Experimental Observation and Characterization of B−HTPB‐based Solid Fuel with Addition of Iron Particles for Hybrid Gas Generator in Ducted Rocket Applications

Abstract

An extensive diversity in the formulation of HTPB‐based solid fuels with metal additives has now been accepted in rocket and missile applications. Boron, which is a metalloid and often occurs in compound form has maintained its dominance mainly due to its significant theoretical energy potential. Therefore, it is preferred as the primary choice for rockets and solid fuel ramjet (SFRJ) or ducted rocket (SFDR). In this paper, performance enhancement of B−HTPB‐based solid fuel is assessed through a rapid screening tool which is called an opposed flow burner (OFB). Screened fuel combinations may be further evaluated in the gas generator of a ducted rocket (DR) to fulfill the intention of the present investigation. The baseline fuel (B−HTPB) is included with a metal fuel/catalyst (iron) with the expectation that it would enhance the combustion performance of boron. Boron−iron loading has been taken 10 % of the total sample weight (wt.) giving a wt. ratio of 90 : 10. Pure oxygen has been used as an oxidizer which impinges on the fuel surface where oxygen mass flux (Gox) varies between 20–57 kg/m2‐s. In this study, the research focuses mainly on regression rate and amount of residual active boron in the condensed combustion product (CCP) of the samples. Addition of iron to B−HTPB increases the regression rate by around 12 % and active boron content in CCP reduces significantly to 2.5 % compared to 16 % of the baseline fuel. In addition to that, the heating value of the fuel samples and identification of gas phase intermediate species (OH, CH, C2, BO, BO2) are the other vital investigations undertaken in the present study.

Exploring the potential of boron carbide in enhancing energy output of solid fuels for SFRJ and hybrid rocket propulsion systems

“…Due to the presence of an oxide layer covering the surface of the particle, the ignition of B 4 C particles can be significantly delayed. The removal of the oxide layer is a slow and kinetic/diffusion‐controlled process that accounts for a significant portion of the total burning time of the particle [46]. Several researchers propose that fluorine could be added to the combustion environment as an oxidizer to overcome such shortcomings [23, 47–49].…”

Enhancing Mechanical and Combustion Performance of Boron/Polymer Composites via Boron Particle Functionalization

“…Unfavored interactions between the hydrophobic polymer matrix and the polar B surfaces lead to agglomerations of B inside HTPB, slowing down the combustion process and limiting the strengthening effect of B particles on mechanical properties. ,, A higher loading of B particles, even though desired for energy density, exacerbates the deterioration of mechanical properties. Therefore, the typical mass loading of B within HTPB reported in the literature is about 30 wt % or less. ,,, …”

“…SFRJ requires high-performance solid fuel grains with excellent mechanical and combustion properties. The mechanical properties of the solid fuel are critical for the structural reliability and stable performance of the SFRJ. − The fuel grain of SFRJ is typically a composite of high-energy particles (e.g., boron (B)) and a polymeric binder (e.g., hydroxyl-terminated polybutadiene (HTPB)). − Many polymeric binders, such as HTPB, paraffin wax, and polyethylene, have been studied for solid fuel applications . Among them, HTPB is the preferred and commonly used binder in solid propellant rocket motor application because of its high specific impulse and good mechanical properties at different temperatures. , B has high volumetric and gravimetric energy densities (140 kJ/cm 3 and 59 kJ/g) .…”

“…Therefore, the typical mass loading of B within HTPB reported in the literature is about 30 wt % or less. 7,8,13,20 Surface functionalization of inorganic particles is an effective strategy to enhance the compatibility between the particles and the polymer matrix, as reported in several particle/polymer systems. 21−24 For example, Hamming et al 21 modified TiO 2 nanoparticles with an amino acid to create an attractive interaction with polymethylmethacrylate, which led to a higher glass transition temperature (T g ).…”