 1-OCTANOL, PERFORMANCE, CATALYSTS, KINETICS, ACID}}, number = {{15}}, pages = {{3329--3340}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{Thermo-oxidative aging of linear and branched alcohols as stability criterion for their use as e-fuels}}}, doi = {{10.1039/d4se00400k}}, volume = {{8}}, year = {{2024}}, } @misc{12823, abstract = {{The energy crisis and dependence on fossil fuels forces societies to develop alternative pathways to secure energy supplies. Therefore, non‐fossil fuels such as biofuels and e‐fuels can help counteract the resulting demand for existing combustion engines. However, biofuels, like biodiesel, have disadvantages in terms of oxidation stability. In general, aging of biodiesel is a complex mechanism due to interaction of various components. In order to develop an ideal fuel, the mechanism must be understood in full detail. In this work, an attempt is made to simplify the system by using methyl oleate as a biodiesel model component. In addition, other fuel components of interest such as alcohols and their respective acids help to clarify the aging mechanism. This work used isopropylidene glycerol (solketal) as the main alcohol, 1‐octanol and octanoic acid. A holistic biodiesel aging scheme was developed by using generated data and evaluating the role of acids. They epoxidize unsaturated fatty acid via Prileschajev reactions. In addition, the role of epoxides in oligomerization reactions is confirmed. Moreover, the alcohols show that the suppression of oligomerization can be achieved by the reaction with methyl oleate. The alcohol‐dependent aging products were determined by quadrupole time‐of‐flight (Q‐TOF) mass spectrometry.}}, author = {{Türck, Julian and Schmitt, Fabian and Anthofer, Lukas and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}}, booktitle = {{ ChemSusChem : chemistry & sustainability, energy & materials}}, issn = {{1864-564X}}, keywords = {{biodiesel aging, epoxide-dependent oligomerization, solketal, Prileschajew reaction}}, number = {{17}}, publisher = {{Wiley}}, title = {{{Extension of Biodiesel Aging Mechanism–the Role and Influence of Methyl Oleate and the Contribution of Alcohols Through the Use of Solketal}}}, doi = {{10.1002/cssc.202300263}}, volume = {{16}}, year = {{2023}}, } @misc{12832, abstract = {{Formulating energy policies at national, European, and global levels is extremely challenging. The move away from fossil fuels is associated with a variety of technological, economic, and social implications, each of which is subject to dynamic changes and societal scrutiny and can hardly be predicted with certainty. Therefore, a fact-based assessment for the path to a sustainable green energy future is sought out in this paper, using the road-based mobility sector of the Federal Republic of Germany as an example. The analysis performed in this paper is built on publicly accessible, reputable sources like DESTATIS and EUROSTAT. In addition, some very simple calculations were made, e.g., on the potential for wind and photovoltaic energy within Germany. Such an analysis needs to start with the overall energy consumption of any one country. A basic assumption of the paper is that the energy system of the future will be based to a large extent on electricity and its storage in chemical energy. It is assumed that, in addition to hydrogen, liquid energy sources will play a significant role due to the simplicity of their logistics and the subsequent implications on cost. Examples of green, electricity-based fuels with great potential are methanol, methane, and ammonia. Additionally, biomass plays an important role, either for direct use as a fuel or as a source of non-fossil carbon. Today, biofuels, i.e., biodiesel and bioethanol, deliver the largest contribution to climate protection in the EU transport sector. The main goal—the reduction of greenhouse gas emissions—often collides with geopolitical circumstances or national political necessities. This includes, for example, the current world market situation and its national impacts caused by the Russian attack on Ukraine. The prospect for a green, sustainable, and defossilized energy supply are discussed in this context. The paper concludes that a defossilized world energy supply and trade based on renewable electricity and its derivatives, eHydrogen and refuels, and on biomass, is feasible.