Direct Injection Spark Plug Sorta

[Robert Harris]

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