12b
2018.03.30
Hi Paul,
another impressive video, making the combustion process visible ;-)
With regards to processing a homogeneous mixture, I've found a
german paper, dated 1976.
Engine was a NSU KKM 871, 2 rotors.
For preparing an ideal mixture they've used a "boiler" / drum. Fuel
was heated up to 200°C + fed into the boiler / big chamber. Mixture
temperature was 70°C out of the boiler with all fuel evenly
vaporized. Intake temperature at ports was ~ 65°C.
Compared to a conventional downdraft carburetor you can see some
advantages. » pict_1 spez. Kraftstoffverbrauch » specific fuel
consumption in g/kWh KKM » RE Idealgemisch » ideal mixture
Vergasermotoren » engines with carb Kraftstoff-Luftverhaeltnis »
Relationship of fuel + air » Lambda Teillastpunkte » part load
"points" / adjustments
Without the availability of fuel injection David Garside has found a
very good solution for the Norton motorbike: air gets into the carbs
with ~ 100°C + will be cooled down because of fuel evaporation to ~
50°C before reaching the chambers. He has used SU carburetors
(variable venturi / constant velocity carbs) - they ensure a pretty
good fuel spray.
In general there are some rules of thumb, one may pay attention to
... » duration of evaporation of a gasoline droplet » at 30°C it
takes 8 times longer than at 80°C » higher temperature is preferable
» 8 million droplets with a diameter of 10 µm will evaporate 200
times faster than 1 droplet with a diameter of 2 mm (same volume) »
the smaller the droplets the better
With fuel injection into the intake manifold or PFI ... » higher
flow velocity in the intake manifold enhances fuel preparation »
lower pressure in the intake pipe (e.g. at WOT) enhances evaporation,
too
It's preferable to get fuel droplets as small as possible. That's
why the Renesis engine has primary injectors / nozzles with 12
holes, generating a relatively fine mist of fuel.
Another solution may be a swirl injector like the one by Mitsubishi,
1996. » pict_2 + pict_3
Very small SMD (Sauter Mean Diameter)
Once the mixture is inside the engine, it's important to avoid
condensation / fall-out of the gas. Was a very big challenge for
Daimler-Benz with the DFI system. Therefore the walls should have a
temperature of at least ~ 40°C. More is better. That's one of the
reasons to "heat" the cold lobe a bit ;-) (Another one is to avoid
deformation of the housing shape)
The disadvantage with warm / hot mixture + walls is, that volumetric
efficiency will decrease. Again, finding the right balance is the
target.
Quenching ... sorry, the next part is a bit "academic" ;-)
Related sketches: t-section.pdf
At all walls of a combustion chamber you will have a wall layer - a
thin film of gas, that will not be burned. Reason: heat loss to the
walls is greater than the amount of energy produced by combustion »
extinction of the flame front.
Wall layer will be smaller / thinner with ... » higher pressure
(exponential effect - good) » richer mixture (simply more energy
available) » higher wall temperatures (limited by compulsions of
lubrication)
The thinner the "chamber" the richer the mixture has to be. But this
will - of course - increase heat losses ...
Near the "cool" walls the disintegration of molecules + atoms of
fuel will be stopped. Termination of chain reactions, free radicals
will partly be bound to the wall + converted into stable species.
Sorry, have forgotten the minimum temperature levels you need for
satisfactory chemical division.
No further chemical reaction will occur - that's the main issue /
challenge. There will be no more conversion, e.g. CO to CO2. That's
the phase, where you will loose a lot of energy / heat / power ...
A simple combustion model may make it more clearly (?) ... 1st step:
emergence of short chains (Alcanes ?)
2nd step: appearing of radicals like H, O, OH ... (Alcenes ?)
3rd step: "cold flame", generating ~ 10% of the energy / heat
4th step: "blue flame", you will "see" CO, H, H2O. Oxidation to CO
delivers ~ 30% of the heat. This phase may be (partly) not reached
in the quenching areas.
5th step: the main heat / energy producing step. Most of the time
this will not be reached in the spheres / sectors of quenching:
conversion of CO to CO2. This step generates ~ 60% of the heat /
usable energy. + only just now you can measure the big / huge rise
in temperature.
Sorry, my English isn't good enough to explain everything correct.
We would need a chemist now ;-)
Another challenge will be to initiate combustion In the mixture +
not at the edge. Flame front is "creeping" along the sliding surface
+ will be cooled down unnecessarily. Possible countermeasures ?
Perhaps laser or some kind of "jet" ignition ... ?
After all, picture_4 + picture_5 show the influence of heat loss,
crevice volume + leakage. The last point is the most important ...
But now it's really time to "shut my mouth". So much blah-blah ...
;-)
Best regards
Frank Herfert
http://www.enginelabs.com/engine-tech/video-the-secrets-of-the-rotary-engine-seen-from-the-inside/
; an interesting video.
Murry Rozansky
I don't know how applicable my observation is to the full scale
automotive version but I did notice, in the slow motion acetylene fueled
take at the end, that the squish zone was where the combustion seemed to
start, i.e. the trailing end of the combustion chamber. The resulting
squish flow seemed to spray the flaming result of the combustion in the
squish area into the main charge area ahead of the squish flow area in
the rotors direction of rotation.
I don't see where the squish flow tends to blow the flame out, as
posited here before, but rather that it seems to act like a "jet"
ignition projecting flame into the main body of the charge.
It appears that the combustion at the trailing end of the combustion
chamber actually completes while the flame is still vigorous in the
leading end of the combustion chamber.
This may be apples to oranges. I don't know how this applies to a full
scale version.
Mark LaPierre
Did you read the U of Vienna paper?
Paul Lamar
------------------------------------------------------------------
Please add your questions or comments at the end of the thread. Not
the beginning.
I am going to enforce that rule. If people don't do that it will not be
forwarded. My ISP changed the rules.
The Rotary Engine free News Letter. Powered by Linux. If you want off
the list PLEASE let me know and I will remove you.
ACRE NL web site.
http://www.rotaryeng.net
You Tube
http://tinyurl.com/beqqxas or PaulLamar2
Copyright 1998-2018 All world wide rights reserved.
