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Building high power sugar rocket

A blog by priitserk in General

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Static fuel testing - like WHAT!?

priitserk

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Last 5 tests have completely failed. Massive explotions.
So clearly there was something very wrong with my design and decided to investigate it a bit more.

 

It always seemed to me, that well published 65/35 % of sugar and KNO3 is too aggressive and with too quick burning speed. And my tests have actually proved it now. Plus, I got extremely good information on how the grain actually burns and the place of ignition is highly important!!!

 

Take a look to these two videos below. Both grains are with the same length and with (6cm and 5cm) and with same core size (2mm).

 

1) Slow motion, 240fps - fuel with 65/35 ratio
Please look carefully what happens!!!! Ignition is done from top -> fire quickly advances to the bottom, ignites the whole bottom and pushes the grain out of the fuselage. Like what? And the place where the ignition happened, is not burning at all!!!


2) Standard speed. Fuel with 60/40 ratio

 

First video clearly demonstrates two main issues with my current design:
1) Ignition from top with 65*35 ratio clearly does not work. Fuel is pushed to the nozzle followed by explotion.
2) Burning is extremely fast, it's way too quick for rocket engine.

 

Second video show nice flame, very high temperature and much much slower burn speed.

Back to the drawing board.

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priitserk

priitserk 3

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now the physics around it!!! Flame in microscopic level is a sphere. What happens there is that heat can escape only upper side. Heat from the other part of the sphere is locked inside the 2mm core and it cant escape. SO what happens? The temperature of the gases inside the core get extremely high extremely quickly and ignite the core and the bottom the grain. So inevitable happens as demonstrated in the video. I have to play with the core size to get better understanding of gases and how they are moving inside the core.

I will probably combain 65/35 with 61/39 and use the first one for liftoff. 65/35 is so fast and powerful and I believe I dont even need the core inside the first grain. I do have to make the core to get the moisture out but I can fill it later quite easily.

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