Carb O-320 LOP Analysis Graphs

Hello,

Alex Peterson and I have been taking data to see how best to lean my O-320. We have graphed the data the Dynon EMS is puking out and it is interesting. Note the #2 EGT has an offset issue - new probe will be installed.

Data taken at 7500 ft MSL.
- Run 1 WOT
- Run 2 WOT - 1" MP
- Run 3 WOT - 1" MP w Carb Heat

See Graphs - notice how the cracked Throttle Plate changes where the Cyls Peak (or don't). Our next step is to try WOT- 0.5"MP to see if the peaks act in any kind of linear manner and find a "happy place" where the peaks come together. If anyone has any insights - pass 'em along.

Pete:

You are inducing turbulence to increase vaporization. The application of partial carb heat works quite well to accomplish this. You might try leaving the throttle WOT and aplying carb heat to find the optimum temperature to increase vaporization. The optimum temperature will be using the least carb temperature that gets the lowest DIF number.

I do not knwo what it is in this engine, but once foud, it will work year round. In a C-182 it is 10dC. In a Twin Beech it is 0-2dC. Each application is different.

I'd like to know what it is in the O-320.

Walter

Thanks Walter

OK I'll leave the WOT and increase the carb heat. Do you think playing with the throttle plate position is worth the effort?

I'll post more data when I get time to fly

Numbers

Great data. Huge spread. With tuned injectors, my airflow performance equipped 320 egts peak within 0.1 gph. Scary to think what might be happening with the lean till rough then rich till smooth method on carb models.

Is this with x-over exhaust?

Yes X-over exhaust

The interesting thing is how cracking the throttle completely changes what cylinders peaked and if and where they peaked - leads you to believe there might be a "happy place" where they all might peak closely.

Kinda fun to take the data - Alex is great at the analysis and I am learning lots of new stuff - very fun

Hummm very interesting

pete nicely done. Data don't lie.

I could be wrong but this is why small 320's and 360's done run LOP very well, the spread in peak's v ff.

ACT I, what I see, normally WOT the fwd cylinder #1 an #2 run leaner than the back two, where the left one #4 is the most rich.

Act II, you close the butterfly a little and change the fuel distribution and almost reverse it front to back and lower the overall FF. (OK makes total sense since the butter fly angles fuel fwd and you have cut overall fuel.)

ACT III, carb heat has an overall leaning effect and seems to have balance the fwd cylinders left/right - #2/#1 peaks. I think this is partially random. I assume you have a Van's FAB. Unlike the carb heat airbox on a Cessna or Piper the flap or valve in not right under the throat of the carb, so carb heat has little effect other than lower MAP and increase air temp, which apparently reduces overall FF due to lower power (restricted airflow and lower density air). There is a technique C-182 guys do with the Carbed Continental that involves cracking the carb heat open to balance the peaks. I do not think this works as well or at all with our air box.

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Theory: Because ALL the fuel originates out the mouth of the carb and than into sump plenum and 4 runners. After that its kind of hit miss where the fuel goes, #1, #2, #3 or #4. Now each cylinder is asking "FEED ME". There may be differences in the cylinders them self or the runners to each cylinders. However a good start is have a balanced feed to the 4 runners.

If you can divert or direct the air flow into one of the four runners you can manipulate the air/fuel balance. You could cut and modify the sump but that has some down side and may be bad news, so what about the air box?

The air flow into the carb mouth can be manipulate with something in the air box. This should have down stream affect on the flow of air/fuel mixture in one of 4 corners of the sump plenum?

Clearly the carb butter fly does a great job with fwd and aft bias. Now we need left right balance that does not use carb heat, which is very inefficient on the RV FAB. (It gives overall loss of power.)

Solution: Some little shape like a vane or cone in the bottom center of the air box that you can manipulate. Once the shape or shapes of the flow divider'(s) and/or guide'(s) are determined they are fixed. Doing this creates different airflow into the mouth of the carb, which in theory changes the output of the carb, favoring or starving one or the another cylinder as needed. Call it an AIR FLOW TRIM VANE or GUIDE.

You could make it fixed and change it between flights to experiment with the shapes in side the air box that balances the flow. The final balance may be good while still WOT and no carb heat! Anything in the base of the air box to divert more or less air into one of those 4 corners may be key to "trimming the air flow".


Cons: The big down side is anything in the induction that can or could come apart and get into the engine is bad, that is why I did not like the magnetic alt air door van offered with the FAB360. (Now he changed to a manual cable operated valve which is better but I don't need or think is needed for VFR ops.)


