M. Kobald

Optical Investigation of the Combustion Process in Paraffin-based Hybrid Rocket Fuels

This paper summarizes the investigations on the combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen (GOX) as oxidizer in a 2D slab burner with windows on two sides. High speed video data and Schlieren measurements have been evaluated to give an insight into the combustion phenomena of paraffin-based hybrid rocket fuels. The combustion flame shows a periodic, wave like structure. This behavior is noticed for different types of paraffin fuels. The values of the liquid layer viscosities are the main difference between the fuels. This affects the droplet entrainment process during combustion and also the regression rates of the fuels. Entrainment and regression rate increase for decreasing fuel liquid layer viscosity.

Viscosity and Regression Rate of Liquefying Hybrid Rocket Fuels

The combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen as an oxidizer has been analyzed in detail. Regression rate tests have been done in a two-dimensional radial microburner at the DLR, German Aerospace Center and at the Space Propulsion Laboratory. Fuel samples have been characterized by viscosity measurements, tensile tests, and a differential scanning calorimeter. Tensile tests showed significant improvement in maximum stress and elongation when polymers in low concentration were added to the paraffin samples. The values of the liquid fuel viscosities differed significantly between the selected fuels. This affected the droplet entrainment process during combustion and the regression rates of the fuels. The entrainment and regression rate increased for the decreasing fuel liquid layer viscosity. An exponential relation has been found between the liquid fuel layer viscosity and the regression rate, which can be used to predict the regression rate of new liquefying fuels by measuring their viscosity.

Evaluation of paraffin-based fuels for hybrid rocket engines

This paper summarizes the investigations on the combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen (GOX) as oxidizer. Combined experimental activities have been done at the DLR Institute of Space Propulsion in Lampoldshausen and at the Space Propulsion Laboratory (SPLab) of Politecnico di Milano. Regression rate tests have been done in a 2D radial micro burner at the DLR and at the SPLab. Fuel samples have been characterized by viscosity measurements, tensile tests and differential scanning calorimeter (DSC). Tensile tests shows significant improvement in maximum stress and elongation when polymers in low concentration are added to the paraffin samples. The values of the liquid fuel viscosities differ signifcantly between the fuels. This affects the droplet entrainment process during combustion and also the regression rates of the fuels. Entrainment and regression rate increase for decreasing fuel liquid layer viscosity. An exponential relation has been found between the liquid fuel layer viscosity and the Regression rate, which can be used to predict the regression rate of new liquefying fuels by measuring their viscosity.

Combustion Visualization and Characterization of Liquefying Hybrid Rocket Fuels

Recent results of data evaluation techniques are summarized in this paper about optical investigations of the combustion behavior of different hybrid rocket fuels. They are analyzed by optical techniques in detail. Tests are performed in a 2D slab burner configuration with windows on two sides. Mainly liquefying Paraffin-based fuels including additives are tested in combination with gaseous oxygen (GOX). High speed video imaging enables the analysis of combustion phenomena at great detail. But at the same time a huge amount of data is created, that has to be evaluated carefully. Clearly, a manual analysis is rather time consuming and probably more susceptible to errors. Therefore, two different techniques are presented in this work, which are used within an automated video evaluation routine. First of all, the Proper Orthogonal Decomposition (POD) technique is applied. Its results deliver linearly uncorrelated variables which are the principal components of the flow field. This method enables a decomposition of the data set into mean, coherent and incoherent parts, thus recognizing 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, thus increasing 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. A comparison between spatial and temporal ICA is also performed. 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.

Sounding Rocket "HEROS" - A Low-Cost Hybrid Rocket Technology Demonstrator

The inherent safety of hybrid rocket propulsion offers some unique advantages com- pared to solid and liquid propellant rocket engines. This makes it especially attractive for space tourism, Micro-launcher and hands-on experiments in the education of students. On November 8th, 2016 at 10:30 a.m. the hybrid sounding rocket HEROS 3 was launched from the ESRANGE Space Center to an apogee altitude of 32,300m (106,000 ft). This set a new altitude record for European student and amateur rocketry and a world altitude record for hybrid rockets built by students. The 7.5m long rocket was using Nitrous Oxide (N2O) and a Paraffin-based fuel to produce 10,000N of thrust. The dry mass of the rocket was only 75 kg thanks to a carbon fibre structure for the most part. The rocket performed the record breaking flight at perfect weather and visibility conditions, reaching a maximum airspeed of 720 m/s and Mach 2.3. The rocket performed a soft landing with two parachutes and can be reused. Flight data and engine performance data are published and analyzed. The flight data shows excellent stability of the rocket. Engine performance data proves very high efficiency and stable combustion as in the ground tests. The subsystem design and verification before the launch is reported. Engine and flight trajectory simulations show very good agreements with the flight data. Furthermore, the overall project, the rocket design, the subsystems as well as the launch campaign are presented here in detail.