Adjustable compression engine
 

On the diesel forum, some discussion has been going on about fuel mixes and the like. One aspect was the installation of a glow plug into a diesel head to try and improve combustion with no ether fuels.

At the same time, I did up a head that could be adjusted for compression, on the fly. That is, while the engine is running.

This was on a Norvel .15 and likely could only be done on that engine but if anyone else has done such a thing I'd be interested in any input.

The run can be seen here. http://www.youtube.com/watch?v=_pN6-rgXEFk

The thread in question, here. http://www.rcuniverse.com/forum/m_4561055/tm.htm

Also, for those with the skills, tools, inclination and need, you can see how to adapt for turbo plugs here. http://www.rcuniverse.com/forum/m_45..._1/key_/tm.htm

RE: Adjustable compression engine
 

I adjust model Diesel engine's compression on the fly all of the time. Did I miss something?

RE: Adjustable compression engine
 

I don't know about you Art but I certainly don't have any Glo-engines that I can adjust the CR on the fly.[8D][8D].......RJ

RE: Adjustable compression engine
 

I made my first variable compression glow head maybe 10 years ago when I wanted to find the ideal compression ratio for zero nitro fuel and used my Enya 60X as the test engine. The original idea was just to find the optimum compression then make a head with the ideal combustion chamber volume but it worked so well I just left it on the Enya and kept flying with it. This isn't such a bad thing because if I ever wanted to try using nitro, change props or experiment with different heat range glow plugs I could very quickly adjust the compression to find the best for any combination. With the Enya on zero nitro I was able to boost the HP by 20% compared to the standard compression.

Later on I made a variable head for my ST G51 in a CL stunt plane because I was having problems with far too much power when it broke into a 2 stroke.

With large engines like these the only problem is that the compression can only be altered by cutting the throttle back close to idle because at full throttle there's just too much combustion pressure to overcome using a Cox spanner similar to what Andy used with his Norvel. With a modified OS 21 I could adjust it at full throttle though.

RE: Adjustable compression engine
 

Yeah Art, ma faute, I wasn't clear. Sorry. The device at the right has a flat bottomed CP with a glow plug installed. It was used on diesel fuel and the glow plug was energized to see if that would help a cold start without having to adjust the compression. And to see if the glow element, although not glowing, might provide a hotspot to aid in ignition of the diesel fuel.

The contra-piston on the left, goes into the same device. Note the slight trumpet shape and the glow plug is of the turbo variety.

Hey, Downunder,

Come to think of it, my limp synapses are struggling to straighten up and tell me that you had mentioned that somewhere, sometime. I marvel that you were able to do it.

And WAIT a minute. No such thing as too much power, is there?

But you've given me an idea for ANOTHER test.

I gather nitromethane is hard to come by "down" there? As is ether? Izzat Howard's fault?

The first picture is of the subject matter.

The second is an attempt to post a picture that the PM function can't handle. I'm trying to get some threaded rod the same size as the threads on the Norvel head clamps.

RE: Adjustable compression engine
 

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It was supposed to be a joke, but I forgot all of the silly faces at the end. [&o]

RE: Adjustable compression engine
 

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Thanks for posting this "stuff". [:-]

This is really interesting and is why I read this column. You and some other folks are very innovative.

RE: Adjustable compression engine
 

Nitro is easy to come by here but hard on the hip pocket :D. Ether can be obtained still but, like in America, it's difficult to persuade a chemical supply company to sell it because of its use in manufacturing illicit drugs. But because of the cost of nitro here for the comparatively small gain I've never bothered with it so I just wanted my engines to make the most of straight methanol. The usual way is to keep adding nitro to match the compression until there's no more gain, I just did it the other way round and made the compression suit the fuel. Of course, if I was crazy :), I could use 50 or 60% nitro and wind the compression down to suit :D.