I made a 2nd ring muffler for my ASP radial engine. This time I incorporated a tube in the exhaust outlet to attach the oil drain line too. The tube is extended downward in the outlet, so a low pressure is created and helps suck out the drainage.





I thought this was a great idea.

I'm not so sure though. Because the engine ran a lot differently this time.

First, I had messed with the carb needles. That was a mistake because the engine ran lousy until I reset the needles back to where they had been on the last two runs. Once I did that, the engine started immediately, had great transition from idle to full power like before. But the peak RPM was down, by about 1100-1200 RPM!

I was thinking at first that maybe the new exhaust ring was more restrictive than the first version and that was the cause of the RPM loss. But the HS needle was much more sensitive this time compared to last. Why would that be? The collector ring? I was not sure. As I ran the 2nd tank of fuel through the engine, I noticed something else really strange. Blow-by oil was bubbling out from the base of the #1 cylinder pushrod tubes. This has never happened before.

So I was wondering if my drain line through the exhaust outlet was not flowing as well as before. Even though, I could literally see the stuff being sucked rapidly through the silicone line into the exhaust outlet. However, when the tank ran dry and the engine shut down, there was a lot of discharge for a few seconds flowing out the drain tube from the exhaust pipe.

If the crankcase was getting filled up a bit, I could see that as the reason for the loss of RPM. Oil attaching itself to the crankshaft and weighing it down.

By why would the drain line from the crankcase now being helped by the suction of the exhaust, instead start to fill up the crankcase?

The OS radial engine has the same drain nipple. Have any OS radial engine users experimented with this drain line, or observed any unusual reactions to a partial restriction or anything?

Tom, you should have cut the drain tubing perpendicular (or very slightly downwards) to the exhaust outlet and not parallel, to act as a venturi.

Remember the exhaust pulses and prop wash can push air between those pulses when pressure drops up the exhaust outlet tube.

This seems to be enough to prevent a good oil flow out of the crankcase in your case.

Thanks for the comment Amador. I think it has merit.

I based my tube on the same idea as used in steam engines. In my steam engine the exhaust vapor is discharged into the boiler exhaust tube, but flowing up instead of down. It works a charm, and there is no slanted cut on the tube. However, there is certainly no propwash!

I can reach the end of the tube, and file a slant cut on the end. I will do this and try it again. But first, I think I will run the engine with the drain tub hanging in free air as before just to see if the engine gains back the lost RPM, which will confirm our suspicions.

I run my Saito 90 the same way with a Keleo ring, except I just put a pressure tap fitting into the tube in the same location you did. No problems for quite a while now....

The exhaust has a complicated flow. You could be seeing high or low pressure at the drain outlet. The pressure at the oil line exit could very with RPM. Pressure in the exhaust is going to be above ambient, it may even be significantly above crankcase pressure. It's possible venturi effect is inadequate to reduce the pressure below the ambient pressure which would otherwise be present at the oil discharge line.

I could see, literally, the oil drain discharge moving rapidly down the line away from the engine. But I did not observe it at all the various RPM settings. That is why I was surprised to see the outflow of drainage after the engine ran out of fuel. I had thought, based on seeing it sucked out through the silicone line and the copious amount of exhaust smoke it created, that it was effectively evacuating the crankcase.

It's all very interesting, anyway.

I have a 55 second video of the drainage after two engine shut downs. It's fairly obvious there was a lot of liquid in the crankcase after each tank of fuel was run.

http://www.vimeo.com/12662759

PS: It's HD, watch it full screen.

it looks like fuel dripping out.... nice motor btw

Tom, how far away from the tip of the exhaust stack is the oil tubing?
If it's too far inside, that could be enough for the exhaust pressure to be higher than crankcase pressure and keep part of the oil from venting properly.
Did you run it already without being connected?

MJ: I agree it 'looks like' fuel dripping but I think it was just very hot oil.

Patxipt: The tube extends down quite a distance, about 1" from the end of the exhaust outlet.

