| From : |
Bruno Ogorelec |
| Date : |
2003-07-22 01:06:50 |
| Subject : |
Valveless PDE |
I find it funny how the PDE mechanics superficially resembles pulsejet mechanics even though it takes place at much higher speeds. The process closely apes the deflagration-heating-overexpansion-suction cycle of the ordinary pulsejet.
Only the spped scenario is much more skewed, with the propagation speed of detonation several times higher than the propagation speed of all the other phenomena. In comparison, the speeds of all the events in a pulsejet are roughly in the same ballpark.
The similarity has apparently let some people to try pulsejet tricks with PDEs. A naval officer, a certain Robert G. Johnson, built a valveless PDE not terribly different from a simple Schubert valveless pulsejet, for the experimental part of his thesis at the Naval Postraduate School in Monterey, CA, in the year 2000.
The thing appears not to have been terribly successful -- he only achieved a single true detonation with a mixture of JP-10 and oxygen -- but looks like the valveless intake worked by choking the detonation and not letting the blast get out.
If anything, the wave propagation/reflection scenario is even more complex than in a pulsejet because of the great disparity in wave speeds, not to mention the disparity between wave speeds and gas speeds. Some waves are completely transsonic (Mach 5, I think), others are sonic at the local conditions, while the gas itself also moves at wildly varying speeds. A very curious device.
The guy is completely unfazed by the fact that he achieved only a single detonation for all his trouble and expense. Much more work is needed to find out the reasons, he writes.
It all sounds just like our own garage tinkering with recalcitrant pulsejet designs, only at a much higher level of complexity and expense.
Bruno
|
|
Valveless PDE
( 2003-07-22 01:06:50)