Richard Nakka's Experimental Rocketry Site

Richard Nakka's Experimental Rocketry Web Site

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:

sucrose	solid	C₁₂H₂₂O₁₁
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).

**Characteristics of KNSU Propellant** (65/35 ratio)
	Parameter		Units	Note
	Process method	Cast
Isp	Specific Impulse, ideal	153.5	sec.	[1]
Isp	Specific Impulse, delivered (typical)	125-130	sec.	[2]
C*	Characteristic exhaust velocity, theoretical	3013	ft/s
To	Combustion temperature, theoretical @1000 psia	1447 (1720)	deg Celsius (K)	[3]
To	Combustion temperature, measured@1000 psia	1350	deg Celsius	[4]
	Density, ideal	1.89	gram/cu.cm.
	Density, as cast (typical)	1.80	gram/cu.cm.	[5]
X	Mass fraction of condensed-phase products	0.424	-
k	Ratio of specific heats, mixture	1.133	-	[6]
M	Effective molecular wt. of exhaust products	42.02	g/mole	[7]
	Burn rate behaviour	de St.Robert
n	Burn rate pressure exponent, strand	0.319
n	Burn rate pressure exponent, erosive	0.323
a	Burnrate constant	0.0665		[8]
ro	Burn rate @ 1 atm.	0.156	in/sec
r	Burn rate @ 1000 psia	0.602	in/sec
Tcr	Auto-ignition temperature	> 300	deg. 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

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

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 March 15, 2023

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