Visualization of the Liquid Layer Combustion of Paraffin Fuel for Hybrid Rocket Applications

This paper describes combined rheological, ballistic, and optical analyses performed on para©n-based mixtures that can be used as high regression rate hybrid rocket fuels. Experimental activities have been done at the DLR Institute of Space Propulsion in Lampoldshausen and at SPLab of Politecnico di Milano [1]. Herein, the experiments that were performed at the DLR are described in detail. Viscosity, surface tension, and regression rate of the fuels have been determined. Furthermore, the combustion was evaluated by optical measurements. Data collected so far indicate an increasing regression rate for decreasing viscosity of the liquid para©n which is in accordance with the current theories. Droplet entrainment, which is related to high regression rates, is only visible for the low-viscosity para©n-based fuels.

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“…In 2012, Chandler et al investigated the combustion of paraffin-based fuels with gaseous oxygen at both atmospheric and elevated pressures. Their results showed roll waves and droplets in the atmospheric tests and filament-like structures along the sides of the fuel grains in the tests run at elevated pressures (Chandler et al 2012a). Moreover, they compared the combustion behaviour of paraffin-based fuels to that of classical hybrid fuels.…”

Section: Optical Investigations On Hybrid Rocket Combustionmentioning

confidence: 99%

“…Moreover, they compared the combustion behaviour of paraffin-based fuels to that of classical hybrid fuels. They reported that for paraffin-based fuels entraining droplets were visible, for high-density polyethylene (HDPE), only little droplet entrainment was seen and for hydroxyl-terminated polybutadiene (HTPB), no droplet entrainment was measured (Chandler et al 2012b). In 2014-2016, many optical tests were conducted from Jens et al with the same facility.…”

Section: Optical Investigations On Hybrid Rocket Combustionmentioning

confidence: 99%

Understanding Kelvin–Helmholtz instability in paraffin-based hybrid rocket fuels

2018

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Liquefying fuels show higher regression rates than the classical polymeric ones. They are able to form, along their burning surface, a low viscosity and surface tension liquid layer, which can become unstable (Kelvin-Helmholtz instability) due to the high velocity gas flow in the fuel port. This causes entrainment of liquid droplets from the fuel surface into the oxidizer gas flow. To better understand the droplets entrainment mechanism, optical investigations on the combustion behaviour of paraffin-based hybrid rocket fuels in combination with gaseous oxygen have been conducted in the framework of this research. Combustion tests were performed in a 2D single-slab burner at atmospheric conditions. High speed videos were recorded and analysed with two decomposition techniques. Proper orthogonal decomposition (POD) and independent component analysis (ICA) were applied to the scalar field of the flame luminosity. The most excited frequencies and wavelengths of the wave-like structures characterizing the liquid melt layer were computed. The fuel slab viscosity and the oxidizer mass flow were varied to study their influence on the liquid layer instability process. The combustion is dominated by periodic, wavelike structures for all the analysed fuels. Frequencies and wavelengths characterizing the liquid melt layer depend on the fuel viscosity and oxidizer mass flow. Moreover, for very low mass flows, no wavelength peaks are detected for the higher viscosity fuels. This is important to better understand and predict the onset and development of the entrainment process, which is connected to the amplification of the longitudinal waves. List of symbols

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Visualization of the Liquid Layer Combustion of Paraffin Fuel for Hybrid Rocket Applications

Cited by 41 publications

References 4 publications

Theoretical and experimental analysis of liquid layer instability in hybrid rocket engines

Theoretical and experimental analysis of liquid layer instability in hybrid rocket engines

Rheological, optical, and ballistic investigations of paraffin-based fuels for hybrid rocket propulsion using a two-dimensional slab-burner

Understanding Kelvin–Helmholtz instability in paraffin-based hybrid rocket fuels

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