Program AHRES and its Contribution to Assess Features and Current Limitations of Hybrid Rocket Propulsion

Kurzfassung

In the year 2011 the German Aerospace Center (DLR) has started the program AHRES (Advanced Hybrid Rocket Engine Simulation). The aim is the development of software engineering tools and CFD tools for conceptual design and optimisation of hybrid rocket engines (HRE). To provide high accuracy software tools, the AHRES program includes complex experiments with hybrid rocket engines in laboratory and prototype scale, for pressures up to 70 bars. For this purpose an existing test facility at the DLR site Trauen (former EUROPA 2 upper stage test range) was enhanced, in order to conduct tests with a HRE. In this paper a short description of the operational test bed is given, which is equipped with sophisticated measurement techniques. The HRE test bed is currently equipped with oxidiser supply systems for high-test peroxide (HTP) and gaseous oxygen. The solid fuel grains are based on hydroxyl-terminated polybutadiene (HTPB) mixed with different metallic additives to improve the performance. Currently conducted tests are aimed to characterise the HRE’s combustion processes and to generate an experimental database to develop the above mentioned simulation tools. Based on experimental test data, calculations on developed simulation tools and literature sources a comparison of the HRE with solid and storable liquid rocket engines is made. To illustrate one possible application of a HRE in near-future a HRE which could be applied as an upper stage is designed and compared with existing solid rocket engines. For the comparison the third stage “Zefiro 9A” of the VEGA launcher is taken. The preliminary results and conclusions are presented, including specific impulse, combustion and engine efficiency, as well as the achievable regression rate dependent on fuel composition. The last factor is of tremendous importance to determine the achievable thrust level of a hybrid rocket engine. This again, determines whether a HRE might be promising for the application as an upper stage. The results are presented graphically, in table form, analysed, and commented.