Angelo Pasini

Testing and Characterization of a Hydrogen Peroxide Monopropellant Thruster

In the present paper, the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets is investigated. For this purpose, a reconfigurable test bench for the characterization of the operation and the propulsive performance of small rocket thrusters has been designed and realized. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on γ-alumina supporting spheres. The results indicated that Pt/Al 2 O 3 is an effective catalyst combination for the decomposition of 87.5% propellant-grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time, and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high-grade hydrogen peroxide (87.5 % by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental setup.

Performance Characterization of Pellet Catalytic Beds for Hydrogen Peroxide Monopropellant Rockets

The present paper illustrates a comprehensive experimental campaign carried out in order to assess the capability of four especially developed catalytic beds to decompose hydrogen peroxide under operational conditions representative of typical application to small monopropellant rocket engines and to characterize the resulting performance of the thruster. The catalytic beds have been integrated in a reconfigurable thruster prototype and tested in a suitable test facility. All beds have shown high decomposition and propulsive efficiencies, well in excess of 90%. In particular, two catalytic beds (indicated as LR-III-106 and CZ-11-600) have been, respectively, able to decompose up to 13 and 11 kg of 90%hydrogen peroxide (equivalent to 433 and 366 g of decomposedH2O2 per gram of catalyst) in 2500 and 2000 s of continuous thruster operation. They exhibited C-star efficiencies higher than 95%. The experimental results have also indicated two main sources of catalyst degradation. In low-porosity catalysts the decay of chemical activity affects the temperature efficiency and causes theflooding of thefirst portion of the catalytic bed,whereas highly porous catalysts experience thermal rupture of the carrier,which leads to excessive growth of the pressure drop across the catalytic bed.

Experimental Characterization of a 5 N Hydrogen Peroxide Monopropellant Thruster Prototype

In the framework of the LET-SME program funded by the European Space Agency, ALTA S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) jointly investigated the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets. To this purpose ALTA S.p.A. designed and realized a reconfigurable test bench for the characterization of the operation and propulsive performance of small rocket thrusters. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on γ−alumina supporting spheres, especially developed by ALTA in collaboration with the Chemistry and Industrial Chemistry Department of Pisa University, Italy. The results indicated that Pt/Al2O3 is an effective catalyst combination for the decomposition of 87.5% propellant grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high grade hydrogen peroxide (87.5% by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental set-up.

A Reduced Order Model for Preliminary Design and Performance Prediction of Tapered Inducers: Comparison with Numerical Simulations

The article recalls the recent development of a reduced order model for the preliminary design, geometric definition and noncavitating performance prediction of tapered-hub, variable-pitch, mixed-flow inducers, and illustrates its application to a typical three-bladed, high-head inducer for liquid propellant rocket engines. The mean axisymmetric flow field at the trailing edge of the inducer blades and the noncavitating head coefficient at both design and off-design conditions are then compared with those obtained from the numerical flow simulations generated by a commercial CFD code. Together with earlier experimental validations, the results dramatically confirm the capability of the proposed model to generate interpretative and useful engineering solutions of the inducer preliminary design problem at a negligible fraction of the computational cost required by 3D numerical simulations.

Performance of a Monopropellant Thruster Prototype Using Advanced Hydrogen Peroxide Catalytic Beds

The present paper illustrates different firing tests carried out on advanced catalytic beds for hydrogen peroxide decomposition in a new monopropellant thruster prototype designed for easier adjustment and control of the main operational and propulsive parameters. The tests refer to the comparison between a pt/α-Al 2 O 3 catalyst (named FC-LR-87) and a similar commercially available space propulsion catalyst. Up to 2 kg of 87.5 % hydrogen peroxide have been decomposed by a single sample of the FC-LR-87 catalyst. Both steady-state and pulsed firings have been carried out in the same reactor configuration. A fresh sample of the FC-LR-87 catalyst has also been tested at a different bed load. Both the FC-LR-87 and the commercial catalysts showed equivalent propulsive performances, with a slightadvantage in favor of the FC-LR-87 catalyst in terms of the c* and temperature efficiencies (up to 94 and 93%, respectively).

Comparative Characterization of Advanced Catalytic Beds for Hydrogen Peroxide Thrusters

In the last two years Alta S.p.A., Pisa, Italy, has been engaged in the development of advanced catalytic beds for hydrogen peroxide (HP) decomposition in collaboration with the Department of Chemistry and Industrial Chemistry of Pisa University. A series of chemical activity tests at atmospheric pressure on a number of catalyst-substrate preparations indicated a platinum catalyst supported on α -alumina and named FC-LR-87 as the most promising candidate for characterization under more realistic conditions in a suitably designed HP monopropellant thruster prototype. Scanning Electron Microscopy (SEM) and X-Ray diffractometry (XRD) analyses have been carried out on FC-LR-87 catalyst samples before and after continuous and pulsed firing tests. These analyses showed that the decomposition of 2 kg of high grade HP did not cause any measurable loss of catalyst from the support, confirmed the stability of the small and well dispersed platinum particles on the alumina surface, and indicated the absence of oxidation of the active phase.

