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Potassium Nitrate-Sucrose (KNSU) Propellant Chemistry and Performance Characteristics

Standard Composition (65/35 O/F)

For KNSU propellant, with an oxidizer-fuel (O/F) ratio of 65/35, the theoretical combustion equation is as follows:

C12H22O11 + 6.288 KNO3 -> 3.796 CO2 + 5.205 CO + 7.794 H2O + 3.065 H2 + 3.143 N2 + 2.998 K2CO3 + 0.274 KOH

at a pressure of 68 atmospheres (1000 psi), and where the following compounds are symbolized as:

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 KNSU Propellant (65/35 ratio)
Process methodCast
IspSpecific Impulse, ideal153.5sec.[1]
IspSpecific Impulse, delivered (typical)125-130sec.[2]
C*Characteristic exhaust velocity, theoretical3013ft/s
ToCombustion temperature, theoretical @1000 psia1447 (1720)deg Celsius (K)[3]
ToCombustion temperature, measured@1000 psia1350deg Celsius[4]
Density, ideal1.89gram/
Density, as cast (typical)1.80gram/[5]
XMass fraction of condensed-phase products0.424-
kRatio of specific heats, mixture1.133-[6]
MEffective molecular wt. of exhaust products42.02g/mole[7]
Burn rate behaviourde St.Robert
nBurn rate pressure exponent, strand0.319
nBurn rate pressure exponent, erosive0.323
aBurnrate constant0.0665[8]
roBurn rate @ 1 atm.0.156in/sec
rBurn rate @ 1000 psia0.602in/sec
TcrAuto-ignition temperature> 300deg. C.

[1] At 1000 psi pressure; exit pressure one atmosphere
[2] Static tests AST-17, AST-18
[3] PROPEP combustion results
[4] Measured with type k thermocouple, static test AST-16
[5] Measured, typical grain
[6] Mixture(2-phase), at chamber conditions
[7] System mass divided by number of gas moles
[8] Use with pressure units of psi. Resulting burn rate is inches per second

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.

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

Last updated

Last updated March 15, 2023

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