Susane R. Gomes

Gaseous Oxygen Injection Effects in Hybrid Labscale Rocket Motor Operations

4Hybrid rocket motor features such as operational safety, thrust tailoring, low investment cost and constructive simplicity are currently widespread. Nevertheless, inefficient combustion reduced mass fraction and mostly low regression rates still play a role in the major disadvantages. Swirling oxidizer flow is known to affect the mixing between oxidizer and fuel, intensifying heat exchange thus increasing regression rate. A laboratory scale hybrid engine was developed, and tests were conducted with gaseous oxygen (GOX) supply, ultra high molecular weight (UHMW) polyethylene, one axial and two swirl injector types. Oxygen mass flow, grain length and diameter and test time were maintained constant in order to evaluate the GOX injection influence on the motor performance and combustion characteristics. Series of six tests for each injector were performed with one unique set of machined throat diameters, to acquire a range of oxidizer mass flux for comparison. The data of oxidizer mass and fuel consumption were collected, and average regression rate values were calculated. Empirical correlations for the regression rate coefficients were obtained for each injection method. The burn grain profiles were analyzed and compared, sustaining that the income oxidizer flow pattern strongly affects the regression rates.

Design and Testing of a Hybrid Rocket Motor

This research aims to provide a methodology for the project of labscale hybrid motors. This development begun with the thermal analysis of the fuel grain using the Flynn, Wall and Ozawa method; this provided the simulation entry data to maximize the motor performance. The computer simulation was performed with the Chemical Equilibrium Specific Impulse Code of the U.S. Air Force, also known as ISP Code. Based on the optimum oxidizer to fuel ratio, the literature was used to supply the mathematical background for the calculation of the motor geometrical parameters whose operating conditions were determined throughout the simulation. Finally, firing tests were conducted to verify the reliability of the project methodology. The firing tests were performed with three injectors: 2 swirling and one axial. The tests showed that the higher the operation pressure the more suitable is the project, meaning the methodology developed works best in hybrid rocket motors with high operating pressures.

Síntese de poliuretanos modificados por óleo de mamona empregados em materiais energéticos

The aim of this work was to synthesize a polyurethane polymer matrix using castor oil as a polymer chain modifier, whose characteristics can be adjusted for use as a binder in the manufacture of energetic materials such as propellant and pyrotechnics for aerospace use. We attempted the partial substitution of hydroxyl-terminated polybutadiene (HTPB), a pre-polymer commonly used as a starting polyol in obtaining energetic matrix composites. Thermoanalytical techniques were employed to characterize the material based on castor oil and the unmodified HTPB. The results showed similar behaviors, confirming the possibility of their use as polymer matrix composites through the proposed adaptations.

Thermal Decomposition Kinetics Studies of Ammonium Perchlorate - HTPB /Al/AP Solid Propellants formulated with Iron Oxide burning rate catalyst in Nano and Micro scale

The thermal decomposition kinetics of ammonium perchlorate (AP)/hydroxyl-terminatedpolybutadiene (HTPB) samples, the AP/Al/HTPB solid propellant, with Iron Oxide burning rate catalyst at nano and micro scale were studied by thermal analysis techniques at different heating rates curves in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) curves in isothermal conditions. The Arrhenius kinetics parameters were obtained by Flynn-Wall and Ozawa method. The Kissinger and Starink kinetics method was also used for obtaining the activation energy value for a comparison purpose. The propellant samples thermal decomposition was studied simultaneously by thermogravimetric and differential thermal analysis (TG-DTA). For this purpose solid propellant grains containing nano and micro scale iron oxide were formulated. The comparison was made with a solid propellant grain formulated without burn rate catalyst additive. The effect of catalysts on the propellant burning rate and the propellant initiation sensitivity were also evaluated by friction and impact. The effect of the catalyst in the propellant binder reaction was evaluated by viscosity and mechanical properties. Scanning electron microscopy with Energy dispersive analysis (SEM/EDS) techniques was used to evaluate the iron oxide morphology. Three bench firing tests were performed with rockets motor in order to konw the ballistics parameters.