Pulsed Chemical Rocket with Green High Performance Propellants

PulCheR (Pulsed Chemical Rocket with Green High Performance Propellants) is a new propulsion concept in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses, reproducing the defence mechanism of a notable insect: the bombardier beetle. The radical innovation introduced by PulCheR is the elimination of any external pressurizing system even if the thruster works at high pressure inside the combustion chamber. At each pulse, pressurization of the combustion chamber gases takes place due to the decomposition or combustion reaction, and the final pressure is much higher than the one at which the propellants are stored. The weight of the feeding system is significantly reduced because the propellants are fed at low pressure, and there is no need for turbopumps, high pressure propellant tanks or gas vessels. The feed pressure becomes independent on the chamber pressure and the performance degradation typical of the blow down mode in monopropellant thrusters can be avoided. The PulCheR concept is able to substitute many currently used propulsion systems for accessing space in both mono and bipropellant configurations. The preliminary assessment of this new propulsion concept has been investigated using green propellants with potential similar performance to the current stateof-the-art for monopropellant and bipropellant thrusters.

Reduced-Order Model for H2O2 Catalytic Reactor Performance Analysis

The present paper describes a steady one dimensional model of the hydrogen peroxide decomposition flow in a pellet-type catalytic bed and its application to the parametric design of a typical reactor for small rocket propellant thrusters. The two-phase liquid-gas-vapor flow through the bed is treated as a homogeneous, adiabatic, chemically reacting flow, for which the properties depend on the local composition. Fast equilibrium hydrogen peroxide adsorption and first-order finite-rate desorption is assumed for the one-step hydrogen peroxide decomposition reaction on the catalyst surface. Standard viscous/aerodynamic correlations for porous media are used to account for pressure losses. The predictions of the model depend on a limited number of uncertain parameters, for which the values can be readily determined by comparison with the available experimental data. Good agreement has been attained between the model predictions and the results of hydrogen peroxide monopropellant thruster firings. The model provides a rational framework for identifying the main operational parameters of catalytic pellet beds, understanding their interactions, and efficiently guiding the reactor sizing and design, using the indications easily obtained from sensitivity analyses.

On the Preliminary Design and Noncavitating Performance Prediction of Tapered Axial Inducers

A reduced order model for preliminary design and noncavitating performance prediction of tapered axial inducers is illustrated. In the incompressible, inviscid, irrotational flow approximation, the model expresses the 3D flow field in the blade channels by superposing a 2D cross-sectional vorticity correction to a fully guided axisymmetric flow with radially uniform axial velocity. Suitable redefinition of the diffusion factor for bladings with non-negligible radial flow allows for the control of the blade loading and the estimate of the boundary layer blockage at the specified design flow coefficient, providing a simple criterion for matching the hub profile to the axial variation of the blade pitch angle. Carters rule is employed to account for flow deviation at the inducer trailing edge. Mass continuity, angular momentum conservation, and Eulers equation are used to derive a simple second order boundary value problem, whose numerical solution describes the far-field axisymmetric flow at the inducer discharge. A closed form approximate solution is also provided, which proved to yield equivalently accurate results in the prediction of the inducer performance. Finally, the noncavitating pumping characteristic is obtained by introducing suitably adapted correlations of pressure losses and flow deviation effects. The model has been verified to closely approximate the geometry and noncavitating performance of two space inducers tested in Altas Cavitating Pump Rotordynamic Test Facility, as well as the measured pumping characteristics of a number of tapered-hub inducers documented in the literature.

Endurance Tests on Different Catalytic Beds for H 2O2 Monopropellant Thrusters

The present paper illustrates a comprehensive experimental campaign carried out in order to assess the capability of four especially-developed catalytic beds to decompose hydrogen peroxide under operational conditions representative of typical application to small monopropellant rocket engines, and to characterize the resulting performance of the thruster. The catalytic beds have been integrated in a reconfigurable thruster prototype and tested in ALTA’s Green Propellant Rocket Test Facility. All beds have shown high decomposition and propulsive efficiencies, well in excess of 90%. In particular, two catalytic beds – indicated as LR-III-106 and CZ-11-600 – have been respectively able to decompose up to 13 and 11 kg of 90% hydrogen peroxide, equivalent to 2500 and 2000 s of thruster continuous operation, exhibiting C-Star efficiencies higher than 95%. The experimental results have also indicated two main sources of catalyst degradation. In low-porosity catalysts the decay of chemical activity affects the temperature efficiency and causes the flooding of the first portion of the catalytic bed, while highly porous catalysts experience thermal rupture of the carrier, which leads to excessive growth of the pressure drop across the catalytic bed.