Keith,
Lots of good info stated elegantly, as usual. One thing that I would
question though is the expansion benefits through out the stroke. As I
understand the combustion process, any expansion past roughly 23 degrees
past TDC is not very effective since the piston moving down the hole
expands the area in the cylinder faster that the gases expand.. As I
understand it, timing advance is desired to start the combustion process
at the proper time, dependent on the mixture quality, to reach peak
pressure about 20 degrees ATDC.
We have run nitrous with moderate success since 1989, when not many were
doing very well with it. We carried it on the car for a few years before
that, but had waited until we got things sorted out on the basic tune-up
to have the courage to use it. I can tell you this, if the basic tune-up
is not right, you will destroy parts when you hit the nitrous, guaranteed!!
Early on, I enjoyed a good relationship with Dale from NOS and gained
some excellent info from him. We have taken a bit of a vacation from
nitrous to pursue the gas class records, but we will be back on the
scene in the future. It is just too much fun to hit the nitrous!
Nitrous does speed up the combustion cycle and therefore needs to be
properly retarded or detonation goes wild! I have seen the results too
often. Just the fact that the nitrous is being introduced, even if it
was the same oxygen content as the air we breath, still fills the
cylinder to a level above naturally aspirated engines which increases
heat and pressure requiring timing reduction.
We also retard 2 degrees for each 50 hp as suggested by the experts. We
us a MSD igniter with the retard function that has worked well for us.
Tom, Redding CA - #216 D/GCC
Keith Turk wrote:
>What I was going to say about Cylinder pressure is this.... within a give
>cycle an internal combustion engine operating at 100% volumetric efficiency
>can produce X amount of HP. We can aid the combustion process by several
>artificial means. lets take a sec and look at what is mechanically
>happening to each of these and experiment with my understanding of
>each..... as it relates to the cylinder pressure and the Manner in which
>it's formed.
>
>I'm sure there is a fancier way of saying here's your choices... Naturally
>aspirated....Turbo/Blower ... Fuel/Nitrous....
>
>In a naturally aspirated situation the fuel is ignited and the flame
>propagation is directly proportional to the fuels octane... the amount put
>in is virtually equal to the size of the bore and stroke of the
>cylinder.... ( assuming your at 100% VE and not over or under it ).... As
>the gases are ignited they start to expand and put a force on all
>components off the combustion chamber... ( yep the head gets the same
>force) The Piston then is Forced to start it's travel down the cylinder
>bore.... the gases continue to expand as the combustion process takes place
>and force is produced throughout the stroke... ( for the most part ) we
>fire that spark plug early to give this flame front time to advance to the
>point it will excerpt Maximum force.
>
>In a Turbo or Blower application we increase the Pressure of the intake
>charge and thereby allow us to install more air/fuel during each combustion
>cycle..... so what happens is that the Volumetric efficiency is that it is
>Radically increased in direct proportion to the amount of Boost and Fuel
>added. ( up to a Point of diminishing returns ) Now when we fire this
>fuel/air charge it's combustion process is greatly aided by the added fuel
>and air... and it then increases not only the force down the stroke but
>continues to expand for the FULL stroke of the motor.... somewhere in here
>ya gotta know it's producing HUGE amounts of Pressure on the crank at 90
>degrees or mid stroke and gob's of Torque are created as a result ... the
>second key is the continued expansion to the bottom of the stroke.... so
>it's making Mass hp.
>
>Okay now on to the only Fuel that I know about .... well I might expand on
>my limited knowledge of Nitro but I would really rather someone with a clue
>do that.
>
>Nitrous oxide is nothing more then a Oxygen rich air.... 33% oxygen by
>content as opposed to around 23% in the ambient air...... N2O + two Parts
>Nitrogen one part Oxygen........ hmmm this is making sense so far....
>scary.... okay... what we are doing is introducing more Oxygen when the
>Valve opens so the intake charge carries more capability to accept Fuel....
>and it is the FUEL that makes the cylinder pressure..... what does happen
>thou is that this Oxygen rich mixture is that it burns FASTER so the actual
>flame propagation within the cylinder is happening quicker and the
>combustion process is almost taken to the point of being a Explosion
>process..... what that means to us the casual observer is that the Flame
>front travels much faster and the actual Fuel air charge is used up more
>quickly..... so to is the power making capacity fuel/air charge..... think
>of this as a tortise and the Hare..... story..... Nitrous charges hard up
>front but by mid stroke it's about spent.....( that maybe exaggerated but
>not much ).....
>So anyway it's got great pressure making ability BUT it's also going to
>impart high degrees of cylinder pressure in the early stages of combustion
>through Mid Stroke..... When you look at these high degrees of cylinder
>pressure you have to understand that it's going to do some damage to any
>component in the process that isn't up to the task.... It also makes sense
>that you would want to start this process a bit later in the combustion
>cycle hence the retarded timing...
>
>Whew.... Now I'm sitting back looking at all those sentences run together
>thinking Dave Freiburger could edit this into usable information.... but so
>could my second grade teacher.... only difference is He would have a clue
>was I was trying to say.
>
>Keith ( Okay Dahlgren.... did I listen or did I miss the class altogether?
>)
>----------
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