Design and Development of a Cost-Effective Reloadable Motor …
445
Fig. 1 Measurement of burning rate of propellent
2.2 Burning Rate Measurement
Figure 1 shows the process of measurement of burning rate. The samples of KNSu
were prepared in the dimensions 50 mm × 12.5 mm × 5 mm using the dry heating
method. ˙ In dry heating method the white mix is heated with little water. When the
mixture is heated the sugar melts and KNO 3 grain suspends. This mixture is heated
until a paste is formed, which is then dried and a bar of the above dimensions is made.
This was fixed in a vise and a graduated scale was placed adjacent to it to enable
the measurement of the burning rate. All five faces of the sample were insulated
using glue to ensure the unidirectional propagation of flame. The remaining face of
the sample was covered with gun powder for rapid initiation of flame. For safety
reasons, a fuse was used to ignite the powder. The burning rate of the propellant
was estimated by measuring the time interval of flame travel between two arbitrary
points. The burning rate was measured to be 7.22 mm/s.
2.3 Nozzle Design
The nozzle in the rocket does the process of transforming thermochemical energy
into kinetic energy [8]. Suitable design of the nozzle is required to ensure optimum
mass flow rate, exit velocity and exit pressure of the combustion gas. Selecting the
combustion chamber radius (r c ) as 16 mm, the cross-sectional area of combustion
chamber was obtained as 804.25 mm
2 . Assuming the ratio of area of combustion
chamber to the area of throat (A c /A t ) as 16, the value of A t was estimated as 50.26 mm
2 .
Hence, the radius of the throat (r t ) was calculated to be 8 mm. The ratio of crosssectional area at the end of nozzle to area of cross-section at the throat section
(A e /A t ) was taken as 20. Considering this, the radius at the exit of the nozzle (r e ) was
obtained as 17.89 mm. Assuming the divergent angle of the nozzle (θ ) as 15° and
the convergent angle (β) as 50°, the length of converging (L cn ) and diverging section
445
Fig. 1 Measurement of burning rate of propellent
2.2 Burning Rate Measurement
Figure 1 shows the process of measurement of burning rate. The samples of KNSu
were prepared in the dimensions 50 mm × 12.5 mm × 5 mm using the dry heating
method. ˙ In dry heating method the white mix is heated with little water. When the
mixture is heated the sugar melts and KNO 3 grain suspends. This mixture is heated
until a paste is formed, which is then dried and a bar of the above dimensions is made.
This was fixed in a vise and a graduated scale was placed adjacent to it to enable
the measurement of the burning rate. All five faces of the sample were insulated
using glue to ensure the unidirectional propagation of flame. The remaining face of
the sample was covered with gun powder for rapid initiation of flame. For safety
reasons, a fuse was used to ignite the powder. The burning rate of the propellant
was estimated by measuring the time interval of flame travel between two arbitrary
points. The burning rate was measured to be 7.22 mm/s.
2.3 Nozzle Design
The nozzle in the rocket does the process of transforming thermochemical energy
into kinetic energy [8]. Suitable design of the nozzle is required to ensure optimum
mass flow rate, exit velocity and exit pressure of the combustion gas. Selecting the
combustion chamber radius (r c ) as 16 mm, the cross-sectional area of combustion
chamber was obtained as 804.25 mm
2 . Assuming the ratio of area of combustion
chamber to the area of throat (A c /A t ) as 16, the value of A t was estimated as 50.26 mm
2 .
Hence, the radius of the throat (r t ) was calculated to be 8 mm. The ratio of crosssectional area at the end of nozzle to area of cross-section at the throat section
(A e /A t ) was taken as 20. Considering this, the radius at the exit of the nozzle (r e ) was
obtained as 17.89 mm. Assuming the divergent angle of the nozzle (θ ) as 15° and
the convergent angle (β) as 50°, the length of converging (L cn ) and diverging section