1,721,005 research outputs found
Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion
Full text linkThis work provides a lab-scale investigation of the ballistics of solid fuel formulations based on hydroxyl-terminated polybutadiene and loaded with Al-based energetic additives. Tested metal-based fillers span from micron- to nano-sized powders and include oxidizer-containing fuel-rich composites. The latter are obtained by chemical and mechanical processes providing reduced diffusion distance between Al and the oxidizing species source. A thorough pre-burning characterization of the additives is performed. The combustion behaviors of the tested formulations are analyzed considering the solid fuel regression rate and the mass burning rate as the main parameters of interest. A non-metallized formulation is taken as baseline for the relative grading of the tested fuels. Instantaneous and time-average regression rate data are determined by an optical time-resolved technique. The ballistic responses of the fuels are analyzed together with high-speed visualizations of the regressing surface. The fuel formulation loaded with 10 wt.% nano-sized aluminum (ALEX-100) shows a mass burning rate enhancement over the baseline of 55% - 11% for an oxygen mass flux of 325 - 20 kg/(m2 s), but this performance increase nearly disappears as combustion proceeds. Captured high-speed images of the regressing surface show the critical issue of aggregation affecting the ALEX-100-loaded formulation and hindering the metal combustion. The oxidizer-containing composite additives promote metal ignition and (partial) burning in the oxidizer-lean region of the reacting boundary layer. Fuels loaded with 10 wt.% fluoropolymer-coated nano-Al show mass burning rate enhancement over the baseline >40% for oxygen mass flux in the range 325 to 155 kg/(m2 s). The regression rate data of the fuel composition loaded with nano-sized Al-ammonium perchlorate composite show similar results. In these formulations, the oxidizer content in the fuel grain is <2 wt.%, but it plays a key role in performance enhancement thanks to the reduced metal-oxidizer diffusion distance. Formulations loaded with mechanically activated ALEX-100-polytetrafluoroethylene composites show mass burning rate increases up to 140% - 20% with metal mass fractions of 30%. This performance is achieved with the fluoropolymer mass fraction in the additive of 45%
A new strategy for the reinforcement of paraffin-based fuels based on cellular structures: The armored grain - Ballistic characterization
Full text linkSlow regression rate of the solid fuel is the main limitation for the use of hybrid rocket engines in high thrust applications. Paraffin-based fuels tackle this limitation thanks to the entrainment mass transfer. In this study, ballistic behaviors of conventional polymeric fuel (ABS) and paraffin-based blends are studied and compared with those of the armored grains. These latter are a new generation of fuels featuring 3D printed cellular structures embedded in the wax-based grain. The ballistic characterization focuses on the evaluation of the regression rate (rf) and its dependence on the oxidizer mass flux. Relative ballistic grading of the formulations is pursued via thickness over time methods and an optical technique for rf determination. The armored grains are reinforced by gyroid structures that are 3D printed using three different polymers (ABS, PLA, and Nylon 6) and two relative densities (10% and 15%). Despite the slow burning behavior of the printing polymers, the embedded reinforcement enhances the rf of the paraffin-based formulations, with percent increases ranging from +48% to +91%. This result could be explained by the uneven and irregular texture of the burning surface promoting turbulence (and therefore, propellant mixing) and convective heat transfer. For both the armored grains and the paraffin-based formulations, blending the pristine paraffin wax with polymeric additives results in more viscous formulations and in a rf reduction. Armored grain combustion performance makes this novel fuel an interesting candidate for high-thrust hybrid rockets
Combustion in a Non-Conventional Hybrid Rocket Engine: Lab-Scale Testing of a Vortex Flow Pancake
No full textInfluence of Operating Parameters on the Ballistics of a Lab-Scale Vortex Flow Pancake Hybrid Rocket Engine
Full text linkParaffin-Based Fuels: Perspectives from Different Reinforcing Strategies and Metal Additives
No full textBoosting Green Propellants: the Sustainable Armored Grain for Hybrid Rocket Propulsion
Full text linkEffects of Vortex Flow Pancake Hybrid Rocket Engine Operating Parameters on Liquefying Fuel Combustion
No full textExperimental results from the vortex flow pancake hybrid rocket engine implemented at the Space Propulsion Laboratory of Politecnico di Milano are presented. Paraffin-based fuels are tested under quasi-steady and forced transient operating conditions. This preliminary investigation shows a database of more than 30 firings with quasi-steady operating conditions, and 4 runs with oxidizer mass flow rate throttling. The three main engine operating parameters varied in the current research are: (i) the oxidizer mass flow rate, (ii) the combustion chamber height, and (iii) the oxidizer injection velocity. The latter parameter is altered by changing the number of injectors for the oxidizer inlet flow. Throttling is performed on selected fuel formulations. Under the investigated conditions, the quasi-steady tests showed a regression rate decrease for increasing reinforcing polymer mass fraction in the paraffin-based blends. Such a result is due to the augmented viscosity of the melt layer of the formulations as the reinforcing polymer mass fraction increases. At the same time, the regression rate showed no direct dependence on the initial combustion chamber height, while oxidizer injection velocity dependence was identified. Forced transient tests showed an immediate response to throttling for the two investigated fuels
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