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Potassium Nitrate-Sorbitol (KNDX) Propellant Chemistry and Performance Characteristics

Standard Composition (65/35 O/F)

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 solidC6H14O6
potassium nitratesolid KNO3
carbon dioxidegasCO2
carbon monoxidegasCO
steam gas H2O
hydrogengas H2
nitrogen gas N2
potassium carbonateliquidK2CO3
potassium hydroxidegasKOH

The mole numbers for each of the products shown above were determined from PROPEP (Propellant Evaluation Program).

Characteristics of the KNSB Propellant (65/35 ratio)
Process methodCast
IspSpecific Impulse, ideal151.5sec.[1]
C*Characteristic exhaust velocity, theoretical2980 (908)ft/s (m/sec)
ToCombustion temperature, theoretical @1000 psia1327 (1600)deg Celsius (K)[2]
ToCombustion temperature, measured@1000 psiaTBDdeg Celsius
Density, ideal1.841gram/
Density, as cast1.82gram/[3]
XMass fraction of condensed-phase products0.436-
kRatio of specific heats1.137-[4]
MEffective molecular wt. of exhaust products39.9g/mole[5]
Burn rate behaviourinverted-mesa
roBurn rate @ 1 atm.0.102 (2.6)in/sec (mm/sec.)
rBurn rate @ 1000 psia0.443 (11.3)in/sec (mm/sec.)
TcrAuto-ignition temperature> 300deg. 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

Data chart

Figure 1 -- This chart shows the variation of theoretical specific impulse with O/F (oxidizer/fuel) ratio.

Data chart

Figure 2 -- This chart shows the variation of combustion temperature and molecular weight of exhaust products with O/F ratio.

Data chart

Figure3 -- This chart shows the variation of theoretical specific impulse with chamber pressure.

Last updated

Originally posted November 13, 1999

Last updated March 15, 2023

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