Hello all,
I am getting ready to build a new engine, low friction rotary valve type.
I am going with the rotary valve for a couple of reasons (valve life for one) also since this engine is primarly for testing I want to be able to play with things like valve timing on a running engine.
My engines goal, as has almost always been the case for me, is to produce maximum static thrust, this engines application will be slightl different however and I would like to be able to increase efficency at speed, I would like to know if anyone has any test data or advice on using a vaiable length tube ?
Between a variable length tube and the adjustable nature of the rotary valve I should be able to "dial in" settings for both maximum static thrust as well as graduating the highest efficency at max speed.
Some years ago I worked out the sealing of the tubing and tested it under heat (and pressure of course:) , worked like a champ. I just never got a chance to apply it.
Any pointers would be greatly appreciated.
Chris Wertman
Variable length tubes
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Bruno Ogorelec
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Chris,
Presuming that you have solved the problems with sealing and/or seizure that have beset all rotary valves on internal combustion engines over the past century or so, you have a winner on your hands. But, it is a big presumption. Despite enormous effort and expense, no rotary or sliding valve I know of has ever been really successful in practice -- with the possible exception of the British Napier aircraft engines with their sleeve valves.
My personal favorite is the Cross valve because it is wonderfully adapted to possible jet engine use and serves as the intake and exhaust valve at the same time. I have often dreamed of a Cross valve servicing a battery of maybe five combustors radially disposed around the valve axis.
Something would have to drive it, though. Also, while among the more successful rotary valve designs, the Cross valve still suffered from the usual expansion problems.
Presuming that you have solved the problems with sealing and/or seizure that have beset all rotary valves on internal combustion engines over the past century or so, you have a winner on your hands. But, it is a big presumption. Despite enormous effort and expense, no rotary or sliding valve I know of has ever been really successful in practice -- with the possible exception of the British Napier aircraft engines with their sleeve valves.
My personal favorite is the Cross valve because it is wonderfully adapted to possible jet engine use and serves as the intake and exhaust valve at the same time. I have often dreamed of a Cross valve servicing a battery of maybe five combustors radially disposed around the valve axis.
Something would have to drive it, though. Also, while among the more successful rotary valve designs, the Cross valve still suffered from the usual expansion problems.
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Bruno Ogorelec
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An additional point. The variable tube length is an obvious answer for variable frequency engines, but again you face the same problem as with rotary valves -- you have to have a well-sealing sliding fit of parts that undergo great changes in temperature and have to contract and expand. I will be greatly impressed if you succeed.
I have entertained the possibility of using propane pressure as the pneumatic force for such things. Have the fuel do all kinds of useful things before being used as fuel. Propane pressure could be driving actuators that would regulate engine length. One of the advantages would be the cooling effect of propane.
I have entertained the possibility of using propane pressure as the pneumatic force for such things. Have the fuel do all kinds of useful things before being used as fuel. Propane pressure could be driving actuators that would regulate engine length. One of the advantages would be the cooling effect of propane.
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Mike Everman
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Chris-
I think you're in for nothing but grief. You'll need a sophisticated servo system to nail an rpm that is a moving target, and the reward for being the slightest bit off is flame-out. It's a resonant engine; it has one happy place, and that frequency will depend on many factors in a steady state, not to mention the wierdness that goes on at start up, which I think are insurmountable in the best case. If saying "impossible" motivates you like it does me, then have fun!
I think you're in for nothing but grief. You'll need a sophisticated servo system to nail an rpm that is a moving target, and the reward for being the slightest bit off is flame-out. It's a resonant engine; it has one happy place, and that frequency will depend on many factors in a steady state, not to mention the wierdness that goes on at start up, which I think are insurmountable in the best case. If saying "impossible" motivates you like it does me, then have fun!
Mike Often wrong, never unsure.
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MajorDick
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Well I wont say that I have it solved yet, but I think its got a real good shot at running well., Ive tested it under heat, and seizing isnt a problem, I am using a forced lubrication system and am having a little trouble with the oil coking but I think part of that is due to the fact I have concentrated the heat there.
But thats exactly what this particualar engine is all about, playing with a variable frequency engine.
I have a belief, it may be incorrect but I have seen it time and time again in other things, water, steam and reciprocating engines, things dont need to seal perfect, or even good, JUST good enough.
This goes for the tube as well, as long as it seals well enough I beive it will suffice.
At least that my hope :)
But thats exactly what this particualar engine is all about, playing with a variable frequency engine.
I have a belief, it may be incorrect but I have seen it time and time again in other things, water, steam and reciprocating engines, things dont need to seal perfect, or even good, JUST good enough.
This goes for the tube as well, as long as it seals well enough I beive it will suffice.
At least that my hope :)