Is there any information on the website showing the timing of the
intake
and exhaust port relative to eshaft rotation? I am specifically
interested
in the overlap and the e-shaft angle at which the apex seal
clears the exhaust port. Inspired by your 555 system, I have
designed a simple digital converter to convert MAP to pulse
width for controlling the injectors. We know that the
volumetric efficiency of the p-port at 6000rpm is 120%. I am
wondering how much of that 120% is represented by intake air passing
through the chamber and out the exhaust during overlap. If this
occurs at all, it would improve efficiency to minimize the
amount of fuel in the bypassed air, suggesting that the
injectors should be opened after the exhaust is at least
partially closed
Victor Roberts
I don't have the numbers for the timing but it is exactly the
same as the Le Mans 4 rotor.
http://www.rotaryeng.net/Mazda_R26B_US.pdf
http://www.rotaryeng.net/Welded-steel-p-port.html
The numbers can be derived from the scale dwg in this last link.
The exhaust and intake P-ports in a rotary never really close.
In that regard it is more like a turbo jet.
What air does not go in one chamber goes in the next.
In a tuned rotary engine however the max pressure in
any given (One of 3) compression chamber depends on the RPM,
pipe length and pipe diameter.
http://www.rotaryeng.net/Mazda-p-port-press-wave-enhanced.jpg
The best place to measure this pressure is the apex oil injector
holes just above the p-port intake. Of course one is not using
these holes for oil injection. One mixes the apex oil with the fuel.
I am coming back to the 555 system and adding a single chip computer
that
has the sole job of adjusting the mixture using a USB port and
storing the trim data in a spread sheet format. The program
becomes extremely simple and easy to comprehend. Merely a look
up table in the single chipper.
Henry Nee came up with this great idea and people can email and
share
trim
tables. Any number of trim tables can be stored in one's PC. It also
makes
editing the trim table simple as you do it in your PC using a spread
sheet
program. This should greatly speed the tuning of your engine and
similar
installations can use the same trim table. We can put them on the
web
site
for rapid download. Parameters affecting the trim are type or
drag of
the airplane, diameter and pitch of the prop, intake pipe length and
gear
ratio used. Assuming all are using a p-port.
Paul Lamar
Victor, I have seen the port timing numbers in the Kenji Yamaguchi
(SP?)
papers. I think there is a link on Paul's site and possibly on
Craigs
Rotary List site also.
george grimes
http://www.turborx7.com/porttiming.htm
cbeazley
From Mark Warner's book Street Rotary, page 34, here's a port timing
chart of various Mazda models. Here's a link to the book:
http://www.amazon.com/Street-Rotary-HP1549-Horsepower-Reliability/dp/
1557885494/ref=sr_1_1?s=books&**ie=UTF8&qid=1321457929&sr=1-1
Tom Sash
Much of this is useless info as it makes no sense to port a side
port engine for aircraft use. If you need to take the engine apart
to port it you might as well P-port it. The p-port intake
manifold and slide throttle are easier and cheaper to make than
a side port manifold. You wind up with 25% more power and a better
BSFC.
Most of the road racers need it because p-ports are outlawed due
to the rotaries over helming domination of most road racing classes.
Only in the Rolex GT class are RX8 3 rotor p-ports allowed and
then they suffer from extra ballast and an enforced red line 500
RPM below the street engine.
Paul Lamar
These numbers for the Mazda P-port are bogus.
As Paul has pointed out, there is an overlap of intake timing between
adjacent rotor faces.
When the apex seal is in the center of the port, two chambers are
open to the intake. From this position, after 360 degrees of shaft
rotation the rotor face which was just beginning intake before the
rotation would still be half open to intake after the rotation.
The intake period exceeds 360 degrees of eshaft rotation.
Reference these numbers to after TDC and it becomes apparent they cannot
be true.
The intake opening at 86 BTDC is 274 degrees of e-shaft rotation
After TDC.
The intake close of 75 ABDC is 255 degrees After TDC.
This gives us 19 degrees of shaft rotation where neither is open.
For the exhaust, opening at 73 BBDC is 107 After TDC, and closing
at 65 after TDC - 42 degrees of shaft rotation when no exhaust occurs.
It appears to me that the interior circumference of the rotor housing
is about 27 inches; so 360 degrees of shaft rotation is 9 inches.
