Jeff, you will probably get a number of
views on this topic.
There are those who believe injecting the
fuel nearer the TB (further from the intake ports) will give better mixing of
air and fuel and more importantly more time for the fuel to turn from liquid droplets
to vapor/gas therefore better efficiency. There are others that
believe whatever mixing benefit you get you lose something because now there is
a longer run with metal walls to cause the fuel to adhere to the walls and not
mix as completely. Like most things probably a bit of validity to both
views.
I have tired it both ways. I had a
75mm TB and four injectors sitting approx 18” from the intake ports.
I could not tell if there were any increase in efficiency or power –
there may have been but with the limitation of my instrumentation you just
could not tell whether there was or not. It certainly wasn’t significant.
However, what I did encounter was if I
suddenly opened the throttle, the engine would bog or hesitate – the
engine never stopped, but I found that this used up more seat cushions on
a go-a-rounds {:>). So I went back to putting the primary injectors in
the block and secondary injectors as close as I could get to the intake
ports. I personally like this arrangement. YMMV.
My 0.02 worth
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Jeff Luckey
Sent: Saturday, February 13, 2010
11:46 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Runner
velocity
After reading this, a question comes to
mind:
What is the difference between throttle
body injection and port injection? I’ve heard people say that w/ the
injectors up near the TB, you get better fuel/air mixing. Is that an
old-wives-tale? Which one makes more horsepower, gives better throttle
response, etc? It seems to me that fabrication of intake manifold would
be easier for injectors near the TB.
Apparently there are benefits of port
injection (‘cause that’s what the production engine uses) but I
don’t know what they are..
What are the pros and cons of each?
BTW – Happy Birthday Ed :)!
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Lynn Hanover
Sent: Saturday, February 13, 2010
08:09
To: Rotary
motors in aircraft
Subject: [FlyRotary] Runner
velocity
This is a free download of the Bernoulli Principal. Fun to play with
and educational.
The amount of fuel air entering the chamber is a function of runner
cross section, velocity and time.
The depression, or vacuum generated is a function of displacement and
RPM. So the depression is about fixed by the 2606CCs and say, 6,000 RPM. The
"M" in RPM is the time. So............
That leaves only Porting to increase intake open and closing time,
(lengthen time period) and manufacturing the ideal intake runner set/ Throttle
body combination.
In my mind the runner size would be identical the the port opening for
4 to 6 inches out from the port opening. Then blend into one "D"
shaped pipe for the 180 bend over the engine top. Then taper to a larger pipe
of about 2 1/2" to blend into a plenum just big enough to fit the throttle
body mounting plate.
So, the cross section would be reduced gradually from the throttle body
to the end of the "D" shape, then remain constant right up to the
port opening.
I would upset the inside radius of the "D" shape with a
number of burs stood up with a three corner punch, to generate some tubulance.in order to keep flow attached.
Just a guess. I could be completely wrong.
Later, I tried a 75MM at one point and
while it did nothing to improve engine power and performance, in my case it had
an undesirable down side – now to be fair it could have been partially
the results of having all 4 injectors back near the throttle body – but
in any case, if you suddenly opened the throttle like in a panic go-a-round
– the engine would bog and hesitate for a fraction of a second (seemed
like minutes {:>)), the engine never stopped, but I just didn’t like
it. So I went back to the 65mm.
So the important thing is to match your induction system to your
real operating regime – NOT what you would in your wildest dream like for
it to be {:>).
Ed Anderson
You are only 70??
Run hard and put away wet comes to
mind..............
Lynn E. Hanover
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