Pyrolysis–gas chromatography of hybrid rocket fuel comprising low-melting-point thermoplastics

Abstract

Solid fuels comprising low-melting-point thermoplastics (LTs) have been developed as hybrid rocket fuels. However, it is necessary to improve the regression rate of such fuels for practical application. In this study, the pyrolysis mechanism of an LT fuel in the absence of oxygen was investigated and the combustion-inhibition species among the gaseous pyrolysis products were identified. Pyrolysis–gas chromatography was used to analyze the hydrocarbon compounds produced from the pyrolysis of the LT fuel and its constituents. Detailed chemical reaction simulations were performed to dissect the pyrolysis mechanism of paraffin oil, the principal constituent of the LT fuel. The results revealed that the pyrolysis and evaporation of the fuel components yield aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), which reduces fuel combustion. Notably, the C2H4 generated during paraffin pyrolysis considerably amplified the formation of aromatic hydrocarbons and PAHs, further inhibiting combustion. C2H4 was also identified as one of the potential chemical species that inhibit combustion. The C2H4 ratio in the fuel pyrolysis gas can be considered as an indicator for evaluating fuel compositions that enhance the fuel regression rate.