What does a solenoid do?

[TonyC]

The OBDII codes come from when you try to do things like this, and it goes wrong. I know the language you're talking, but does fussle? Better explain it better to him.

I saw him ask a question about solenoids - - what is the purpose of a starter solenoid - - but I missed the part where he said he was having car trouble.

 

[qmaster3]

You didn't miss it. If he hasn't had starter problems yet.....He will


I can see someone asking that question, because some shop told him/her it was his starter solenoid. Is that why mom tells me to take the riddelin Tony C?

 

[avbug]

We've morphed. After all, how much time can you spend explaining a solenoid?

 

[fussle]

Thanks for all the responses, helped alot. I am not having car troubles yet, however, that info may be useful later on. I mainly wanted to know more for myself.

 

[hortonhcci]

Back to what does a solenoid do...

Hi -
I'm building a free piston jet engine from some old plans and am thinking of using a pair of heavy duty starter solenoids as a kind of linear motor to get the free piston oscillating (the original plans call for using compressed air, which I think is less elegant).

Basically, the engine consists of a cylinder with a flat head at either end. A rod passes through the center of the cylinder heads, and also passes axially through a solid, flat, double-faced piston which is rigidly attached to it. I need to get this rod/piston assembly oscillating back and forth in the cylinder to generate enough compression at either end that I can get the thing to fire and (hopefully) take off on its own.

My real question is this, then: what 's the difference beween a solenoid and what one might call a linear motor? As I see it, if my rod is iron or steel, or has iron or steel at the tips, then attaching two small coils to the outside of the cylinder heads and allowing the rod to pass through them ought to allow me to run current alternately through through one "solenoid," then the other, etc.

But as I understand it, solenoids work by pulling a ferrous object into the center of the coil. This would probably work, but it seems to me that it would make the coil unnecessarily long.

What if I instead attach permanent magnets to the ends of the oscillating rod rather than pieces of iron or steel? What I'm hoping that will do, if I reverse the polarities of magnet and coil, is "push" the rod/piston assembly to the other side, rather than having the coil at the other side trying to draw the iron tip toward its center.

Thoughts?

 

[A Squared]

Thoughts?

yeah, use compressed air. I'm guessing the forces required to get the cycle started are going to be significant. I'm thinking it is goingto be a lot easier to generate these forces with compressed air than electromotive force. A solenoid big enough to get the whole thing going may be pretty large, and heavy, to say nothing of the problem of timing the force to produce an oscillation. Compressed air on the other hand, is a by product of your engine, once it's running, and desn't require any extra machinery to provide starting power. To me that seems much more elegant than adding a large coil and actuating rods which serve no other purpose.

 

[hortonhcci]

Ummm...

But how does one get the compressed air in there fast enough? Open a valve? This is what the original designer did, but I don't think it worked real well. Plus one will need a reservoir of compressed air for starting, which means an air pump, and valves, . . . . doesn't it?

Actually, the actuating rods serve all kinds of purposes, including driving pump pistons to get scavenging pressure (the thing's a two-stroke, as I'm pretty sure all free-piston engines have to be). The actuating rods are also used to deliver intake charge, and I plan on using them to deliver lubricating oil . . . . . . . .

 

[avbug]

I'm building a free piston jet engine from some old plans and am thinking of using a pair of heavy duty starter solenoids as a kind of linear motor to get the free piston oscillating (the original plans call for using compressed air, which I think is less elegant).

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?

 

[A Squared]

Ummm...

But how does one get the compressed air in there fast enough? Open a valve?

.

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.

This is what the original designer did, but I don't think it worked real well. Plus one will need a reservoir of compressed air for starting, which means an air pump, and valves, . . . . doesn't it?.

Yeah, you need a reservoir, obviously. Buth the engine itself is an air compressor, right?

Actually, the actuating rods serve all kinds of purposes, including driving pump pistons to get scavenging pressure

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.

 

[A Squared]

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, that floating piston is pretty tough on compresser blades <g>

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.