Summary: I think this has some merit. Clearly the Cessna C-182 airbox carb heat valve does fuel balancing as claimed by those operators. It's a big "seesaw" valve right under the carb. May be a little valve seesaw cable operation valve in the bottom air box may be a solution but at greater complication.

Experiment: My first shape would be a cone that slopes up from the bottom of the air box near the edge of the air filter to the center of the carb. It would be symetric at first and 360 degrees around. Offsetting the center of the cone (left/right/fwd/aft) relative to the carbs center, would smooth and bias the air flow. The result would be to enrichen or lean one or more cylinder as needed.

(click pic below)

Thanks George

I give Alex credit for the analysis - I am still learning about leaning. If throttle plate and carb heat don't work - I like your idea for a "flow director"

We do have to make sure nothing gets sucked into the engine.......

Thank you

petehowell said:

I give Alex credit for the analysis - I am still learning about leaning. If throttle plate and carb heat don't work - I like your idea for a "flow director"

Click to expand...

Well thanks to you and Alex. This is just what I thought. When Walter "Lean of Peak" came on the scene he enlightened many of us about LOPs, good info, no argument, but many of us flying 4-cylinder Carb 320's and 360's. This is Lycs position, its not consistently possible with their 4 cylinder engines, so they don't recommend it. Also with out full instrumentation its hard to know whats going on with large spreads in peaks.

My contention was LOP is not practical for 4-cyl with carbs. Of course this lead to urination matches. Never did I say LOP does not work, only its not practical for many or most of us with Carbs. Walter and his cronies expertise is more with Continentals in Bonanzas than 320 Lycs in RV's.

However with that said some folks say they can get their O320/O360 RV LOP? One gent who said this has a single CHT/EGT gauge. That concerns me. If you are going to do LOP, carb or FI, I still feel you needed all cylinders monitored, but that's my opinion.

Thanks again to you and Alex for the data, it confirms what I thought, Carb-ed 320's and 360's can ( I say can) have poor fuel distribution. I also have a theory that it varies wildly from engine to engine. The sump castings for example are not all the same. Some I have found have a lip near the carb, others don't. Its like the casting flash on some cylinders fins that blocks airflow and causes high CHT. I know ECI or Superior (one of them) makes a big marketing show of how their sump has ridges. It would be interesting to repeat this on other Carbed engines. ANY TAKERS?

May be, just may be LOP operations with a Carb can be done with some simple mods and/or technique. Even the FI guys have to money with their injectors. May be a simple mod, like the air box or sump will improve distribution so much we can run LOP routinely.

O360 FI for contrast

Perhaps this should be a whole new thread, but here is some data on an Airflow Performance FI system:

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The first graph indicates that the injectors are balanced nicely, with #4 perhaps needing a slightly smaller orifice. They all peak within a .2 gph range, which is about 3% of total fuel flow. Also shown is how the IAS drops when moving LOP. All three graphs are of the same data, I've separated it to make it clearer.

The second graph demonstrates very clearly how CHT's climb towards a maximum in the range of 30F ROP (at these MAP and rpm settings, at least), but drop dramatically as one gets on the lean side of peak. I do not know if the offsets are due to calibration errors or cooling airflow differences from cylinder to cylinder.

Graph #3 is interesting in that it shows that maximum fuel economy is achieved around 60 to 70 F LOP or so. That is typically where I have run my engine, right at about 23 sq, 7.2 to 7.3 gph.

**carb heat has an overall leaning effect **

I think you meant to say that carb heat has a richening effect. Hotter air is less dense, same FF = richer mixture, right?


As for the LOP in carbed engines it all comes down to ONE issue. Vaporization. If the fuel can be fully vaporized before the induction runners split off after the carb, the F:A ratios will be very close and the engine will run very smoothly LOP. It's not about re-directing air, it's about getting the fuel fully vaporized--FULLY--before it splits off to go into the runners. Remember the carb does not vaporize the fuel, it atomizes it. These various-sized liquid droplets of fuel are going different directions and the cylinders that get the big droplets are richer than the ones that get the little droplets. That's why the F:A ratios are so poor in most carbed engines.

Cracking the throttle plate induces turbulence which improves VAPORIZATION, not a change in where the air goes. Adding carb heat improves vaporization. That's what it all about. If you can do it with carb heat only, you get to keep WOT. Once you find the optimum carb temp to accomplish that, it works year round. Each installation can be a bit different on that.

Walter Atkinson
Advanced Pilot Seminars

yes and no

Walter Atkinson said:

Cracking the throttle plate induces turbulence which improves VAPORIZATION, not a change in where the air goes. Adding carb heat improves vaporization. That's what it all about. If you can do it with carb heat only, you get to keep WOT. Once you find the optimum carb temp to accomplish that, it works year round. Each installation can be a bit different on that. Walter Atkinson, Advanced Pilot Seminars

Click to expand...

