טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPelosi Avishag
SubjectSolid Propellant Enhancement by Liquid Oxidizer Addition
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Alon Gany
Full Thesis textFull thesis text - English Version


Abstract

Solid propellant motors are well known for their simplicity, which makes them suitable for multiple and diverse purposes, from small anti-tank rockets to huge boosters for space missions. The main disadvantage in the use of solid propellants stems from their relatively low energetic performance, which shows in a standard specific impulse Isp of 200-250 seconds, whereas liquid propellants provide much higher energetic values (Isp from 250 to 400 seconds). This significant gap results mainly from the relatively poor energetic potential of solid oxidizers.

The present work aims at investigating a new family of solid propellants, whose performance is enhanced by liquid oxidizer addition. The revolutionary concept combines solid fuel (or propellant) and liquid oxidizer in a unified propellant grain, enhancing its energetic performance dramatically. Small capsules containing liquid oxidizer are dispersed within the solid propellant, just as in conventional solid propellants the small solid oxidizer granules are mixed within the polymeric binder (fuel). Intuitively, one expects the new propellant to conserve the structural simplicity and burning characteristics of a conventional solid propellant, yet potentially improving its specific impulse by up to 1 2 %.

The research includes both theoretical and experimental works. The theoretical part shows the theoretical performance of different propellant combinations and develops an original one-dimensional model, which describes the main characteristics of the flamelet formed by an evaporating oxidizer droplet contained within a volatile (typically polymeric) fuel component, at sub-critical and supercritical pressure operations. The model predicts fuel and oxidizer surface temperatures, fluxes, flame height and fuel regression rate as a function of operating pressure, droplet size and oxidizer to fuel ratio. The transient nature of the combustion process is emphasized, revealing a combustion cycle at the individual droplet scale, with pressure-dependent average burning rates typical to solid propellants. It is predicted that, within a micro burning cycle, oxidizer droplet evaporation always exceeds the surrounding binder pyrolysis rate.

The experimental study focuses on the observation of the phenomena involved in the combustion of a fuel-rich solid propellant strand containing a liquid oxidizer droplet or column. The use of a pressure-regulated windowed test chamber and a high-speed video camera enables the observation of the relevant combustion phenomena. Interesting combustion features (oxidizer boiling, flame structure, surface irregularity) are qualitatively observed. The measured pressure-dependent average regression rate values are typical to solid propellant combustion.

The innovation of the topic makes each finding an original contribution to the combustion and propulsion fields.