The pursuit of sustainable and renewable development of the energy sector is a global challenge of great environmental, social and economic importance. While, for electricity production, there are some effective alternatives to combustion (wind, solar, hydroelectricity, nuclear, etc.), the considerable energy demand for road, sea and air transport embraces biofuels as the main feasible and realistic alternative. Thanks to the blending of components from renewable sources (alcohols, esters), into hydrocarbon fuels from fossil sources (gasoline, diesel, kerosene, etc.), it is possible to decrease the dependence on petroleum without altering the performance of the propellant. Furthermore, from an environmental point of view, due to undeniable and drastic climate changes, there is the necessity to develop fuels and new technologies able to reduce the production of polluting components as greenhouse gases (CO2, NOx) and soot emissions. Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphtenes, olefins and aromatics. Regarding aviation propellants, the main components are linear or branched alkanes and cycloalkanes with a typical carbon chain length distribution of C6-C16. To properly analyze their behavior, it is possible to reduce their compositional complexity by adopting surrogates. These mixtures, by containing a limited number of components, are able to reproduce the global reactivity more easily. In this work, three branched iso-alkanes have been chosen (iso-octane, iso-dodecane and isocetane) due to their wide presence in the majority of fuel surrogates and their consistency in the chemical structure. Additionally, to characterize a specific combustible or fuel mixtures from a reactive point of view and evaluate the compatibility in terms of efficiency and pollution, the evaluation of a kinetic mechanism is a useful tool. The aim of this thesis is the development of a kinetic mechanism for these components to extend the previous model developed by Chemical Reaction Engineering and Chemical Kinetics (CRECK) modeling team. Accordingly, the Lawrence Livermore National Lab (LLNL) mechanism has been taken as a reference. The latter is a detailed model built upon the state-of-the-art fundamental calculations. Kinetic parameters for iso-octane have been updated based on the LLNL values, while iso-dodecane and iso-cetane kinetic schemes have been evaluated by adapting the kinetic parameters evaluated for i-C8. Moreover, the model has been tested with real fuels mixtures such as Gevo ATJ, Farnesane, and Fischer-Tropsch fuels. Thanks to self-consistency, proper lumping, and small manual adjustments, the results from kinetic simulations succeed in matching the experimental values. The model validation includes: ignition delay times both from shock tubes and rapid compression machines, species concentration profiles from jet stirred reactor and single pulse shock tubes, and laminar flame speed simulations.
La ricerca di uno sviluppo sostenibile e rinnovabile del settore energetico rappresenta una sfida globale di importanza ambientale, sociale ed economica. Mentre per la produzione di energia sono presenti efficaci alternative alla combustione (vento, sole, idroelettricità, nucleare ecc.), la considerevole richiesta di energia per il trasporto su strada, via mare, e aereo include i biocombustibili come principale alternativa possibile e realistica. Grazie alla miscelazione di composti ottenuti da risorse rinnovabili (alcoholi, esteri) con combustibili fossili (benzina, diesel, kerosene ecc.), è possibile diminuire la dipendenza dal petrolio senza alterare la performance del carburante. Inoltre, da un punto di vista ambientale, a causa degli innegabili e drastici cambiamenti climatici, è necessario sviluppare combustibili e nuove tecnologie in grado di ridurre la produzione di inquinanti come le emissioni di particolato e i gas serra (CO2,NOx). I carburanti comuni sono miscele complesse formate da migliaia di idrocarburi che includono paraffine lineari e ramificate, nafteni, olefine e composti aromatici. Per quanto riguarda i combustibili utilizzati nell'aviazione, i principali componenti sono alcani lineari o ramificati e cicloalcani con una tipica lunghezza di catena di C6-C16. Per analizzare correttamente il loro comportamento, è possibile semplificare la complessità delle loro strutture utilizzando dei surrogati. Queste miscele, contenendo un numero limitato di composti, sono in grado di riprodurre la reattività globale più facilmente. In questa tesi, tre iso-alcani ramificati sono stati selezionati (iso-ottano, iso-dodecano e iso-cetano) per la