Electric micropropulsion systems

A two-fluid 2-D model of the supersonic plasma flow in a propulsive magnetic nozzle (MN) is extended to include simple electron and ion thermodynamics to study the effects of electron cooling and ion thermal energy on the expansion. A faster electron cooling rate is seen to reduce plasma jet divergence, increase radial rarefaction, and enhance detachment from the closed magnetic lines. Ion thermal energy is converted to directed kinetic energy by the MN without the mediation of an ambipolar electric field, and alters the electric response of the plasma.

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Influence of Electron and Ion Thermodynamics on the Magnetic Nozzle Plasma Expansion

Trade-off between paraffin-based and aluminium-loaded HTPB fuels to improve performance of hybrid rocket fed with N2O

ADAMANT: A surface and volume integral-equation solver for the analysis and design of helicon plasma sources

In this work, single-port, cylindrical grain laboratory-scale hybrid rocket motors are numerically simulated to study the effect of diaphragms. The effect of single and multiple diaphragms is investigated by varying diaphragm height, its axial location (for a single diaphragm), and spacing (for multiple diaphragms) at selected inlet GOX. A single diaphragm increases the local regression rate and its influence is prominent only in the region immediate downstream. Therefore, a tangible increment in average regression rate with a single diaphragm can only be realized for motors with small L/D( 10), use of multiple diaphragms are required to increase the regression rate and combustion effici...

Effect of Diaphragms on Regression Rate in Hybrid Rocket Motors

This paper is focused on the description of simulation codes developed to design a helicon plasma thruster for a small satellite under development in the research project Helicon plasma hydrazine combined micro (HPH.com) conducted within the 7th Framework Program of the EU by a European consortium.

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Design of 50 W helicon plasma thruster

Combustion efficiency in standard hybrid rocket motors is usually low. This is due to the poor mixing of the core oxidizer flow with the gasi fied fuel from the walls. Motor scale increase usually worsens this issue. Large and volu metric inefficient post combustion chambers are common devices used to improve efficiency, while mixers are somewhat more complex, but more effective devices. The addition o f a mixer at grain aft-end was originally suggested by Marxman [1], but literature data on mixers, and in general on techniques to improve combustion efficiency is lacking. The resea rch activity herein presented aim at further investigate this issue: a mixer placed in f uel grain was selected as efficiency enhancing device. This work starts from experiments performed by Dr. Grosse [1] and more testing, both at lab scale and at increased scale h ave been carried out. Simple 1-hole diaphragms fixed at 25% of the grain length were used. Centre-hole diameter has been optimized. Moreover, CFD simulations have been carried out to further understand the enhanced mixing phenomena. N2O was selected as oxidizer and as fuel the same par affin Sasol Wax 0907 mixture used by Dr. Grosse was chosen. Lab scale experiments showed that combustion efficiency is raised from 76% (without diaphragm) up to 95% using diaphragms. Also good agreement has been found with CFD simulations. At increased scale (three times the thrust of lab scale), the referenc e combustion efficiency was 80%, and it was raised at 94% with the addition of a diaphragm. Als o combustion stability was enhanced. Another plus of the diaphragm on post-chambers and aft-end mixers is to enhance regression rate downstream it. At lab scale and wit h the smaller diaphragm regression rate was increased up to +90% (4.5 mm/s) compared to literature data without diaphragm. At increased scale the increase was of +65 % (4.2 mm/s). Further research is needed, but these experiments showed that diaphragms can be used to design compact and efficient single-port and paraffin based hybrid rocket motors.

