טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYoash Mor
SubjectInvestigation of Mechanisms for Containment and Combustion
of Liquid Oxidizer in Solid Propellant
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Gany Alon


Abstract

Solid propellants are widely used in many rocket systems, due to the simplicity of their motor structure, maintenance and operation. However, their energetic performance is lower than that of liquid propellants, mainly due to the relatively poor energetic potential of the available solid oxidizers. 

The present study examines a novel, innovative approach that combines the benefits of both propellant groups - a solid propellant augmented by (storable) liquid oxidizer (SPALO). The SPALO’s structure is similar to that of a conventional solid propellant; it consists of a solid fuel matrix and small discrete liquid oxidizer units, dispersed within it. Thermo-chemical simulations predict a significant improvement in the theoretical specific impulse relative to conventional solid propellants - up to 12% in aluminized propellants and even higher in non-aluminized propellants.

The study includes an experimental and a theoretical work. The goal of the experimental work was to find an efficient method for containment of a liquid oxidizer within hermetically closed discrete small units, with a future objective of incorporating such units in a SPALO. In the experimental investigation, we found a solution for the containment challenge, demonstrating mechanical encapsulation of water within a welded bisectional thin shell, made of polyethylene sheet or aluminum foil. We assess, with high confidence, that this method can be applied for containment of a liquid oxidizer.

A theoretical combustion model for a SPALO was developed. The model divides the propellant to many small characteristic cells, each of them consists of a liquid oxidizer unit and a binder shell. It describes the combustion process with multiple flame sheets, conducting heat to the oxidizer and binder, which can have different surface temperatures. The model is applicable to SPALO augmented by monopropellant or regular liquid oxidizers, in various oxidizer-to-fuel (binder) mass ratios: stoichiometric, slightly rich in fuel, and very rich in oxidizer.   

One of the main achievements of this study was the development of an original modified thermal resistance model (MTRM) accounting for multiple heat transfer mechanisms. The MTRM was developed in the course of the formulation of an analytical combustion model of the SPALO. The MTRM deals with heat transfer situations involving heat sources from chemical reactions or phase transition. It describes the various heat transfer mechanisms by three common thermal resistors, radiation, convection, and conduction (in media with no internal mass diffusion), adding a new coupled thermal resistor that stands for conduction and enthalpy flow in the gas phase. Similarly to the classical thermal resistance approach, the present model is valid for one-dimensional, quasi-steady heat transfer problems, but it can also handle problems with an internal chemical heat generation source. The model was demonstrated on two combustion case studies - a liquid fuel droplet and liquid fuel contained within a porous particle. These examples imply the advantage of the new thermal resistance approach - it can be a useful and powerful modular tool for solving relatively easily and quickly complex problems involving chemical reactions and phase transition, such as combustion problems.