Atkinson Differential Engine - Making it work?

[mayhugh1]

Maybe try warming with a heat gun or hair drier?

 

[dsage]

By a "gap" do you mean that maybe a little cutout or notch in the edge in the piston? Might be an idea. I'll keep in mind. Thanks.
It's hard to see in the animation (and it's not exactly like the real engine) but the piston does go slightly past the spark plug gap/tip.
Also I actually have to be careful to set the timing so the mechanism is just past TDC where the pistons just barely start to move apart. Otherwise the mechanism may not move in the right direction (or at all) when ignition occurs.

Your idea of a multi-spark ignition is a good one. I have such a driver already made and I use it on a hit-miss engine. It's a good idea to give it multiple chances to fire.
I'll look into moving it over to this engine.
Thanks for the suggestion.

 

[dsage]

Terry:
Heat. Hmmm. A good idea. All suggestions are welcome.
Another one for the list.

To all:
Thanks for all the suggestions.

 

[Nikhil Bhale]

Hi Dsage,
I am new to this site and new to this hobby so my idea may be completely wrong.
Can you use starting fluid to see is the engine runs?
I work in offshore industry and we spray CRC contact cleaner on TC inlet sometimes if engine is not responding.
It works most of the time.

Nikhil

 

[dsage]

Thanks
Yes I tried starting fluid, propane and butane and of course the regular fuel (naptha). Still no action.
Those things work on engines that were known to be previously working. In this case the engine has never run and it is quite likely it has other issues.
I'm currently working on a better exhaust valve. Maybe that with make it act more normally.
Thanks for your interest.

 

[bluejets]

Last pic shows a highly inviting path for the spark to jump to the frame from the plug cap.

Did you investigate this..??

 

[dsage]

BlueJets:
No. There is no need to investigate it. Go back and look at the SECOND LAST pic (post 66) you're referring to OR even more obvious the first and second pics of post 76 and you can see for yourself there is lots of clearance - even without the silicon rubber spark plug cap.

 

[bluejets]

Yes well if you say so.
I have seen spark jump a lot further than that at times in free air.
Especially since you say you have a really strong spark and you are not even getting a murmur of a bang.
Have you tried it without the boot on the plug?

 

[dsage]

I've been spending some time making proper poppet valves for the engine. Both exhaust and intake. I had to scale the intake height down to avoid the interference with the oscillating arm and did the same for the exhaust valve body. Internally they are about the same as the book valves.
The engine sounds more "normal" as it cranks over now so maybe I can rule out the valves as the issue now. Intake suction and exhaust pressure seem more usual now.

As suggested, I also added the multi-spark (buzz coil) type coil driver. That puts multiple sparks into the cylinder over the full duration of rotation where it could possibly fire. (Thanks for reminding me to try that).
I tried starting it again with no carburetor at all. Just spraying starting fluid into the open hole in the valve body. It did not appear to be trying to start but the cylinder was getting warm and I noticed a puff of smoke once from the exhaust valve. So maybe now with a proper mixture it will respond. I also forgot to try the other suggestion of butane from my small torch.

SO
I went back to my drawings for the carburetor that is supposed to go on this engine and noticed it has an extraordinarily small air intake hole in it. It's only 0.078" diameter. Which to me seems crazy especially when the piston is a bit over 1" in diameter. The rest of the passage to the cylinder is 0.25" diameter. The only reason for such a small hole I can think of is that maybe the air passing through it would be moving at a pretty high speed. Maybe the air blasts into the fuel jet that is right behind the hole and makes for better atomization? I suppose also with such a small hole it would work like a throttle and keep the engine from running away (it has no throttle). It all seems pretty sketchy to me.
One thing that is for sure, the carb I was using from my V-twin that has an air intake well over 0.25" probably isn't going to work. Even though it does have a throttle that can close the air passage down.

A question for Gordon:
Have you fiddled with the carburetor and the size of the hole? Any insight into it's use. I don't care much for it and was not considering using it. But it's very simple so maybe I'll make one up and see how it goes. Maybe I'll add a variable opening somehow.
At that point my engine will be pretty much as per the book except for the increased compression and modified port timing.

Below are pictures of the exhaust valve followed by both the valves installed on the engine.

 

[bluejets]

My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
Piston is 32mm diameter and no, it is NOT sucking from elsewhere.

 

[dsage]

My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
Piston is 32mm diameter and no, it is NOT sucking from elsewhere.

