Paul, This is a composite of what my pressure traces look like at
5000 rpm. This is from a side-port intake and peripheral exhaust
rotary. I added the combustion trace for reference. The system I use
can record 50K/sec and the data becomes very dynamic.... the pressure
peaks seem to slowly increase and there position retreats about 80
degrees between 3000 and 8000 rpm.
Barry Bordes
I am not sure what I am looking at here but there appears to be
something seriously wrong with that engine. I suspect one or more
apex seals are leaking. Good engines are more consistent.
Take some pictures of where the pressure sensors are located.
Please load that first picture into MS Paint and label the lines.
Which one is intake and which one is exhaust?
What brand of data acq are you using?
The first two pictures are yours. The rest I took on a P-port. The
sensors were looking at the apex seal oil holes in the rotor
housing.
I just installed an exhaust pressure sensor on the TTC engine so if
all goes well I will have some data on that.
Paul Lamar
Paul, My focus was on overlap pressures in the area between the
ports. The intake sensor is plumbed at the front plate opposite the
secondary port itself. The exhaust was first tapped into the exhaust
sleeve area but because of a weak signal was moved to the EGT port on
the exhaust pipe 2" from the flange.
The system is by TFX Engine Technology
http://www.tfxngine.com/
The pressure sensors for intake and exhaust are non-TFX. (TFX
sensors are $1000 each). I am using GM MAP sensors and have attempted
to scale them properly for the charts. The taller trace is the
intake.
Do you do Face Time? I could show you the program results live.
Barry Bordes
That is very interesting to me Barry. I have always wondered what
went on in that area. Due to the bath tub depression in the face of
the rotor there will always be some over lap. I suspect the inertia
of the gases enter into the successful functioning of the rotary.
The analogy is a turbo jet engine.
The inertia of the gases exiting the compressor section cause them to
flow into the combustion chamber. If one looks at it strictly from a
pressure point of view that may be misleading. I would love to see a
flow visualization in that area.
So little is known about what actually goes on inside a Wankel.
What we need is glass Wankel with a pulse of high pressure colored
gas applied to the spark plug hole at the right time.
There is a free idea for you Simon Saba :-)
I don't do Face Time. What is it?
Paul Lamar
Paul, with FaceTime if you have common iPhones you can talk with
video for free. My wife talks with her sister in England no charge.
Maybe my best bet would be to make a video and send it to you.
Back to the overlap reversion... the best way to port the exhaust
is to do things that help the bottom of it flow but leave the stock
anti-reversion steps in the top of the port.
The exhaust sleeves and your 20 B have another approach....
by separating the top and bottom of the exhaust.
With the combustion testing... the best verified success was
an experiment for speeding the burn rate. I had to take 2° of
advance out of the timing after the modification to get the peak
pressure located back to the proper 45° ATDC.
Barry Bordes
Barry,
Can you clarify what is the scale used in your pressure charts
Hey Paul
I just did a quick measurement on the factory exhaust p-port and it
looks to be around 55 mm wide by 30 mm. when the edge reaches the
exhaust the port width is around 25 mm wide then increases to the 55mm.
Its pretty safe to assume that as soon as the cross section of the
opening is 25 square mm, the pressure drops drastically and by the time
you are up to 100 mm it is practically identical to the exhaust chamber
average pressure and no work is being done from that cycle. It would be
interesting to look at the simulation and even better a see through
engine as you suggested (or a couple of Quartz windows and a laser
raster scan to see what is really happening in that region). A couple of
years ago I visited Sandia's Combustion Research Labs in Livermore, CA
and they had a similar laser based raster scan that enables viewing the
inside flows in the chamber as fuel is injected and combusted at very
high frame rates with really good resolution. This was done through a
quartz window installed at the piston dome region. I was more envious
than a little kid in a candy store. I am sure the setup cost many
millions of dollars to set up. I heard Georgia Tech has a similar setup
Since unlike Uncle Sam we don't have the pleasure of a few million $$
worth of equipment to tell us exactly what is really happening at that
junction........ My gut feeling is that there will be a lot of
scavenging effects going on. As the apex seal starts to cross the
exhaust port, the gas is flowing into the pipe at the peak exhaust flow
velocity (venturi effect of flowing through a narrow passage, plus the
peak chamber pressure at the beginning of the purge). At that instant,
the flow is very directional (I am guessing around 45 degrees or so to
the housing tangent). As the apex seal passes further across the exhaust
port, even though there is an opening to flow back into the adjacent
intake chamber, the scavenging effect (or inertia as you described)
"pulls" the rest of the gasses out the exhaust pipe. There is
undoubtedly some residual burned gasses that remain and go into the next
stroke
If anyone has the time and interest there is a thesis on Wankel
simulation and maybe he covers this particular topic. Here are the
details (Its on my "to read list" but have not read it yet)
COMPUTATIONAL STUDY ON MICRO-PILOT FLAME IGINTION STRATEGY FOR A DIRECT
INJECTION STRATIFIED CHARGE ROTARY ENGINE
A thesis submitted in partial fulfillment of the requirements for the
degree of Master of Science in Engineering By Zachary Steven Votaw B.A.,
Wright State University, 2011
Regards
Simon Saba
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