}}, author = {{Atzler, Frank and Türck, Julian and Türck, Ralf and Krahl, Jürgen}}, booktitle = {{ Energies : open-access journal of related scientific research, technology development and studies in policy and management }}, issn = {{1996-1073}}, keywords = {{eFuels, biomass, bioFuels, energy transition, energy supply, defossilation, mobility, energy storage, energy transport, regenerative energy}}, number = {{12}}, publisher = {{MDPI AG}}, title = {{{The Energy Situation in the Federal Republic of Germany: Analysis of the Current Situation and Perspectives for a Non-Fossil Energy Supply}}}, doi = {{10.3390/en16124569}}, volume = {{16}}, year = {{2023}}, } @misc{12836, abstract = {{The complexity of biodiesel aging has shown that the mechanism needs further research. The rate of aging product formation and associated interactions can help improve fuel quality. Since biodiesel is a multicomponent system and constant changes occur in the chemical environment, which interactions yield which products must be shown in more detail. Particularly under observation was the correlation between peroxides and epoxides. In addition, it is critical that the influence and interactions of new drop-in fuel candidates be investigated. In this work, the kinetics of the formation of aging products of methyl oleate (C18:1) are studied. The aim was to reduce the complexity in order to be able to make more precise and detailed statements about the mechanism. Ketones, acids, peroxide, and epoxide values were recorded. A distinction is made between pure methyl oleate and mixtures with 3 wt% isopropylidene glycerine (solketal). After solketal decomposed in the blends, the aging process showed changes. The influence of solketal resulted in a higher number of acids and epoxides over time. It implied that peroxides are not necessarily the precursor of epoxides. In summary, correlation and solketal’s influence showed that a sequence of aging products could be detected.}}, author = {{Türck, Julian and Schmitt, Fabian and Anthofer, Lukas and Lichtinger, Anne and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}}, booktitle = {{Energies : open-access journal of related scientific research, technology development and studies in policy and management}}, issn = {{1996-1073}}, keywords = {{oxidation kinetics, biodiesel aging, methyl oleate, solketal, alcohol influence, sequence of aging products}}, number = {{7}}, publisher = {{MDPI AG}}, title = {{{Oxidation Kinetics of Neat Methyl Oleate and as a Blend with Solketal}}}, doi = {{10.3390/en16073253}}, volume = {{16}}, year = {{2023}}, } @misc{12843, abstract = {{This article contributes to the ongoing dialogue regarding the future application of renewable e‐fuels as part of a holistic solution to the energy crisis. In order to be able to continue using internal combustion engines in a sustainable manner, it must be ensured that these engines are operated exclusively with renewable, CO2‐neutral fuels. One way to achieve this is the use of a fluorescence sensor in the vehicle in combination with fuels that are labeled with a fluorescence marker. This study presents an investigation into the use of the benzophenoxazine dye Nile red as a fluorescent marker for distinguishing fossil from renewable fuels. In addition to assessing the stability of the fluorescent marker against thermo‐oxidative aging, the study probes its antioxidative impact on fuel aging, by comparing unlabeled and with Nile red labeled aged fuels. Furthermore, an examination of fuel‐specific parameters underscores the positive effect of Nile red on fuel stability. A comparison with the antioxidant butylated hydroxytoluene confirms the antioxidant effect of Nile red.}}, author = {{Lichtinger, Anne and Poller, Maximilian J. and Türck, Julian and Schröder, Olaf and Garbe, Thomas and Krahl, Jürgen and Singer, Anja and Jakob, Markus and Albert, Jakob}}, booktitle = {{Energy technology : generation, conversion, storage, distribution}}, issn = {{2194-4296}}, keywords = {{antioxidants, climate policy, climate-neutral, e-fuels, fluorescence markers, oxidation}}, number = {{11}}, publisher = {{Wiley}}, title = {{{Nile Red as a Fluorescence Marker and Antioxidant for Regenerative Fuels}}}, doi = {{10.1002/ente.202300260}}, volume = {{11}}, year = {{2023}}, } @misc{11817, author = {{Dörr, Sebastian and Schulte, Thomas and Dally, Benjamin}}, booktitle = {{Kraftstoffe für die Mobilität von morgen: 4. Tagung der Fuels Joint Research Group am 10. und 11. Juni 2021 in Dresden-Radebeul }}, editor = {{Bünger, Jürgen and Eilts, Peter and Krahl, Jürgen and Munack, Axel}}, isbn = {{978-3-7369-7440-1}}, location = {{Dresden-Radebeul}}, pages = {{32--40}}, publisher = {{Cuvillier Verlag}}, title = {{{Propulsion for sustainable mobility by the example of public transportation }}}, volume = {{30}}, year = {{2022}}, } @misc{8030, author = {{Klepp, Georg Heinrich}}, booktitle = {{Kraftstoffe für die Mobilität von morgen: 4. Tagung der Fuels Joint Research Group am 10. und 11. Juni 2021 in Dresden-Radebeul }}, editor = {{Bünger, Jürgen and Eilts, Peter and Krahl, Jürgen and Munack, Axel}}, isbn = {{978-3-7369-7440-1}}, location = {{Dresden-Radebeul}}, pages = {{54--62}}, publisher = {{Cuvillier Verlag}}, title = {{{Adsorptionsspeicher für die Kraftstoffe von Morgen}}}, volume = {{30}}, year = {{2022}}, } @inbook{9476, author = {{Krahl, Jürgen}}, booktitle = {{Natur und Landschaft sind... ja was? Und überhaupt: wozu?