1967brutus

simple one-liner question, but the answer will take a few more

To me (this is something I strictly theoretically deduced) the keyword is "apparently"...

Way I see it, and knowing what I know about combustion processes under various conditions, the following is most likely to be what is actually to happening:
In a gasser, the apparent edge of "optimal", smack in the middle of "too fat to run properly" and "too lean to ignite" (which is where we all want to run our engines, because that is where they make the most power), is in the ratio of air/fuelVAPOUR. The liquid fuel does not take part in the ignitability of the mixture. Liquids do not burn, only their vapours. So the better the evaporation, the leaner the absolute ratio can be while maintaining optimal ignitability. The poorer evaporation, the richer the absolute ratio has to be in order to maintain that ignitability.
If you ever wondered why old cars had a choke (whether auto or manual) and apparently needed a richer mixture for a cold start, now you know...

The spraybar itself, without the solenoid, does a poor job in atomizing the fuel, so not all fuel evaporates. That means you need to increase the total amount of fuel in order to achieve the correct, ignitable air/vapour ratio.

But once that ignition is achieved, and the charge is burning, the heat will instantly evaporate the liquid fuel, which has the effect of adding fuel to the fire but not oxygen. And when that happens, the burn gets rich and sooty.
What is worse, is that this remaining liquid fuel is still mixed with oil, and logic says that those tiny droplets consist of a fairly "fat" mix, because the oil does not normally evaporate.
So let's assume, we have a 10:1 fuel oil mix, and 90% of the fuel evaporates on its way to the combustion chamber. That means that basically the remaining liquid fuel is a 1:1 fuel/oil mix.
That causes the droplets of this fat mix to "explode" and burn on the surface, causing that dispersed oil to overheat and decompose (and maybe a bit of it burns, who knows?)
Lots of soot is formed in this rich burn, and the soot is formed IN a cloud of dispersed, burning and decomposing oil, so that oil residue will be black and tar-like, because its detergent properties will cause it to absorb the soot. The burn having excess fuel means there are combustibles in the exhaust gas, so there is some afterburning going on in the muffler as well (I have noticed that the solenoid also lowers the muffler temperature. Indicators are significantly reduced deterioration of the sacrificial pieces of silicone tubing for muffler pressure, and for example fingerprints do not burn into the surface anymore. Heck, I have even seen the presence of liquid water IN the muffler of a running engine, witnessed by a drop of grey emulsion coming out of the tailpipe )

Now we introduce the solenoid, and what that solenoid does, is it interrupts the fuel flow 25~30 times per second. The engine by and large requires the same amount of fuel, because the difference in consumption between pre and post solenoid really is not that large, from what I have seen about 10% or less (the only plane I actually did "test" this with, was the 5 cc fourstroke: it managed 65 minutes on 6 oz pre-solenoid, and a touch over 70 post).
But this means, that this "roughly the same fuel flow" has to not only happen in less time (meaning a greater velocity at the spraybar exit) it also is "chopped" which also promotes evaporation.

I have actually visually seen this effect when I did the first tests (a veco 19 running glow fuel and the solenoid) about 8 or 9 years ago.
Back then my at the time availlable camera did not allow me to record it on video, but what I saw:
The perry carb, as most of us know, does not really have a spraybar across the venturi, but rather a tiny nozzle that only protrudes something like 0,02~0,03" into the intake.
Looking straight into the intake of the Perry carb, running on the needle there was a jet of fuel visible that frayed a bit at the edges, but reached all the way to the other side of the intake bore where liquid fuel would splash against the wall.
When running on the solenoid, there was no jet of fuel visible, but a "misty area" in the vincinity of the fuel nozzle, and reached only roughly about halfway of the intake. In other words, a finer mist and a better mixing with the air inflow.

Back then, I did not bother myself with fuel consumption and such, as gasoline and spark were not yet even on the horizon for planes, heck, I was not yet even occupying myself with fixed wing period! So those observations are just what they are and back then I noticed the difference but never tied a conclusion to it, as the entire reason for testing this device was to get a glow carb for planes, to behave properly in a helicopter, running methanol and spark. I never actually finished that project by the way, marriage and life got in the way, but that is another story.