Kinetics Parameters Evaluation of Paraffin-Based Fuel

In recent years, Hybrid Propulsion is turning into a significant alternative to Liquid and Solid Propulsion Systems, it presents attractive features and good balance between performance and environmental impact. Thus, paraffin based propellant grains are indicated as a substitute for hydroxyl-terminated polybutadiene (HTPB), the actual solid propellant fuel grain. Despite being a well-known material, scarce data on the relation of activation energy (Ea) and molecular weight (WCxHy) of paraffin is available. In this work, the kinetic parameters (activation energy and pre-exponential factor) of microcrystalline 140/145°F paraffin have been raised through Thermo Gravimetric Analysis in conjunction with the Arrhenius kinetic mechanism, according to ASTM-E1461 and the dependence of molecular weight with melting point from Etessam and Sawyer approach. The 140/145°F paraffin activation energy calculated in this study was compared with different activation energy from alkanes and substances used as fuel in the propulsion systems field. The analysis indicated that the microcrystalline 140/145°F paraffin, manufactured by Petrobras, presents activation energy of 224 KJ.mol−1 and pre-exponential factor of 5.48×1022 min−1. Ignition was achieved with a 50 W pyrotechnic igniter. The firing test with 140/145°F paraffin fuel and gaseous oxygen (GOX) mass flux of 130 Kg.s−1 m−2 at pressure above 0.80 MPa, was easily sustained.Copyright

Evaluation of polyurethane binder additivated with paraffin and tested with a swirl injector

The fuel was synthesized with polyurethane (binder) based on pre-polymer technology modified with castor oil with the addition of 30% of paraffin and 10% of aluminum powder. An axial and a swirl injector were used. The regression rates doubled with the addition of paraffin and the mechanical properties increased drastically. Thrust measurements indicate that the addition of paraffin increased thrust at about 57% and regression rates at about 70%. The mixture that produced the best ballistic parameters was polyurethane plasticized with castor oil and 30% w/w of paraffin with gaseous oxygen injected with a swirler. The swirl injector improved the efficiency and regression rate values.

Infrared Camouflage of the Warfighter’s Equipment through Enhanced Coating Technology

Infrared reflective coatings allow the operator to change the wave signature of military assets. The coatings have the capability to reflect electromagnetic waves in order to match the signature of the observed object to the signature of the corresponding environment, in the visible and near infrared spectra. Consequently, the object blends into the surroundings reducing its vulnerability. The reflectance profile and gloss level of the coating are defined in accordance to the specific environmental constraints, related to the reflectance of soils and vegetation. The paint developed in this study was made with a polyurethane-acrylic based resin, pigments and additives. The final configurations were tested and the reflectance matched those of foliage, sand and soil. The concepts and products developed in this study will be used in the ASTROS Artillery Saturation Rocket System produced by Avibras.

Experimental Study of Vegetal Based Polyurethane Fuel filled with Paraffin Particles for Hybrid Rocket Motors

Experimental investigation was conducted to determine the relative propulsive and combustion behavior of a polyurethane-based solid-fuel formulations containing 30% w/w of paraffin. In total, 4 solid fuel formulations were investigated. The thermal decomposition of the solid fuels was studied at different heating rates in dynamic nitrogen. Fuel containing paraffin was investigated with electron microscopy, paraffin spheres were visualized and measured. Firing tests with 4 configurations were performed. Thrust measurements indicated that the addition of paraffin increased thrust at about 57% and regression rates at about 83%. It was found that increase in regression rate is proportional to paraffin content.

Combustion evaluation of PU solid fuel based on pre- polymer technology additivated with paraffin and Aluminum for hybrid rocket engines

The aim of this work is to develop a high regression rate fuel for hybrid rocket motors, this research encompasses binder synthesis and the addition of paraffin and aluminum metallic particles. The project started with the synthesis of polyurethane (binder) based on pre-polymer technology modified with castor oil. These binders were filled with granulated paraffin and micron-sized aluminum particles. Firing tests with 7 configurations were performed. Thrust measurements indicate that the addition of paraffin increased thrust at about 57% and regression rates at about 70%. No relevant improvement in performance was obtained with aluminum addition. Specific impulse decreased when aluminum particles were added to the fuel. The mixture that produced the best ballistic parameters was polyurethane plasticized with castor oil and 30% w/w of paraffin with gaseous oxygen injected with a swirler.