You make two points, about vaporization, turbulence and heat. In theory there may be merit, but in this case the data does not show that and respectfully disagree on both points.

Carb Heat?
Walter, we run VERY hot carb temps, too hot to touch the carb. We have exhaust pipes that actually wrap around the carb with in a few inches.

I understand your heat and vaporization theory, but the CARB HEAT ON RV'S IS ANEMIC. Walter, you don't understand RV's do NOT really have carb heat, it's alternate air from inside the cowl. The temp rise is nil, negligible, small, insignificant compared to the temp of the carburetor (which cooks) and hot oil sump. This is not a cold induction of a Continantal. The cowl on RV's is tight. The cowl on a Bonanza is like a living room compared to a kitchen pantry. The induction on a TCM is like the north poll compared to the Lyc induction, hot like the arabian desert mid day summer time.

You are right carb heat makes it richer, thanks for the correction, but I was referencing to relearning after carb heat is applied; you will have lower FF at peak or less power. The only conclusion I can make from the data is that carb head had some effect, but it was small. You say the heat made better vaporization? It could be, but I'll stand by my theory and the data. It makes little difference in a RV installation, and probably is more aligned with your turbulence theory, causing random changes in air flow into engine. All it did was drop the #3 egt peak FF. Other wise the other cylinders are basically the same.


Turbulence?
I don't agree with the turbulence theory either, unless you could prove it. Clearly with partial throttle, the MS carb throttle plate (butterfly), shifts the fuel towards the forward cylinders. It literally aims fuel forward in the plenum towards the fwd runners. Its pretty obvious from the data.


Again small Lyc does NOT equal big Continental. They work differently.


This is why RV'ers with 4-cyl Lycs with carbs will always have a hard time getting LOP. HOWEVER! with partial throttle we can balance front to back just a little better for better leaning, even if we're still run ROP for smooth ops. Carb heat? Not recommended in my opinion. It's unfiltered and causes less power. If you want to save fuel pull the throttle back. We do NOT need any more heat in a Lyc powered RV. Our Carb temps are HOT all the time, unless under extream conditions (low ambient temp and low power).

Cheers

Good points about the RV carb and cowl. Thanks. One must take those issues into account.

It should be remembered that the AIR FLOW is the same to all cylinders... depending on their volumetric effciency, they SUCK the air in. It's the fuel mix IN that airflow that matters.

Walter

George - on my RV-6, with standard Vans cowl and carbed O-320, the carb heat is in fact, filtered, as the carb heat is sourced from the cross-over exhaust and runs into the top of the airbox prior to the K&N filter. Just a small point. And I agree that the Lycomings don't seem to need carb heat, probably because of all the heat that is picked up by the air/fuel mix passing thru the hot sump and induction pipes located next to the exhaust pipes. I used exhaust insulation wrap on my induction pipes to try and minimise the heat being picked up. I imagine a cold air induction system would work well.

Cheers

Martin

doha!

Harvey said:

George - on my RV-6, with standard Vans cowl and carbed O-320, the carb heat is in fact, filtered, as the carb heat is sourced from the cross-over exhaust and runs into the top of the airbox prior to the K&N filter. Cheers,Martin

Click to expand...

Of course I lost my mind (again), yes its all filtered, you are right, thanks for the correction. I was thinking of traditional (factory planes) carb heat that by-pass the fiilter. merci, danke, gracias.

Walter Atkinson said:

Good points about the RV carb and cowl. Thanks. One must take those issues into account.

It should be remembered that the AIR FLOW is the same to all cylinders... depending on their volumetric effciency, they SUCK the air in. It's the fuel mix IN that airflow that matters.

Walter

Click to expand...

I can pretty much guarantee that airflow is not the same to each cylinder with the carb and manifold bolted on. Dynamic effects due to charge inertia, butterfly angle, flow reversion on valve closing and acoustic/ pressure effects from the adjacent cylinders all conspire to change the mixture distribution and mass flow to each cylinder on carbureted engines. Studies on pulsed, wet flow benches prove this. Technically air is not sucked into cylinders, it is pushed in by the pressure differential between manifold pressure and the intake cylinder pressure. Air always flows from high pressure to low pressure.

