To get the right mixture you need to measure the intake manifold
air temperature and the manifold pressure..
The fuel injected is then proportional to the product of
the inverse of the air temperature and the absolute manifold
pressure. Hotter air less fuel. Colder air more fuel.
The absolute manifold pressure measurement is no problem with a
Free Scale pressure sensor connected to an A to D pin
on the MM.
However MM BASIC has a special function for measuring
temperature called DS18B20( pin )
Measuring Temperature The DS18B20() function will get the
temperature from a DS18B20 temperature sensor. This device can
be purchased on eBay for about $5 in a variety of packages
including a water proof probe version. The DS18B20 can be
powered separately by a 3V to 5V supply or it can operate on
parasitic power from the Maximite as shown on the JPG.
Multiple sensors can be used but a separate I/O pin and
pullup resistor is required for each one.
To get the current temperature you just use the DS18B20() function in
an expression. For example: Any PRINT "Temperature: " DS18B20(pin)
I/O Pin Where 'pin' is the I/O pin to which the sensor is
connected. You do not have to configure the I/O pin, that is
handled by MMBasic. The returned value is in degrees C with a
resolution of 0.25oC and is accurate to ±0.5 oC.
The time required for the overall measurement is 200mS and the running
program will halt for this period while the measurement is being
made. This also means that interrupts will be disabled for this
period.
If you do not want this you can separately trigger the
conversion using the DS18B20 START command then later use the
DS18B20() function to retrieve the temperature reading. The
DS18B20() function will always wait if the sensor is still
making the measurement.
For example: DS18B20 START 15
< doother tasks >
So you start it every second and come back when the next second tick
comes along.
Locate (x,y)
PRINT "Temperature: " DS18B20(15) 'EFIS
Then divide that number into one and multiply by the manifold
pressure.
1/ DS18B20(15) X manpress = injector pulse width
Quite simple.
BTW You don't really need timed injection for a AC engine.
MM BASIC command PWM freq, ch2, ch1
ch2 & ch1 are dedicated PWM pins.
freq’ is the output frequency (between 20 Hz and 1 MHz)
This works in the back ground and does not affect the time
available for programming.
Typical injector turn on time is 1.2 msec.
Turn off time is .9 msec.
20 HZ is 50 msec. So if the injectors are on for 45 msec that is
about max flow. The injectors will be on most of time.
Tracy Crook used 2 injectors at low manifold pressure and 4 injectors at
higher pressure. This caused a lot problems around the 2 to 4 transition
causing
the engine to run rough. The RX8 engine uses six injectors.
You might use a 555 to send a fixed width to a couple of injectors out
of six
just for the idle mixture. This will give a way to adjust the idle mixture.
We can learn something from Megasquirt.
http://www.megamanual.com/v22manual/minj.htm
Fuel injector calculator.
https://www.rbracing-rsr.com/calcinjpulse.html
Here are the results for a 2 rotor P-port with 250 HP
at 7500 RPM. Looks like idle is still a problem with all four
injectors working all the time.. Maybe we can get away
with just two bigger ones.
Paul Lamar
That all sounds good, but I still think using the arduino to run
the engine is the best shot, that is all it is going to do. The
Maximite or cgcolormax can run the efis and recieve data from
the arduino.
Within the engine parameters I believe I can pull off
instructions to change the sets of injectors from 2 at idle to 4
or more as rpm increases past a certain threshold. Now I
"think" I can pull it off with only 2 at idle. When I say 4 or
more I mean it to say "all" injectors above a threshold rpm.
I would have to rethink a few things, I never planned the VE
being such a radical curve as seen in rotary's. Like I say I am
learning more and more about them.
David Jr.
Well there certainly is a big advantage to 2 processors. Each has more
time to
do its job. Is it true that the PWM freq on Arduino is 500HZ ? Two msec
period?
The VE is amazing on a p-port rotary. Typical VE is 120% when it comes on
the pipes. That stems from the lack of intake valves.
I think the expansion problem could be over come with three separate caps.
4140 rotor?
That is a really good idea.
4140 has much lower heat transfer than cast iron.
Might have to be machined in two pieces and welded
together.
Maybe three separate 4140 caps on an aluminium rotor.
Stainless would work too.
That way the rest of the rotor can be one piece aluminium and
hollowed out on an NC mill. If one can get the rotor weight
down the RPM can go up with more HP.
The idea is to keep as much heat in the combustion chamber as
possible which improves the BSFC. That would also cut the oil cooling
requirements. The rotor housing liner is hard steel. Maybe chrome molly.
I covered this stuff in my book How to Cool Your Wankel.
http://www.rotaryeng.net/cooling.htm
MazdaTrix sells it.
Thermal Conductivity W/(m K)/
Material/Substance Temperature C
............................ 25 ... 125 ... 225
-----------------------------------------------------------------------
Aluminium .... .....205 215 250
Chrome Nickel Steel
(18% Cr, 8 % Ni) . 16.3
Chromium ........ 94
Iron, cast .......... 55
Magnesium .......... 156
Molybdenum......... 138
Monel ..... .......... 26
Nickel..... , ......... 91
Titanium .. ......... 22
Steel, Carbon 1% 43
Stainless Steel..... 16 17 19
------------------------------------------------------
When ceramic comes off it destroys the rotor house wear surface.
It is not that good of an insulator as it is too thin.
All the other ideas are good.
Dave quote:
"Or a rotor that can be completely disassembled? Each combustion face
internally over lapping the other, very close tolerance interlocking
attachment points. The gear/bearing housing also removable adding
strength and support to the rotor faces? Side plates of the same
material, where the edge of the side plate once installed creates the
gap for the side seals? That would allow replacement of any one damaged
part instead of a whole rotor. I know balancing could become a issue so
in the design you would have to incorporate points inside each part that
would allow the removal of material without compromising strength." End
Dave quote.
Paul Lamar
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