This page will document my burn rate tests of KNO3/sugar using both the KNO3 and powdered sugar in the as obtained form. No grinding or ball milling of the mix was performed. The two ingredients were simply shaken together for 4 or 5 minutes in a sealed plastic container.
Richard Nakka has fully characterized the finely ground KNO3 and sugar propellants, but there are times when using the "as obtained" ingredients are beneficial.
This page is a log of ongoing tests, and final data will not come until the tests are complete. So bear with me on this.
Test: KNSU1
As a benchmark, I did my first test using a strand of ball milled propellant. Here are the results of that first test.
Strand Length: 1.9"
Strand Weight: 13 grams
Maximum Pressure: 402 psi
Burn Time: 3.4 Seconds
Average Burn Rate: .558"/Second
Chamber Pressure start: 0 psi
Average Pressure 201 psi
Strand Length: 1.75"
Strand Weight: 5.5 grams
Starting Pressure: 105 psi (air)
Maximum Pressure: 499 psi
Average Pressure: 302 psi
Burn Time: 4.26 seconds
Burn Rate: .411"/second
Strand Length: 1.5"
Strand Weight: 5.5 grams
Starting Pressure: 201 psi (air)
Maximum Pressure: 1,183 psi
Average Pressure: 491 psi
Burn Time: 2.1 seconds
Burn Rate: .714"/second
If you look at the data above, you may notice some interesting points. Max pressure of 1,183 psi and a burn rate of .714"/second, how can this be? Well, it wasn't unexpected. I was using air to pressurize the chamber for these tests, and I knew that using air would skew the results, the increased partial pressure of oxygen in pressurized air at 201 psi is 14.6 times that of air at atmospheric pressure. I wasn't sure how great the difference would be. The previous test (KNSU2) had me wondering, and this test proved the point. What it means is I must use an inert gas for chamber pressure. I had rather assumed it anyway.
Other things I learned. The strand burner will handle over 1,000 psi. That's good to know but not really the way I wanted to test it. I did blow out one of the epoxy wire plugs after the test. I suppose the heat and very high pressure combined were the cause. Next, I need to find myself a nitrogen tank.
Just for fun here is a graph of the transducer pressure/time trace. The graph was created in Excel after saving the file in csv format from WinDaq Lite. The drop in pressure early in the test was some sort of anomaly. Notice the rapid drop in the pressure at the end of the graph, that is when the one epoxy held wire blew out.
| Strand Length: 2.5" Strand Weight: 16.4 grams Maximum Pressure: 498.91 psi Burn Time: 6.033 Seconds Average Burn Rate: .4144"/Second Chamber Pressure start: 0 psi Average Pressure 249.45 psi |
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| Strand Length: 2.6875" Strand Weight: 19.9 grams Maximum Pressure: 590.91 psi Burn Time: 6.45 Seconds Average Burn Rate: .4166"/Second Chamber Pressure start: 0 psi Average Pressure 295.45 psi |
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| Strand Length: 2.685" Strand Weight: 22 grams Maximum Pressure: 704.94 psi Burn Time: 6.00 Seconds Average Burn Rate: .4475"/Second Chamber Pressure start: 0 psi Average Pressure 352.47 psi |
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| Test | Sample Weight/Length | Burn Rate In/sec | Max PSI | Time | Start Pressure | Aver. Psi | CPVC Pipe Diameter | Density grams/cc |
| KNSUP1 | 5.0 grams/1" | .4016 | 782.19 | 2.49 | 299.36 | 540.775 | .5" | - |
| - | 5.1 grams/1" | - | - | - | - | - | .5" | - |
| - | 5.0 grams/1" | - | - | - | - | - | .5" | - |
| - | 5.0 grams/1" | - | - | - | - | - | .5" | - |
| - | 4.9 grams/1" | - | - | - | - | - | .5" | - |
| - | 5.0 grams/1" | - | - | - | - | - | .5" | - |