ESE's works engine tuner

[ken seeber]

I know, like everything else it has been done before, but has anyone recently pumped water through the transfer passages for a visual study of the flow stream?

Such a simulation would be done to represent the peak gaseous flow rate of the transfer stream. Obviously one would need to correct for the dynamic similarity between the 2 fluids to establish the appropriate water flow rate.

Such a test could be done by one passage at a time up to all passages at once. Whichever way, it’ll be a messy experience. While it could/would be done with a piston in place, the head could not be in place to allow the water to escape and also to allow visual access. One could use a current “state of the art” cylinder, eg KZ TM R25.

[Frits Overmars]

Ken, I can’t think of a single reason why flowing with water would provide any more information than flowing with air on a standard flow bench.
As you say, flowing with water will be a messy business. After the first second, all you can see is water everywhere, so you can no longer see the direction of the flow. Moreover, the flow direction is deflected by gravity, so even if you could still see anything, it would be a distorted image.
A flow bench with the right software can provide information on mass flow and flow velocity.
And if you’re interested in flow directions, I’d recommend using a gas flame, as that produces clear images.

[Vannik]

I agree completely with Frits, a critical part of the flow, that coming off the hook in the B-port and curling back under the flow from the C-port is just not duplicated by the water.

[Flettner]

I agree, it will form an unscavenged core.



Towards the end he moved to megaphone only.



This is an interesting take on the comustion chamber issues of an opposed piston engine - and it will probably need the 4 plugs.

Probably not a lot of people have real life experience with petrol OP uniflow
I have had a bit of real world experience, my first uniflow, a 100cc twin cylinder, had a combustion chamber similar, two dome pistons facing each other. Initially it ran badly with just a single plug per cylinder. A lot of advance needed. There was swirl set in the transfers and you could see carbon on the pistons on the 'down wind' side of the plug.
A second combustion plate with twin plugs halved the advanced needed, still 20 degrees though, too much.
The next uniflow I changed transfers, two ports pointed straight across the cylinder, opposite each other and four more pointing slightly up and generating a swirl. Combustion chamber was different this time, still twin plug, but the transfer end piston was 56mm dia, dome, exhaust piston at 50mm giving some squish. Also meaning the combustion chamber was smaller in dia and longer (exhaust piston flat top) bringing a quicker burn again.
This was the 440 engine we used extensively in a small jet boat.

https://youtu.be/BPr694nlUKE?si=V85p_urEwK7y86m8

https://youtu.be/uiXsPkP9jvw?si=ySatuIKtWvata11F 9200 rpm at 5,20 minutes coming back across the lake. This was the second time ever run under load. First time the day before, in the Waikato river, the first part of the video. I was taking it easy in the river, not sure what was going to happen.

[lohring]

If you don't mind, what was the crankshaft phase angle you used? Also, did you only use one crankcase for the intake? I don't see a tuned pipe so were there issues with back flow into the transfers?

Lohring Miller

[Flettner]

If you don't mind, what was the crankshaft phase angle you used? Also, did you only use one crankcase for the intake? I don't see a tuned pipe so were there issues with back flow into the transfers?

Lohring Miller

Exhaust was 6 degrees advanced. Exhaust duration was 180 degrees, transfer 130 degrees, normal twostroke stuff apart from the 6 degree Exhaust advanced.
We ran the engine with tuned pipes one time, I have a picture somewhere, that certainly 'supercharged' performance with much higher BMEP, but only for a very short time. First time the gearbox failed with my half arsed welded gears, second time after I made new gears at great expense, the exhaust pistons failed. As you would expect. Pistons were cast from LM13 as that's all I knew how to cast. (Car piston alloy, higher expansion rate than hypereutectic alloy) and the bores were shrunk in cast iron sleeves, because of cost.
The worst heat transfer scenario.
It did teach me something about exhaust piston cooling and how to combat it that thermal loading.
Found it, the picture. Mid section outlets.

[Peter1962]

In a regional british championship, this guy got second place with his BRC 500 against an armada of 450 four stroke MX bikes. https://www.youtube.com/watch?v=ePiw7xli-6s

[F5 Dave]

Are we really celebrating a guy on a bigger cc bike losing to a smaller bike that has an inferior cycle stroke system?

