| dc.description.abstract | This thesis is concerned with theoretical investigations on some
aspects of monopropellant droplet combustion. The burning characteristics
have been obtained by solving the governing differential
equations which are essentially nonlinear in character due to chemical
kinetics.
The problem of a monopropellant droplet, burning under adiabatic
conditions has been studied, to examine the assumption of constant
physical properties in the analysis. This study has revealed that the
constant property assumption does not introduce any significant errors
in the prediction of some gross characteristics like the mass burning
rate, provided the constant properties are evaluated at an average
temperature obtained from the study. A simple expression for the
exponent (p) of the droplet radius (r?) in the burning rate (?)
variation (? ? r??) has been obtained. The controversies prevalent
in the literature over the limiting values of p have been completely
resolved.
The effects of inert non adiabatic conditions on the burning
characteristics, in particular on the ignition and extinction characteristics,
have been obtained. Increasing activation energies and
decreasing ambient temperatures beyond some critical values led to
multiple transition solutions which have been interpreted in terms of
ignition–extinction characteristics. The effects of increasing
activation energy and decreasing ambient temperature on the ignition and
extinction states have been evaluated. The solutions indicate that
a monopropellant droplet can be ignited if the size is increased beyond
a critical value (by internal mass addition) without violating the quasi steady
conditions. Further, the constant size droplet, burning in an
inert atmosphere, has been investigated for its ignition and extinction
characteristics brought about by varying the ambient temperature.
The problem of a monopropellant droplet burning in a reactive
environment has been studied using a two step reaction model. A numerical
procedure has been developed for the solution of this two eigenvalue
problem. The solutions indicate that the oxidant atmosphere greatly
reduces the extinction droplet radius (roughly by 1/100 for oxygen
atmosphere and by 1/6 for air, ambient temperature being 300°C) in
comparison to that of the inert atmosphere. The solutions further show
that the two flames - the decomposition flame and the diffusion flame -
tend to separate with the former thinning at a faster rate than the
latter as equilibrium is approached.
The unsteady burning of a monopropellant droplet under supercritical
conditions has been studied with the droplet being replaced by a gas
pocket. This study is primarily motivated towards a critical examination
of the utility of profile methods in such problems. The temperature
profiles obtained by solving the partial differential equations exhibit
similar characteristics (at various times) in the radial coordinate, with
a quadratic profile describing the similar shape adequately. The
solutions obtained by the profile method using these findings have
good agreement with those of the partial differential equations.
The basic results of the burning rate, obtained as above, have
been used to study monopropellant rocket motor combustion under idealized
conditions. The results of chamber lengths obtained, over a
wide range of parameters, have been correlated in a simple form which
is accurate to within five percent. The effect of pressure on the
chamber length has also been discussed. | |