Not to confuse the two engines:.
MY Atkinson CYCLE engine also runs as you suggest. That's why it has an air bleed hole (for idle) But it also has a throttle.
But we are talking about the Atkinson DIFFERENTIAL engine in this thread and the carburetor it's supposed to run on.. It's a whole different beast and I'd rather not confuse the two.
BUT you bring to mind another idea. Maybe this was your intent?
I could possibly try the carb off the CYCLE engine to see if it works.
Thanks for the idea.

 

[bluejets]

Yes, engine type is irrelevant, point was the capacity of the cycle engine I built used around 32mm piston and it will run on very little air volume passing the throttle and needle valve, in this instance, through an idle air bleed hole of only 40 thou diameter.
In the photo you can see the main throttle inlet is capped off and only relies on air draw through the air bleed hole.

 

[dsage]

Point taken. I can give the carb a try if it fits.

 

[Gordon]

The carb needs high speed air flow because there is such a short intake cycle.
Attached is the carb I finally had the best luck with. I used 1/4" throat dia but since the throat is constricted by the main jet the air flow is high speed.
I give no guarantee that anything will work on this temperamental beast.
I will have try to figure out how to embed PDF files in the message body.

Gordon

 

[dsage]

Thanks Gordon.
I'll look it over. Looks easy enough to build too. So it could be another in the arsenal.

Thanks

 

[dsage]

Gordon:
As pointed out in the first post in this thread I always model drawings I receive to be sure I understand them.
Can you tell be what diameter of the small hole is that the needle tip goes into?
The #50 comes down and the 1/16 comes up but what is between is not dimensioned.
Thanks
Also the 0.190 needle assembly must be loose in the 13/64 (0.203) body hole - No? Or are you just letting the two hexes seal it.

What I have so far. You can see where the hole should go at the end of the needle to join the two existing holes.

 

[Gordon]

Gordon:
As pointed out in the first post in this thread I always model drawings I receive to be sure I understand them.
Can you tell be what diameter of the small hole is that the needle tip goes into?
The #50 comes down and the 1/16 comes up but what is between is not dimensioned.
Thanks
Also the 0.190 needle assembly must be loose in the 13/64 (0.203) body hole - No? Or are you just letting the two hexes seal it.



View attachment 115718


What I have so far. You can see where the hole should go at the end of the needle to join the two existing holes.

View attachment 115719

Per the note: It is #60 drill. It is 1/16 dia x 7/16 dp and then drill #60 through to the #50 hole on the top. The #60 is actually the fuel passage into the main body. The #60 in the side is actually the jet. The jet must be pointed downstream.

Yes the .190 hole is sealed by the hex of the needle assembly and the #10-40 lock nut on the top. I have put some sealer on those surfaces if I thought that I was getting too much leakage.

That is the problem with making drawings for yourself and and not for distribution. I understand what I am trying to do but it is less clear to others. I generally am just trying to record or clarify my build or check out the design.

As you can see opening up the throttle body makes more air flow % and less velocity.

Note: I used brass hex because that is what I have but it does not have to be hex.

Gordon

 

[dsage]

Ah Yes. I didn't read the whole note. Makes sense now.
I noted some useful details of your carb that I think can be used to improve the original carb. The original looks easier to make if I remove some of the outside details. Also the air flow can be played around with by replacing the simple piece in the front with the hole in it.
Yes the notes on the air path are interesting.

Thanks.

 

[teeleevs]

My Atkinson cycle engine will run with the carburettor main throttle 1/8" diameter closed completely off and running on just the air bleed hole 40 thou.
Piston is 32mm diameter and no, it is NOT sucking from elsewhere.

I will ask one question, how much compression does it have? I have a small engine that has never run, Putting a timing light on it revealed that the spark would fire each side of top centre but miss the full compression one, it too would get warm when driven by the lathe but so too does a bicycle pump, conclusion too much compression. I am still to investigate that.

 

[dsage]

I will ask one question, how much compression does it have? I have a small engine that has never run, Putting a timing light on it revealed that the spark would fire each side of top center but miss the full compression one, it too would get warm when driven by the lathe but so too does a bicycle pump, conclusion too much compression. I am still to investigate that.

70 pounds. measured with a compression gauge. But that doesn't really tell the whole story.
Theoretically - just by the measured spacing between the pistons when intake stops and when they come together at maximum compression I calculated approx 7:1 but that's by no means accurate. The measurements were just something I used to compare between changes to see if I was making headway. It's about where I quit trying to make it better and things started colliding etc.
I does bounce back when spun into the compression cycle. That's usually a good sign (sometimes).
Yes I don't make much of the cylinder getting warm. It was just an observation. Although I did see a puff of smoke from the exhaust once - just once.

In your case perhaps your ignition is not strong enough to fire the plug under full compression.
Not the case here.

Thanks