SOLID PROPELLANTS

Gas generated in a solid propellant is produced by reaction of reducing and oxidizing agent in the combustion chamber. The oxidizing agent is usually an inorganic slat or one or more organic nitro compounds. The reducing agent is usually a polymeric organic binder compound of carbon hydrogen and sometimes sulphur. The reducing agent imparts mechanical strength to the propellant.

SOLID PROPELLANT ROCKET ENGINE

Construction:

The construction of solid propellant rocket engine is shown in figure

• Solid propellant is the combination of solid fuel ( plastic or resin material) and oxidizer

(Nitrates & per-chlorates)

• Solid fuel & oxidizer is homogeneously mixed & packed inside the shell.
• A liner is provided between the shell and the propellant. The purpose of the liner is to protect the shell as high temperature will be generated during combustion process.

              Working:

• The igniters is located at the top and ignites the spark. So combustion takes place.
• When the combustion take place in the combustion chamber , very high pressure and temperature gases are produced
• The highly heated products of combustion gases are then allowed to expand in the nozzle section.
•  In the nozzle pressure energy of the gas is converted into kinetic energy. So the gases come out from the unit with very high velocities.
• Due to high velocities of gases coming out from the unit, a force or thrust is produced in opposite direction. This thrust propels the rocket.

       Advantages:

• Simple in design and construction
• They do not require feed system. So they are free from the problems of  moving parts such as pumps, valves etc
• Less vibration due to absence of moving parts.
• Less maintenance 
• Suitable for short range applications.
•  Problems arising from the sudden emptying of propellant tanks are absent.

Disadvantages:

• In case of emergency it is difficult to stop the engine in the midway.
• Decrease of speed is not possible
• Low specific impulse
• At the end of an operation, the burnt up debris cannot be reused. So it is uneconomical.
• Nozzle cooling is not possible.
• Nozzle erosion is unavoidable due to the presence of solid particles in the high temperature and high speed gases.
• Transportation and handling of these rockets before firing require due to the presence of propellant throughout.

               SOLID PROPELLANTS

1. Heterogeneous  or composite propellants
2. Homogeneous propellant

In heterogeneous solid propellants, plastic polymers and polyvinyl chlorides are used as fuels. Nitrates and per-chlorates are used as oxidizers. In homogeneous solid propellants, nitroglycerine and nitrocellouse are used. It combines the properties of fuel and oxidizers.

              PROPERTIES OF SOLID PROPELLANTS

• Should release large amount of heat during combustion
• Physical & chemical properties should not change during processing.
• It should have high density
• Should not be poisonous and hazardous
• Should be cheap and easily available

• Should be noncorrosive and nonreactive with the components of the engine.

Storage and handling should be easy

References

1. Compressible fluid flow  - A. H. Shapiro
2. Fundamentals of compressible flow with aircraft and rocket propulsion   - S. M. Yahya