Getting back to the issue at hand: this greatly enhanced atomisation and thus evaporation of fuel, leads to a "fresh charge" that has the correct air/vapour ratio to ignite, and contains basically only an oil mist, without (or barely any) liquid fuel present before ignition. This means that when the charge ignites, basically not much happens to the dispersed oil, because there is no burning going on at the surface of the droplets. Thus the burn does not "richen up" after ignition (no soot) and the oil does not or barely deteriorate from the burn, and precipitates on the relatively "stonecold" (relative to the burn temperature) cylinder wall in basically the same conition it was when it was still in the bottle it was bought in. Oil does that, same like moisture from air condenses on cold beerbottles.

I have seen it in all engines where the solenoid was introduced, that the exhaust residue cleared up considerably. Not all the same, not every engine became "spotless" and I also cannot really put a finger on WHY some engines ran cleaner than others (I have for example three identical ASP FS52, they even run the same or equivalent props, 2 ran near spotless, one still produces a bit of dark exhaust residue, but even the two that run clean, do not run identically clean).

Whether the above is true, heck, I do not have X-ray vision, no engine with an observation port, or the possiblility to shoot a combustion process at a gazillion frames per second and stretch the event to a 5 minute affair to closely study, but the explanation is at least consistent with what is I know about combustion processes and combustion technology in general.

1967brutus

Chris, if you would want to know more about this,, I'd say, try and look straight into the intake of one of your home-made carbs, and observe, if possible, the fuel outflow of that 3D printer nozzle.
Then de-energize the solenoid and temporary install a remote NVA in the fuel line, start it and adjust it to run "as lean as possible" on the NVA, and look again.

There should be a distinct visual difference in how the fuel leaves the nozzle. That will help you understand how this effect works.
I am pretty sure you will also, given a bit of time, notice your exhaust residue turn black and cruddy.

And if you have the equipment to catch it on video or photo, that would be a great learning tool for us all.

Cat 1

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Great suggestion Bert - When I get chance I will try this out. The nozzle pattern is quite easy to see with the EFI carbs as its out in the open.

Your explanation makes perfect sense.

1967brutus

Since the engine can run leaner with the Solenoid than is possible with only a NVA, it should be possile to tune to "perfect" on the NVA, and then activate the solenoid at somewhere in the neighbourhood of 90% duty cycle or so, and the engine should basically remain running exactly as well as it did on the NVA alone, because the improved evaporation should cancle out the reduced fuel supply. The difference in the nozzle pattern should be visible as if flipping a switch, and in 2-strokes the exhaust should go from a blue hue to clear and invisible likewise. A simple unplugging/plugging in of the solenoid driver, with the throttle af full and the fuel curve set at the proper value allready should do the trick...

Those are interesting things to observe and greatly help to understand how things work.
Everyody benefits by better understanding, and who knows what possible bright epiphanies result from it. I mean, Dave came up with the atmospheric correction, you came up with the EFI carb, who knows what the next reader will bring in?

1967brutus

In fact, back then this meant very little to me, but this is the very first "proof of concept" test to determine that a bi-state valve with modulating dutycycle could actually be used to proportionally control a fluid flow, and here the effect is allready "somewhat visible": It can be seen that as soon as the solenoid goes silent in the full open position, immediately the flow smoothes out and the liquid surface in the cup calms down.


In hindsight, I am pretty convinced that had I done this test outdoors in moderate windy conditions, the 100% open valve would still allow me to aim the stream from some height into the bucket, but the modulating valve combined with the wind would have made a big mess with droplets all over the place

As said, back then it meant little to me, and althoug I absolutely DID observe the nozzle pattern change in the running Veoc's intake, since it was glow, and I was not even busy with gasoline conversions back then, I never made the connection to "better evaporation".
In fact, the solenoid was put aside about 2 years before the first fixed wing gasser conversion, and it took me another two years of messing about with modifying carburettors, before I remembered I still had that Stihl thingy somewhere.
It was only then, and not even immediately but after several weeks of running the solenoid in an actual plane, that I started noticing those differences and had to figure out a way to explain them. Initially, I was fairly baffled to be honest, because I would never have guessed that stock spraybars would be so bad at atomising and evaporating fuel. After all, the average glow engine has an intake-air velocity of somewhere in the order of magnitude of 60 to 100 mph (displacement x RPM / throat cross section).

