Re: LOX clenliness (was: peroxide compatibility question)
Doug Jones <[email protected]>
| Newsgroups | gmane.technology.erps |
|---|---|
| Message-ID | <[email protected]> |
Brandon Fosdick wrote: > [email protected] wrote: > >> A useful reference: >> >> http://www.gmcscuba.com/engineering_nitrox.htm >> Global Mfg. Corp. / Techsupport > > > That article only discusses GOX at relatively high pressures and at > least room temperature. If one was working with LOX, the temperature and > pressure would be much lower. How does this effect the risk/danger of > explosion? > > I'm surprised to see that they claim adiabatic compression to be the > source of GOX-related accidents. To initiate combustion both the fuel > and the oxidizer have to be at proper temperatures. By definition, > adiabatic compression doesn't transfer heat outside of the gas. So how > does the fuel get hot enough to combust? Maybe they should call it > near-adiabatic compression, or maybe non-adiabatic compression. > "Adiabatic" is, of course, an approximation. Perhaps the better term would be "compression heating" or "dieseling". I like dieseling since it succinctly explains the process. The GOX, if quickly admitted to a blind-ended passage, can locally raise the pressure very quickly, and will (nearly) adiabatically heat. If a potential fuel such as a grease spot or a metal filing is present, the hot GOX can heat the fuel sample enough to cause ignition. In dieseling, the GOX can heat up at rates approaching a million degrees/s (a thousand degrees in a millisecond), so the fuel need only be present as a thin film or small particle- that a grease spot is sitting on a piece of stainless steel doesn't matter since the heat flux is too high to be conducted away. Over 1000 psi, even stainless steel once ignited will continue to support combustion. This is why Monel is sometimes used in GOX plumbing, since it is much more resistant to continued combustion in oxygen at high pressure. Pressurized gaseous oxygen is in many ways more dangerous than low pressure LOX- it has an energy source for ignition that LOX does not. We did a series of experiments with LOX, deliberately introducing aluminum filings and alumina grit, then flowing it at 400 psi through an aluminum orifice, with no drama. Such filings in GOX with a blind tube would have been far more exciting... -- Doug Jones, Rocket Engineer XCOR Aerospace POB 1163 Mojave CA 93502 (661) 824-4714