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

Kobald, Mario; Verri, Isabella; Schlechtriem, Stefan

doi:10.1007/s12567-015-0076-2

Cited by 22 publications

(10 citation statements)

References 29 publications

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“…The ignition, steady-state and extinction phases were clearly recognized with this technique. Moreover, the HTPB combustion flame showed no wave-like behaviour, in contrast to paraffin-based fuels (Kobald et al 2015;Petrarolo and Kobald 2016).…”

Section: Optical Investigations On Hybrid Rocket Combustionmentioning

confidence: 93%

“…A test sequence is programmed before the test and is run automatically by the test bench control system. More details about the test bench and test settings are given in Kobald et al ( , 2015 and Petrarolo and Kobald (2016).…”

Section: Test Set-up and Data Acquisitionmentioning

confidence: 99%

“…At the end, the power spectral density (PSD) of these coefficients is performed, to obtain the most excited frequencies and wavelengths during the combustion. Further details of the applied methods are given in Kobald et al (2015) and Petrarolo and Kobald (2016).…”

Section: Video Analysismentioning

confidence: 99%

“…The effect of viscosity on shear stress is neglected and both fluids are considered homogeneous and irrotational. The equations are linearized and sinusoidal solutions are applied (Kobald et al 2015). A small sinusoidal perturbation h is introduced at the interface between the gas and the liquid:…”

Section: Kelvin-helmholtz Instabilitymentioning

confidence: 99%

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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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Section: Optical Investigations On Hybrid Rocket Combustionmentioning

confidence: 93%

Section: Test Set-up and Data Acquisitionmentioning

confidence: 99%

Section: Video Analysismentioning

confidence: 99%

Section: Kelvin-helmholtz Instabilitymentioning

confidence: 99%

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

2018

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“…The POD method was already applied in previous tests and the first results were described in (Verri, 2014, Kobald et al, 2015. First of all, the POD method was successful in highlighting characteristic frequencies and their amplitude, which are related to vortex shedding events.…”

Section: Proper Orthogonal Decompositionmentioning

confidence: 99%

Evaluation techniques for optical analysis of hybrid rocket propulsion

Petrarolo

Kobald

2016

JFST

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This article summarizes recent results of data evaluation techniques obtained with optical investigations on the combustion behavior of hybrid rocket fuels. Tests are performed in a 2D slab burner configuration with windows on two sides. Liquefying paraffin-based fuels are tested in combination with gaseous oxygen (GOX). High speed videos of combustion tests are recorded in order to investigate the combustion phenomena of this kind of fuels. Hybrid combustion of liquefying fuels is dominated by transient flow dynamics like Kelvin-Helmholtz instability and vortex shedding, also due to the characteristic turbulent diffusion flame. In order to better evaluate these flow phenomena, characteristic frequencies and wavelengths of the main structures of the flow field and of the combustion flame appearing in the video data have to be found. In this work, a spatial and temporal analysis of these structures is carried out by using two different techniques, applied within an automated video evaluation routine. First of all, the Proper Orthogonal Decomposition (POD) technique is used. Its results deliver linearly uncorrelated variables, which are the principal components of the flow field. This method enables to recognize the main structures of the flow field and the combustion flame appearing in the video data. Secondly, the Independent Component Analysis (ICA) technique is applied to the same data. It is able to search for statistically independent, or as independent as possible, structures hidden in the data. It increases the independence to higher statistical orders with respect to POD. The basis functions found with the ICA are expected to describe the essential structure of the data and to resemble some physical processes involved in the combustion. With both methods it is possible to compute spatial and temporal coefficients, which can be later analyzed by applying a Power Spectral Density (PSD) in order to obtain the excited frequencies and wavelengths during the combustion. Finally, the results of the two methods are compared in order to better understand and interpret them. The results collected so far and the comparison of both techniques show that their application is consistent and useful for the automated evaluation of combustion data. Petrarolo and Kobald, Journal of Fluid Science and Technology, Vol.11, No.4 (2016) fuel grains for high thrust applications. The multiport design increases the residual mass of unburnt fuel and thereby decreases the delivered specific impulse. Instabilities are also more likely with this type of design.Liquefying hybrid rocket fuels were only found recently. Cryogenic solid n-pentane showed regression rates 5-10 times higher than polymeric hybrid fuels (Carrick and Larson, 1995, Larson et al., 1996, DeRose et al., 1997.Paraffin-based fuels, tested at Stanford University, show a 3-5 times higher regression rate at similar mass fluxes compared to polymers , Karabeyoglu, 1998. This is achieved by a different combustion mechanism. Paraffin fuels form a liquid layer on the...

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Thermal, Viscosimetric and Thermomechanical Combined Assessment of Mixture Modelled Composite Fuels for Hybrid Propulsion

Araújo

Maschio²,

Gouvêa

et al. 2022

Propellants Explo Pyrotec

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Paraffin‐based fuels have received attention in hybrid propulsion studies towards their regression rate assessment, although little efforts have been dedicated to a consistent selection of their formulations. This work deals with melting enthalpy, dynamic viscosity, and linear thermal expansion characterization of novel low‐density polyethylene‐macrocrystalline paraffin‐ammonium nitrate composite fuels, followed by model fitting under mixture modeling principles and subsequent optimization through the desirability method. This approach allowed a better understanding of the raw materials’ roles and provided a trade‐off formulation, which was satisfactorily produced and characterized in a confirmatory experiment, thus making it a suitable candidate for further regression rate measurements.

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

Cited by 22 publications

References 29 publications

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

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

Evaluation techniques for optical analysis of hybrid rocket propulsion

Thermal, Viscosimetric and Thermomechanical Combined Assessment of Mixture Modelled Composite Fuels for Hybrid Propulsion

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