*Edit: Officially official: I just measured it. 1/2" from the bottom of the exhaust pipe outlet.



I am beginning to wonder if a straight tube in the flow of gases blasting by it actually creates a suction on the tube?

BTW, how does the angled cut on the end of the tube create more suction?

I understand how a true venturi tube works, but this setup could never be a true venturi even if I made the tube into a true venturi shape because it is closed at one end.

I have not run the engine again. Maybe later today.

One other thing, this 2nd version collector ring sounds a lot different than the first. I have no understanding why. I am guessing maybe the straight down 6 o'clock exhaust outlet versus the curved rearward 8 o'clock outlet.

The way you have it set up it works like an ejector nozzle. The angled cut improves suction when the pipe is perpendicular to the airflow and the open side of the angled cut points downstream. It's all dependent on actual pressures as I mentioned before. Say you're vent line is getting 0.5psi less than the pressure in the exhaust. That would be great if the pressure in the exhaust is 0.5psi or less above atmosphere. If the pressure in the exhaust is say 1.0psi above atmosphere, then you are 0.5psi above what the vent would normally see.

You could try putting a water manometer on your fitting to see if you have suction or pressure. Even easier, just mount a length of fuel tubing (that you can see through) on that fitting on the muffler and see if it will pick up water out of jar or if it's blowing bubbles.

The sound will change with the relative distances of the exhaust to the individual manifolds. Just like a cast manifold sounds different that a header on your V8.

In the 80s I messed around with drag race cars. We ran crankcase pressure evacuation systems to the headers. The tubes went into the header collector at an angle and we had a one way check valve to prevent pressure from going into the engine.

Tower sells a small check valve http://www3.towerhobbies.com/cgi-bin...?&I=LXG850&P=7 and they should be fairly easy to find at auto parts stores.

Carrell

Carrell, I have one of those check valves somewhere around here. Good idea, thanks!

Greg, I think I might be able to hook something up and give it a test. Thanks!

Okay, test results are in!

And they are not what I expected.

First some observations and conclusions:

1) I think Metallica Junkie may be correct, and that was raw fuel dripping and not oil. I have no clue why it would drip raw fuel after the engine shut down because the fuel tank ran dry. But in any case, there is no excess oil in the crankcase.

2) The loss of 1100 RPM was due to the restrictive nature of my ring collector Version 2. Not because there was excess blow by oil in the crankcase being whipped up by the crankshaft and weighing/slowing down the crank.

3) The tube inside the exhaust outlet does not cause a restriction in the breather. It does not cause back flow or back pressure. It does not suck, it does not blow. In fact, it does absolutely nothing. Zero. It is merely an extension of the silicone hose attached to the drain nipple.

4) The blow by oil seeping past the pushrod tube bases on #1 cylinder that I observed was not because the crankcase was full of blow by oil and it was being forced out the base of the pushrods. I believe now it was simply due to increased back pressure of the exhaust system.

Bottom line, is the engine ran slower on Collector #2 simply because it is a more restrictive muffler than Collector #1.

And that is not necessarily a bad thing. I have wanted to test the largest prop this engine is rated for, a 22". As you know, the slower a radial turns the more authentic it sounds. I am thinking I can use this muffler in conjunction with a 22" prop and get the thrust needed to fly a plane and turn the engine slower for a more authentic and pleasing sound. So I am not going to scrap this collector!

The reason it is more restrictive is because I inserted the exhaust stubs 1/4" deep into the ring. Collector #1 has them inserted only 'maybe' a 1/16".

Anyway, I did the bubble test. So as not to have prop blast blowing everything I ran the engine with just a stub of a prop. The line did not blow bubbles, and it did not draw up any water into it. No matter the RPM.

I next ran the engine with the propeller I have been using all along, an MA 18x10. With the drain line not connected to the exhaust pipe, the RPM was the same as yesterday when it was connected.

