From: toby@ccl.umist.ac.uk   
      
   "Henry Spencer"  wrote in message   
   news:HrJMvw.Bou@spsystems.net...   
   > In article ,   
   > toby   wrote:   
   > >> To answer your question, water injection (either straight de-ionised   
   water   
   > >> or a DI water/alcohol mix (50/50, IIRC) ) is still used occasionally on   
   some   
   > >> freight/commercial aircraft to increase thrust on take-off.  It is   
   stored in   
   > >> a separate tank on the aircraft and is injected directly into the   
   combustion   
   > >> chamber as required.   
   > >   
   > >Any idea whether this combustion chamber injection is fuel rich or is a   
   > >lean mixture.   
   >   
   > Turbojet/turbofan engines invariably run lean, to keep turbine   
   temperatures   
   > within the bounds of the turbine-blade materials.  That's why afterburners   
   > are useful, because there's unused oxygen in the exhaust.   
   > --   
      
   > MOST launched 30 June; science observations running     |   Henry Spencer   
   > since Oct; first surprises seen; papers pending.        |   
   henry@spsystems.net   
      
   Sure, this is how I understood it.  I just wondered if the added water in ,   
   what   
   I now know to be called power boost fluids (thanks Cameron), would allow   
   one to reach stoichiometric combustion without hitting these temperatures.   
   As it seems that it is this temperature constraint which prevents   
   the engine from generating even more thrust.   
      
   If we are aiming at maximum thrust regardless of efficiency then we need to   
   add as much energy as possible. Unfortunately, with conventional fuels this   
   results in these intolerably high temperatures. The whole point of this   
   question is   
   to find out whether it would be possible to utilise all the available oxygen   
   by   
   absorbing this excess heat in the creation of super-heated steam from the   
   water   
   dilutent. Or, alternatively, whether it would be more effective to absorb   
   this excess   
   heat by running very FUEL RICH, with the water dilutent  absorbing the extra   
   heat by   
   'steam reforming' the unburnt hydrocarbons. The second method might be   
   better   
   as it would produce an exhaust with a lower average molecular mass. And   
   produce   
   a cool fiery tail!   
      
   The paper I found online detailed experiments in injecting water and fuel   
   into the   
   combustion chamber separately, but they weren't happy using more than 20%   
   water,   
   as they felt it would mess up the combustion process.This is why I asked   
   whether   
   anyone had tried to get around this problem by using fuels with very high   
   water   
   contents, and that were effectively  pre-mixed. The answer was, yes:   
   power-boost   
   fluids. I want to know if this had been taken to the extreme, and whether   
   mixtures which   
   allowed complete use of all the oxygen had been tried.   
      
   We know from watching brandy burning on a christmas pudding that even   
   fairly dilute   
   alcohol will combust in air without too much problem, so it seems that there   
   is considerable   
   scope to use mixtures like power-boost-fluids, or maybe ones even more   
   dilute, as   
   fuels in their own right. The point being that if you can double or triple   
   the T/W of a   
   jet engine it might be worth taking the efficiency losses for space apps   
   (Glen Olsons   
   Pogo and other vertical takeoff concepts in particular) because the   
   reduction in burnout   
   mass might  pay for the lower isp.   
      
   Toby   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)