The subject of the present work is the study of paraffin-based fuels for hybrid rocket propulsion. This experimental thesis focuses on solid, low-temperature melting fuels made up of paraffinic hydrocarbons, which form a liquid layer on the surface when heated up. In particular, an accurate analysis has been conducted to investigate the melted fuel entrapment by the gaseous oxidizer flow (entrainment). The understanding of this phenomenon is crucial to achieve higher regression rate (rf) in hybrid fuels, which despite the remarkable advantages are still not largely employed due to the low generated thrust. First, a devoted experimental set-up has been designed and manufactured at the Space Propulsion Laboratory (SPLab) of Politecnico di Milano, with the aim to capture the phenomenon described above during combustion. Then, a preliminary analysis to evaluate parameters such as viscosity and surface tension has been conducted for different paraffin-based fuel formulations. Three different formulations have been examined: the macro-crystalline paraffin JW1, JW1 + 10% wt. SEBS and eventually W1, a micro-crystalline paraffin fuel. The copolymer SEBS has been added to the JW1 paraffin in order to enhance its mechanical properties, raising simultaneously the viscosity and thus removing entrainment. Finally, an high-speed video recording technique was exploited to display the formation of tiny paraffin droplets during combustion. A first qualitative investigation has explained the entertainment phenomenology, while a numerical analysis of the recorded frames has validated the theoretical results available in the open literature. Globally, this thesis has developed a new methodology for the study of entrainment and thus of the regression rate of paraffin-based fuels for hybrid rocket propulsion, an interesting application among the space propulsion technologies.
Lo scopo del presente lavoro è lo studio di combustibili a base paraffinica per la propulsione di razzi ibridi. La tesi, di carattere sperimentale, riguarda combustibili solidi bassofondenti costituiti da idrocarburi a base paraffinica, che a seguito di riscaldamento formano uno strato liquido in superficie. In particolare, è stata condotta una attenta analisi dell'inglobamento di combustibile fuso nel flusso ossidante gassoso (entrainment). La comprensione di tale fenomeno è di cruciale importanza nel tentativo di innalzare la velocità di regressione (rf) dei combustibili ibridi i quali, pur presentando notevoli vantaggi, ad oggi non sono ancora ampiamente utilizzati a causa della scarsa spinta generata. Inizialmente, una nuova linea sperimentale è stata studiata e costruita all'interno dello Space Propulsion Laboratory (SPLab) del Politecnico di Milano, con il preciso scopo di rendere visibile il fenomeno sopra descritto durante la combustione. Successivamente, è stata condotta una analisi preliminare volta alla valutazione della viscosità e della tensione superficiale di diverse formulazioni di combustibili a base paraffinica. Sono state esaminate tre differenti formulazioni: la paraffina macro-cristallina JW1, JW1 + 10% wt. SEBS ed infine W1, un combustibile paraffinico micro-cristallino. Il copolimero SEBS è stato aggiunto alla paraffina JW1 per migliorarne le proprietà meccaniche, aumentandone contemporaneamente la viscosità e sopprimendo di conseguenza l'entrainment. Infine, l’utilizzo di una tecnica di ripresa video ad alta velocità ha consentito di visualizzare la formazione delle gocce di paraffina durante la combustione. Una prima indagine qualitativa ha spiegato la fenomenologia dell'entrainment, mentre un esame numerico dei fotogrammi raccolti ha convalidato i risultati teorici presenti in letteratura. Complessivamente, grazie a questo lavoro di tesi è stato proposto un nuovo metodo per lo studio dell'entrainment e, conseguentemente, della velocità di regressione di combustibili a base paraffinica per razzi a propellente ibrido, una applicazione di grande interesse nell’ambito delle tecnologie legate alla propulsione spaziale.
Entrainment phenomenon in liquefying solid fuels combustion
MAZZALI, SARA
2018/2019
Abstract
The subject of the present work is the study of paraffin-based fuels for hybrid rocket propulsion. This experimental thesis focuses on solid, low-temperature melting fuels made up of paraffinic hydrocarbons, which form a liquid layer on the surface when heated up. In particular, an accurate analysis has been conducted to investigate the melted fuel entrapment by the gaseous oxidizer flow (entrainment). The understanding of this phenomenon is crucial to achieve higher regression rate (rf) in hybrid fuels, which despite the remarkable advantages are still not largely employed due to the low generated thrust. First, a devoted experimental set-up has been designed and manufactured at the Space Propulsion Laboratory (SPLab) of Politecnico di Milano, with the aim to capture the phenomenon described above during combustion. Then, a preliminary analysis to evaluate parameters such as viscosity and surface tension has been conducted for different paraffin-based fuel formulations. Three different formulations have been examined: the macro-crystalline paraffin JW1, JW1 + 10% wt. SEBS and eventually W1, a micro-crystalline paraffin fuel. The copolymer SEBS has been added to the JW1 paraffin in order to enhance its mechanical properties, raising simultaneously the viscosity and thus removing entrainment. Finally, an high-speed video recording technique was exploited to display the formation of tiny paraffin droplets during combustion. A first qualitative investigation has explained the entertainment phenomenology, while a numerical analysis of the recorded frames has validated the theoretical results available in the open literature. Globally, this thesis has developed a new methodology for the study of entrainment and thus of the regression rate of paraffin-based fuels for hybrid rocket propulsion, an interesting application among the space propulsion technologies.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150521