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Post by peterberg on Apr 20, 2012 1:36:25 GMT -8
Peter, What do you mean by a "tile roof shape"? Oeps! I've used a literal translation of the word 'pannendak', but maybe the expression isn't the same in the English language. Let's stick to the same metaphor and describe it as a shape like a slated roof. Running from the feed to the riser, the highest ridge in the middle and the gutters left and right against the walls. The sloped sides are about 10 degrees to the horizontal. So in the middle of the burn tunnel ceiling the space is higher than the sides. Hope this is clear? Have you tried running your stove without a chimney? I didn't, but I could take the whole contraption outside and try it again with and without a chimney pipe. Spring has been cold and wet up till now, so I'm not highly motivated. It's interesting that pulse-mode only works with an extra large barrel gap, also interesting that the barrel is important to the action. I wouldn't have guessed that outcome, though somehow, it rings true. I'll have to show this thread to my brother (who studies rocket science) and see what he thinks. It's got something to do with the diverging and converging taking place in the barrel. Here's a drawing of the principle. The diverging and converging is taking place in the opposite direction in my case, but it's the same principle nevertheless.  As you can see, the widening of the riser is about 10 degrees, the constricting side 20 degrees. When the temperature is around 900 C (1650 F), the velocity of sound will rise up to 900 m/s (2950 ft/sec). That's the cause of the acoustical resonance, pressure and vacuum in very rapid succession, end result is a suction of about 0.5 bar. So the drum has to be there. All the above has been told to me just yesterday by a knowledgeable guy on another forum, so if I'm lying I'll do so in commission. ;D More numbers how it worked out here: the drum csa is 5 times larger compared to the riser. Total length of the space around riser is 2', top gap is 1'. So, the riser is reaching to 2/3 of the total space. |
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Post by Donkey on Apr 20, 2012 8:39:32 GMT -8
Ok.. I've seen that image before, drawn it in subconscious doodles.. That's a ramjet!
I'm off to work, gotta think a bit before I post a decent reply.
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Post by peterberg on Apr 20, 2012 11:24:42 GMT -8
This afternoon, the rain stopped and we've had some sunshine. I took the opportunity to wheel 'the thing' outside in order to try whether it would be willing to reach pulse mode without a chimney. In short: it didn't. The smallest option with only one drum and 1 ft above the riser resulted in fire creeping up after one hour of impatiently prodding and fiddling. The second attempt I've used the longest option, 2 ft above the riser and two drums stacked upon each other. This last one appeared to come up to temps in a little over an hour, but wasn't willing to do more than 10 seconds of faint pulse mode. Conclusion: the air speed wasn't high enough to enter pulse mode, so it won't work without an adequate chimney. Both attempts have been done with a stove pipe of 6.5 ft as a chimney stack. Not only is the system not self-starting, it do need specific circumstances in order to kick into the spectacular department. Alas...  |
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Post by Donkey on Apr 20, 2012 16:36:39 GMT -8
Hmm..
"The thing" has a small system size, doesn't it? It's a 4 inch, right??
I wonder if it would make a difference with a larger system?
Another thought..
If velocity is what's needed, how about reducing the air input? Try a reducer cap on the feed and see what happens.. ??
How much heat is dumped to the barrels? Can the exit be reduced as well or instead?
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Post by peterberg on Apr 21, 2012 5:51:54 GMT -8
"The thing" has a small system size, doesn't it? It's a 4 inch, right?? I wonder if it would make a difference with a larger system? Hmm... I don't know, all the strange ideas I've come up with proved to be scalable, I do fail to see a reason why this isn't. If velocity is what's needed, how about reducing the air input? Try a reducer cap on the feed and see what happens.. ?? How much heat is dumped to the barrels? Can the exit be reduced as well or instead? Right, I've thought about reducing air input, and tried it. The only difference was creeping up of the fire. Mind you, the pulse mode is quite violently with fire spitting up now and then, but no creeping up at all. Dumping more heat to the barrels will create a greater temperature difference between upper and downer, which should be a good thing. I have to think about that. |
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Post by kirkerik on Nov 4, 2012 12:46:47 GMT -8
i hope the image was not too big, i just copy and pasted it w/ image brackets
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Post by Rinchen on Nov 16, 2012 2:33:09 GMT -8
Vacuum and micro-gravity are not the same thing.
The reason for the clean burning is the metering of the fuel being burned, which is exactly what is being done in a J-tube rocket.
They were on to this already some 100 years ago when developing good clean burning oil lamps and resulted in the development of the "aladdin blue flame heater" which burns oil with a blue flame. You can look it up in google image search.
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