Re: Fuel Flow Jabiru Engine
Posted: Thu Jul 07, 2022 1:46 pm
Hi All,
Well, here is an update on my Fuel Flow Sensor's really bad pulse frequency fluctuations.
I decided to remove my Fuel Flow sensor and bench test it. The results on the bench test where the same as in the plane with the pulse count fluctuating all over the place for any given gravity feed rates between 2Lph to 35Lph.
So I cleaned out the impeller and found nothing that might have block the impeller. I check the 2mm jet was seated all the way in and put the sensor back together. Using a length of 8mm tube, I then blow a very light amount of air through the sensor and watched the impeller turn under a bench magnifying glass. At these very slow rotation rates and at faster rotation speeds, I could not see the slightest hesitation or binding in the rotation of the impeller at slower rotation speeds or as it slowed down from spinning faster.
I was hoping the problem may have been fixed, so I put the sensor back on the bench test rig. Sadly the oscilloscope continued to showed a wide range of pulse fluctuations, I mathematically calculated this could cause up to +-15% variation in fuel flow rate.
So I ordered a new fuel flow sensor from Stuart the MGL Dealer in New Zealand, I have found nothing but great service to me here Australia.
So as soon as the Flow sensor arrived, I bench test this new unit to find the pulse frequency was very stable with in 0 to 0.5Hz for the lower fuel rates and from 0.5Hz up to 1Hz for the higher fuel rates of 35lph. I also used Stevo's box, as I called it with the 12v DC input supply to 10v regulated DC output.
I certainly like the look of the oscilloscope fuel flow pulse as in the pic with both the regulated 10v DC supply and the new flow sensor.
So what's wrong with old fuel flow sensor, my guess it has a problem with the internal electronics that is causing those wild pulse fluctuations.
I also used a spread sheet to keep a check on what the K-factor would calculate out to be for any given Lph and pulse frequency. The bench testing of this new Flow Sensor and my spread sheet calculations showed the k-factor very close to 7000 as in specs for the 2mm jet. I my case the K-Factor worked out to be 6665.
So where to next, well I am going to connect and send a pulse signal down the flow sensor wiring in the plane to the RDAC/EFIS, to emulate the pulse rates for different LPH I recorded during my bench testing for the new fuel flow sensor.
If all the pulse frequency show a correct solid LPH on the EFIS and these fuel rates don't change as the Avionics, Lighting, Radio or the electric fuel pump are turn on or off. I will then start the engine and ground run it to see if this causes any interference to the emulated pulse rates and the EFIS's indicated fuel flow rates.
Cheers
JimJab
Well, here is an update on my Fuel Flow Sensor's really bad pulse frequency fluctuations.
I decided to remove my Fuel Flow sensor and bench test it. The results on the bench test where the same as in the plane with the pulse count fluctuating all over the place for any given gravity feed rates between 2Lph to 35Lph.
So I cleaned out the impeller and found nothing that might have block the impeller. I check the 2mm jet was seated all the way in and put the sensor back together. Using a length of 8mm tube, I then blow a very light amount of air through the sensor and watched the impeller turn under a bench magnifying glass. At these very slow rotation rates and at faster rotation speeds, I could not see the slightest hesitation or binding in the rotation of the impeller at slower rotation speeds or as it slowed down from spinning faster.
I was hoping the problem may have been fixed, so I put the sensor back on the bench test rig. Sadly the oscilloscope continued to showed a wide range of pulse fluctuations, I mathematically calculated this could cause up to +-15% variation in fuel flow rate.
So I ordered a new fuel flow sensor from Stuart the MGL Dealer in New Zealand, I have found nothing but great service to me here Australia.
So as soon as the Flow sensor arrived, I bench test this new unit to find the pulse frequency was very stable with in 0 to 0.5Hz for the lower fuel rates and from 0.5Hz up to 1Hz for the higher fuel rates of 35lph. I also used Stevo's box, as I called it with the 12v DC input supply to 10v regulated DC output.
I certainly like the look of the oscilloscope fuel flow pulse as in the pic with both the regulated 10v DC supply and the new flow sensor.
So what's wrong with old fuel flow sensor, my guess it has a problem with the internal electronics that is causing those wild pulse fluctuations.
I also used a spread sheet to keep a check on what the K-factor would calculate out to be for any given Lph and pulse frequency. The bench testing of this new Flow Sensor and my spread sheet calculations showed the k-factor very close to 7000 as in specs for the 2mm jet. I my case the K-Factor worked out to be 6665.
So where to next, well I am going to connect and send a pulse signal down the flow sensor wiring in the plane to the RDAC/EFIS, to emulate the pulse rates for different LPH I recorded during my bench testing for the new fuel flow sensor.
If all the pulse frequency show a correct solid LPH on the EFIS and these fuel rates don't change as the Avionics, Lighting, Radio or the electric fuel pump are turn on or off. I will then start the engine and ground run it to see if this causes any interference to the emulated pulse rates and the EFIS's indicated fuel flow rates.
Cheers
JimJab