Very interesting

rv6ejguy said:

I can pretty much guarantee that airflow is not the same to each cylinder with the carb and manifold bolted on. Dynamic effects due to charge inertia, butterfly angle, flow reversion on valve closing and acoustic/ pressure effects from the adjacent cylinders all conspire to change the mixture distribution and mass flow to each cylinder on carbureted engines. Studies on pulsed, wet flow benches prove this. Technically air is not sucked into cylinders, it is pushed in by the pressure differential between manifold pressure and the intake cylinder pressure. Air always flows from high pressure to low pressure.

Click to expand...

Very interesting insight.

Q: What can we do to balance a Carb-ed Lyc's better?

I recall some of those words and concept you used. I forgot that flow in the induction does pulse and reverse. I did not know that before but it makes sense. The valves open and close. It's not a continuous flow engine like a jet turbine.

The Cafe Foundation found exhaust pipe changes, changed induction flow, like the way 4-into-1 exhaust affect the scavenging in the intake, taking advantage of the pulse and inertia.

As you say adjacent cylinders all conspire together. It's all one big air pump with inter-connected tubes, plenums, via valves and cylinders.

I guess the Lycoming does not have perfectly tuned length intake tubes. The sump is not bad but far from perfect and there may be manufacturing variations. On some sumps, there is a lip near the carb flange. As far as I know there is not reason for the lip and is just left over from the casting.

Any (simple) idea on ways to "trim or balance" would be great.

This is intriguing

I am learning a lot just reading this post, lots of good info and I know nothing about it really.

But is seems if you want to disturb or redistribute the air flow, why couldn't you put a small windmill like ball bearing fan at the bottom of the carb where the intake is. Seems like air flowing thru it would make it turn and "swirl" the air. Kind of like how the fan on a turbo works.

hecilopter said:

But is seems if you want to disturb or redistribute the air flow, why couldn't you put a small windmill like ball bearing fan at the bottom of the carb where the intake is. Seems like air flowing thru it would make it turn and "swirl" the air. Kind of like how the fan on a turbo works.

Click to expand...

Seems I remember something like this many years ago--a small "windmill" that mounted between the carb and manifold on cars to better vaporize fuel. Fell into the same catagory as pyramid shaped storage boxes that kept your razor sharp. Probably was injested into more than one engine before it was taken off the shelves. There ought to be something better, though. I have heard about something called "fuel injection" that I will look into when I am once again on the positive side of "broke."

Seriously, great thread and I am learning a lot from it.

Bob Kelly

More data

Guys if the WX clears and work lets up - I'll get more data - with carb heat and throttle position, something might work.

Just to keep things interesting - I'll throw the Ellison TBI out there. The guys that get them to work love em and say they will run smooth till they quit (almost) .

Air balance

One measure of the "imbalance" of airflow (not fuel flow) is the relative volume of fuel fed to each cyl. in a fuel injected model. In my case, on a IO-320 with Airflow Performance, it took a five percent adjustment in injector orifice diameter on two cyls to cause all cyls to peak EGT at the same total fuel flow. I think this suggests that the "airflow" blance is also within five percent on this particular set up. This with x-over exhaust which introduces imbalance to the overall system by better scavenging the cyls with "long" pipes. This is a B2A with the stock bottom fed sump that started life with a carb.

Based on the curves presented early in this thread, the fuel distribution varies far more than 5 percent between cyls in a carb model. Fuel distribution on a carb model seems therefore to be a much bigger issue than "air distribution". That's where I would focus my retrofit efforts if trying to get better balance in a carb model.

Smaller droplets, some sort of baffling in the manifold to redistribute fuel after it eminates from the fuel horn, more distance between the carb and the runners or more volume in the "shared area" come to mind. Or maybe the Acme Miracle Vortex Cyclone Vaporizer device.

hecilopter said:

But is seems if you want to disturb or redistribute the air flow, why couldn't you put a small windmill like ball bearing fan at the bottom of the carb where the intake is. Seems like air flowing thru it would make it turn and "swirl" the air. Kind of like how the fan on a turbo works.

Click to expand...

www.hicloneqld.com/
and
http://www.fuelsaver.com.au/hiclone.php

Fin
9A

Research.....

I might buy a copy

Accession Number : ADA139475

Title : The Influence of Mixture Distribution on Emissions from an Aircraft Piston Engine.

Descriptive Note : Final rept. Jun 74-May 78,

Corporate Author : MICHIGAN UNIV ANN ARBOR DEPT OF AEROSPACE ENGINEERING

Personal Author(s) : Mirsky,W. ; Nicholls,J. A.

