Fuel pressure
in 912iS Technical Questions
9 years ago
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by Claus Mortensen » 9 years ago
Dear Stefano
It does look like Dynon is doing the same as Integra. Take a look here. It clearly indicates that it use the manifold pressure to make it differential.
I think the G3Xperts will be getting an email from me soon :-)
Kind regards, Claus
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by G3Xpert » 9 years ago
Hello Claus (and others),
As you know, the 912iS engine has a separate fuel pressure regulator module which maintains a positive fuel pressure of ~3 bar and the 912iS Operators Manual specifies that the fuel pressure in flight must be 3 bar +/- 0.2 bar (2.8 bar to 3.2 bar).
The fuel pressure regulator module maintains fuel pressure to 3 bar above manifold pressure, not ambient pressure, so this is key to understanding how fuel pressure must be measured and displayed to the pilot.
A typical fuel pressure gauge like used on a Lycoming engine measures gauge fuel pressure, relative to ambient pressure, so a different measurement is needed for the 912iS engine since fuel pressure is regulated in reference to manifold pressure.
With such a tight tolerance on acceptable fuel pressure, it is especially important that the fuel pressure measurement be as accurate as possible. We considered taking the inputs from multiple pressure sensors and calculating a differential fuel pressure relative to manifold pressure, but when we logged the data from these pressure sensors in flight and studied the results of using this data to calculate differential fuel pressure, we were not convinced that the accuracy of this method was acceptable. We understand that some who use this method even have a "correction factor" that must be manually adjusted before the reading is usable.
As shown on page 29-3 of the Rev. Z G3X/G3X Touch Installation Manual (and attached), we added support for a specific differential fuel pressure sensor for the 912iS engine. This sensor connects directly to the fuel line and to the intake manifold airbox and thus works independently, and in a similar fashion to the fuel regulator module, which also connects to the airbox.
Please make sure your installation uses this differential fuel pressure sensor. You may contact us at G3Xpert@garmin.com if you have additional questions.
Thanks,
Steve
GEA24Rotax914_912iS_DiffFuelPressure.pdf (You do not have access to download this file.)GEA24Rotax914_912iS_DiffFuelPressure_2016-10-19.pdf (You do not have access to download this file.)
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by Richard Boslaugh » 9 years ago
I contacted the folks at Advanced Flight Systems concerning this issue. They use the formula:
Fuel pressure=Analog pressure+Ambient pressure-Manifold pressure. I have never had the
fuel pressure go below 41psi at any altitude and over 46 psi one time when the new version
Rotax filter was clogged due to contaminated fuel from an airport fuel tank.
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by Peter Bugg » 8 years ago
I have a Pipistrel Virus SW and factory send me an AD a couple of years ago about the Andair Gasolator fitted. The mesh was too fine and gummed up although if you removed looked OK and clean. The fix was to replace with a coarser mesh screen. This may be a factor in your fuel pressure problem?
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by Bill Hertzel » 8 years ago
The pressure you measure is dependent on how it is measured.
The regulator maintains the fuel pressure at ~3Bar (~44psi) above the Intake Manifold Pressure (MAP)
This assures that the fuel injector will always be working against a constant fuel to MAP differential pressure.
If your fuel pressure measuring method does not take the MAP pressure into account, you are measure "Gauge" Pressure instead of the "Differential" Pressure that the regulator is trying to maintain and will be displaying varying and skewed readings.
As the following table shows, 2.7-2.9 bar (42-43 psi) in flight is a normal "Gauge Pressure".
2.3 -2.5 bar (34-36 psi) at idle on the ground is also typical of uncorrected pressure readings.
Either your EMS system needs to take the MAP measurement into account,
or your Pressure sender needs to be the differential style with two(2) pressure ports.
Example: UMA-N1EU70D
Otherwise, just get used to seeing pressure as ~0.2bar(~3psi) low in flight.
or ~0.6bar (9psi) Low on the ground.FuelPressure_2017-04-19.pdf (You do not have access to download this file.)
Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.
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