Delft Aerospace Rocket Engineering has developed a 1 kN hybrid rocket motor, using Nitrous Oxide as oxidizer and a mixture of Sorbitol and Paraffin as fuel. During the campaign, different motor configurations were tested. The thesis starts with the numerical simulation of the rocket motor firing in the different tests, modelling the discharge of self-pressurized Nitrous Oxide. The simulation provides the trend over time of motor parameters such as mass flow rates, vapor quality of the oxidizer, and fuel grain thickness. Once validated through comparison with the test data, these values have been used to setup CFD simulations of the combustion chamber. An instant of the burning is simulated in steady state conditions using the eddy dissipation combustion model, gaseous injection of the fuel and no entrainment of liquefying paraffin with the oxidizer flow. The oxidizer is injected in both liquid and gas phase using the results of the numerical simulations to initialize the boundary conditions. The results are compared with the numerical data, the experimental data and the values predicted by the theory, to show the improvements that CFD simulations can provide to the designer during the development of a new hybrid rocket motor.
Hybrid rocket propulsion systems have proved to be a suitable option for some specific applications in the space transportation domain such as in launch vehicle upper stages, orbit transfer spacecrafts, decelerator engines for re-entry capsules, and small satellites launchers. Part of the renewed interest in hybrid rocket propulsion is due mainly to the safety aspects, cost reduction, and the use of paraffin-based fuel that impacts positively in terms of the solid fuel regression rate. However, paraffin solid fuel grains have poor structural characteristics and sometimes low performance due to the fuel internal ballistics behaviour. More recently, various studies have been carried out to overcome these drawbacks of paraffin-based fuels, such as the addition of energetic nano-sized metallic powder and 3D printing techniques. This study presents a review of the principal concepts of 3D printing processes and extrusion techniques that can be suitable for paraffin grains manufacturing and the conceptual design of a prototype for a 3D printer system under development at the Aero-Thermo-Mechanics Department of Université Libre de Bruxelles.
As an emerging trend, green propulsion has been exponentially growing over decades in the space sector. This paper assesses different technologies in a trade-off study weighing their applicability to a specific class of upper stage systems currently developed by many companies and often referred to as "kick-stages" or "orbital stages." In a generic two-stage-to-orbit scenario, many launchers require a system able to go the extra mile to deliver one or multiple payloads on orbit(s). That is where the kick-stage plays a crucial role. The trade-off study reported here is based on a well-known decisionmaking tool, the analytical hierarchy process (AHP), and is divided into two parts: low-thrust class engines, such as monopropellants including pre-mixed blends usually employed for attitude and reaction control, and high-thrust engines, such as hypergolic bi-propellants combinations used for apogee maneuver. Hybrid thrusters are also considered in the analysis with a dedicated parallel trade-off. This paper is published with the permission of the authors granted to 3AF - Association Aeronautique et Astronautique de France (www.3AF.fr) organizer of the Space Propulsion International Conference.
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