K

kiwipete

Well Known Member
Yesterday I thought I'd see how well balanced my engine was.
RV7
Superior XP-IO-360 with forward induction

OAT 39F
Manifold pressure 23'
Rpm 2300
Alt 1200 ft
ASI 145

Results according to the dynon EMS

Cylinder 1st to peak:

3) 7.375 Gal/Hr 1508 EGT
1) 7.25 1457
4) 7.1875 1454
20 7.1875 1454

Then I progessively reduced the fuel flow over the next min until I got down to 6.125 gal/hr. At this point it started to run rough. At the same time the EGT's (all 4) started to increase. They had dropped about 30 degrees from peak.
As soon as I noticed the increase in EGT's I pushed the mixture in to richen it.

Over this time all 4 CHT's steady decreased even as the EGT's started to increase.

Any thoughts on why the EGT's would start to increase when the engine started to run rough?
Number 3 EGT has always indicated greater then the others and I might try to swap it around to see if it's the probe.

Peter
 
As your LOP went to extreme lean the burn was taking place at a different place in the chamber / exhaust pipe, hence the rough running engine.

Running LOP at 1,200 MSL and 23 squared? Try getting up to 5-6K MSL and 75% power.

Placement of the probes can throw the actual readings off by quite a bit. I would not worry about the reading.

It is not the temperature reading you have on your EGT's it's when they peak. Have you balanced your injectors? Do they all peak at the same time / fuel flow? There is a simple procedure to perform to see if your injection system is balanced and ready to run LOP. If a cylinder is peaking before or after the rest then you need to change the injector nozzle. Contact Don @ Airflow Performance.

http://www.airflowperformance.com/
 
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Short hop

Larry

I was just seeing what it would do when leaning on a short flight back from where I do my maintenance. Thats why I was at 1200 ft, Also to keep under the control zones. Normally I criuse at around 8000' 23 square and 8 gal/hr giving 147 knots IAS

I'm just starting to see what it will do leaning wise now that my engine has more than 50 hours on it. So I was interested in how closely they all peaked.

1st peaked at 7.35 gal/hr last at 7.1875 so there pretty close to start with.

Just seeing the EGT's start increasing again was what took me by surprise.

Peter
 
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LOP

I watch my EGT numbers like a hawk and often run out 100 LOP and have never seen a reversal, I.E. a climb in egts with or without engine roughness. Your results are interesting, particularly at just 30 LOP.
 
I would be very careful experimenting with LOP at low altitude and would not spend "minutes" pulling back from peak. You really need to get from slightly ROP to LOP quickly.
 
A 0.2 gph difference is excellent from my reading on the subject of LOP per Avweb/Deacon. 23 inches at 1200 msl may be way too much power for lop operation however, not sure so check power charts.

As for the egt rising with rough running; I'd guess that combustion was so slow at extreme lop that combustion was continuing into the exhaust phase and thus resulting in higher temp at the egt probe in the exhaust header.

Getting down to 6.1 gph after last peak at 7.2 is pretty darn good.

For real test you'll have to verify running 65% and do it again at proper cruise alt. Don't know if the spread will be greater at altitude but it looks very promising from this test.

I would expect more than a 30 degree drop however so curious what will happen at cruise alt and 65%
 
EGT's reverse trend below LOP

"At the same time the EGT's (all 4) started to increase. They had dropped about 30 degrees from peak.
As soon as I noticed the increase in EGT's I pushed the mixture in to richen it.

Over this time all 4 CHT's steady decreased even as the EGT's started to increase.

Any thoughts on why the EGT's would start to increase when the engine started to run rough?
Number 3 EGT has always indicated greater then the others and I might try to swap it around to see if it's the probe."

_____________________________________

Peter,

What you noticed is not that uncommon. As the mixture becomes progressively leaner, it is harder and harder to ignite. Also, as the mixture gets very lean, the flame front, or speed it burns, slows. This phenomena is why electronic ignition helps if running L.O.P., because it has a hotter and longer duration of spark to ignite the stubborn lean mixture, as well as built in advance to give the lean mixture longer time to burn. The reason the E.G.T.'s reverse at some point, is because the mixture becomes so hard to burn and also slow burning, that the exhaust valve is starting to open before the burn is complete. This shows up as more heat in the exhaust, because you have actual burning after the valve opens. At this point, you have gone slightly too far in leaning, and only need to richen back the mixture slightly. This is NOT a sign of detonation, or pre-ignition. Even if you don't enrichen, the C.H.T.'s will still be less with the E.G.T.'s climbing, because the power is not contained in the cylinder, but is rather going out the exhaust. Don't be concerned with this phenomena at all, it is very normal from the very lean mixture just burning so slow it can't complete its burn before the exhaust valve opens....

