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I appreciate your concern. I am aware of the complexities of intake
design such as Finite Amplitude Waves and the Inertia. What I am looking
for is a starting point because all the lengths and diameters are
interrelated in their effect on tuning.
I am specifically looking for the Helmholtz and Ohata model equations
that have been adapted for the rotary. If on one has them then I will
take the time to modify them from 4-stroke myself (I have the 4-stroke
equations).
Alex Madsen
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Friday, May 07, 2004 7:40 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Intake manifold tuning
Ah! If it were only that simple, Alex. I have done an extensive amount
of
study of the rotary engine (as well as induction systems in general) and
it
is not simple one shoe fit all feet. There are two basic phenomena that
exists in any Internal combustion induction system that affect the
ability
of an intake system to feed a rotary the air/fuel it needs. One is
referred
to as Inertia or Momentum filling or charging and is basically the
surging
flow of air molecules (and fuel) with an average velocity (depending on
tube
dia,length, rpm) of around 200-400 fps. This the airflow due to the
pressure differential created by the opening and filling of the
combustion
chamber. The second phenomena which the Mazda engineers were able to
use to
great effect is the Finite Amplitude Waves (FAW), these are basically
pulses
of energy or shock waves that are created by port opening/closing
events,
they travel at the speed of sound. You can picture the basic flow as a
surging stream of water flowing down hill and the FAW
as waves (very strong waves!) racing up and down that stream.
Depending on your consideration of these two phenomena in your design
they
can either reinforce one another or oppose one another (They are
interrelated) and so can greatly improve the airflow into the engine or
can
adversely affect the flow. What makes it worst is that
interrelationship
changes as operating conditions change, in other words they may
reinforce
each other at some operating regimes and oppose one another at a
different
operating regime.
There are many considerations such as port overlap timing, port timing,
runner sizes, ignition timing, exhaust, etc., etc. I think you get the
picture.
Probably port characteristics and rpm are the two most significant
factors.
As some of us have found out, what works well for 9000 rpm racing
engines
suck for rotaries running 5000-6000 rpm
What would made your objective it easier in designing such a standard
intake is:
1. Everyone use the same port characteristics (size, timing, number)
2. Everyone use the same RPM range
3. Everyone use the same Exhaust system
4. Everyone use Naturally Aspired Induction ( or everyone use
turbochargers
{:>))
5. Everyone use the same number of rotors
6. Everyone place their injectors at the same location in the induction
system
I will leave it up to you to consider the odds of everyone doing those
four
things.
OK, OK, I don't mean to be a spoil sport. To build an optimum induction
system it would have to be designed for a specific set of engine and
operating parameters. But, that does not mean you could not design a
"Good"
induction system that probably satisfy say 70% of the need. Here is my
view of the two dominate factors (well, actually only one)
1. Airflow - that's what is all about. Unfortunately a number of
factors
go into determining airflow
a. How many rotarys (or more basically what will the airflow demand of
the
engine likely be? 2 rotor, 3 rotor?. I would assume that the two rotor
would be your design target as there are many more in use or projects.
b. Tied closely to 1 is what will the rpm range be. Right now most are
using a 2.17:1 gear ratio which keeps the engine rpm range between 4000
and
6000 (roughly). However there are those who will be using the 2.85 gear
ratio which means they will likely be operating from 5500-7000 rpm and
will
demand more airflow.
c. Airflow velocity appears to be a key factor in filling a combustion
chamber, that in turn is directly dependent on the rpm (air flow) of
your
engine as well as the diameters of your runners. So the diameter of
tube
that works well for 4500 rpm will probably be restrictive at 7000 rpm.
The best suggestion I can offer is to look at what Mazda engineers did
with
their NA rotary engines. While their induction design favored lower rpm
torque in order to get that "sports car" feeling, they did succeed in
producing power up into the 7000 rpm range. That would indicate that we
might want slightly larger diameter tubes to slew the torque/power band
up
in rpm and perhaps slightly shorter runner lengths for the same reason -
to
favor the mid to high rpm band - say 5000-7000 rpm. But, remember that
people are frequently doing non-stock things to their engines such as
porting from "Mild Street" to "bridge port" which will change the
induction
system needs.
So I hope you are successful in your project as I know there are a
number of
folks who would love to buy an "off the shelf" induction system. One
that
is light, safe and produces acceptable power levels will undoubtedly
sell,
but I think it will take a considerable amount of development for the
reasons I've mentioned and more.
I am more than willing to give you my opinion and assistance on intake
design considerations, but since your the man making the intakes, the
finally call is naturally yours to make. I just wanted to ensure you
have a
realistic picture of what you are considering.
FWIW
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: "Alex Madsen" <madsena@rose-hulman.edu>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, May 07, 2004 5:48 PM
Subject: [FlyRotary] Intake manifold tuning
> I am trying to get a general idea of what size tube people are using
for
> their intake manifolds. I will uses these numbers for a starting point
> and modify them for my design using tuning equations and such.
>
> 1. Runner diameter
> 2. Runner length
> 3. Plenum diameter
> 4. Plenum length
> 5. Location of fuel injector
>
> Speaking of tuning equations I am looking for the tuning equations of
> rotary engines. Could someone point me to a location that has them or
> send them to me.
>
> Thank You
> Alex Madsen
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
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