Mailing List lml@lancaironline.net Message #45890
From: Douglas Brunner <douglasbrunner@earthlink.net>
Sender: <marv@lancaironline.net>
Subject: Pressurized Injectors
Date: Sun, 20 Jan 2008 13:48:45 -0500
To: <lml@lancaironline.net>
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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