1,721,119 research outputs found
Diagnostic Techniques for Regression Rate of Paraffin-Based Fuels in a VFP Hybrid Rocket Engine
No full textBallistic Characterization of Armored Grains with Vortex Flow Pancake Hybrid Rocket Engine
No full textThis work deals with a combustion behavior assessment of paraffin and paraffin-based fuels burning in a vortex flow pancake (VFP) hybrid rocket engine. Blending of paraffin wax with reinforcing polymer is a commonly implemented strategy pursuing the design of fuels with fast enough regression rate and suitable mechanical properties. Being the wax regression rate strictly related to the entrainment of melted fuel droplets, blending has the drawback of limiting the solid fuel ballistic response. A new reinforcing strategy based on 3D-printing of scaffold structures to be embedded in the solid fuel grain has been proposed by the Space Propulsion Laboratory (SPLab) of Politecnico di Milano and is here applied to the VFP engine configuration. This reinforcing strategy enables a reduction of the polymer mass fraction in the blend, thus enabling a more tailorable combination of ballistic and mechanical properties. In this paper, a microcrystalline wax is blended with 5 wt% of a styrene-based copolymer; the blended fuel is used as the embedding matrix for gyroid structures serving as reinforcement for the fuel grain. The ballistic response of the reinforced fuel is characterized under quasi-steady and forced transient operating conditions. Ballistic performance of the gyroid-reinforced fuel is contrasted with those of paraffin-based blends where mechanical properties improvement is afforded loading the wax with a styrene-based reinforcing polymer. Overall, the testing campaign consisted of nearly 29 firings under quasi-steady conditions, and 9 tests with forced transient operating conditions. The main observable parameters of interest for the quasi-steady campaign were the solid fuel regression rate and the engine propulsion efficiency (evaluated in terms of both characteristic velocity and thrust coefficient). For forced transient analyses, the engine ballistic response was characterized by pressure trace and overall system behavior. The proposed reinforcing strategy provided encouraging results, and the paraffin-based fuels showed suitable response to the forced transient operating conditions
Accelerated ageing of micron- and nano-sized aluminum powders: Metal content, composition and non-isothermal oxidation reactivity
Full text linkNano-sized Al (nAl) is an attractive candidate for the performance enhancement of current solid propellant formulations, and its characteristics are relevant for the development of innovative solid fuels for hybrid rocket propulsion. Nano-sized Al powders feature a higher reactivity than their micron-sized counterpart. While desirable for effective energy conversion during the combustion, this characteristic yields possible powder storage issues. This paper investigates the ageing behavior of air-passivated nAl powders under two different relative humidity conditions (RH) of 80% and 10%. Fresh and aged powders are characterized by active metal content determination (CAl), electron microscopy, X-ray diffraction, and thermal analysis. The marked sensitivity of nAl (40 nm) to ageing is testified by a nearly full CAlloss in just 24 h (with RH = 80%). Under the same condition, the conventional 30 μm-counterpart loses only 13% of the original active metal content in a time of 336 h
Analysis of Quasi-Steady and Transient Burning of Hybrid Fuels in a Laboratory-Scale Burner by an Optical Technique
No full textBurning of hydroxyl-terminated polybutadiene in gaseous oxygen is investigated using a timeresolved optical technique. Combustion tests are performed in a two-dimensional radial micro-burner under quasi-steady and forced transient operating conditions. Under quasi-steady operating conditions, the high initial regression rate at the beginning of the run is followed by a smooth monotonic decrease as combustion proceeds. This behavior is captured by a purposely developed regression rate simulation model. Under forced transient operating conditions, for oxidizer mass flow throttling down, solid fuel exhibits a non-monotonic regression rate response. Earlier phases of the transient are characterized by a noticeable regression rate decrease followed by faint oscillations
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