From: paulm@storcon (Paul Moreau)
Subject: Re: FAQ? (questions about engines)
Organization: Storage Concepts, Inc.
Date: Thu, 3 Sep 1992 15:13:15 GMT



In article <1992Sep2.215912.4276@rtsg.mot.com>, svoboda@rtsg.mot.com (David Svoboda) writes:
|> Well, I hate to get into this one, but...
|> In article <1992Sep2.040508.27545@c3177208.ssr.hp.com> bill@c3177208.ssr.hp.com (Bill Chidester) writes:
|> |
|> |:>     Actually, adding nitromethane to fuel will make an engine run cooler, not
|> |:>     hotter (allowing lower temperature for a given RPM, or higher RPM for a
|> |:>     given temperature).  From the engine's point of view, "cold" = "good", so
|> |:>     it will run faster and more efficiently.  I agree with the water contami-
|> |:>     nation, especially if you leave fuel sitting in an unsealed container in
|> |:>     your flight box.
|> |:
|> |:I don't think the laws of thermodynamics can be violated!  Nitro gives you 
|> |:more power thru more heat per power stroke.  Have you measured the 
|> |:head temperature of an engine running more nitro???  I'd bet a big dinner 
|> |:on this one.
|> |:
|> |
|> |  You're on!
|> | 
|> |  I'm not sure what law of thermodynamics is being violated.  This ain't
|> |a steam engine we're talking about here -- an internal combustion engine is
|> |not an adiabatic engine!  The object of an internal combustion engine is to 
|> |produce mechanical power, not heat.  The heat energy is a byproduct that is 
|> |lost during the process, it isn't stored anywhere to later be put back into
|> |the cycle:  Hence all those ugly fins we have glued onto the cases.  If
|> |you are delivering the same RPM into a prop at a higher engine temperature,
|> |your engine is running LESS efficient.  The addition of nitro is to make the
|> |engine more efficient, i.e., run cooler at the same RPM, or ultimately, more
|> |RPM (power, when twirling a prop) at the same temperature. 
|> 
|> PV=nRT.  That's the thermo law you are violating.
|> 
|> The only way for a fuel additive, in the absence of engine mods, to produce
|> more power is for the burning reaction to produce more pressure, and the above
|> equation says that with that pressure comes temperature, in proportion.
|>
 
   I know several Pros (Henry Bartle, Lyle Larson to name a couple Formula 1)
   that would argue this point with you.   Thier FAI engines run much hotter than
   with nitro.

|> |  As to the why of nitro running cooler, I don't know.  It may be that it
|> |because it is more volatile, it produces more gas volume per unit of heat
|> |during detonation.  My buddies, the engine wizards, tell me there's more to
|> |it than that; they say the gas produced is a better heat conductor and it
|> |draws more heat out of the engine.  I guess this would translate into a hotter
|> |exhaust for the same head temperature.  If this is the case, the exhaust will
|> |be hotter, but the engine won't be.
|> 
|> The bottom line is that if a fuel combination produces more heat, then the engine
|> will produce more power, and the engine will run hotter.  That's just what nitro
|> does.  And that's just why high octane in your car (burns cooler) produces less
|> power than low octane (unless you modify your engine to take advantage).
|> 
|> Look at it this way: if nitro cooled the engine down, then 50% nitro would be
|> the answer for tightly cowled engines.  It's not.
|>

   Not quite.   Higher nitro causes other problems with detonation and knocking.
   To run higher nitro in my YS.120 I must remove the head and add a few head
   gaskets.
 
|> |   Time for a "quality is worth the money" pitch!  Let's assume that an
|> |inexpensive plug cost $1.50 and and expensive one goes for $5.00.  Arguably,
|> |you may get three times the lifetime out of the dead cold plug (it has a
|> |thicker element and two to three times the platinum, that's why it costs
|> |$5.00), so you pay $4.50 for three cheap plugs or $5.00 for one not so cheap
|> |plug, lasting the same amount of time.  
|> 
|> Most sport flyers go all season on a single cheap plug.  I recommend changing
|> the plug every season, just in case.  Nevertheless, my record for a K&B idle
|> bar plug is four years (on an old OS Max 35).
|> 
|> There is no sense in spending more money than necessary.  But don't hesitate to
|> spend as much as *is* necessary.
|> 
|> |   How do you figure out when a plug is going bad?  
|> 
|> Well, most of the time (on sport engines), the engine doesn't run, and the
|> glow panel shows an open circuit.
|>
 
   Give me a break.   Is that the only way you can tell a plug is GOING bad ?

|> |   Anyhow, your instinct was right -- if you are having idle problems on new 
|> |plugs and you're loosing RPM after you take the battery off, go to a plug
|> |with a bigger element.  Those are most definitely "cold" plugs.         
|> 
|> Other way.  You need a hotter plug if it won't idle without a battery.  Go 
|> with the hottest plug that will last in your particular engine.
|> 
|> 			Dave Svoboda, Palatine, IL

-- 
          _____________________________________________________________
          -                *                      _______   _~;       -
          -            Paul Moreau               |       =_= /        -
          -    Sr. Diagnostics Software Eng.     \   USA    /         -
          -         Irvine, California      --->  *-_  ___ /          -
          -     UUCP: ..!uunet!storcon!paulm         \/   \\          -
          _____________________________________________________________