flyrotary@lancaironline.net Mailing List Archive

Good questions, Thomas.

Al indicated that the EC2 does indeed expect a manifold referenced (vacuum for NA and vacuum/boost for forced induction) pressure regulator. Therefore, the default fuel map for the EC2 is set up expecting the pressure differential across the injector to remain constant at all manifold pressures. Having the pressure differential between the fuel rail and the manifold remain constant simplifies the calculations for determining the PW to meet the engine demand.

You can certainly run the engine with a constant fuel pressure ( I have - for close to 10 years) using the EC2. However, if the computer needs to adjust every fuel map quantity for every pulse based on a constant fuel pressure - which means the pressure differential is NOT constant the problem becomes more complex. For instance, I suspect to do that you would now need a fuel pressure sensor to feed the EC2, so the CPU could determine what the fuel pressure differential is for each firing and adjust the PW accordingly. So its much simpler to simply have the fuel pressure regulator hold the pressure differential constant. This way the EC2 only has to keep tabs on the manifold pressure instead of it AND the fuel pressure.

At least that is how it appears to me.

----- Original Message -----

From: Thomas y Reina Jakits

To: Rotary motors in aircraft

Sent: Thursday, September 21, 2006 11:19 PM

Subject: [FlyRotary] Re: Fuel Pressure Regulator Vacuum or Boost??

Ignorant Question:

a) Does Tracy's system need/use manifold referenced fuel-pressure?

b) If not shouldn't the fuel pressure stay constant (absolute), so that the electronic control takes care of mixture with a fixed fuel pressure and adjusts injector pulse according to manifold pressure?

c) What advantage would you have in a system where the fuel is manifold referenced directly? It still is controlled by the pulse width....

Andvanced thanx for enlightening me!

Thomas J.

----- Original Message -----

From: Ed Anderson

To: Rotary motors in aircraft

Sent: Thursday, September 21, 2006 3:26 PM

Subject: [FlyRotary] Re: Fuel Pressure Regulator Vacuum or Boost??

Thanks, Bill, for confirming my suspicion. The 9 year old regulator I am using was purchased because it had a manifold reference line and was listed as a regulator for boost. I assumed (wrongly it appears) that because it was referenced to the manifold that it would adjust fuel pressure for manifold "vacuum" as well as positive boost.

After noting that some pressure regulators were for "Boost" and others for "Vacuum/Boost" I came to suspect that the difference was not just semantics in advertising. But, wanted someone who realllllyyyy knew to put me straight.

Ed

----- Original Message -----

From: wrjjrs@aol.com

To: Rotary motors in aircraft

Sent: Thursday, September 21, 2006 3:42 PM

Subject: [FlyRotary] Re: Fuel Pressure Regulator Vacuum or Boost??

Ed,

You are correct, the "boost reference" is only changed at more than 1 atmosphere. The usually more expensive vacuum and boost referenced unit would lower the pressure at idle.

Bill Jepson

-----Original Message-----
From: joeh@pilgrimtech.com
To: flyrotary@lancaironline.net
Sent: Thu, 21 Sep 2006 11:48 AM
Subject: [FlyRotary] Re: Fuel Pressure Regulator Vacuum or Boost??

I presume your pressure gauge remains steady as you adjust throttle ?

Yep, no real change in FP over the entire range from idle to WOT.

Joe Hull

Cozy Mk-IV N31CZ (65 hrs - Rotary 13B NA)

Redmond (Seattle), Washington

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