טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentScheuer Ron
SubjectThermodynamic Aspects of Boron Combustion in Propulsion
Systems
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Alon Gany


Abstract

Boron is a metal element, exhibiting a remarkable theoretical heat of combustion in air on both gravimetric and volumetric basis, exceeding that of common hydrocarbon fuels. Therefore, it is highly attractive for use as a fuel additive in air breathing propulsion, mainly in ramjet engines. Despite the promising potential, practical boron containing fuels often demonstrate low motor performances, mainly due to the existence of a molten B2O3 layer, which covers the boron particle entirely from the beginning of the ignition phase. In order to attain ignition and stable combustion, this layer must be completely removed.

The main objective of this research  was to theoretically determine the conditions in which  gaseous B2O3 saturation occurs during boron-containing hydrocarbon fuel combustion in air. These conditions were studied by constructing a database, using NASA’s thermochemical simulation program, of the combustion products of air and fuel, composed of boron and HTPB, for various conditions: equivalence ratio, boron enrichment level, stagnation air temperature and combustor pressure.

The database enabled the construction of an envelope indicating the boundaries between the operation points in which the evaporation of liquid B2O3 is possible and those in which such evaporation is impossible.

Main conclusions:

1.  Relatively broad ranges of practical operating conditions do not enable complete boron combustion because of thermodynamic blocking of B2O3 evaporation due to saturation conditions. Such situations may result in low combustion efficiencies.

2.  Distributed air inlets as well as working at appropriate equivalence ratios can help recovering a larger fration of the  combustion energy of boron.