Recycled Flyer

Would be interesting to see if these engines run as well without their respective mufflers in place Dave, I suspect not though.

Hobbsy

My Feedback: (102)

I am going to run the OS fp .60 again, I removed its baffle because of the muffler filling up with oil during extended idling.

qazimoto

My Feedback: (1)

Pe, what I'm saying is that the bowl shaped head in the Parra in performance is no different to the flat shaped one. That's tuning, smoothness and rpm.

If you had two engines side by side with either type of head you wouldn't be able to differentiate between them.

I notice that you don't use Ignition Improver in your fuel. That would effect the smoothness of your engine run and confuse any observations.

Chris,

I'm going to disappoint you by agreeing (at least I think I do), however "Davis Type heads" (ie O-Ring sealed diesel heads) are not used in Team Race Diesels anywhere.

It's because the they don't give good hot hand starts. probably because they leak when they're really hot.

Ray

Recycled Flyer

Hi Ray,
in the context of this thread, that of 'Diesel Combustion shape,' I refer to a Davis type head's shape not its use of construction materials.

In other words, a model diesel head consisting of two major parts, the fixed head clamp and the movable central contra piston within that clamp that is smaller in diameter than the bore.

It is possible though to have a 'Davis' type head as descrided above but does not use O rings (our mutual friend Geoff Potter of team race fame was going to make me one but at the time I wisely decided that a lowly Sokol diesel was not worth the effort).

Perhaps hot starts with O ringed diesels deserves a new thread?

qazimoto

My Feedback: (1)

The Enya 15 D uses such a head but it doesn't have an O-Ring. There's some interesting contributions on this thread from people who actually have made diesels heads and a few interesting designs.

http://www.dkd.net/forum/viewtopic.php?f=6&t=31

Don't start a new thread on hot starts on my account because I'm going down the shed to continue my efforts to stuff a Parra piston/liner into the crankcase of an obscure brand of plain bearing glow engine.

Recycled Flyer

I hope that said 'obscure' engine is not Soviet era derived mate!

P.S. Any chance of posting Bob Fishers attempts with the ASP 15 diesel conversions as well as your own then?

Good luck in your hunt for ever decreasing lap times!

Recycled Flyer

There is mention of what a domed combustion chamber does here -

http://www.the.elmores.btinternet.co...ta_15_am0.html

pe reivers

Since I was a youngster, I ran my engines on 3-3-3 fuel, no ignition improvers. My oil always came out honey colored, and power at the time was much better than the sorry OS engines that needed lots of nitro to perform anywhere near the diesel.
My pet engine was a Webra MACH1, with tapered piston top, and matching CP.
My recent test engine is a glow MVVS ABC .15 with own design diesel head with 10mm dia CP.
I would not consider an O-ring design. why? there is lots of space for compressed gasses to go in and out of the O-ring groove and CP part below the groove. At 15,000 rpm, multiply that space with 15,000 to get the amount of gas that has become lazy and escapes doing any work at all. I cannot see how such a design will be very powerful. It will be a nice running engine for sure, with easy handling CP for stunt fliers, but not for racing where fuel economy and speed rule.

AMB

Pe it seems to me that the volume between the contra and cylinder wall in an o ring fitted contra would be a very small constant and easily compensated for by just lowering the contra a tiny amount, it would be such a small amount quite hard to measure it
thus maintaining the same volume, as far as how much is lost by bypassing the O ring do not know. In sport use it is not an issue martin

Recycled Flyer

Has anyone actually tried an O ring designed diesel engine in real racing conditions?

The only one that I have seen was on a Thunder Tiger 46 ball race engine was was used as a pylon racer.
The diesel head conversion was fractionally down on straight line speed but bear in mind that this simply was a successful glow engine with a new head bolted onto it - nothing else was done.

So it seemed to me to run extremely well and had an unlimited vertical performance.

And it hand started just fine after a full flight.

pe reivers

Martin, not talking of gas bypassing. The rationale behind my remark is the same as using turbo plugs in glow engines. The turbo plug seals at the combustion chamber. A normal plug has the threaded part inside the combustion area, but not taking part in combustion. In racing, it is the summing up of multiple factors that make a winner. For sports use, who cares about those very small gains/losses.

Recycled Flyer

Hi Pe´,
            I don't get part of your last post mate, if combustion emanates from the coils of a glow plug outward into the rest of the chamber how is the plugs recess (where the coil is in fact held) NOT taking part in combustion?

I have always thought that the plugs recess spoiled gas flow, not eliminated it entirely.

In other words a turbo plug provides better gas flow and combustion at high rpm by keeping as close as possible to the intended true shape of the chamber.

Similarly I would suspect that any recess in a diesel head would support limited combustion but not of course to ideal specifications.

I wonder though if there is any carbon build up in Davis type head in the recess described between the contra, the fixed head clamp and below the O ring seal?

