This web page describes the impressive research undertaken by fellow rocketry experimentalist Denis Claude to develop a rocket propellant based on Ammonium Nitrate, Aluminum and Magnesium. This research has been of particular interest to me, as it parallels my own on-going experimental work with aluminumized Ammonium Nitrate formulations. Denis has kindly written up his efforts and experiments, to date, in the following report. Denis lives in Europe, and as such, the products mentioned are those that are available there.
B] OxidizerAmmonium nitrate (NH4NO3) ”AN” is the oxidizer of choice where ammonium perchlorate isn’t available.
In its pure form, AN has a 35% nitrogen content. This implies that there are some impurities in the fertilizer grade (33.5% nitrogen). This will probably somewhat lower the theoretical performance.
C] FUEL and BINDER
There are two candidates:
As HTPB isn’t available, all my usual resins:
D] PRELIMINARY TESTSThe CP technologies formulation is taken as an starting point (60%AN/ 20%Mg/ 20%HTPB)
a) preparation and mixing
I try to mix a spoon of preparation about 1 minute without effect (no ignition).
For the first tests, I prepare 100g total and try to cast a 20mm cylinder in a PVC tube to check density, ignitability and burn rate. 96hour curing time at 20/25°C
b) Composition in %
c) First Conclusions
None of the formulation is castable, a pressing process must be used..
Polyurethane resin seem to be the only one binder to investigate.
E] USABLE FORMULATION
a) second trial of formulation
-preparation as in D] a)
-Burn rates still very low but “seem” to increase with the % binder decreasing
b) packing process
As demonstrated by Richard Nakka, a hydraulic pressing process is feasible and is tried.
97/98% theorical density is obtained.
A motor test is decided to be attempted with the 65/10/10/15 formulation as a starting point.
F] FIRST STATIC TEST AND FIRST TEST MOTOR
a) motor design
For the 65/10/10/15 formulation, PROPEP gives the following results.
b) grain design
c) Grain shaping
Inhibitor is also used as the “pressing” tube.
Cut allows to remove the tube after curing. fabric is 200 x 540 mm which gives a 1mm final thickness.
Cut allows removal of the tube after curing. Fabric is 200*540 mm which gives a 1 mm final thickness.
The grain is good with a 98% theoretical density.
d) Static test result
G] SECOND STATIC TESTa) formulation
85/5/5/10 formulation is tried.
The packing process is better than with the earlier formulation as the mix is more dry (solid content increase), no waste!
A 98% of the theoretical density is achieved -> it doesn’t take into account the impurity of AN.
b) test motor
It ‘s the same as the first test.
c) Static test results
H] STATIC TEST 3a) Configuration
I] STATIC TEST 4a) Formulation
78/7/7/8 formulation is chosen.
b) Preparation and mixing
No special problem, the mix is now very dry but just wet enough to be easily pressed.
Preparation is the same except for the fabric which is now 200 x 1080 mm and gives a 2 mm final thickness.
d) Grain shaping
The PTFE cylinders are decreased in diameter from 71 to 69 (inhibitor is about 72 mm ID now). the pressing process stays the same.
e) Motor design
Special care is taken to have parallel sides (and perpendicular to the cylinder) for the inhibitor to bond the sides together (with the termite disc sandwiched) and as such, limit the thermal leakage.
Motor design is the same 3 bates grains as the earlier tests.
Average Kn is 500 (throat diameter is 12mm) as I don’t know the behavior of the reduced 8% binder formulation
J] STATIC TEST 5, 6, 7The objective is to validate the static test 4 with respectively a 3, 4, 5 grains motor.
But Kn is decreased to 450 to reduce pressure to ~4Mpa. In this purpose, I adjust the throat diameter from 12.6, 15, 16 mm.
All the tests give 185 seconds Isp, a nearly flat curve and a 8.40” burn time.
A throat diameter reduction occurred each time.
A 1200N maximum thrust/6810Ns total impulse was achieved with the last test (complete motor weight 8Kg).
K] CONCLUSIONSThe beginning of this “study” is encouraging, and a lot of work has to be done to obtain a motor suitable for a flight.