}}, editor = {{Riedl, Ulrich}}, pages = {{76--80}}, publisher = {{Technische Hochschule Ostwestfalen-Lippe. Sustainable Campus Höxter}}, title = {{{Antworten auf drei Fragen von Professor Riedl}}}, year = {{2022}}, } @misc{12829, abstract = {{Due to the fact that modern diesel engines require very well-defined fuel properties to ensure high efficiency, low emissions and a long durability, the fuel properties and their determination methods have to be standardized. Most diesel fuel standards allow a certain volume fraction of biodiesel that can be blended to fossil diesel fuel. Biodiesel consists of saturated and unsaturated fatty acid methyl esters (FAME) which are more susceptible to oxidation compared to fossil diesel fuel. Oxidation products formed by autoxidative processes can lead to higher emissions, a higher corrosiveness, fuel filter blocking, clogging of fuel injectors, the formation of deposits in the entire fuel system and a decreasing lubricity [1]. Therefore, oxidation needs to be prevented by the addition of oxidation inhibitors. These antioxidants are consumed during storage, resulting in partial loss of their efficiency against oxidative stress. After this induction period all antioxidants have been consumed and harmful oxidation products can be formed. For the determination of the long-term storage stability of diesel fuels rapid oxidation stability test methods were developed and defined by standards. In Europe, the most important determination methods are the Rancimat method and the rapid small scale oxidation test (RSSOT). Both methods differ in the construction of the measurement device and various parameters. However, it is not clear whether the results of both methods can be correlated in general. Due to the importance of the oxidation stability, we here describe the results of a literature research that was carried out using 17 literature sources. Possible correlation factors between the Rancimat and the RSSOT method were analyzed, showing that a universal correlation cannot be found. In contrast, a comparison of individual series of measurement, e.g. with the same antioxidant at various concentrations, can show a good correlation between the methods.}}, author = {{Bär, Ferdinand and Knorr, Markus and Schröder, Olaf and Hopf, Henning and Garbe, Thomas and Krahl, Jürgen}}, booktitle = {{Fuel : the science and technology of fuel and energy}}, issn = {{1873-7153}}, keywords = {{Rancimat, PetroOxy, RSSOT, Biodiesel, Diesel, Fuel, Oxidation stability}}, publisher = {{Elsevier BV}}, title = {{{Rancimat vs. rapid small scale oxidation test (RSSOT) correlation analysis, based on a comprehensive study of literature}}}, doi = {{10.1016/j.fuel.2021.120160}}, volume = {{291}}, year = {{2021}}, } @misc{12838, abstract = {{The need for new bio based drop-in components for combustion engine fuels and the availability of sustainable glycerol from biodiesel production has focused attention on isopropylidene glycerol (solketal). The present study investigates the physical and chemical behavior of solketal in ternary blends with diesel fuel/biodiesel. Hydrotreated vegetable oil (HVO) was used as renewable non-polar aliphatic diesel fuel substitute in biodiesel/ solketal blends. HVO can be considered a prototype for other non-polar fuel components such as paraffinic fuel streams from Fischer-Tropsch or BtL processes. Surface tension, permittivity and aging behavior were analyzed. Furthermore, the cetane number (CN) and the viscosity was determined. Permittivity reflects the polarity of blends and their components with its change being an indicator of loss of physical and chemical stability. The antioxidant triphenyl phosphorothioate (TPPT) was also tested in some blends. The biodiesel blends B20, B30 and B40 enables single phased diesel fuel or HVO with varied solketal content (2 and 10%) at a constant biodiesel amount. No effect of solketal on fuel aging was observed. However, HVO-containing blends tend to lower the thermo-chemical stability relative to diesel fuel.}}, author = {{Türck, Julian and Singer, Anja and Lichtinger, Anne and Almaddad, Mohammad and Türck, Ralf and Jakob, Markus and Garbe, Thomas and Ruck, Wolfgang and Krahl, Jürgen}}, booktitle = {{Fuel : the science and technology of fuel and energy}}, issn = {{1873-7153}}, keywords = {{Solketal, Biodiesel, HVO, Diesel fuel, Miscibility, Fuel aging, Cetane Number}}, publisher = {{Elsevier BV}}, title = {{{Solketal as a renewable fuel component in ternary blends with biodiesel and diesel fuel or HVO and the impact on physical and chemical properties}}}, doi = {{10.1016/j.fuel.2021.122463}}, volume = {{310}}, year = {{2021}}, }