Evaluation of Regression Rate and Combustion Efficiency of Silver Loaded Boron-HTPB-Based Solid Fuel in Ducted Rocket equipped with an Innovative Mixing Chamber

Relevance in the current rocket propulsion discipline is the status of ducted rockets as an important technology with a high ranking for their capabilities to provide specific thrust in missiles and tactical propulsions. Among the different fuel candidates explored for ducted rocket applications, boron (B) has garnered considerable interest based on its extremely high gravimetric and volumetric energy densities, which renders it one of the most prospective metallic fuels for next-generation solid propellant applications. Yet, notwithstanding its theoretical benefits, actual application of boron to propulsion systems is confronted with a serious limitation: the development of a passivating oxide layer (B?O?) on the outer surface of boron particles. The oxide layer serves as a barrier that impairs effective ignition and burning of the underlying boron core, thus lessening the achievable energy release and combustion efficiency.To tackle this problem, the current study examines the use of silver (Ag) nanoparticles as thermal conductivity additives in a boron-loaded hydroxyl-terminated polybutadiene (HTPB) matrix. Silver, which has higher thermal conductivity and chemical stability during combustion, is speculated to enhance the local heat transfer environment in the fuel grain, thus speeding up the ignition process of boron particles and improving their overall combustion performance. By enabling speedy energy transfer to the boron cores, silver nanoparticles should prevent the inhibitive effects of the B?O? layer and release the total energetic potential of boron-based propellants.To analyze experimentally the performance of such new solid fuel formulations, a static laboratory-scale ducted rocket motor (DRM) arrangement was utilized in controlled laboratory settings. The research rigorously tested three different fuel grain formulations: pure HTPB (used as a reference baseline), 5% boron-loaded HTPB (HB), and 5% boron-loaded and 1% silver nanoparticle-loaded HTPB (HBA). All formulations underwent severe combustion testing at a constant oxygen flow to maintain steady oxidizer supply and to mimic realistic operating environments.In addition to the combustion experiments, detailed material characterization was carried out with the help of sophisticated analysis methods, i.e., X-ray diffraction (XRD) and scanning electron microscopy (SEM). These techniques were both applied to the as-received feed particles (boron, silver, and HTPB) and the condensed combustion products (CCPs) that were recovered after firing. The XRD examination gave valuable information on crystalline phases both before and after the combustion process, whereas SEM images showed morphology alteration, surface roughness, and microstructure transformation during combustion. Combined, the characterization tools imparted good insights into combustion mechanism and role played by the addition of silver as an additive within the fuel system.The main emphasis of this research was the assessment of major combustion parameters, such as regression rate and chamber pressure, which are main indicators of fuel performance in hybrid propulsion systems. The experimental data showed that the boron-HTPB mixture (HB) provided the maximum regression rate among the samples tested, showing an about 10.13% increase over the pure HTPB fuel grain. This improvement highlights the considerable effect of boron addition on the energetic performance of the fuel system. Although the addition of silver nanoparticles (HBA) introduced added complications, the research offers an elemental understanding of how metal additives can affect combustion behavior, heat feedback, and overall fuel regression.To recap, this research provides significant additions to the production of boron-based solid propellant systems for ducted rockets, presenting experiential verification of the efficacious role played by silver nanoparticles as thermal energy promoters. Results have the possibility of guiding eventual fuel formulation initiatives, with prospects of maximizing fuel combustion efficiency, energy release maximum, and optimizing the performance of future solid rocket propulsion technologies.