Jim Baker
RV-6
N699JB
 
same thing happened to me

Jim,
great response. I experienced the same phenomenon while leaning lop with our IO-360. my injectors are not as well balanced, though and I only saw it on one cyl. It has had me baffled since (until now). Thanks
 
Jim

Thanks for the info.

I hope to fly later in the week on a long x-country so will try leaning it at 8000' or so and see what the results up higher are like. I was pleased that the peak's seemed quite close, considering this engine is as per assembled by the UK superior rep Jadeair.


Cheers

Peter
 
LOP

I HAVE A IO-360 ANGLE VALVE RV-6. I RUN 50-80dgr. LOP AT 7500'. 22"-2200RPM. CHT's, OIL TEMP. ALL DECREASE 20-30dgr. I WILL RUN ABOUT 165kt. ON 7.4-8.0gph. THIS IS A LOSS OF ABOUT 7kt.
DON AT AIRFLOW HAS BEEN VERY HELPFUL IN BALANCING THE INJECTORS.
DENNIS McCRIGHT RV6,RV8,RV4. 9364433562
 
Higher Alt

Well I managed nearly 5 hours flying on sat and played around while in the cruise.

This time I was at between 7500 and 8500,

22' 2300

With the Dynon set to lean mode I have a spread of .2 gal/hr between the first (#3) and last (#1)

Once lean of peak I kept slowly reducing the fuel flow but still can't seem to get much over 30 lean of peak before #3 starts to go up again and it starts to feel rough with a noticeable power loss.

I'm wondering if my plug gap could effect it. At my annual I set the gaps to .16 thinking that they'll open up over the next 100 hours. Maybe my spark is too weak at these lean settings??
I checked the timing and the slick mags are both at 25 before TDC.

The engine seems happy at 30 LOP on #3 and the others cylinders are LOP around 20. I notice a little drop on speed approx 5 knots with fuel flow around 7 1/2 gal/hr

Peter
 
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My data is similar

Peter,

I noticed with your last post that you are running mags. LOP is somewhat limited by 25 degree advance, especially in the lower MAP settings. Additionally, the plug gaps needed by mags of .016" to ~.022" range doesn't help either.

My engine is similarly balanced from an injector point of view, and when I was running the Lasar system, I could turn off the EI and run off mags only. It was difficult to get more than just a little LOP before I had the same problem. You can see the data summary here. Look at the green line in the second chart. It shows the exact same upturn around 20C LOP that you are experiencing. It is a summary line, I could dig up the raw data if you wish.

I've since added the section called "Article on Mixture and CHT Management" to the site, and you can see from that the large difference in LOP capability that the larger gap and Lightspeed EI systems gave my plane.
 
Interesting reading

Alex

Thanks for reference's. Very informative.

I think from reading on Gami's site that .2 gal spread is not worth messing around with.
Maybe in the future I might look at replacing the mag's with electronic ignition.

thanks

Peter
 
Hey Alex,

I really enjoyed/appreciated the article and information that you've gathered and posted on your web-site. Some very nice work on your part. I will start phase I testing on my RV-8 after its inspection on Tuesday. I've got a superior XP-IO-360 (silver hawk FI) and Light Speed plasma II+ in place of the right mag. I was curious about your switch from the LASAR system to the Light Speed set up. What drove you to that change, and have you seen any reportable difference in performance?

Thanks, Mark
 
Thanks Mark and Peter for the kind words.

I removed the Lasar due to several in flight failures. I would guess a search for my name and Lasar on these forums will dredge the postings up.

Regarding performance change from Lasar to dual Lightspeed systems, no noticeable change in my typical LOP cruise. Where I did notice the difference is in runup roughness - I think I always had at least one plug crudded up (and yes, I taxi with max leaning). Also, the engine is definitely smoother in cruise now than it was. It can be leaned much further, although this is not of practical significance since I run somewhere in the 50 LOP range, a point at which the LS performs identically to the Lasar. Overall the system is a few pounds lighter also than the Lasar.
 
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