Solid Propellant Rocket Nozzle Erosion

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Solid propellant

rocket nozzle erosion

By:-S.Rup Kumar (09D41A2101)

K.Saraswathi (09D41A2144)

M.Shefali (09D41A2140)



ABSTRACT

In this project we are predicting the characteristics

of graphite nozzle throat erosion of a solid

propellant rocket and developing a minimization

code for its control.

The nozzle throat erosion is a one of an important

input parameter for predicting the solid rocket

motor ballistics performance accurately.

This must be accounted at the design stage of solidrocket motor.



The nozzle throat back wall temperature(skintemperature) can also be predicted precisely byapplying moving boundary method with unsteadyheat transfer analysis. The throat erosion will bemore in the case of large size motors and long

burning motors.

The erosion rates will be different for variousnozzle throat materials under attack of hightemperature combustion gases from different solid

propellants and for different operating conditions.

Among various materials, graphite is widely usedfor nozzle throat inserts, due to its excellentthermal and physical properties.



The main disadvantage is poor erosion resistance

especially at high gas temperatures and long

burning times. The relative importance of different variables

influencing the erosion mechanism is not known.

various mathematical models have been developedto find out some significant variables only , which

are really affecting the throat erosion.

No mathematical model was developed to account

all significant variables .



Consequently the dimensional analysis is

commonly employed in such a situation to indicate

logical grouping of the significant variables andfond the correlation from the number of

experiments.



Project overview

Literature survey

Numerical calculations of graphite nozzle

erosion characteristics

Coding in C-programme



LITERATURESURVEY



From the literature survey, we have found that the

graphite erosion is occurred due to the following:

1. Chemical reaction of propellant gases with

graphite material. (CHEMICAL EROSION)

2. Mechanical scrubbing of solid particles of

combustion with carbon surface.

(MECHANICAL EROSION)



The effectiveness degree of thesefactors will depend on:

Composition

Temperature

Pressure of the reacting products

Density of Graphite



Nozzle



Nozzle Erosion

Due to the flow of high

temperature and high velocity

gases through nozzle, its layers

are removed gradually from its

surface. This process is called as

nozzle erosion.



Eroded nozzle



Graphite

Excellent shock resistance

High vaporization temperature

Much lower density thanmetals



Graphite material



NUMERICAL

CALCULATIONS



Correlation for Graphitethroat erosion

For calculating the erosion at graphite throat

correlation technique has been used. In this

technique results are correlated with dimension

less groups and ratios and determined in unknown

exponents from those experimental data. The least

squares is used to find out the unknown

coefficients.



the erosion rate is mainly dependent on the following parameters:

Dco,mix:diffusion coefficient Dt: Initial throat diameter

V: Average velocity of gas

ρgp : Density of gas particle

ρm : Density of graphite µ : Gas viscosity

t : Burn time

Cp : Gas heat capacity

K : Thermal conductivity

χ : Subsonic entry length

β : Blowing parameter

ε : Alumina gas Cloud Emissivity



Dt, V, ρgp,ρ, m,µ,t,C p,K χ are the inputs ,we will vary

accordingly.

Dco,mix, β,ε are the variables to be found.

Blowing parameter(β): The primary constituents in the

exhaust stream of composite propellant reacting with

graphite were found to be H2O, C2O, O2 & OH. Thesereactions are :

C + H2O → CO+H2

C + CO2 → 2CO

C +½O2 → COC + OH → CO + ½H2

C + O → CO



For these reactions, the blowing parameter β is

defined as

where

MWcarbon = molecular weight of carbon

MWgp = molecular weight of graphite

X= mole fraction.



Diffusion Coefficient(Dco,mix):

Chemical reaction rates at high surface

temperatures are very high, and consequently, thereaction controlling phenomenon are diffusion-

limited. A mean diffusion coefficient that

characterizes the system is selected as the binary

diffusion coefficient for carbon monoxide since itis the main product of erosion. For mixtures, the

binary diffusion coefficient was determined by:



The binary diffusion coefficient for non-polar

gases is given by :

The binary diffusion coefficient depends uponthe type of gases whether the polar gases or non-

polar gases. Collision integral vary in this case

accordingly with polar and non polar gases.



• For polar gases collision integral is

• For non polar gases collision integral is



Alumina Gas Cloud Emissivity (ε ):

Important parameter, which strongly influences thethroat erosion, is a total alumina gas cloud

emissivity at nozzle throat. This is the emissivity

of products of exhaust gases of solid propellant at

nozzle throat.

The empirical relation of emissivity in terms of

nozzle throat diameter is given by:



The Correlation is given

by:



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50 60

Burn time

E

R

O

S

I

O

N

R

AT

E



REFERENCES

PREDICTION OF GRAPHITE THROAT EROSIONIN SOLID ROCKET MOTOR NOZZLES byM.Ratnam,scientist,directorate Of Solid Propulsion Systems

Centre,ASL,DRDL,hyd.

IMPORTANT FINDINGS AND OBSERVATIONS OF THEROCKET NOZZLE EROSION PROCESSES AND

THEORETICAL/NUMERICAL SIMULATIONS,chia-yung lin.

The Pennsylvania State University.

Solid Propellant Rocket Nozzle Erosion

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