Report Date : OCT 1980

Pagination or Media Count : 83

Abstract : Cylinder-to-cylinder mixture ratio distributions were measured for both the injected and carbureted versions of the AVCO-Lycoming 0-320 engine to determine the effects of non-uniform distribution on the exhaust emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen. Data for both normal and lean-out conditions were obtained. An experimental Turbulent Flow Manifold for the carbureted engine was tested as a potential means for improved cylinder-to-cylinder distribution. Results showed improvements for the low power operating modes but deterioration for the high power modes. An analysis based on test results predicts that the EPA emission requirements can be met, for this engine, by improving mixture distribution and leaning both the taxi-out and approach modes. Improvements in fuel economy are also predicted. (Author)

Descriptors : *Aviation fuels, *Piston engines, *Emission control, *Exhaust gases, Fuel air ratio, Variations, Mixtures, Distribution, Nonuniform, Nitrogen oxides, Turbulent flow, Manifolds(Engines), Hydrocarbons, Carbon monoxide, Aircraft carburetors, Taxiing, Approach, Civil aviation, Data acquisition, Air pollution, Standards

Subject Categories : COMMERCIAL AND GENERAL AVIATION
FUELS
RECIPROCATING AND ROTATING ENGINES
AIR POLLUTION AND CONTROL

Distribution Statement : APPROVED FOR PUBLIC RELEASE

Interesting

That could be very interesting!

No need to buy it!

http://deepblue.lib.umich.edu/bitstream/2027.42/6650/5/bad5594.0001.001.pdf


Gotta love the web! I say it for the first time in my life....

Hail to the Victors!

Me Like-ee free! thanks

petehowell said:

http://deepblue.lib.umich.edu/bitstream/2027.42/6650/5/bad5594.0001.001.pdf

Gotta love the web! I say it for the first time in my life....

Hail to the Victors!

Click to expand...

Thanks Pete. I read through it quick and I guess the bottom line is we know that the fuel distribution is poor. The disappointing thing was their experimental turbulent manifold was not very good at higher power, which is pretty much where you want it to be optimized. Too bad they did not try other configurations.

Never the less cool report, awesome test facility. It also shows manifold changes can have effect. Of course cams, exhaust go into the mix as well. I did not see a lot of detail about the exhaust in the report. It seems like there is more work that could be done, however I guess that is where fuel injection comes in. Still for us "OH" operators, running carbs it would be cool to add something to easily adjust fuel-air mixture balance.

P.S: Like Fin said, what about those marvelous mystery mpg adders for cars, under names like Turbonator / Tornado / Spiralmax / Vortec Cyclone, Here is one of those AS Seen ON TV fuel boosters.

http://www.turbonator.com/index.html?id=adWordsTurbonator

(Makes me laugh because my dear Father was a sucker for any of those miracle add on goodies, he bought every one of them. )

That is assuming no occult transfer of fuel in the induction plumbing from one cylinder to the next. We know that that is not the case.

New Data

I was able to get more data today and I think that I might have an answer. By running full carb heat and using the cracked throttle to balance the mixture between the front and the back cylinders, I was able to get the mixture pretty well balanced. The engine ran well down to 5.9GPH. IAS at 6.1 GPH = ~160mph it dropped off to 155mph at 5.9GPH. All testing @ 7500ft with ECI O-320- CS prop - carb. My OAT is way off due to the heater - need to move the probe. Carb temp was 113 degF on this run.

Here are the graphs:



Here is a picture of the Dynon EMS - It pukes data right in to my laptop. The LEAN MODE shows degF LOP.



Finally Dynon showing 30.6 mpg!:

Cool data

Thanks Pete. That is cool.

So you got it to run down to 6.1 or 5.9 gal / hr with smooth ops. Cool, There is hope.

Looking at the chart, I had a hard time with the scale (non-linear?), but at 5.9 gal/hr it looks like you got almost 70F LOP! awesome I don't know if I am reading it right but that's what I got. Is that right. #4 looks like 25-30F LOP?

At 6.1 gal/hr was about 50F LOP.

The fuel savings is at least 0.7 gal/hr better than PEAK EGT (0.9 gal/hr at 70F LOP). Not too shabby. Assuming you have 2.5 hr in cruise, that's a saving of almost 20 min endurance or 50 miles range. Of course that is at least $3.00 per hour savings. That's enough to buy lunch.

I guess I'll have to eat my words, the carb heat looks like it worked or helped better than I thought. I'm not sure about the down side. I am not fond of the idea of running hotter induction air, but +0.7 gal/hr is not too shabby.

Wounder what you can do to trim #4 better. Thanks for the data, Cheers

Pete et al,
Here is your data put into a more standard way of looking at it, and it looks very nice. #4 is running a slight amount more rich than the others at that particular setting.

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edited by AP - fuel flow numbers cropped before