Atkinson Differential Engine - Making it work?

[dsage]

I made a really crappy Youtube video of the motion works. I just videoed my PC screen.
My explanation timing is bit off on the exhaust port but hopefully you'll get the idea. Don't forget the reed valves are over each port controlling which way gasses move. I deleted the valves from the model so you can see the slotted ports.
Also sorry I couldn't zoom it more but I had to leave access to the flywheel on the screen so I could rotate the engine.
Maybe you'll catch something I hadn't noticed.

 

[dsage]

Stay tuned I'm not done with it yet
After consulting a fellow club member there is some suspicion that my crude reed valves may be leaking.
I have another idea worth a try.

 

[jquevedo]

i just finished building an Atkinson engine, designed loosely copied from Jan Ridders and inspiration form an engine built by an old friend Frank Kurtz,.

Trying to get my engine running i experienced something similar to your situation, IO was using an ignition built from a designed published in Model engine builder ( loos very similar to the one in your pictures),
My problem was the ignition, changed to a trusty CH ignition added a new Hall effect sensor and played with timing and guess what it started running, after that was playing with fuel and timing and the engine now runs quite nice.

Timing for spark is supposed to be around 135 Deg, i placed my spark at 110 deg to make it run, I Know all events in the engine are happening at the right time like opening and closing of valves, compression, expansion, intake duration are of the right duration and timing so not sure why the need to advance that much the ignition spark but that is where my engine desired it to run.
Tried posting a short video of it running but this site does not allow .MOV files (?)

I understand the frustration but once your head cools down you may want to think about the ignition, mine was giving very strong initial spark and then going dead silent and then spark again..

 

[awake]

jquevedo, nice build on your Atkinson. I'd love to see the video. You are right that you cannot upload .MOV files to the forum - in general, video files are way too large - so most people put the video on YouTube and post a link.

Note that Dave (dsage) is building the opposed-piston Atkinson, which, by all accounts, is a much more difficult animal to tame. There are a lot of successful builds of the style that you have made (though yours is the first I've seen with a belt-driven OHC!), but as I understand it, very few if any of the opposed-piston style that will run consistently.

 

[dsage]

jquevedo:

Nice looking engine I'd like to see the video as well. I have the Gingery version of that engine. But (as mentioned by Andy) this is differential engine - a different beast.
Yes. A lot of folks have problems with their ignition systems.
If anything is right about this engine it's the ignition system. It has a very hot white spark. The coil driver is laughing at such a calm application.
But thanks for being concerned about it. It is a common problem.

The timing on this engine only has a very narrow range because the pistons are only in front of the spark plug hole for a certain number of degrees.

Thanks

 

[RonC9876]

Dave: Are you one of us guys that can’t get gasoline to burn? Sometimes it seems that way. I went through the same problems with my Novi engine. Your description of the smells of fuel burning and the unloading of the starter work load brought back the frustration of all that work and no results. That engine sat on the shelf for a couple of years. I know I told you all about it. Just a faster cranking speed was all it took and it was off and running. Something so simple but not understood. Keep on plugging. It will run eventually.

 

[dsage]

Yes Ron. It seems it is so
Your solution to the Novi was certainly un-expected and strange.
I can give it a try but my next fastest drill is about 3600 rpm. The wacky mechanism might fly apart
Once I get the motivation I'll try simply adding a light spring behind the reed valves to ensure they are seated.
Motivation is low today.

 

[Gordon]

Yes Ron. It seems it is so
Your solution to the Novi was certainly un-expected and strange.
I can give it a try but my next fastest drill is about 3600 rpm. The wacky mechanism might fly apart
Once I get the motivation I'll try simply adding a light spring behind the reed valves to ensure they are seated.
Motivation is low today.

I would be inclined to think that the spring tension on the intake valve would be too high, not too low. When you turn the engine over do you get a good suction at the intake? If you have good suction it should draw fuel into the cylinder. Correct mix is a different question.

