Thermogravimetric Analysis of the Decomposition of a Paraffin Particle/HTPB Fuel Grain for Hybrid Rocket Motors

Abstract

Paraffin has been identified as a promising alternative for use in propellant grains for hybrid rocket motors. Studies have been conducted using grain as fuel paraffin or liquid hidroxylated polybutadiene polymer (HTPB) due to the high thrust generated during firing. However, in consequences the low mechanical properties of pure paraffin, this study aims to evaluate the kinetics of degradation of a mixture composed of paraffin particles (PP) and HTPB compared with grain fuel pure paraffin and pure HTPB. For this we used a thermal analysis technique thermogravimetric in conjunction with the application of kinetic methods based on ASTM E1641 and Vyazovkin theory. Based on these results we can say the activation energy results are in agreement with the literature and the mixture PP / HTPB presents intermediate activation energy values as expected.

Experimental evaluation of HTPB/paraffin fuel blends for hybrid rocket applications

“…The differences in their results highlight the importance of how atmospheric composition and paraffin inclusion procedures can play significant roles in mixed-fuel system decomposition under heating in quiescent conditions. [12][13] and Cardoso et al [14] are of particular noteworthiness. Sinha et al [12] coupled DSC data [12] and specific heat capacity measurements [13] to compute thermal degradation kinetic parameters of plain HTPB, plain paraffin (probably a macrocrystalline wax), and mixed-fuel systems.…”

“…Many research efforts have focused on the evaluation of HTPB/paraffin fuel blends for hybrid rocket applications, mainly through thermal decomposition [11][12][13][14][15][16] and combustion [11,[17][18][19][20][21][22][23][24][25][26] experiments. A detailed and comprehensive literature review on this topic is provided in the Supplementary Material and is summarized, as follows.…”

“…In general, the findings amongst all of the thermal decomposition literature regarding mixed HTPB/paraffin fuel systems are in good agreement and indicate that the addition of paraffin to HTPB enhances the first stage, low-temperature mass loss, but there are some minor discrepancies between different studies. For example, Sinha et al [12] noted a 35% mass loss in the first decomposition stage with the addition of only 27.75% paraffin, while Cardoso et al [14] noted a 35% mass loss corresponding to a 60% paraffin loading. The two notable differences between those experiments were that Sinha et al [12] utilized an inert, helium atmosphere and included paraffin as a dissolved liquid during the fuel mixing process, while Cardoso et al [14] utilized an oxidant atmosphere and included paraffin as dispersed solid particles during the mixing process.…”

“…For example, Sinha et al [12] noted a 35% mass loss in the first decomposition stage with the addition of only 27.75% paraffin, while Cardoso et al [14] noted a 35% mass loss corresponding to a 60% paraffin loading. The two notable differences between those experiments were that Sinha et al [12] utilized an inert, helium atmosphere and included paraffin as a dissolved liquid during the fuel mixing process, while Cardoso et al [14] utilized an oxidant atmosphere and included paraffin as dispersed solid particles during the mixing process. The differences in their results highlight the importance of how atmospheric composition and paraffin inclusion procedures can play significant roles in mixed-fuel system decomposition under heating in quiescent conditions.…”

“…The reported increases are due to a reduction in activation energy and a corresponding increase in fuel vaporization, and should not be confused with the previously mentioned entrainment effect. Cardoso et al [14] utilized TGA mass loss data to calculate the activation energy of plain HTPB, plain paraffin, and a mixed-fuel sample (60% paraffin) according to the Ozawa-Wall-Flynn method [30]. The plain HTPB and paraffin samples exhibited single activation energies over the measured temperature range of approximately 300 and 100 kJ/mol, respectively.…”