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Test Campaign on a 10 kN Class Sorbitol-Based Hybrid Rocket Motor for the Stratos II Sounding Rocket
... Furthermore the port diameter of the grain was chosen such that the oxidizer mass flux was limited to 500 kg/s/m^2 at the start of the burn. The reason for this was to prevent "high mass flux related instabilities" from occurring which were observed during the Stratos II test campaign and other test campaigns [3,4]. Lastly the grain was sized such that the optimum O/F of 3.235 occurred roughly halfway through the burn, meaning that the engine is running oxidizer rich for approximately the first half of the burn and fuel rich for the second half of the burn. ...
... Throughout the test campaign the number of holes was varied to account for inaccuracies in earlier predictions. Other injector types such as selfimpinging and higher injection angles were researched and tested on a small scale, but these types of injectors did not significantly increase performance compared to the parameters measured during the Stratos II test campaigns [3]. ...
... First: the oxidizer mass flow observed during the tests was slighlty lower than the design value of 6 kg/s, leading to an overal reduction in mass flow and thrust. Secondly, even though the mass flow was slighlty lower, the mass flux at the start of the burn was still 481 kg/m²/s, which was very close to the value of 476 kg/m²/s measured during the Stratos II test campaign [3]. Since the regression rate can be estimated for a certain fuel and oxidizer combination based on the regression rate using equation 1, it was therefore expected that the regression rate would be similar for both motors considering that both motors had the same fuel and oxidizer combination and roughly the same burn time. ...
Full text available upon request. Abstract:
In 2015 Delft Aerospace Rocket Engineering (DARE) broke the European altitude record for amateur rockets by reaching an altitude of 21.5 km with their Stratos II+ rocket. Since then this record has been broken by a team of students from the university of Stuttgart and the record currently stands at 32 km. Because of this DARE has started the development of the Stratos III rocket, with which it aims to break the European altitude record for amateur rockets once again. In order to break the record DARE is developing a new 25kN hybrid rocket engine to power the Stratos III rocket named the "DHX-400 Nimbus". The design of the engine is mostly based on the lessons learnt from Stratos II+ and the engine uses a similar oxidizer and fuel combination consisting of nitrous oxide and a combination of Sorbitol, Paraffin Wax and Aluminium micro particles. Furthermore a small scale test campaign was performed to test out different concepts which could potentially be used in the full scale version of the engine. Two different versions of the engine were developed: a "heavy" version, which features an aluminium shell and a graphite nozzle and a "lightweight" version, which features a 3D printed titanium nozzle and a composite combustion chamber. The heavy version is more robust and was used for testing the internal ballistics of the engine. The second lightweight version was intended to be used for the Stratos III rocket. It should be noted that the "DHX-400 Nimbus" is more than twice as powerful as its predecessor, which lead to several complications during the design and production process. This paper aims to describe the development process of the "DHX-400 Nimbus", including the complications that were found during the scaling up of the engine and how these complications were eventually resolved. This paper shall discuss the design and production of the "DHX-400 Nimbus", along with relevant data from several static hot fire tests. Finally, recommendations for future improvements shall be given.
... A series of tests have been performed on this motor in a flight configuration to characterize its performance [13]. In total 14 tests were conducted at both 'Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek' (TNO) and 'Deutsches Zentrum für Luft-und Raumfahrt' (DLR). ...
... The internal motor geometry of the first design iteration, which was used for tests 1-5 was purely based on first order sizing and experiences from preceding small scale test articles. With the order of 75% the combined motor efficiency was however far below the desired value of 90% [13]. ...
... The issue of assessing the limit states of products, the development of which is damage (destruction) of the shell as a whole or the loss of tightness of such a shell, remains especially relevant. Thus, if the destruction of cylinders and containers, both multilayer and single-component, are sufficiently described in works [13,14], then the issue of destruction of products obtained by FDM is only partially covered in works [15,16]. However, in these publications, the authors mainly focused on the experimental study of the destruction of thin samples under static force loading, without establishing the mechanism of development of damage in the material itself. ...
