Viscosity and Regression Rate of Liquefying Hybrid Rocket Fuels

Kobald, Mario; Schluechter, C.; Ciezki, Helmut; Schlechtriem, Stefan; Toson, Elena; Luca, L.T. De

doi:10.2514/1.b36207

Cited by 51 publications

(24 citation statements)

References 18 publications

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“…2. Recent tests with different paraffin-based fuels and gaseous oxygen (GOX) showed an exponential relation between the liquid layer viscosity and the overall regression rate (Kobald et al 2017c), which proves the predicted entrainment correlation in Fig. 1.…”

Section: Hybrid Rocket Propulsionmentioning

confidence: 79%

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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: Hybrid Rocket Propulsionmentioning

confidence: 79%

“…Early viscosity measurements at different shear rates showed that all the paraffin-based samples have a Newtonian behaviour, except for the paraffin with nanoclay particles (Kobald et al 2017c). Therefore, the viscosity of the paraffin with polymer does not depend on the shear rate.…”

Section: Paraffin-based Fuels Characterizationmentioning

confidence: 99%

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

2018

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“…In order to obtain a suitable paraffin-based fuel with both good mechanical properties and combustion performance, additives should be selected not increasing the melt liquid viscosity of the compound. As a matter of fact, an exponential relation was found in Reference [39] which correlates the regression rate of liquefying fuels with their liquid viscosity. Thus, the regression rate data of the tested paraffin-based fuels could be related directly to the viscosity of the corresponding liquid fuel samples and an increase in the liquid layer viscosity resulted in a decreased regression rate [32].…”

Section: Paraffin Fuels With Better Mechanical Propertiesmentioning

confidence: 97%

Innovative Methods to Enhance the Combustion Properties of Solid Fuels for Hybrid Rocket Propulsion

et al. 2019

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The low regression rates for hydroxyl-terminated polybutadiene (HTPB)-based solid fuels and poor mechanical properties for the alternative paraffin-based liquefying fuels make today hybrid rocket engines far from the outstanding accomplishments of solid motors and liquid engines. In this paper, a survey is conducted of several innovative methods under test to improve solid fuel properties, which include self-disintegration fuel structure (SDFS)/paraffin fuels, paraffin fuels with better mechanical properties, high thermal conductivity fuels and porous layer combustion fuels. In particular, concerning HTPB, new results about diverse insert and low-energy polymer particles enhancing the combustion properties of HTPB are presented. Compared to pure HTPB, regression rate can be increased up to 21% by adding particles of polymers such as 5% polyethylene or 10% oleamide. Concerning paraffin, new results about self-disintegrating composite fuels incorporating Magnesium particles (MgP) point out that 15% 1 μm- or 100 μm-MgP formulations increase regression rates by 163.2% or 82.1% respectively, at 335 kg/m2·s oxygen flux, compared to pure paraffin. Overall, composite solid fuels featuring self-disintegration structure appear the most promising innovative technique, since they allow separating the matrix regression from the combustion of the filler grains. Yet, the investigated methods are at their initial stage. Substantial work of refinement in this paper is for producing solid fuels to fulfill the needs of hybrid rocket propulsion.

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“…Detailed studies have been presented by Karabeyoglu [4,5], where it is demonstrated that the fuel composition and its thermo-mechanical properties strongly affect the liquid layer instability and, therefore, the fuel regression rate.…”

Section: Introductionmentioning

confidence: 99%

Design and Testing of a Paraffin-Based 1000 N HRE Breadboard

et al. 2019

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The paper presents some relevant achievements in hybrid rocket propulsion carried out by the Italian Aerospace Research Centre. On the basis of the experimental results obtained on a 200 N thrust class engine, a 1000 N class breadboard, fed with gaseous oxygen coupled with a paraffin-based fuel grain, was designed and experimentally tested in different conditions. The breadboard exhibited a stable combustion in all the firing test conditions; the testing campaign allowed the acquisition of different experimental data, as pre and post-combustion chamber pressure, throat material temperature, pre-combustion chamber temperature. The new breadboard was characterized by higher measured regression rate values with respect to corresponding data obtained with the smaller scale one, highlighting that the oxidizer mass flux is not the only operating quantity affecting the fuel consumption behavior, which could be also influenced by scale parameters, such as the grain port diameter, and other operating conditions, such as the mixture ratio. Aerospace 2019, 6, 89 2 of 15Detailed studies have been presented by Karabeyoglu [4,5], where it is demonstrated that the fuel composition and its thermo-mechanical properties strongly affect the liquid layer instability and, therefore, the fuel regression rate.In this scenario, the present research was mainly focused on the investigation of the fuel characteristics, in order to ensure high performance in terms of regression rate but maintaining good mechanical properties. In a previous authors' work, results of an experimental test campaign, performed at subscale level on a 200 N breadboard, demonstrated very good performances and mechanical properties of the analyzed paraffin-wax formulation [6].Based on these results, the main objective of the present work is the scale-up of the fuel grain, adopting the same fuel formulation, and the design of a new breadboard, moving towards the 1000 N thrust class. A new experimental test campaign was carried out on the 1000 N breadboard, allowing for the investigation of the paraffin-based fuel blend behavior on a larger scale. In particular, with respect to subscale experiments, the oxidizer to fuel mixture ratio range was extended. Numerous data were acquired, including chamber pressure, thrust, temperature of the flow in the pre-chamber and temperature inside the graphite nozzle material. The latter parameter allows for the estimation of the convective heat transfer coefficient in the nozzle region, which is strictly linked to the graphite nozzle thermo-chemical erosion. This is an extremely important parameter to be evaluated, since the throat area enlargement directly affects the motor performances [7].The results of the experimental test campaign show that hybrid rocket engine can operate, with good efficiency and stability, in a wide range of operating conditions, confirming some of the advantages over both solid and liquid technologies often mentioned in the relevant literature [1,2,8,9]. Methodology and Design Design LogicThe procedure, ad...

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Viscosity and Regression Rate of Liquefying Hybrid Rocket Fuels

Cited by 51 publications

References 18 publications

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

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

Innovative Methods to Enhance the Combustion Properties of Solid Fuels for Hybrid Rocket Propulsion

Design and Testing of a Paraffin-Based 1000 N HRE Breadboard

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