Direct Injection Spark Plug Sorta

Gary Derian gderian at oh.verio.com
Fri Apr 30 20:45:57 GMT 1999


Good point Robert.  Diesels are wonderful for large engines, low engine
speed and excess air.  They also improve with turbocharging, more excess air
and all that.  But you can't get much power per displacement because power
requires high rpm.
Gary Derian <gderian at oh.verio.com>

> First two cycle vs four.  The middle size and above diesels are all two
cycle.
> When you think big block - check this puppy out.
>
> http://www.pacifier.com/~rboggs/SULZER.HTML
>
> The biggest advantage a diesel has over an Otto is efficient and FAST
> combustion of fuel.  Look at an Otto engine - typical spark advance is
around
> 30 degrees before TDC whereas a diesel fires very close to TDC or Oh NO
after
> TDC.  All this wonderful spark advance does is make negative power by
building
> pressure opposing the piston so the maximum pressure can occur just after
TDC
> at the power sweet spot.
>
> So why.  First - all droplet combustion occurs at stoic.  No exception -
no
> matter how finely atomized.  Sorry guys.   The combustion burns local
stoic
> until either fuel or air runs out. See Irwin Glassman - Combustion Third
> Edition or similar text on Combustion - not putt putts.
>
> An Otto sort of hopes that enough of the fuel will be in small droplets
and
> "atomized" so that the flame will consume all of them.  The Otto starts
from a
> small plasma explosion "spark" at controlled point (s) and moves in a
> leisurely wave from there.
>
> Mr Diesel, on the other hand, starts his flame by blasting the entire fuel
> into the chamber in high velocity small droplets that penetrate and ignite
> throughout the entire chamber, starting droplet combustion from literally
> millions of points - counting on physical not electrical force to cause
the
> ignition.
>
> Mr Diesel, by extremely fast burning of much more of his fuel near the
ATDC
> 'sweet" spot makes much more pressure at the point that it counts than any
> Otto can.  Much larger flame front and higher temperature and pressure
WHERE
> IT COUNTS.  Ignore peak theoretical nonsense.  A very lean mixture makes
> incredible heat - near bottom dead center just as the exhaust valve opens.
> Heat, temperature and the other theoretical stuff don't move the piston -
> pressure laddies, pressure - applied timely and properly does and all
other
> factors aside, Mr Diesel makes much more pressure where and when it counts
> than Kick Sand in My Face Otto.
>
> The most efficient burning of fuel is around 10 to 20 per cent "weak" or
lean.
> This allows droplets/vaporized molecules best access to oxygen.  But at
20%
> weak, the flame front is 22% slower than at stoic and slows even more as
we go
> weaker.  If instead of air, we use exhaust as the dilutant, the flame
speed
> falls 55% for the same amount of dilutent - remember that EGR is actually
> water injection at ~ twice the percentage of EGR ( ~ 1 gallon of fuel
makes
> about 2 gallons of water - what did you think happens to hydrogen and
oxygen
> in combustion ????).  Courtesy of John B. Heywood.
>
> Compound this with the flame speed is inversely proportional to the
pressure
> and Mr Otto may take more time than available even at low speed to burn
his
> fuel.  Ever wonder why lean combustion is so hot yet makes so little
power?
> Much longer exposure of flame to metal and mixture may even still be
burning
> as it enters the exhaust.
>
> Flame speed of gasoline is about .3 meters per second at atmosphere.  At
part
> throttle light cruise, many engines don't exceed 3 atmospheres at TDC.
> Consider that as a clue.
>
> Mr Diesel however, has maximum pressure at all times.  This markedly
increases
> flame speed.  Also, as temperature goes up, so does the flame speed.
Sissy
> Otto has to worry about denotations so is carefully about temperature.  Mr
> Diesel simply uses the extremely high temperature at around TDC to not
only
> ignite his fuel, but to radically speed the combustive consumption of
fuel -
> again right near TDC at the piston sweet spot.
>
> Diesel wins Power Torque Efficiency by applying more pressure when and
where
> optimum than Otto can.  Note I did not say total - just much better timed.
>
> Think of pushing a swing.  Its not only how hard you push - but when you
push
>
> Otto takes over at very high loads because it can burn more fuel at peak
loads
> than Mr Diesel.
>
> 1963 Ford C-600 Prison Bus Conversion "Home"
> 1971 Lincoln Continental 460 "Christine"
> 1972 "Whale" Mustang awaiting transplant
> 1978 Dodge Long Bed Peeek Up "Bundymobile"
>
> Habaneros - not just for breakfast anymore




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