Very fascinating stuff, this...

Glowgeek

Indeed!

Cat 1

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The "Oscillation" is readily visible in your video Bert.. the break in flow is definitely interrupting the Laminar flow tendency of the non pulsed stream - only makes sense that this should assist in better atomization / evaporation.

Your suggestion of a test method would be easy to set up and try.

Indeed - Very interesting!!

1967brutus

Meanwhile, in Indonesia:

After 3 years of storage under tropical conditions without any form of conservation (I defuelled the plane and stored in its wooden box, the box was clean 3 years ago but now has some fairly big mould stains inside) I reactivated my holiday plane today.
I had to replace both Ailleron servos (they were extremely cheap chinese 12 gram servos that probably suffered internal corrosion and did not work properly anymore), and minor issues with rust here and there.

The engine (still with the uncompensated "curve only" solenoid driver of the first generation) immediately showed signs of life, but needed quite a bit of motivation to keep running. Probably a bit of dried oil or other residue here and there. After about 15 minutes of runtime and opening and closing the main needle a few times in order to flush through that residue, it steadied up.

Left it to cool down completely, and a simple prime (identical to the video titled "start procedure" on my YT channel: At WOT one flip with a finger on the carb, then three flips to distribute the fuel), was enough to achieve a consistent single-flip start.
Still running smokeless and with barely any oil from the muffler. Indonesian gasoline is pretty "stinky" compared to Europe's counterpart, and my daughter, standing behind the plane, was very surprised that she barely smelled anything (She saw how much oil I added to the fuel when I mixed it and is familiar with smelly two-strokes ).
The solenoid seems to have survived the 3 years of storage also without problems.


I hope to get her in the air Saturday and Sunday.

Glowgeek

It's alive!......ALIIIIIVE! Lol

Good to see.

1967brutus

Believe it or not, but that is EXACTLY what went thorugh my head this afternoon. Including the intonation...

Because I was as curious as anyone, after seeing the corrosion here and there, like on the bolts holding the LG... That corrosion was strictly from humidity in the air, so I had no idea how the solenoid, and the carb internals would have held up. The engine initially firing meant nothing, but when it basically kept running after a few 5 second barks... that was what went through my mind: It's ALIVE!

I still LOVE those ASP/Magnum 52's, they are excellent little low budget workhorses.

hmeijdam

Good to know that the solenoid driver did not corrode away......yet.
Probably won't hurt to peek under the shrinking tube to see if there is not all sorts of corrosion going on at the solder joints.
I never realized you would take it to a tropical storage :-)
Hans

1967brutus

To be honest.... it never crossed my mind that that could corrode also... The other electronics (receiver, main servos, BEC) seem not to be affected, and I also never really heard anyone here about that being an issue. I was fairly surprised that the ailleron servos gave out. I expected them to fail due to being cheap, not due to being corroded, but both servo's (same type) failed in idential manner, hence the conclusion. The servo extension leads seem to be a bit affected as well, probably good for now but I will replace them next year.

I have no way of re-shrinking the driver, so I won't open it, but it is good that you pointed me to it: Next year I'll bring a driver, shrink tubing and some laquer.

But humidity is at times extremely high here, and I have flown a few times when I ended the flight due to rain threatening to start (Noticable by the plane passing through the lower cloud-base), so it is very possible that the ailleron servo's were exposed to water mist and that did them in. After all, the corrosion on the bolts and such was also mainly external. The leg of the tail wheel was even pretty heavily corroded.
IF the old driver turns out to be corroded, I'll replace it, but if it still works, I'll cut off the shrink tube, coat the electronics, and reshrink it.

hmeijdam

Luckily I used leaded solder wire, so that has a lower chance to suffer from "solder whiskers" than leadfree solder tin. Those tin whiskers have even plagued NASA disabling a satellite.

