What does a solenoid do?

[hortonhcci]

avbug: (sorry, I don't know how to paste pieces of earlier responses in here)
Backing up there just a little bit...you're building a piston jet engine? Is that like a reciprocating turbine? Or a reticulated fetzer valve? Or is it merely a jet engine that is built of free piston parts; the ones that don't cost anything? Where do you put the piston in a jet engine? Or does it just float around in there, hence it's title; free?

Yeah, it's truly free. The piston is attached to nothing at all. It's called a free-piston gasifier. All it does is generate a flow of hot exhaust gases which serve as the working fluid for the power turbine of a gas turbine (if you choose to put a power turbine in the stream). Otherwise, you just use the exhaust gases as a jet, which is what the original designer did.

 

[hortonhcci]

A Squared:
well yes, you'd have to have valves sequenced with the oscillation of the pistons, but then, you already do, don't you? Many diesel engines in stationary or marine applications are started like this, by introducing compressed air into the cylinders to turn the engine over.

No, the engine has no valves, just intake ports and exhaust ports. Well, not true - there are reed valves on the intake ports prior to the pump pistons' compressing the intake charge. The thing has a central power cylinder and then two smaller pump cylinders on either side. The rod passes through the power heads, and there are pump pistons attached to the either end ot the connecting rod. The whole of connecting rod, power piston in the center and pump pistons on the ends (concentric with the power piston) forms a single, rigid unit. The engine gets scavenging pressure much like a pressurized crankcase in a regular crank piston two-stroke: as the power piston moves down its expansion stroke, the pump piston outside of the power head compresses a fresh intake charge that then scavenges and fills the chamber once the piston passes the exhaust ports in the center of the power cylinder. Same process on the other side. It's a pretty cool design.

 

[hortonhcci]

A Squared writes:
Hmmm, ok the designs I've seen, the scavenging pressure is generated on another face of the piston. three chambers, combustion chamber, bounce chanmer and compressor chamber, one piston that serves them all.

I dunno, you're the guy building it, so you gotta do what makes sense to you. It just seems to me that it would be easier to use compressed air to drive the engine like when it's running than it would be to add machinery.

>>Yeah -- poo-poo on the bounce chambers. That's what the original free piston gas turbine designs did. I think they're not optimal, for a bunch of reasons related mostly to strength and power density.

A Squared writes:
Actually, it's sort of like a 2 stroke diesel engine with no crankshaft and a power turbine on the exhaust pipe. The diesel engine part is the gas producer, and the power turbine is turned by the gas flow. They've been used in marine applications, and back when Detroit was building turbine automobile prototypes and testing them, some, perhaps most, were free piston turbines, rather than "pure" turbines, in which all stages are turbine wheels of one type or another.

>>You're exactly right. the original design is by Raul Pateras Pescara, 1924, built by the Swiss engineer R. Huber. There was a flurry of activity from 1953 - about 1959 by Paul Klotsch (Crossley, then Ford, 1953), (Ford "Typhoon" tractor); A.F. Underwood at GM (GMR 4-4 Hyprex siamesed free piston-gas turbine); A.L. London (Bendix? Hamilton?), and about ten others, including the U.S. Navy. They were all two-stroke diesels employing two opposed pistons in a single cylinder with combustion in the center and air-filled "bounce chambers" in separate, um, pump cylinders at the distal ends of the power cylinder to provide scanvenging pressure and at the same time to provide compression for a new stroke through recoil from air pressure in the bounce chambers. This thing is basically the same idea but no stinkin' bounce chambers. It's why I want to try it and see what happens.

But back to the original question: it's true I'm building it, and I haven't shelved the idea of electronic starting just yet. So if I use magnets at the ends of the connecting rod rather than iron, can I make my coils shorter? Will the thing have more kick than a straight solenoid configuration?

Also: how massive, and how long, should my magnets (or ferrous material, for that matter) be to get maximum oomph? Say I'm using a coil that can handle, oh, 750 amps at 12V, and I'm working with a 1" diameter for the connecting rod tips. If I could actually afford rare earth permanent magnets, would that help?

I'm also not sure how big/ how many wraps the coil should have. I'm eying 2 Detroit coils (whatever those are - someone else's suggestion) with a 1" stroke and 30 lbs. force when employed as a solenoid. I think they're starter solenoids for a big diesel.

Sorry to be a moron about electromagnetism. I can't understand it -- I don't know why.

