A while ago there was a thread on the effect
of pressurized injectors on fuel atomization. It was suggested that
pressurizing the injectors improves fuel atomization and leads to a smoother
running engine LOP at high altitudes.
Recently, we ran tests to see what effect the use
of Ram Air had on smoothness of operation at high altitude.
Engine: IO-550N, 10:1 compression, ram air,
magnetos, GAMI injectors, GAMI spread of .2 gallons
Conditions: Altitude
= 17,500, OAT = 1 C
Without Ram Air (MAP = 15.2) the engine ran
smoothly down to about 60 deg LOP or 8.8 gal/hr
With Ram Air (MAP = 16.3) the engine only
ran smoothly to Peak or 11.2 gal/hr
The only difference between these two settings
(that I can think of) is that in the first, ambient air pressure is
probably slightly above manifold pressure (accounting for the filter)
- which means the injector is pressurized very slightly. In the second,
ambient pressure is probably about 1.0 less than manifold pressure
(accounting for ram effect) so pressurization of the injector is reversed.
This would seem to confirm the fact that unpressurized injectors
reduces fuel atomization and makes for a rougher running engine LOP at
altitude.
I would like to run smoothly LOP at altitude
using ram air. It seems to me that I can go ahead and pressurize my
injectors by running tubes off the ram air tube to the injectors and using turbo
injectors. (Is Mike Mahar still selling this setup?) Not sure
that I want to go to the time, trouble and expense to do this
though.
I am also wondering if using a "hotter" spark from
Electronic Ignition would improve the problem. (I would try to use an
Electronic Ignition system that had the same advance as mags)
Your thoughts?
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