 

[dsage]

Gordon:
I did say I was going to try a spring behind the reed valve(S) meaning both just to be sure they are both sealing to some degree. As you say the intake should be very light but a slight pressure might be beneficial just to be sure there is no funny business going on.

Upon a bit of investigation the intake reed with no spring pressure does snap shut on the exhaust stroke (there is nothing coming back out the carb). So it's probably ok to leave it as is. So I did.
BUT keep in mind that there is a lot of volume and pressure of air on the exhast stroke pushing on that valve so that's why it snaps shut.
Read on
Yes I have very good suction on the carb. BUT I think this could be a false indication of what's going on because if you put your finger over the carb - a complete blockage - then vacuum will build quickly making it look like everything is ok but it might be a different story under slight vacuum.
Read on
The exhaust reed is a different story. I added a spring behind it because there is a distinct possibility that if it is leaking only slightly then air could be sucked back in through the exhaust reed rather than through the carb especially on low intake vacuum and low flow that might not be high enough to snap the exhaust reed closed.

So I did add a spring behind the exhaust reed and there was a distinct difference in the sound while cranking. The engine did not even pop though. Now it might be a mixture issue.

I slept on it a bit and I think what I'm going to do is smoke test the engine i.e get a big fat cigar an blow the smoke through a small hose in front of the carb and see where it goes while cranking. I'll leave the spark plug out at first to see if the air/smoke is even being transferred to the spark plug end. After that I'll put the spark plug in and see if the smoke makes it's way to the exhaust port (or anywhere else it shouldn't be). This should also indicate compression issues if the smoke comes out the ends of the cylinder past the rings.

Gordon:
This might be something you can try on your engine and report back.

Gotta go find a cheap cigar. I don't smoke.

Later.

 

[awake]

Dave, good idea. If a cigar is not handy, what about some burlap bag? Yeah, probably not something lying around either, but that's what my uncle used to used to burn in a little bee smoker (to calm the bees).

 

[dsage]

Dave, good idea. If a cigar is not handy, what about some burlap bag? Yeah, probably not something lying around either, but that's what my uncle used to used to burn in a little bee smoker (to calm the bees).

A good idea. I tried just a wooden stick but it didn't produce enough smoke.
I found an old cigar in my golf bag - really old. I guess 30 years ago it was cool to smoke a cigar while golfing.
I blew some smoke through a small hose in front of the carb and it was tough to tell where it was going. Certainly some went in but it may have also been blown out. Again not enough smoke in one dose (mouth full) to analyze it properly.
So I stuck the cigar right on the carb. My poor carb has nicotine stains now but the engine did pump the smoke to the spark plug hole and when the plug was put back in it came out the exhaust.
But I'm still skeptical because the cigar requires a bit of draw probably increasing the vacuum and maybe masking a lazy valve.
What might be required is a densely smoke filled container for the engine to draw freely from.
An automotive EEVAP system smoke machine would be ideal. Might have to cobble something up.

Better still, I think I'm going to get rid of the reed valves and investigate fitting poppet valves in somehow.
Back to the CAD drawings.

It'll be a while.
Suggestions welcome.

 

[mayhugh1]

Your version is too well thought out (and great looking, by the way) to not run. After getting over the disappointment of it not immediately taking off, that area of your brain that just won't let things go will eventually figure it out. It'll signal you one evening just as you're about to fall asleep or one morning right after you wake up. - Terry

 

[dsage]

Thanks Terry:
I think a running engine is in there somewhere. It's just a matter of figuring out what it wants. It's a weird one for sure.

 

[Gordon]

Thanks Terry:
I think a running engine is in there somewhere. It's just a matter of figuring out what it wants. It's a weird one for sure.