Cat 1

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Can't Wait to hear of a flight report Bert.. Im going to fly vicariously with you as is turned nasty cold here again.

We had an atypical January with some very warm temps (relatively for us) but the bottom has fallen out again - Would trade a little corrosion for the super dry cold we have here.

Glowgeek

We're not as cold as you are Chris but we have had very bad weather. Last week we got snowed in with 13" of the wettest snow I've ever seen. Broke trees all over the place so we lost power for 3 days. Then it warmed up for 3 days, melted everything and turned the place into a muddy mess. Then early this week we had sleet and freezing rain for 3 days. It's been 24°f or colder every day since, so nothing has melted. The ground and roads are sheated with 1-1/2" of solid ice. 10 minutes ago I slipped and busted my ass trying to load firewood into the outdoor furnace. Lol

Cat 1

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Lonnie - That sounds like terrible weather.. It got warm here and got a bit sloppy and refroze but nothing like the crap you are getting.

As a "Canuck" the best winter days a crystal clear sunny and mild (-15 to -20C) and zero wind. They are wonderful and we get them quite often. We get grumpy if it warms up and melts because it causes the mess your seeing.

Careful with the slips - Bad ones can hurt... I have a close friend who moved here from Germany a few years ago - Its hilarious to watch him walk on ice . I guess not many German kids grew up with Skates on their feet for half of their childhoods.

Glowgeek

Here's what we're dealing with at present. My F250 Super Duty won't break through it. Lol

Melted and refrozen sleet

Raleighcopter

I feel you. It's positively miserable here at 43°F with light rain all day. I had to put shoes on to get the mail.

1967brutus

I feel for you guys... Over here the home only has AC in the main bedroom so poor me is forced to either stay in my bedroom or leave the door to the living room open in order to allow some of that conditioned air into the livingroom... Oh, the horror...

Cat 1

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Lonnie - That looks absolutely Ugly... Glad we don't get that kind of stuff here..

NO shoes and AC man..... Very funny .. although 43 and damp doesn't sound like much fun.. would like to have to crank the AC on though.

Raleighcopter

i grew up in florida. when it got down into the 50s it was miserable; high humidity and those temperatures don't mix well. also, as a floridian, i didn't own any winter gear.

Cat 1

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Well.. on other non weather related news - Just found another 160 Boxer.... an OS flavour one that apparently is smooth but low compression - Looks nice with no external damage or wrench marks. Got it for a decent price so even if its a parts engine i'm OK.. we will see..

Anyone ever have an OS one - I think there are some differences as I think I saw it has different bearings than the ASP/Magnums..

Raleighcopter

My 120 is an os. It's a beautiful machine. Mine had low compression in one cylinder when I got it. It was gummed up with castor and a cam follower was stuck. I'm sure Bert can tell you anything you need to know.

1967brutus

The OS is a beautiful machine indeed.
Where the SP/Magnum makes use of a basically "standard 90 fourstroke carb" that interchanges with any 90 single OS/ASP/Magnum, the OS 160 twin does not. The carb mount is different..
The ASP/Magnum make AFAIK (I never personally checked) use of standard bearing sizes, the OS, from what I know, uses a fairly hard to find odd size bearing at the forward crankthrow. Apparenly Boca can supply them. But also AFAIK that odd size bearing is odd in its width, so theoretically it is possible to fit a standard size with two filler rings. Not that I would want to recommend it, but in a pinch...

Running them both, side to side I could not determine any difference in power or behaviour between the OS and its cheaper counterpart, but the OS is way more beautifully made,

Glowgeek

I've overhauled a few OS FT160 twins, the bearings (5) are available from Boca Bearings. I buy the Hard Chrome version and use a 2RS ( rubber seals ) in the nose. The front cam bearing can be a challenge to remove. You'll need a high quality precision hex driver to remove the rod cap screws.

I recommend removing and measuring the bearings prior to ordering. Boca's site is not always correct when ordering by engine type/model.

I typically replace the rings with a pair of RMJ Machineworx/Bowman rings.