Testing and CFD Simulation of Diaphragm Hybrid Rocket Motors

A study on vortex injection in hybrid rocket motors with nitrous oxide as the oxidizer and paraffin as the fuel has been performed. The investigation followed two paths: first of all, the flow field was simulated with a CFD code, and then burn tests were performed on a lab-scale rocket. The CFD analysis had the dual purpose to help the design of the lab motor and to understand the physics underlying the vortex flow coupled with the combustion process. Numerical analysis was focused on the comparison with axial injection. Vortex injection produces a more diffuse flame in the combustion chamber and improves the mixing process of the reactants, both aspects concurring to increase the efficiency of the motor. A helical streamline develops downstream the injection region, and the pitch is highly influenced by combustion, that tends to straighten the flow due to the acceleration imposed by the temperature rise to the axial velocity component. The tangential velocity, on the contrary, is far less influenced by this effect. Experimental tests with the same chamber geometry have been performed with both pressurized and self-pressurized oxidizer. Measured performances showed an increase in regression rate up to 51% and a combustion efficiency that rises from values lower than 80% in the axial injection configuration up to more than 90% with vortex. Moreover, a reduction of the instabilities in the chamber pressure has been measured. Issues requiring further investigation concern the motor exhausts: both experimental and numerical analyses showed that there is a residual tangential velocity component in the plume; this, coupled with a noise suppressor system downstream the nozzle in the test apparatus, showed severe instabilities in the vortex configuration thrust measurements, not reported in chamber pressure burn data and not affecting axial injection.

Numerical and Experimental Investigation on Vortex Injection in Hybrid Rocket Motors

This paper deals with an experimental and numerical project intended to study fully tangential vortex injection in a hybrid motor of 1kN class. Due to the knowledge of the CISAS Hybrid Team, the choice for oxidizer has been pressurized nitrous oxide, while paraffin wax has been used as fuel. This investigation follows a previous project where a mixed axial/vortex device has been tested: also if an increase in performance has been observed, a non-uniform grain consumption showed an issue of such device. The work starts with a mission scenario that gives the design drivers for the subsequent preliminary design, performed with an iterative, transient and 0D numerical code. A successive step is the detailed design of the combustion chamber and test bed. The aim of the study was to investigate three objectives: vortex injection and a comparison with axial; throttling behavior at fixed mass flows (reduction of 75% and 50% of oxidizer flow); combustion chamber performance changing its configurations, in particular using inside a mixer. Performance parameters taken into account were chamber pressure oscillations, combustion efficiency and regression rate. In the preliminary phase two different issues have been discovered and solved: the first regards a chamber pressure behavior variation, linked to a too long postchamber; the second is referred to pressure pikes in the ignition phase, solved using a longer prechamber and a different ignition configuration. It has been shown that vortex injection lowers the chamber pressure oscillations respect to axial case from more than 7% down to 4%. Moreover, regression rate has been increased of 41%, and the a coefficient of its law up to 67% from axial. This last value, indeed, shows a constant behavior throttling down the oxidizer mass flow. The increase is due to the higher wall heat flux in the grain surface, given by the higher velocity and thermal gradient of the fluid. Combustion efficiency has been increased with vortex injection given by the higher turbulence flow that enhances the mixing of the reactants. Axial case showed a value of 76% of this last parameter, while vortex case went up to 90%. Coupling of injection and mixer (a diaphragm-like device inside combustion chamber) increases this value up to 96%. A cost analysis has been performed for this project, showing that hybrid propulsion is a low cost technology.

The "Vortex Reloaded" project: experimental investigation on fully tangential vortex injection in N2O - paraffin hybrid motors

This paper describes the experimental layout under development to test a helicon plasma thruster for a small satellite. The thruster class is 50 W 1mN. This work is done within the research project Helicon Plasma Hydrazine Combined Micro (HPH.com) in the frame of the 7th Framework Programme of the EU by a European consortium. Experimental tests are foreseen to validate codes, to support thruster design and to verify thruster performances. Two different test beds will be designed, an engineering model and a

G. Colombo

Papers

Design of 50 W helicon plasma thruster

Testing and CFD Simulation of Diaphragm Hybrid Rocket Motors

Numerical and Experimental Investigation on Vortex Injection in Hybrid Rocket Motors

The "Vortex Reloaded" project: experimental investigation on fully tangential vortex injection in N2O - paraffin hybrid motors

Experimental set-up to test a 50 w helicon plasma thruster