Does the pressure increase have a solid 'step' at the exact staging point, or is it just rising in that area?

Yes, solid steps.
One second sampling intervals.

How much increase on the gauge? Where is the reference for fuel pressure measurement?

18 to 64 psi, about 36 average.
At end of secondary fuel rail.

The pressure *regulator* should be referenced to MAP (manifold pressure), and will raise absolute fuel pressure as manifold pressure rises. If the gauge is referenced to atmosphere (or absolute), it would indicate a rise in pressure as the throttle is opened.

The regulator does respond to MAP changes. Originally I thought it was too sensitive and the source of the wild swings in fuel pressure. But there is a high-pressure fuel filter between the regulator and the fuel rails. Figured that would dampen any pulses before they reach the regulator but probably not true.

Actually I don't have a dampener in the MAP line to the regulator. Should probably try that. Since it wasn't an issue when tuning the engine I forgot about it. The EC3 probably averages MAP samples.

The more I think about it, if there are pressure pulses caused by injectors opening and closing, the one-second sampling of the fuel pressure sender could be randomly be hitting highs and lows. I really should hook up an O'scope to the pressure sensor to see what the signal from it looks like.

Finn

Charlie

On 5/4/2021 12:44 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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