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Very interesting and novel idea, Jim.
There is no doubt that temperature does affect the DIE RPM point. Also,
my newest manifold (completed before the analysis was {:<() has the DIE
effect at 6500 rpm due to its shorter length. I can not reach that rpm with
my engine prop combination on the average OAT day such as 59F where my
static is around 5200 rpm.
However, on this manifold I place all 4 injectors in the throttle body
area at the beginning to the tubes. The evaporation of the fuel does
definitedly lower the temperature in the manifold tubes. While I have not
yet seen frost, I have seen the outside of the tubes running with condensed
mositure and they are in the airflow of my hot radiator exhaust air. Jim
Mosur, who also has thin tubes reports he frequently sees frost on his tubes
due to the vapor phase transition of the gasoline. So it appears that the
temp in the intake can get down right chilly with the injectors up stream.
The reason I bring this up, is this manifold while clean and light was
disappointing because I no longer saw the DIE effect due to its shorter (42"
vs 48") length.
Well, the morning I flew down to Shady Bend the OAT was approx 35F AND I
saw 5800 rpm again!. I decided that if the OAT was 35F then it was probably
not unreasonable to assume the temp of the air in the tubes was approx 15F
cooler or 20F.
When I got back, I plugged 20F into my DIE calculator and it showed that
temperature supported the DIE effect at less than 5400 rpm with that
temperature, whereas the DIE rpm was 6500 rpm with the manifold air temp set
at 180F (my calculation base).
So I think this supports the concept that you have postulated. So here
again, the concept is fairly simple, but I think the devil is clearly going
to rear its head in the details.
I can think of no way to separate the temperature drop you want from a
certain quantity of fuel that must evaporate to give you that temp drop.
However, that fuel quantity might not be consistent with the best air/fuel
mixture for power in the engine. On second thought, I suppose a chemist
could figure it out, and it may be that less fuel evaporation is need with
less airflow mass to bring the air temp down and more fuel evaporation to
bring a larger quantity of air mass to a lower temperature. So perhaps the
two conditions are not mutually incompatible.
But, I agree it would take come on-the-fly data collection and computing
to manipulate the injection cycle to maintain a certain DIE rpm and also
provide the right air/fuel mixture for the engine operating regime.
An interesting "Brain Fart" Jim.
Perhaps someone better versed in such things that I am would care to
comment?
Best Regards
Ed Anderson
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
----- Original Message -----
From: "Jim Sower" <canarder@frontiernet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, November 05, 2003 3:42 PM
Subject: [FlyRotary] Re: DIE Summary
> Ed,
> Great job. Wish I'd been more alert at the forum at Tracy's. Anyway, I
just
> had another brain fart.
> The time it takes the FAW to get from one port to another is a function of
> Temp. The time you WANT it to take is a function of RPM. You would like
to
> have DIE at several temperatures and RPMs but since you can't control the
temp,
> the RPM will be a function of whatever temp you end up with that day.
What if
> you had two each primary and secondary injectors - one at the top of the
runner
> and one at the flange or in the block or wherever (where it is now). If
you
> could bias the fuel injected between the two injectors, the heat of
vaporization
> of the fuel would have a big impact on charge temp and might very well
make
> intake temp (and therefore Tr) controllable.
>
> I don't know how big an engineering challenge it would be to vary the fuel
> delivered to "upper" and "lower" injectors so as to control the intake
temps,
> but perhaps it could be done with fuel pressure. It would be arguably
more
> reliable to do it electronically by biasing the pulse width of the
injection
> event between the injectors, but any way you do it, controlling intake
temp
> might turn out easier to accomplish than modulating the runner length.
>
> Some brain farts are just brain farts .... Jim S.
>
>
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