loro larga presenza nella maggior parte dei surrogati di combustibili e la loro consistenza nella struttura chimica. Per meglio caratterizzare la maggior parte dei surrogati e i diversi combustibili per quanto riguarda la loro reattività e valutare la compatibilità per quanto riguarda la loro efficienza e produzione di inquinanti, la stesura di un modello cinetico è un valido strumento. L'obiettivo di questa tesi è quello di sviluppare un modello cinetico per questi composti aggiornando il meccanismo sviluppato dal Chemical Reaction Engineering and Chemical Kinetics (CRECK) modeling team. Il modello cinetico di Lawrence Livermore National Lab (LLNL) è stato preso come riferimento. Quest'ultimo è un meccanismo dettagliato costruito sullo stato dell'arte del calcolo fondamentale. I parametri cinetici per l'iso-ottano sono stati aggiornati basandosi sui valori di LLNL, mentre gli schemi cinetici per l'iso-dodecano e l'iso-cetano sono stati sviluppati adattando i parametri cinetici dell'i-C8. Inoltre, il modello è stato testato con miscele di combustibili attualmente in uso come Gevo ATJ, Farnesano e combustibili Fischer-Tropsch. Grazie ad un approccio consistente, un lumping specifico e piccoli aggiustamenti i risultati ottenuti sono in accordo con i dati sperimentali. La convalida del modello include: tempi di iniezione, ottenuti da shock tubes e rapid compression machines, analisi di speciazione condotte in jet stirred reactor e single pulse shock tube e simulazioni di velocità di fiamma.
Kinetic modeling of jet fuels : reaction mechanisms for branched alkanes
Carena, Andrea
2020/2021
Abstract
The pursuit of sustainable and renewable development of the energy sector is a global challenge of great environmental, social and economic importance. While, for electricity production, there are some effective alternatives to combustion (wind, solar, hydroelectricity, nuclear, etc.), the considerable energy demand for road, sea and air transport embraces biofuels as the main feasible and realistic alternative. Thanks to the blending of components from renewable sources (alcohols, esters), into hydrocarbon fuels from fossil sources (gasoline, diesel, kerosene, etc.), it is possible to decrease the dependence on petroleum without altering the performance of the propellant. Furthermore, from an environmental point of view, due to undeniable and drastic climate changes, there is the necessity to develop fuels and new technologies able to reduce the production of polluting components as greenhouse gases (CO2, NOx) and soot emissions. Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphtenes, olefins and aromatics. Regarding aviation propellants, the main components are linear or branched alkanes and cycloalkanes with a typical carbon chain length distribution of C6-C16. To properly analyze their behavior, it is possible to reduce their compositional complexity by adopting surrogates. These mixtures, by containing a limited number of components, are able to reproduce the global reactivity more easily. In this work, three branched iso-alkanes have been chosen (iso-octane, iso-dodecane and isocetane) due to their wide presence in the majority of fuel surrogates and their consistency in the chemical structure. Additionally, to characterize a specific combustible or fuel mixtures from a reactive point of view and evaluate the compatibility in terms of efficiency and pollution, the evaluation of a kinetic mechanism is a useful tool. The aim of this thesis is the development of a kinetic mechanism for these components to extend the previous model developed by Chemical Reaction Engineering and Chemical Kinetics (CRECK) modeling team. Accordingly, the Lawrence Livermore National Lab (LLNL) mechanism has been taken as a reference. The latter is a detailed model built upon the state-of-the-art fundamental calculations. Kinetic parameters for iso-octane have been updated based on the LLNL values, while iso-dodecane and iso-cetane kinetic schemes have been evaluated by adapting the kinetic parameters evaluated for i-C8. Moreover, the model has been tested with real fuels mixtures such as Gevo ATJ, Farnesane, and Fischer-Tropsch fuels. Thanks to self-consistency, proper lumping, and small manual adjustments, the results from kinetic simulations succeed in matching the experimental values. The model validation includes: ignition delay times both from shock tubes and rapid compression machines, species concentration profiles from jet stirred reactor and single pulse shock tubes, and laminar flame speed simulations.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/179381