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  #11  
Old 08-09-2018, 08:09 AM
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Thanks for the responses. Internal combustion engines are a bit of a hole in my thermo education.
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  #12  
Old 08-09-2018, 09:08 AM
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Quote:
Originally Posted by maniago View Post
Well, 'wasted' in this case means a stoichometric mixture richer than what is required for the engine to run at the operators requirements. So yes, as we all know, mechanical systems, like carb systems, provide fuel at a "onesize fits all" ratio, with an open loop system design. EFI, allows that flow to be tuned better reducing over rich ie wasted fuel conditions mostly because of its a closed loop system. Which is why we get better fuel economy from EFI...... at the expense of introducing an electrical "component" into the system and its associated complexities......

But yes, wrt aviation systems, they all are flowing fuel constantly......just better mouse traps.
My FM200 is closed loop. I have a large meat servo with its own CPU (apparently running DOS) monitoring exhaust temperature, with additional aural and tactile inputs.

Seriously, both Bendix style constant flow injection and the current electronic offerings are open loop, and there is no reason for any significant quantity of "wasted fuel" with either kind.

As Ross said, the typical constant flow system with .028" restrictors doesn't meter as well as an EFI system at low flow rates. At idle, the constant flow delivery is more dribble than squirt. Atomization is less than ideal, so vaporization is poor, thus cycle to cycle variation tends to be worse. In cruise, fuel divider accuracy drops off below roughly 6 GPH. That's not a big deal for most of us, as we tend to cruise above that, even LOP. Smaller engines can substitute .022" restrictors for an improvement. The EFI will generally deliver a smaller GAMI spread at very small fuel flows, as Dave Anders has demonstrated.

Dave, you should find all the basics in these two articles:

https://www.danhorton.net/Articles/B...%20(1).pdf

https://www.danhorton.net/Articles/F...and%20Fire.pdf
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Last edited by DanH : 08-09-2018 at 10:28 AM.
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  #13  
Old 08-09-2018, 09:40 AM
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DanHorton dot net.

Cool.
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Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

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"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #14  
Old 08-09-2018, 10:05 AM
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Quote:
Originally Posted by rv6ejguy View Post
While all automotive EFI systems have used closed loop AFR control for about 30 years now, typically we are not using closed loop in aviation with leaded avgas. With a switch to unleaded, that's all possible. We already flew an RV10 back in 2007 with this technology.

The Bendix type injection works pretty well in cruise and high power with balanced nozzles actually. We see the majority of fuel savings using EFI in the start/ warmup/ taxi/ descent phases or at low power settings up high where the mechanical injection does not meter very accurately by comparison.
Hmm. I submit to your expert knowledge Ross, but your suby isnt O2 monitored? Guess I figured all the EFIs in aviation went the O2 route....why wouldnt they? Seems like without it, one is missing the easiest of the feedbacks available.

I yield to being schooled in aviation fuel mgmt as I'm mostly a car guy just thinking Im getting close to first flight...with Bendix inj!
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MustangII (FoldingWing) "FirewallFwd&sundries": IO360B1E,RSA,C2YR-BF/F7666-2,Superior sump,James; 2xHXr,MiniX,EIS,480,327,240,SL30,Navworx; SteamAlt,AS,VSI
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  #15  
Old 08-09-2018, 10:07 AM
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Originally Posted by maniago View Post
Guess I figured all the EFIs in aviation went the O2 route....why wouldnt they?
Seems I recall that the lead in the fuel kills the O2 sensor rather quickly.
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Flying as of 12/4/2010

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Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #16  
Old 08-09-2018, 10:20 AM
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Quote:
Originally Posted by Mike S View Post
Seems I recall that the lead in the fuel kills the O2 sensor rather quickly.
Oh duh. I knew that......
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MustangII (FoldingWing) "FirewallFwd&sundries": IO360B1E,RSA,C2YR-BF/F7666-2,Superior sump,James; 2xHXr,MiniX,EIS,480,327,240,SL30,Navworx; SteamAlt,AS,VSI
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  #17  
Old 08-09-2018, 11:39 AM
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Quote:
Originally Posted by maniago View Post
Hmm. I submit to your expert knowledge Ross, but your suby isnt O2 monitored? Guess I figured all the EFIs in aviation went the O2 route....why wouldnt they? Seems like without it, one is missing the easiest of the feedbacks available.

I yield to being schooled in aviation fuel mgmt as I'm mostly a car guy just thinking Im getting close to first flight...with Bendix inj!
In aviation systems currently, we only monitor AFR for informational purposes to the pilot via the programmer in gauge mode, for data logging and auto mixture enrichment on some auto conversions to prevent meltdowns.

In our automotive systems, closed loop control is frequently used during cruise conditions to keep mixture near stoich automatically.

We'd love to be doing closed loop control with a wideband O2 sensor in our aviation offerings but don't feel it's reliable in the long term with leaded fuel as Mike pointed out. Hopefully Swift and Shell will change that soon with wider availability of unleaded avgas.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 424.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #18  
Old 08-21-2018, 12:59 PM
Norcalrv7 Norcalrv7 is offline
 
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I guess this thread is sort of drifting off topic a bit, But I would love to see more development towards closed loop in the aviation ECU's. it's benefits are numerous, but I also understand the reasons it might not be a good idea.

My O2 sensor has lived for 210 hours so far on a pretty constant diet of avgas. I would like to think that it will keep going for some time ( I haven't noticed any change to its responsiveness).
My fuel map also is tuned quite lean up to 65% power or so which probably helps keep it from fouling.

Given its precision and ease of use compared to EGT, I'd be more than willing to replace a relatively cheap O2 sensor every 100 hours if necessary.


Caleb
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Last edited by Norcalrv7 : 08-21-2018 at 01:04 PM.
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  #19  
Old 08-21-2018, 01:19 PM
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Quote:
Originally Posted by Norcalrv7 View Post
I guess this thread is sort of drifting off topic a bit, But I would love to see more development towards closed loop in the aviation ECU's. it's benefits are numerous, but I also understand the reasons it might not be a good idea.

My O2 sensor has lived for 210 hours so far on a pretty constant diet of avgas. I would like to think that it will keep going for some time ( I haven't noticed any change to its responsiveness).
My fuel map also is tuned quite lean up to 65% power or so which probably helps keep it from fouling.

Given its precision and ease of use compared to EGT, I'd be more than willing to replace a relatively cheap O2 sensor every 100 hours if necessary.


Caleb
Caleb, are you using a narrow or wide band sensor?

With W/Bs, we've seen some die in as little as 2 hours on 100LL. Conversely one long time user had over 350 on his and it was still working. All Bosch 4.9s.

We are not sure why the variation in lifespan and are talking to suppliers to see if some counterfeit ones may be leaking into the supply chain perhaps. If we can regularly get at least 150 reliably hours out of a WB, we'd implement closed loop control on aviation systems like we've offered on our automotive ones for a couple of decades now.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 424.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #20  
Old 08-21-2018, 02:36 PM
Canadian_JOY Canadian_JOY is offline
 
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Dumb question, full of "what if's"... Keep in mind I burn a fair bit of 91 octane premium mogas (zero ethanol).

For engines like our O-360 where a 4-into-1 Cessna-style muffled exhaust is installed (with the goal of harvesting maximum cabin heat), where would a WB O2 sensor be installed? It would seem the only logical location for a summative measurement would be in the final exhaust stack, downstream from the muffler, but this is a long way from the exhaust ports on the cylinders. Just wondering, simply because when my one magneto bites the dust I'll likely end up with an SDS system of some sort replacing it.
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