Fuel injection plugs

[steve ravet]

> > An Otto cycle engine burns its fuel at a nearly constant VOLUME, and at an
> > approximately stoich a/f ratio--therefore its peak pressure and temperature
> > go quite a bit higher than a diesel's do!!!
> 
> This can't be right, "If the volume of a system (such as a gas) is held constant,
> that system can do no work."  That being said, a constant volume reaction would do
> no net work.

The spark engine burns it's fuel much faster than the diesel engine.  It
burns fast enough that it's simplified to a constant volume compression
because it burns while the size of the combustion chamber is not
changing size that much (right around TDC).  The volume then changes of
course, when the piston moves down under the pressure of the hot burned
mixture.  That's where the work comes from.  The whole cycle isn't
constant volume, just the part where the heat is added.

The diesel engine injects and burns fuel during the whole power stroke. 
While the fuel is burning and trying to raise pressure, the piston is
moving down and releasing pressure.  It's modeled as a constant pressure
expansion.

--steve

> 
> > These facts are exactly why an Otto cycle is inherently more efficient than
> > a diesel cycle!!
> 
> I think I am missing something here, maybe just my flimsy grasp of the 1st law of
> thermodynics.  But my automotive books do indicate that a diesel has greater
> thermal efficiency, by virtue of maintaining more of the heat produced.
> 
> James Ballenger
> 
> btw, what do you guys have your word wrap set to?  Every message I write now seems
> to come out with the wrong word wrap.

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com