A two-inch port opening then requires 80 degrees of shaft rotation
to transit, so the trailing port opening occurs 80 degrees ahead
of the leading port closing. The intake period including overlap
is about 440 degrees of shaft rotation. The exhaust port appears
to be half the size of the intake, so 400 degrees of shaft
rotation from opening to closing.
Tell me where I am wrong.
Victor Roberts
The intake period is 270 degrees of e-shaft rotation as are all other
strokes. In a p-port there is a depression in the rotor face that
connects the intake port with the exhaust port. Surprisingly the
pressure in the intake is higher than the pressure in the exhaust.
Therefor air flow, if any, goes from intake to exhaust in theory.
However air has mass, friction, adhesion and inertia. So what
goes where and how much is arguable.
Here is a Racing Beat 3 rotor P-port turbo making 900 HP as I recall.
Some of the end housing are aluminum.
Note the size of the turbo charger :) One would think the
injectors, being on the plenum side of the long intake runners,
would lose fuel to the exhaust. Jim Medere told me that was not
the case. In fact the BSFC was slightly better with the injectors
at the start of the runners. I can't wait to see what happens when
Dave Lemon builds a welded p-port with a slide throttle RX8
engine. Should be around 600 HP or more instead of only 420 HP :)
As I recall the 3rd gen RX7 stock body land speed record at 268
MPH was set with a 3 rotor, 3 turbo side port engine making only
about 750 HP. It had an ice water inter-cooler as I recall.
BTW a picture taken from my C182 made the centerfold of Pop Sci
mag the year of the flood at Bonneville. That was the first year the
recording holding R.B. 3rd gen 3 rotor RX7 showed up.
http://www.youtube.com/user/PaulLamar2#p/u/11/JUf_aWVVl7o
With our man on here Csaba Csere narrating no less.
I got my 2 cents in at the end.
Paul Lamar
I have to wonder about the concern everyone has been showing about
overlap.
There is considerable overlap in any piston engine. The exhaust and
intake
valves are both open on even a low output piston engine. There is even
more
overlap in a high output engine. I haven't timed any cams lately
but iirc the cams have about 30 degrees of overlap. Due to the
velocity and mass of the intake charge some will often flow out
the exhaust. Since the rotary doesn't have valves in the way timing
is very important, but a lot of the overlap events are similar.
Bill Jepson
My concern was in the volume of air that passed from the intake through
the chamber and out the exhaust, and the amount of fuel in that
flow. It appeared to me that if the injector timing could be
manipulated so that at cruise power the air passing through to the
exhaust carried the least possible amount of fuel, better efficiency
would result. It may be that the volume lost is inconsequential, or
that the timing cannot improve the loss - but since lean cruise fuel
flow is less than half max power flow and therefore injectors are on
less than half the time, it seems reasonable that some injection
timings will be better than others. One reason direct injection
engines can get better fuel mileage is that they lose no fuel out
the exhaust during valve overlap. It is also one reason that port
injection engines can get better mileage than those with throttle -
body injection. I ask the group's forgiveness for my intrusions - I
know I have a gift for causing unintentional irritation.
Victor Roberts
You have a valid point there Victor. When the fuel is injected
relative to top dead center could be important.
So far we have no control over that as Tracy does not publish the source
code of his system. We think he injects fuel once a rev. I'll find
out as soon as I get my engine instrumented with a data aq system.
Paul Lamar
To the best of my knowledge, direct injection engines do not inject at close
to TDC on the compression stroke. They inject close to exhaust valve closing.
As per Mazda Skyactiv technology, they use the latent heat of evaporization to
cool the intake charge. This can be used to increase the density, reduce knock
resistance or a bit of both. The start of injection does keep fuel out of the
exhaust helping with emissions as the primary OE focus with improved MPG as a
result.
I have a '91 GMC S15 with throttle body injection. I get 25 MPG US from it.
The newer ones with the CPI went to hell with MPG. CPI is a screwed up MPI
system. It would have been better for the General to go directly to port
injection. I still have not figured out why they spent the money to design and
emission certify the 2.8/3.1 series engines or the 3.8/4.3 Chev engines when
they had the proven 3.0 and 3.8 Buick engine. Rates as one of the best engines
ever!
Dale Davies
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