 

[TonyC]

(sorry, I don't know how to paste pieces of earlier responses in here)

How about a quick tutorial?

The easiest way is to Click on the QUOTE button at the bottom right of an individual post. What you'll see is something like this:

{QUOTE=GuyThatPosted}This is the text of the original post{/QUOTE}

(I used { instead of [, and } instead of ] so you can see what it looks like BEFORE you submit the post. You'll need to substitute [ and ] for { and }. )

When you click on Submit Reply, that will look like this:

This is the text of the original post

You can always "build" those brackets manually, too. If you don't need the "Originally Posted by SoAndSo" tag, you can omit the "=SoAndSo" part. Also, you can use lowercase "quote" if you like.

{quote}Here's another example{/quote}

looks like:

Here's another example

Now, as for this solenoid thing...

Don't you think you need to build a lab or a shop and just start experimenting with these solenoids? Experiment with different sizes of rods, and different materials, throw in a couple of different types of magnets, change the number of wire wraps, etc.,? That sounds like too much fun to me.

 

[hortonhcci]

Umm.. like this?

How about a quick tutorial?

Now, as for this solenoid thing...

Don't you think you need to build a lab or a shop and just start experimenting with these solenoids? Experiment with different sizes of rods, and different materials, throw in a couple of different types of magnets, change the number of wire wraps, etc.,? That sounds like too much fun to me.

Well, I'd love to play and experiment, but I unfortunately have

a.) no shop or lab; and
b.) very limited funds.

So I tend to try to get as much as I can on paper, assuming that, even though my theory is likely pretty far off, it might be close enough that I end up with three prototypes rather than 10. So I try to find unsuspecting souls who know a lot more than I do to maybe give me some guidance and steer me in the right direction...

 

[qmaster3]

Umm.. like this?



Well, I'd love to play and experiment, but I unfortunately have

a.) no shop or lab; and
b.) very limited funds.

So I tend to try to get as much as I can on paper, assuming that, even though my theory is likely pretty far off, it might be close enough that I end up with three prototypes rather than 10. So I try to find unsuspecting souls who know a lot more than I do to maybe give me some guidance and steer me in the right direction...

If you need/want anything blueprinted PM me. You are right. Working drawings make production easy.

 

[A Squared]

No, the engine has no valves, just intake ports and exhaust ports.

Not to pick a nit, but what are intake ports but valves which open and close as the piston covers and uncovers them. When I said valves, I didn't mean in the narrow sense of poppett valves.

Yeah -- poo-poo on the bounce chambers. That's what the original free piston gas turbine designs did. I think they're not optimal, for a bunch of reasons related mostly to strength and power density.

Hmmm, OK, so if you don't have bounce chambers, what returns the pistons from the power stroke? I'm not sure I'm following your description of your machine.

Also: how massive, and how long, should my magnets (or ferrous material, for that matter) be to get maximum oomph? Say I'm using a coil that can handle, oh, 750 amps at 12V, and I'm working with a 1" diameter for the connecting rod tips. If I could actually afford rare earth permanent magnets, would that help?

OK, how big this engine you're building? The *starter* that you just described is a 9 kilowatt device, equivilant (in a loose sort of way) to a 12 horsepower moter. As far as suggestions on specing the right size coil, I don't know. I think my approach would be to seek out commercially availabele solenoid devices and look ath te specs availbale for them and use that as a starting point. Yeah, if you included permenant magnets it would increse the force .. or perhaps reverse it if you got the polarity of the magnet oriented the wrong way. How robust are the magnets? I understand that magnets can loose much of thier magnetisim if they are subject to shock (physical, not electrical) that might be a consideration if you're putting them on the reciprocating portion of an engine

 

[hortonhcci]

Not to pick a nit, but what are intake ports but valves which open and close as the piston covers and uncovers them. When I said valves, I didn't mean in the narrow sense of poppett valves.

OK - but I'm thinking if the thing just runs on intake ports being opened by piston motion, or reed valves being opened by a difference in pressure between atmosphere (or, in fact, turbocharged intake) and combustion chamber pressure, which is the case in the present design, it'll be hard to use valves to admit pressurized air for starting. I think I'd need postive valving, which at present I ain't got.

Hmmm, OK, so if you don't have bounce chambers, what returns the pistons from the power stroke? I'm not sure I'm following your description of your machine.