AMB

Recycled flyer some time back I backed off the allen compression screw enough that I could push in the contra maybe an 1/8 inch after just a light punch with a piece of wood dowel I did not see a trace of carbon build-up, think is was an irvine 53 Davis head ABC davis fuel

I do have some O Ring Non Davis heads, you can see a very slight gap between the contra and the head, the davis head I can not see one very very close excellent fit

pe reivers

You do not seem to grasp the difference between a turbo plug and a standard plug. The standard plug has the threads BELOW the washer, so compressed gas (mixture) can enter into the small voids between the threads of the plug and the head. This gas escapes combustion. The turbo plug seals at the very thread bottom. The gases are retained completely inside the combustion bowl, including the plug cavity, and no gas escapes combustion.
Same with a CP. A good CP will seal the combustion chamber at the bottom. A loose CP that relies on an O-ring will have a gap leading up to the O-ring groove, which has a small gas space as well before it is pushed up to seal against the tremendous pressures, deforming the ring in the process. The compressed gas (mixture) involved in this action escapes combustion, and thus reduces engine efficiency.

Recycled Flyer

Hi Martin,
                I have two AJC heads that have a very close fit also and would hesitate to call the clearance between the moving contra and the head clamp a 'recess' in a classical sense.

They are obviously not a gas tight but it looks fairly close to it.

Thanks.

Recycled Flyer

[quote]ORIGINAL: pe reivers

You do not seem to grasp the difference between a turbo plug and a standard plug. The standard plug has the threads BELOW the washer, so compressed gas (mixture) can enter into the small voids between the threads of the plug and the head. This gas escapes combustion. The turbo plug seals at the very thread bottom. The gases are retained completely inside the combustion bowl, including the plug cavity, and no gas escapes combustion.
Same with a CP. A good CP will seal the combustion chamber at the bottom. A loose CP that relies on an O-ring will have a gap leading up to the O-ring groove, which has a small gas space as well before it is pushed up to seal against the tremendous pressures, deforming the ring in the process. The compressed gas (mixture) involved in this action escapes combustion, and thus reduces engine efficiency.
Ah, I see where I went wrong now.

I misread your previous post concerning the "threads of the plug" part.

But Ido know how Turbo plugs work, it's just that my grasp of English (at times) seems to fall behind yours!

Thanks.

pe reivers

English is not my first language either

pe reivers

I have made a drawing of my glow to diesel conversion head for the MVVS 2.5cc glow engine. I started this project some time ago, when MVVS diesels went out of production. Since then, they produced a batch to serve long enough. This thread revived my project, so now I finished it.
The bowl squish works best of all. Last runs were using 25% castor (putoline kart tech 2), 40% ether, 35% lamp oil (Farmlight kerosene C5-20, flashpoint >61°C. Beware: many sub standard lamp oils with higher flash point limit are on the market)
Less oil can be used to be replaced by kero. Oil decreases the fuel cetane number, so less oil can be of advantage in starting and running. With this fuel the CP came exactly flush with the cylinder button, using a squish of 0.3mm.
The tapered CP is made of brass, the cylinder head button is 6060 aluminum. With the dimensions provided, the CP will operate hot and cold. and click back on engine firing.

Recycled Flyer

Well done Pe´.

I see that you have gone to the bowl design here and that proved to be better than the flat combustion chamber?

I read in an old engine test that the squish with a bowl helped engines start forwards and have no idea has this works (apart from the envisaged softening and perhaps retarding ignition process.)

Thanks.

AMB

Just checked my Enya CX11d , First time head off, contra is in head and large in diameter , almost or same as bore, it has a bowl in the contra which starts almost at the edge of the contra then after putting it back on mounted an 8x4 prop, a little Davis ABC fuel down the carby and right off after about 5 flips
the squish area with the bowl shape way to go even on smaller OS10 Davis head with its smaller contra dished and of course on all his others
martin

pe reivers

Indeed I have no problem with oscilating in a cold start. However, the cold start is in need of "procedure". Like it is:
prime two drops into the venturi. flip three times. prime one drop again. flip three times. prime two drops and get a short burst on the second flip. prime three drops and the engine starts running on the second flip. When warm, prime three drops and the engine starts running the second flip time and again. No need to touch that tommy bar.
The flat design started quicker cold. Prime three drops, start on third flip. Tommy bar however needed adjustments between cold and warm.

pe reivers

double post deleted.
added:
I checked on the Moki Cobra TR engine chamber shape on Barton's forum. It has a wide shallow bowl. Ido not know if the same mechanics apply to diesel or glow heads?
wide and shallow = high rpm
narrow and deep = low rpm

edit 2:
The MVVS steel diesel set (latest diesels) have an iron CP which has a narrow outer ring of about 1mm wide. Then a chamber about 0.3mm deep. In the middle of that chamber is a small dome.
Running that engine without IPN:
9x4 12000 rpm very nice and stable running CP 3/8 turn open
9x5 11000 rpm, would bog down slightly on extended lean cackle.
8x3 13,000 rpm, very crappy cackling running. no CP established

after adding sone 15% Wynn's diesl+ fuel treatment which contains about 7.5% octyl-nitrate (ethylmethyl nitrate): equals 1% pure octyl nitrate.
9x4 12200 rpm CP 5/8 turn open
9x5 11100 rpm (bogged completely down to standstill if a tad too lean) CP 5/8 turn open
8x3 16000 rpm Nice stable running, lean cackle if forced, CP 3/8 turn open

This engine is not yet run in, which maybe explains the bog down on second test