The emergence and development of additive technologies (in particular, fused deposition modeling, FDM) determine the intensification of research in this area, given that there is currently a transition from applied and artistic applications to the use of FDM in solving engineering problems. The paper analyzes the behavior of thin-walled shells obtained by FDM (tanks of various technological purposes) under internal thermobaric loading. The damage and destruction of the tanks were simulated. The mechanism of damage development was checked experimentally. It was concluded that an essential physical and mechanical characteristic is the product’s crack resistance, characterized by the stress intensity factor (SIF) and differs between the initial filament and the finished product. The SIF value depends on the existing defects and leaks in the formed body of the product. It is also determined by both the material used and the printing modes. It is shown that applying thin sealing films and various printing techniques can improve the mechanical characteristics of the product as a whole.Keywords3D PrintingStrengthCrack ResistanceFractureServiceability PredictionProduct Innovation
... A series of tests have been performed on this motor in a flight configuration to characterize its performance. 5 In total 10 tests were conducted at both 'Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek' (TNO) and 'Deutsches Zentrum für Luft-und Raumfahrt' (DLR). Six of these tests resulted in a structural failure of the combustion chamber. ...
... A series of tests have been performed on this motor in a flight configuration to characterize its performance. 5 In total 10 tests were conducted at both 'Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek' (TNO) and 'Deutsches Zentrum für Luft-und Raumfahrt' (DLR). Six of these tests resulted in a structural failure of the combustion chamber. ...
In this paper, a commercial CFD code is used to simulate different hybrid rocket motor configurations applying liquid N2O as the oxidizer and paraffin wax as the fuel. This work is the prosecution of a previous study performed to simulate hybrid rockets with diaphragms of different geometries placed inside the combustion chamber, where N2O was injected in gaseous phase, instead of using liquid. With respect to the previous study, liquid injection has been introduced, together with the droplets vaporization inside the combustion chamber and their full coupling with the eulerian gas phase, in terms of both heat exchange and momentum exchange. The main objective is the description of the proper numerical models to be applied in test cases in which liquid injection has to be represented. The most important differences with respect to the simulations where only gas is injected are also discussed. In order to validate the CFD output, experimental results coming from two different design scales are used: a laboratory scale and an increased scale. For each of these two scales, different rocket configurations and geometries have been studied. The different geometries studied include: a lab-scale rocket with a cylindrical grain and with a 4-hole diaphragm inserted at the 24% of the grain length, a 1-hole diaphragm lab-scale motor and an increased-scale hybrid rocket with a 1-hole diaphragm and without any diaphragm. For each test case, a comparison with the related experiment is presented and discussed. The simulations have been run in steady state conditions, with simplified chemical reactions, liquid oxidizer injection and no paraffin entrainment. The simulations show a good agreement with the experimental results of the different rocket configurations analyzed: the maximum error on efficiency is 7%. The CFD predicts (both in the case of gas and liquid injection) a higher efficiency for the rocket geometries provided with a diaphragm with respect to the same geometries without a mixing device and this is in accord with experiments. CFD results also show some peculiar phenomena about liquid injection.
In 2009 Delft Aerospace Rocket Engineering (DARE) broke the European altitude record for amateur rockets with the launch of Stratos I to 12.5 km. Currently, DARE is developing its successor, the Stratos II rocket, which is designed to reach 50 km altitude. To overcome the limitations from the relatively low specific impulse of 110 to 130 seconds of DARE’s current solid rocket motors, a team for the development of an alternative propulsion concept has been established. In 2010 a group of international students within DARE started the DAWN project focusing on the development of a N2O-sorbitol hybrid powered engine for Stratos II.
