flyrotary@lancaironline.net Mailing List Archive

Not confident about anything at all :)

If I remember Tracy correctly, pulse width of primary injectors are cut in half and secondaries turned on for the same amount of time (but compensated for size difference -- reduced in this case).

Note that fuel flow is calculated by the EM3 by measuring the pulse width of rotor 1 primary injector. When non-staging (primary and secondary both on) the EM3 compensates accordingly (it knows when staging/non-staging from data sent from EC3). So there is at least one second delay where FF is incorrect.

But you are right, flowing less through primaries and perhaps secondaries not yet on could increase fuel pressure. Looking at engine data on EM3 it seems it's updated every second. So there could be a second delay. Maybe that's what I'm seeing. But doesn't explain why it goes lean when engine is hot.

Fuel pressure flutuations may be a red herring.

Finn

On 5/4/2021 1:44 PM, William Schertz wschertz343@gmail.com wrote:

Finn
No rx-8 injector experience, but if at the staging point, if the EC-2-3 shuts off the primary injectors, and the secondaries haven't opened, fuel out of the manifold decreases, so the pumps would raise the pressure. Are you confident that the controller is reducing the primaries and starting the secondaries at the same time?

Bill

On Tue, May 4, 2021 at 11:07 AM Bobby Hughes BHughes@qnsinc.net <flyrotary@lancaironline.net> wrote:

Is the fuel pressure really increasing or is it the EM2/3 reading? Steve B. has posted good advice for tuning around the staging point with different size injectors.

Bobby

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Tuesday, May 04, 2021 11:46 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Renesis secondary injectors

I noticed that my indicated fuel consumption appeared to be about 50% higher than actual.

So I decided to start calibrating engine monitor fuel flow.

The first step is to check/adjust fuel flow around the staging point (20"Hg) where the secondary injectors open (secondary injectors are larger than primary injectors on the 4-port Renesis).

I thought I had previously tuned the engine for a smooth transition around the staging point, at least to the point when I didn't notice anything when dvancing throttle through the staging point.

However, now doing stationary run ups around the staging point (especially when engine is getting hot) I get the weird phenomenon of it going very lean when secondary injectors (supposedly) open. Another odd thing is that fuel pressure increases markedly.

On the HomebuiltAirplanes.com forum a guy that raced RV-8s for a couple of seasons mentioned troubles with the stock Renesis injectors.

Now I'm wondering if I have (intermittently) bad secondary injectors -- not opening when they should.

However, I'm confused by the rise in fuel pressure. Is there a injector failure mode where pressure in intake runners could push back through the injector into the fuel line?

Note that these are factory-new, maybe 10 to 20 hours of total engine run (or attempted run) time.

Another possibility is heated secondary fuel rail. But if there were boiling fuel there the fuel pressure should still drop when secondary injectors open...

I tried to look but didn't find a chart of 87 octane 10% ethanol boiling point vs temperature.

Anybody here had any trouble with stock Renesis injectors? Symptoms? Other ideas?

Finn

RX-8 4-port:
Primary: Denso 195500-4430 33.3 lb/hr @ 43.5 psi (350cc/min) 13.8 ohm
Secondary: Denso 195500-4460 51.4 lb/hr @ 43.5 psi (540cc/min) 13.8 ohm

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