With my engine getting fuel to the combustion chamber was not the problem. Flooding was the problem. I turned the engine over via Gingery method of a V belt to an electric motor which allowed fine tuning fuel mix on the fly. When I got it running for short periods the fuel mix adjustment was extremely fussy. Just a very slight adjustment of the mix went from starved to flooded. 1/32 to 1/64 of a turn. The problem is with the combustible mix. I believe that is a combination of limited compression and a very short combustion stroke which is not enough to actually create the proper mix. Actually your guess is as good as mine.

Gordon

 

[dsage]

Gordon:
Thanks. Those are good clues. I've decided to ditch the reed valve on the exhaust. I have a poppet valve almost designed (no chips yet). I'll see what happens with that.
For now I'm hoping the reed intake valve will be ok since there appears to be enough volume and pressure to hold it closed on the exhaust stroke.
Yes lots of guessing going on with this one.
I have lots of compression now. I hope that helps.
Thanks for the feedback.

 

[Peter Twissell]

When engines are reluctant to for up for the first time, I have used butane gas to get them started.
Butane will ignite over a very wide range of mixtures, so it's easy to get going and then add in the liquid fuel.
I use a little pencil torch, filled with lighter gas. It has a regulator (of sorts) and I can pull the head off the end, leaving just a small outlet tube which can be pushed into a length of silicone tube to direct into the intake.

 

[dsage]

When engines are reluctant to for up for the first time, I have used butane gas to get them started.
Butane will ignite over a very wide range of mixtures, so it's easy to get going and then add in the liquid fuel.
I use a little pencil torch, filled with lighter gas. It has a regulator (of sorts) and I can pull the head off the end, leaving just a small outlet tube which can be pushed into a length of silicone tube to direct into the intake.

Good idea Peter. I'm glad you pointed out that trick. I have one of those torch pencils and will give it a try.
Thanks again

 

[awake]

Dave, I found myself thinking about the video you posted above, early this morning when I woke up for my nightly OMB* call. Not sure why that was what popped into my head, but as I pondered it, I got to wondering about the way the spark plug is exposed just before it fires, and the fact that it is a very narrow space between the pistons that is acting as the combustion chamber. Is it possible that the mixture does not have a chance to come into adequate contact with the spark? This may be a complete red herring, but just in case ...

*OMB = old man's bladder.

 

[dsage]

Dave, I found myself thinking about the video you posted above, early this morning when I woke up for my nightly OMB* call. Not sure why that was what popped into my head, but as I pondered it, I got to wondering about the way the spark plug is exposed just before it fires, and the fact that it is a very narrow space between the pistons that is acting as the combustion chamber. Is it possible that the mixture does not have a chance to come into adequate contact with the spark? This may be a complete red herring, but just in case ...

*OMB = old man's bladder.

Yes. This is a possibility. But what else can be done. If you want compression the pistons need to be close together.
I tried changing the timing to various positions. Some way after TDC where the space would be wider (and of course less compression) and it didn't change anything.
FWIW There is a bit of space under the spark plug (not much) to gather a bit of charge that might ignite and carry into the gap. Wishful thinking though.
I'm guessing as (Gordon suggested) the whole thing is going to be very dependent on the mixture. I'm thinking it will need to be very lean to be more combustible. I think he also mentioned his engine was temperature dependent. That might indicate a change in mixture (like most engines) as it warms up.

Who knows.
One thing at a time I guess.

 

[teeleevs]

I made a really crappy Youtube video of the motion works. I just videoed my PC screen.
My explanation timing is bit off on the exhaust port but hopefully you'll get the idea. Don't forget the reed valves are over each port controlling which way gasses move. I deleted the valves from the model so you can see the slotted ports.
Also sorry I couldn't zoom it more but I had to leave access to the flywheel on the screen so I could rotate the engine.
Maybe you'll catch something I hadn't noticed.

Seems to me in the video that the orange piston may need to have a little gap to uncover the spark plug sooner, also a trembler coil might work better, there would be no need for timing, just switch it on.