As part of the development, various fuel recipes have been investigated experimentally. For this a battleship motor has been developed. Also work has started on a small hybrid engine capable of launching Stratos II to 1 km altitude. The design of this engine is unique in that it includes an all composite structure, with the skin of the oxidizer tank and the fuel casing as load carrying structure.
This paper presents the results of the research on the fuel recipes, consisting of the investigation on the regression rate and burn stability of sorbitol with varying amounts of opacifying additives, and the comparison of these results with tests applying paraffin.
Furthermore we present the modular design of the flight engine, and the systems engineering approach used to assure that the design meets the safety requirements for launch on a professional launch site. For the flight engine, we discuss the various components, including the composite tank with a liner that is compatible with the cold oxidizing liquid, the feed system section with an in house developed and tested pyrovalve, and the composite combustion chamber with a liner that is compatible with the hot combustion gasses.
Despite the many challenges faced by the team to develop this engine in just 1.5 year, the successful realization of this engine provides great opportunities for innovation, and brings DARE one step closer to space.
To further develop and demonstrate the applicability of liquefying-fuel hybrid rocket technology to low-cost launch applications, a small team of engineers is developing a medium-scale liquefying-fuel hybrid sounding rocket using storable propellants (paraffin wax and N2O) that will carry a 5 kg payload to the edge of space. This rocket, known as Peregrine, is being developed by engineers from NASA Ames, Stanford University, Space Propulsion Group Inc. (SPG, Sunnyvale, CA) and NASA Wallops, with a launch from Wallops anticipated at some point in the future. This paper focuses on the propulsion ground test results obtained to date. Results from the first round of ground testing showed that the design peak oxidizer mass flux of 1300 kg/m2-sec in the fuel port was too high to achieve satisfactory flame holding with any of the injector configurations tested. Furthermore, a strong first logitudinal acoustic mode response was observed in a majority of the tests and the average c* combustion efficiency design target of greater than 95 percent was not achieved. To address these issues, the motor was redesigned to accommodate a larger fuel grain and a second phase of ground testing is currently underway. Recent ground test results show significant improvements in combustion efficiency (average c* efficiency of 93% achieved in the most recent test) and combustion stability, but further development is required to bring the propulsion system to operational status.
The purpose of this study was to characterize the regression rates of three traditional hybrid rocket fuels along with one novel fuel using nitrous oxide as the oxidizer. In order to complete these tests, a robust test facility was developed for use in this study as well as in future hybrid rocket programs at Stanford University. This stand allowed for rapid successive hot fire testing and the capability to test multiple fuel grain configurations. To date it has been used to conduct 40 hot fire tests. Performance values and fuel regression rate data are presented for HTPB, PMMA, HDPE, and sorbitol.
On March 17, 2009, a rocket named Stratos was launched, by Delft Aerospace Rocket Engineering, or DARE in short. The purpose of this rocket was to break the European altitude record for amateur rockets which was 10.7 km at that time. A design of a small sounding rocket, such as Stratos, is a good example of an interdisciplinary challenge. An optimal design is a combination of structures, manufacturability, propulsion, aerodynamics, electronics and many other aspects The Stratos rocket achieved an apogee altitude of 12.551 meters at the Esrange Space Centre, thereby setting a new European altitude record for amateur rockets. A detailed flight trajectory reconstruction is done, whereby differences between simulation and reality are explained. The objective of this thesis is to give a detailed insight in the design, the simulation tools, the production process and the results of the mission. The design philosophy of the Stratos rocket, simulation software and the production planning concept are valuable tools in the development of newer and more powerful rockets, which could ultimately result in a successor of the Stratos rocket.
The paper provides a brief review of theoretical and experimental studies concerned with hybrid rocket instability. The instabilities discussed include atomization and mixing instabilities, chuffing instabilities, pressure coupled combustion instabilities, and vortex shedding. It is emphasized that the future use of hybrid motor systems as viable design alternatives will depend on a better understanding of hybrid instability.