For the KNSB propellant, with an oxidizer-fuel (O/F) ratio of 65/35, the theoretical combustion equation is as follows:
C6H14O6 + 3.345 KNO3 -> 1.870 CO2 + 2.490 CO + 4.828 H2O + 2.145 H2 + 1.672 N2 + 1.644 K2CO3 + 0.057 KOH
at a pressure of 68 atmospheres (1000 psi), and where the following compounds are symbolized as:
Sorbitol | solid | C6H14O6 |
potassium nitrate | solid | KNO3 |
carbon dioxide | gas | CO2 |
carbon monoxide | gas | CO |
steam | gas | H2O |
hydrogen | gas | H2 |
nitrogen | gas | N2 |
potassium carbonate | liquid | K2CO3 |
potassium hydroxide | gas | KOH |
The mole numbers for each of the products shown above were determined from PROPEP (Propellant Evaluation Program).
Parameter | Units | Note | ||
Process method | Cast | |||
Isp | Specific Impulse, ideal | 151.5 | sec. | [1] |
C* | Characteristic exhaust velocity, theoretical | 2980 (908) | ft/s (m/sec) | |
To | Combustion temperature, theoretical @1000 psia | 1327 (1600) | deg Celsius (K) | [2] |
To | Combustion temperature, measured@1000 psia | TBD | deg Celsius | |
Density, ideal | 1.841 | gram/cu.cm. | ||
Density, as cast | 1.82 | gram/cu.cm. | [3] | |
X | Mass fraction of condensed-phase products | 0.436 | - | |
k | Ratio of specific heats | 1.137 | - | [4] |
M | Effective molecular wt. of exhaust products | 39.9 | g/mole | [5] |
Burn rate behaviour | inverted-mesa | |||
ro | Burn rate @ 1 atm. | 0.102 (2.6) | in/sec (mm/sec.) | |
r | Burn rate @ 1000 psia | 0.443 (11.3) | in/sec (mm/sec.) | |
Tcr | Auto-ignition temperature | > 300 | deg. C. |
[1] At 1000 psi pressure; exit pressure one atmosphere
[2] PROPEP combustion results
[3] Measured, typical
[4] Mixture (2-phase), at chamber conditions
[5] System mass /number of gas moles
Figure 2 -- This chart shows the variation of combustion temperature and molecular weight of exhaust products with O/F ratio.
Figure3 -- This chart shows the variation of theoretical specific impulse with chamber pressure.