To save time, I did not remove the engine from the mount, but I did pull off the collector ring and ran the engine again with straight open pipes. I got back the RPM it had lost. I forgot to observe the drain line when I shut it down, so I don't know if there was any after drainage. (Maybe it's on the video.) I did observe the #1 pushrod base when running without the collector and there was no blow by oil seepage thee.

I will process the video and upload it later today.

Video of the bubble test:

http://www.vimeo.com/12683168

STOP THE PRESSES!

A new revelation! I was looking at the video again of the bubble test, and I noticed what looked like a particle lifting up. So I zoomed in and cropped it, and sure enough a particle of dirt in the line starts to lift up as the RPM is increased.

That means the tube has a low pressure, vacuum, SUCTION!

At the 12 second mark you can see it start to lift:

http://vimeo.com/12697462

Yep, I could see it...

Thanks BW!

More revelations, and surprises, and knowledge gained this afternoon! [sm=thumbup.gif]

I just finished running the radial with a 22x10 MA wood prop (don't have a 22x8) and even though it is a bit large I figured it would be okay for a test run.

Once again I had trouble getting fuel up to the engine by hand propping so I hit it with the electric starter. It would not start! What the????

I fooled around a lot, cranking and cranking the engine, getting more and more perplexed, and finally pulled the fuel line and tried to force fuel through it and nothing would come out. I removed the fuel filter I have been using and fuel started to pour out the line! The fuel filter was blocking fuel from flowing. And the weird thing is the fuel filter element is spotless clean! I screwed the body back together sans the filter screen and reattached to the engine. Gave it a few turns and it lit off like normal.

I am now of the opinion that:

A) Fuel filters as well as fuelers and all other fuel fittings on the market are a waste of time, money, and cause numerous frustrations. This is not the first time I have had issues with an aftermarket fuel gizmo.

B) Part of the reason I was experiencing loss of power was due to the fuel filter restricting the amount of fuel the engine was demanding.

I ran the engine with the big prop, the more restrictive collector ring Version 2, with the drain line attached to the pipe in the exhaust outlet. It ran flawless! Idle speed due to the bigger prop was 1320, for as long as I wanted it to idle. Max RPM was 5100. Now an excuse: I drilled the prop slightly off angle. My drill press is a crappy, loose, sloppy, 24 year old drill press from China. I think the table is not 100% perpendicular to the drill column. I was able to notice, at idle, a very slight wobble at the tip of the spinner hub. Soooooooo, I think if the prop were perfectly drilled it would have gained some RPM. Not that it matters because I won't use a 22x10 normally anyway. Just sayin'...............

And about the drainage that comes out after the engine stops? I was ready this time, with a clear plastic bottle. As soon as the prop stopped turning I had the bottle under the exhaust outlet to catch whatever came out. Although on video it looked like it might have been clean, clear fuel drops, it is in fact used oil. When it is collected it is dark.

So I am happy! I have discovered and fixed a fuel delivery problem. My idea for having the crankcase drain feed into the exhaust outlet was not so far fetched after all, and the engine keeps running better and better. I think I have 2 gallons through it now. I believe I will see more rpm than ever before on the 18x10 prop since the fuel filter is out of the equation.

I use one of these in my fuel jug.

Okay, I can see using that. Once the fuel is in the airplanes tank though, I am going to stop using anything except the fuel line to the engine.

Video of the engine running on the 22" prop, please

http://www.rcuniverse.com/forum/fb.asp?m=9814526

Kmot, just an idea here. Have you ever thought about using a larger tube for the ring? I'm thinking something like the Moki radial exhaust collector, maybe 1" ID tube. I don't think that it would make a difference performance wise, but I suppose it would produce an even deeper sound, even at high speed.

Also, with such a large tube ID, having the inlet connectors of the ring protruding a fraction of an inch inside the ring would not restrict the flow as much as with the smaller ID tube you are using now .

Radial.

No, I had not. But I am now!

If you make it sound like a moki 250, I have to buy one from you