As of today, in the field of hybrid rocketry there are two main types of fuels, traditional and liquefying fuels. The liquefying fuels form a liquid film of melt fuel on the grain surface which becomes fluid-dynamically unstable under flow intense shear stresses and releases droplets to the free stream. This phenomenon is known as entrainment and effectively increases the fuel mass transfer to the flame region with respect to traditional fuels. This additional mass transfer increases the regression of the fuel surface. Typical liquefying fuels are cryogenic fuels and paraffin waxes. The generalised hybrid theory by Karabeyoglu derives the theoretical formulation for the analysis of liquefying fuels, studies the stability criteria of the liquid film and onset conditions of entrainment and predicts the regression rate based on fuel properties and operational parameters. Most of the experimental work conducted to date has focused on visual observation of the entrained fuel droplets and on experimental calculation of regression rate to contrast with theoretical predictions. It is widely accepted that liquid fuel viscosity plays an important role, with low viscosities leading to higher regression rates. The scope of this thesis is to study the thickness of the liquid film for a range of paraffin mixtures with different levels of polymeric additive and different viscosities (and other thermophysical properties). The objective is to understand how different fuel compositions and thermophysical properties will have an effect on film thickness and ultimately on regression of the fuel surface. The method chosen to assess film thickness is to infer it from the temperature readings of thermocouples inserted in the fuel grain. Note: During the development of this thesis Covid-19 worldwide crisis has prevented from conducting any experimental work. In such special circumstances, the author has decided based on personal circumstances to compromise the work scope and conduct a literature research and analysis type of thesis, laying the foundation for the future development of the test campaingn.
Ad oggi, nel campo della missilistica ibrida esistono due tipi principali di combustibili, quelli tradizionali e quelli a bassa temperatura di fusione. Questi ultimi formano un film di combustibile liquido sulla superficie del grano solido che diventa fluidodinamicamente instabile sotto forti sollecitazioni di taglio e rilascia goccioline liquide nel flusso libero. Questo fenomeno è noto come trascinamento e aumenta efficacemente il trasferimento della massa di combustibile alla regione di fiamma rispetto ai combustibili tradizionali. Questo trasferimento di massa supplementare aumenta la velocità di regressione della superficie del combustibile. Detti combustibili sono i criogenici e le cere paraffiniche. La teoria ibrida generalizzata di Karabeyoglu sviluppa la formulazione teorica per l’analisi dei combustibili a bassa temperatura di fusione, studia i criteri di stabilità del film liquido e le condizioni di inizio del trascinamento e prevede il tasso di regressione in base alle proprietà del combustibile e ai parametri operativi. La maggior parte del lavoro sperimentale condotto fino ad oggi si è concentrato sull’osservazione visiva delle goccioline di combustibile intrappolate e sul calcolo sperimentale del tasso di regressione a confronto con le previsioni teoriche. È ampiamente accettato che la viscosità del combustibile liquido riveste un ruolo importante, con basse viscosità che portano a tassi di regressione più elevati. Lo scopo di questa tesi è di studiare lo spessore del film liquido per una serie di miscele di paraffina con diversi livelli di additivo polimerico e diverse viscosità (e altre proprietà termofisiche). L’obiettivo è quello di capire come le diverse composizioni di combustibile e le diverse proprietà termofisiche esercitano un effetto sullo spessore del film e, in ultima analisi, sulla regressione della superficie del combustibile. Il metodo scelto per valutare lo spessore del film è quello di dedurlo dalle letture di temperatura delle termocoppie inserite nel grano del combustibile. Nota: Durante lo sviluppo di questa tesi la crisi mondiale Covid-19 ha impedito di condurre attività sperimentale. In tali circostanze particolari, l’autore ha deciso, sulla base di considerazioni ed esigenze personali, di compromettere lo sviluppo del lavoro e di condurre un tipo di tesi di ricerca bibliografica e analisi, ponendo le basi per il futuro sviluppo di prove sperimentali.
Characterization of liquefying fuels for hybrid rocket propulsion
COLL VAQUER, BARTOMEU
2018/2019
Abstract
As of today, in the field of hybrid rocketry there are two main types of fuels, traditional and liquefying fuels. The liquefying fuels form a liquid film of melt fuel on the grain surface which becomes fluid-dynamically unstable under flow intense shear stresses and releases droplets to the free stream. This phenomenon is known as entrainment and effectively increases the fuel mass transfer to the flame region with respect to traditional fuels. This additional mass transfer increases the regression of the fuel surface. Typical liquefying fuels are cryogenic fuels and paraffin waxes. The generalised hybrid theory by Karabeyoglu derives the theoretical formulation for the analysis of liquefying fuels, studies the stability criteria of the liquid film and onset conditions of entrainment and predicts the regression rate based on fuel properties and operational parameters. Most of the experimental work conducted to date has focused on visual observation of the entrained fuel droplets and on experimental calculation of regression rate to contrast with theoretical predictions. It is widely accepted that liquid fuel viscosity plays an important role, with low viscosities leading to higher regression rates. The scope of this thesis is to study the thickness of the liquid film for a range of paraffin mixtures with different levels of polymeric additive and different viscosities (and other thermophysical properties). The objective is to understand how different fuel compositions and thermophysical properties will have an effect on film thickness and ultimately on regression of the fuel surface. The method chosen to assess film thickness is to infer it from the temperature readings of thermocouples inserted in the fuel grain. Note: During the development of this thesis Covid-19 worldwide crisis has prevented from conducting any experimental work. In such special circumstances, the author has decided based on personal circumstances to compromise the work scope and conduct a literature research and analysis type of thesis, laying the foundation for the future development of the test campaingn.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/164685