Richard Nakka's Experimental Rocketry Site

Richard Nakka's Experimental Rocketry Web Site

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

Standard Composition (65/35 O/F)

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

C₆H₁₂O₆ + 3.31 KNO₃ -> 2.116 CO₂ + 2.300 CO + 4.512 H₂O + 1.424 H₂ + 1.655 N₂ + 1.585 K₂CO₃ + 0.133 KOH

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

dextrose (anhydrous)	solid	C₆H₁₂O₆
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 the KN-Dextrose Propellant** (65/35 ratio)
	Parameter		Units	Note
	Process method	Cast
Isp	Specific Impulse, ideal	152.6	sec.	[1]
Isp	Specific Impulse, measured	130	sec.	[6]
C*	Characteristic exhaust velocity, theoretical	2992 (912)	ft/s (m/s)
C*	Characteristic exhaust velocity, measured	2922 (891)	ft/s (m/s)	[7]
To	Combustion temperature, theoretical @1000 psia	1437 (1710)	deg Celsius (K)	[2]
To	Combustion temperature, measured@1000 psia	TBD	deg Celsius
	Density, ideal	1.879	gram/cu.cm.
	Density, as cast	1.859	gram/cu.cm.	[3]
X	Mass fraction of condensed-phase products	0.426	-
k	Ratio of specific heats	1.131	-	[4]
M	Effective molecular wt. of exhaust products	42.42	g/mole	[5]
	Burn rate behaviour	plateau
ro	Burn rate @ 1 atm.	0.084	in/sec
r	Burn rate @ 1000 psia	0.509	in/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 flow), at chamber conditions.
[5] System mass /number of gas moles
[6] Typical
[7] Typical

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.

Originally posted December 10, 2000

Last updated March 15, 2023

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