There is only one piston, one cylinder in this design. Or rather, one power piston and one power cylinder. I could do multiple cylinders, but I'm thinking that's, like, a long ways down the road. The piston develops compression on one side by the power stroke on the other. It's a double-acting 2-stroke - some would call it a "one-stroke." Power at every stroke, at any rate. Actually, most of the force of combustion goes blasting out five exhaust ports arranged radially around the center of the cylinder, taking up about 1/3 of its circumference. So the force needed for compression is actually to some extent piston momentum.

OK, how big this engine you're building?

4" bore, 1.25 inch stroke, each side. If you subtract the area of the connecting rod, I make that out to be 13.345 cu. in each side, or 26.69 cu in for the engine. So, around 437 cc. Except its exhaust stroke is longer than its intake (it's a modified Miller cycle), so that kind of figures in.

The *starter* that you just described is a 9 kilowatt device, equivilant (in a loose sort of way) to a 12 horsepower motor. As far as suggestions on specing the right size coil, I don't know. I think my approach would be to seek out commercially availabele solenoid devices and look ath te specs availbale for them and use that as a starting point. Yeah, if you included permenant magnets it would increse the force .. or perhaps reverse it if you got the polarity of the magnet oriented the wrong way. How robust are the magnets? I understand that magnets can loose much of thier magnetisim if they are subject to shock (physical, not electrical) that might be a consideration if you're putting them on the reciprocating portion of an engine

Ooo -- this is a very good point. Thanks! Yeah, they will get some very rapid acceleration and deceleration - not a hammer blow, but pretty hard nonetheless. I guess I could try it and see if they disintegrate or the starter loses power.

You say that if I include perm magnets it will increase the force. Yeah! that's what I want to hear! I'm thinking power doesn't mean a lot here, force does -- Pounds, KiloNewtons. I'm developing psi/ kPa in compressing the charge. I know PV=nRT, but I'm having trouble calculating how much force I need to compress a normally aspirated charge in a ~200cc combustion chamber to a CR of 20:1. I think it's around 300psi at TDC, but I think it might be a lot more, like 600psi.

And I'm unsure about how to translate that pressure to the force needed to compress it. If I know the force in pounds or Newtons, I think I can then shop for a solenoid that develops that force using, well, a car battery. But If I can multiply force by reversing polarity, so I push one side at the same time I'm pulling the other, I'm thinking I may be able to improve on the rated force of the solenoid. I.e., say, a solenoid force of 30 lbs. turns into 60 lbs when it's getting pushed by one solenoid on one side and pulled by another solenoid on the other.

 

[A Squared]

There is only one piston, one cylinder in this design. Or rather, one power piston and one power cylinder. I could do multiple cylinders, but I'm thinking that's, like, a long ways down the road. The piston develops compression on one side by the power stroke on the other. It's a double-acting 2-stroke - some would call it a "one-stroke." Power at every stroke, at any rate. Actually, most of the force of combustion goes blasting out five exhaust ports arranged radially around the center of the cylinder, taking up about 1/3 of its circumference. So the force needed for compression is actually to some extent piston momentum.

Ahh, OK, I get the idea now.

I'm thinking power doesn't mean a lot here, force does -- Pounds, KiloNewtons.

Yeah, I mentioned the 12 hp motor as sort of an inexact way of describing the magnitude of what you were proposing.

but I'm having trouble calculating how much force I need to compress a normally aspirated charge in a ~200cc combustion chamber to a CR of 20:1. I think it's around 300psi at TDC, but I think it might be a lot more, like 600psi. And I'm unsure about how to translate that pressure to the force needed to compress it.

Yeah, if you assume an ideal gas and no temp rise it would raise the pressure to 300 psi ... of couse in reality there will be some heating so the pressure will be more. How much I don't know, but even neglecting temp, the force required will be a of the pressure multiplied by the area of the piston. If I understand you correctly, you have a piston with an area of 10.6 sq. in so you'll need somewhere upwards of 3100 lb to compress it.

 

[hortonhcci]

Yeah, if you assume an ideal gas and no temp rise it would raise the pressure to 300 psi ... of couse in reality there will be some heating so the pressure will be more. How much I don't know, but even neglecting temp, the force required will be a of the pressure multiplied by the area of the piston. If I understand you correctly, you have a piston with an area of 10.6 sq. in so you'll need somewhere upwards of 3100 lb to compress it.

Hmm. I was afraid of that. In thinking about it and trying out some guesstimates, that seems right, and I'm not sure how to get around it. Gotta get some mechanical advantage, somehow. I've written a linear motor outfit in the UK about it, so I'll see what they say.