THEONE Posted August 25, 2011 Posted August 25, 2011 (edited) I was trying to make a dual phase engine but it CATOed, i do not know why2 r-candy grains each phase, and a grain without a core for the delay 1.avi 1.bmp Edited August 25, 2011 by THEONE
r1dermon Posted August 25, 2011 Posted August 25, 2011 your middle grain wont hold that pressure...even supposing it did, once your top "chamber", which is unpressurized, suddenly pressurizes, it'll likely blow the forward closure due to the immediate pressure spike.
r1dermon Posted August 25, 2011 Posted August 25, 2011 as your middle grain burns, it'll fracture once it gets thin enough. sugar propellent is fairly brittle, so all the more catastrophic. the most pressure in any motor, is at the furthest point from the nozzle. as propellent is burned, it is accellerated towards the nozzle, gradually picking up speed, but at the head end, the mass flow is almost stagnant. with all that pressure, like i say, once that forward closure (which is really a grain of propellent) burns through enough, it will fail and overpressurize your motors second "chamber". the middle grain would have to be thicker than the diameter of your fuel grains. once your bottom fuel grains extinguish, your middle grain will act as a delay while the motor de-pressurizes...once the grain burns through, the top grains ignite. couple of problems i can see here are...the obvious pressure load in such a long casing. once the bottom grain burns through, what is protecting your liner/casing from hot exhaust gasses. a few things i would expect would be, forward closure blowout, casing burn-through, or liner/nozzle seal burn through. perhaps if you increase your nozzle throat diameter, you'll have better luck. it'll lower your chamber pressure.
dagabu Posted August 26, 2011 Posted August 26, 2011 the most pressure in any motor, is at the furthest point from the nozzle. as propellent is burned, it is accellerated towards the nozzle, gradually picking up speed, but at the head end, the mass flow is almost stagnant. Could you flesh this out a little more? It sounds as if you are saying that a chamber has more pressure at the closed end then anywhere else in the vessel. -dag
r1dermon Posted August 26, 2011 Posted August 26, 2011 That is correct. The upstream chamber pressure will be greater than the downstream (vented by the nozzle) chamber pressure. The mass of byproducts (exhaust gases) are flowing much slower at the head end than at the aft end.
dagabu Posted August 26, 2011 Posted August 26, 2011 You seem to be at odds with the Boltzmann constant. -dag
THEONE Posted August 26, 2011 Author Posted August 26, 2011 (edited) My top fuel grain was much more thicker than the web thickness of my fuel grain, also if the most pressurized point is near the heat end, most CATOes will be by blowing out the heat but we have got many CATOes by blowing the nozzles Also something else, the first phase ignites near the top head for immediately pressurized but the second one ignites at the starts of the fuel grains... this is not a problem ? Edited August 26, 2011 by THEONE
dagabu Posted August 26, 2011 Posted August 26, 2011 In what regard? "The pressure distribution within the chamber is asymmetric; that is, inside the chamber the pressure varies little, but near the nozzle it decreases somewhat."-Robert A. Braeunig- What I am saying is that the pressure in the chamber is the same regardless if it is at the fuel grain or bulkhead, the pressure only decreases at the nozzle so your theory of the bulkhead being under more pressure then the rest of the burning chamber is not correct. The bulkhead needs to be able to withstand the same pressures as the vessel walls, not more. The Boltzmann Constant provides the molecular reasoning why this is so. -dag
r1dermon Posted August 26, 2011 Posted August 26, 2011 My name is Robert A. Braeunig and I am the creator of Rocket and Space Technology. After viewing my webpage you may come to the conclusion that I may be some sort of 'rocket scientist' or perhaps a model rocketry enthusiast. Both of these assumption would be incorrect. My education is in the field of civil engineering and I currently work for a construction company in Dayton, Ohio. I have never designed, built or launched a rocket of any kind. I am simply an average guy who is fascinated by rocketry and space flight. http://www.scss.tcd.ie/Stephen.Farrell/ipn/background/Braeunig/about.htm There are some simple gas effects that we can model fairly easily using ideal rocket assumptions. The major item is a pressure differential that develops between the head end and the aft end of the grain. If you’ve ever bought an Aerotech 38/1080 motor and wondered why it needs a seal disk, while a 38/240 does not, it’s because of this pressure differential issue. (The seal disk keeps the gas leak from focusing over the edge of the liner, eroding it quickly and leading to forward end heat problems.) This pressure differential develops because mass is being added down the length of the rocket motor, and this mass needs to be accelerated by the gas flow to sonic velocity at the nozzle throat. Since temperature is constant throughout the motor, the energy lost to accelerating the gas shows up as a pressure loss. http://www.tdkpropulsion.com/2010/04/port-to-throat/ -David Reese he works herehttps://engineering.purdue.edu/Zucrow/index.html and also owns daveyfire inc. also of interest would be rasaero.com that's chuck rogers website rogers aeroscience. the pressure differential is different for different length motor designs and grain geometries...you could say it's a small difference, but everything is relative. flash powder gives off a small amount of energy compared with TNT...small anomolies within a motor system can translate into a wide array of differing performance characteristics.
allrocketspsl Posted August 28, 2011 Posted August 28, 2011 I was trying to make a dual phase engine but it CATOed, i do not know why2 r-candy grains each phase, and a grain without a core for the delay keep it simple one stage at a time,mastered, move to more!
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