flyrotary@lancaironline.net Mailing List Archive

Ed,

I used 80% duty cycle as the injector open time at 6500 RPM since my test stand could not achieve that RPM the way it was set up. The 80% is often quoted as a conservative max duty cycle for reliable injector operation. The period at 6500 RPM is 9.2 ms so 80% of that is 7.4 ms.

10.6gal/hr * 6500 RPM/ 5265 RPM * 7.4 ms/ 4.4ms = 22 gal/hr

This estimate is conservative since the effect of the injector dead time is to make the injector act like a larger one as the pulse width increases.

Thanks for looking at this.

Steve

From: Rotary motors in aircraft [flyrotary@lancaironline.net] on behalf of Ed Anderson [eanderson@carolina.rr.com]
Sent: Saturday, November 17, 2012 6:43 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: renesis injectors

Hi Steve, I attempted to verify your math but believe I am missing a crucial factor - injector opening time at 6500 rpm

Check my math:

10.6 gal/hr = 10.6/60 = 0.17666 gal/second = 0.17666/1000 = 0.00017666 gal/msec flow for all four injectors combined

for an "average" of 0.00017666/4 = 0.000044166 gal/msec per single injector

Taking 0.000044166 * 4(injectors) = 0.00017666 gal/msec = 0.00017666*1000 = 0.17666 gal/sec * 60 sec/1 hr = 10.596 gal/hr, so that checks

Now since there was no different opening times given for the injectors at 6500 rpm, I have to assume the opening time was the same as at 5265 rpm (4.4 msec - which is not likely to be correct). But, following this assumption - then the increase for the flow at 6500 rpm is simply the ratio of 6500/5265*10.6 gal/hr = 13.086 gph a bit short of the 20 gph figure.

So , I strongly suspect the injector opening time would increase at the higher rpm (it does on my rotary) which would account for the increased flow - did you happen to measure the injector opening time at 6500 rpm?.

From: Steven W. Boese

Sent: Saturday, November 17, 2012 1:26 AM

To: Rotary motors in aircraft

Subject: [FlyRotary] renesis injectors

Charlie,

My Renesis engine on the test stand uses the same injectors that Richard has. Today, I recorded some data that should indicate whether or not these injectors might work for your application. At 23" MAP, fuel pressure of 40 psi, and 5265 RPM, the fuel flow was 10.6 gal/hr and the pulse width on all four injectors was 4.4 ms. From this data, it appears that those injectors should support a fuel flow of slightly over 20 gal/hr at 6500 RPM with an injector duty cycle of less than 80%. It would be good if you (or anyone else) would independently check if my calculation is reasonable.

Steve

Hi Richard,

The only info I could find on the green ones seems to indicate that they are 230cc. I can't find numbers for the brown, but based on the model number, they are probably slightly larger. I suspect, but don't actually know, that I need 400+cc(normally aspirated Renesis). The yellows are somewhere between 380 & 430 cc, depending on where you look & what pressure they run at.

Thanks for checking, & if it turns out that my research is wrong on the flow figures, we'll need to talk further. :-)

Charlie

Charlie,

are you still looking for injectors?

Would the ones in the picture of any help?

They are out of a 2009 2nd Gen Renesis. The numbers are: green 827 12 , 297500-1220 .

Brown 827 08 , 297500-1230 .

I can not interpret these number.

Richard Sohn
N2071U

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