[lohring]

Thanks, that seems like a more reasonable exhaust lead. Was the flow from one crankcase enough or did you use both crankcases?

Lohring Miller

[lohring]

I have a friend who worked for the now defunct Eco Motors. His main work was on their electric turbocharger and he still works on it. Below is some of the information he sent me years ago on their small opposed piston engine with a cylinder bore in the 30 mm area. It was not successful. One of the most interesting articles was the effect of lead angle on power due to mechanical losses. It concluded that cylinder offset could give the same effects without the mechanical friction losses. The conclusion:

The effective design of an opposed piston two-stroke engine requires a compromise of crank phasing between the optimal phasing to achieve the desired scavenging performance and the resulting loss in work transmission efficiency - the amount of work actually transmitted to the crankshafts compared to the work done by the gases on the pistons. Non-zero phasing is required for effective scavenging and thereby achieving high power density, however this also results in the trailing piston trying to back-drive the crank during part of the stroke. Historically, phasing of the intake crank behind the exhaust crank of between 10 and 20 degrees has been typically selected. The high observed efficiency and power density of these engines has disguised the fact that one crank is fighting the other during part of the expansion stroke, which subtracts substantial work while contributing significant stresses to the trialing side components. The lost work can be eliminated by phasing the two pistons together, but this requires use of a valve mechanism on either the intake, exhaust, or both in order to restore effective scavenging. An alternative is to offset the two cranks in the same direction off of the bore centerline. This allows an effective phasing of the port openings similar to what is achieved with phased pistons for good scavenging and which realigns the torque contribution to eliminate the back-driving torque on one crank. There remains a small difference in torque contribution from each crankshaft with the in-phase crankshafts with the bore centerline offset.

Lohring Miller

[Peter1962]

Are we really celebrating a guy on a bigger cc bike losing to a smaller bike that has an inferior cycle stroke system?

3 rounds, and he finished second overall. Do you call that losing ?

The 50 cc difference is a detail when it comes to 450cc of 500cc. The point is that 'the industry' had the rules book changed in such a way that two strokes were handicaped at first in the world championship MX , (250cc two stroke versus 450 four stroke), and then just ruled out to kill every opposition. The younger generation that did not see the days when 250cc two strokes ruled MX do not know better than that two stroke technology is obsolete.

A practical -and public- experiment like this one proves to everyone that 2 stroke tech is totally competitive even in 2026 in direct comparison with four stroke in a competition setting.

[Frits Overmars]

...below is some of the information he sent me years ago on their small opposed piston engine...

That is quite an interesting paper, Thanks Lohring. However it also contains some points that bother me, such as comparing the parts count of the OPOC engine to that of a four-stroke engine. I would have preferred a comparison to the parts count of a conventional two-stroke engine or even to that of a conventional opposed-piston two-stroke engine. There is no doubt who would have been the winner.
One comment bothered me in particular, because it undermines the credibility of an otherwise interesting paper:
"One of the unique features of the OPOC engine is its ability to utilize uniflow scavenging with asymmetric port timing."
There is nothing unique about that; any opposed-piston engine can do that. Just ask Neil Hintz.
Below are the Jumo 205 aircraft diesel engine of 1932, and a DKW blown opposed piston race engine showing the crankshaft phase difference.

[Flettner]

Thanks, that seems like a more reasonable exhaust lead. Was the flow from one crankcase enough or did you use both crankcases?

Lohring Miller

All crankcases pumped, note the four carburetors in the video.

[Niels Abildgaard]

Two gentlrmen from University of Michigan, Drallmeier and Siegel ,have analysed and measured on a single Achates OP diesel cylinder.
For most load cases exhaust crank lead was detrimental;
not much but measurable.
There was a case of four degree lead where thermal efficiency (47%)was 1.oo4 times better than none.

[MINGRET01]

Hello, I'm Bruno from France.

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring.




I now want to disassemble the fork, but I don't know how. Perhaps Frtis, who is on this forum, knows this type of fork and could help me.



Bests regards

Bruno