Long Stroke Engine

[OrangeAlpine]

I'm looking for a new shop project, leaning toward an I.C. engine. Requirements are that it has to be interesting, slow running and something I can build. Right now, I'm thinking of a long stoke, hit or miss, horizontal engine with 1" bore. By long stroke, I mean than four times the bore. The idea being that the long stoke would be an attention getter and make slow running easier. The engine would have an auxiliary exhaust to compensate for the necessarily smaller exhaust valve.

As I search the internet, I find nothing on this subject. Stroke seems to be bore size (approximately) up to about 1.5 times bore. Why is that? I posed this question on a site heavy with automotive types, very smart guys whose normal mode of thinking is out of the box. Responses ranged from "Hmmm" to "That's the way we make power".

Its almost to the point I may have to make one to see what happens. All input is welcomed.

Bill

 

[Tin Falcon]

Bill look into the designs of Hamilton "Dick" Upshur

http://hamiltonupshur.tripod.com/
these engines are 3/4 bore.
Tin

 

[sssfox]

Two reasons why you don't see strokes that long.

It only takes the gas so long to expand, so past a certain point, it doesn't help the power generation.

The longer the stroke, the wider the crankshaft needs to be. So past a certain point, the crankcase becomes too big to be practical. If you are making a conversation piece, you don't really need a crankcase. The crankshaft would still be large. For instance, a 1" bore with a 4" stroke would have a crankshaft a somewhat over 4" in diameter.

The longer the stroke, the lower the top RPM.

 

[kf2qd]

You would have to have a jointed connecting rod like a steam engine.

More complexity, and gas expansion would not help you, and it might even pull a vacuum before it hit bottom dead center.

 

[Philjoe5]

Requirements are that it has to be interesting, slow running and something I can build. Right now, I'm thinking of a long stoke, hit or miss, horizontal engine with 1" bore. By long stroke, I mean than four times the bore.

Of course, that's exactly why some of us build steam engines that can run at 30 rpm

Phil

 

[cfellows]

Don't know about a 4x stroke, but the Henry Ford engine has a pretty long stroke to bore ratio. The model I built has a 13/16" bore and a ratio of about 2.25:1

[ame]http://www.youtube.com/watch?v=P_No_FrDhSY[/ame]

The following video is a full size model of the Henry Ford engine. You can see in the video that it has a large stroke to bore ratio. The cylinder is made from a 1" pipe nipple which gives it a bore of around 1 5/16". Plans for this engine are available.

[ame]http://www.youtube.com/watch?v=PDnbtU_1EOA[/ame]

Chuck

 

[cfellows]

Here is some additional information and pictures for the Henry Ford Engine

http://www.nbutterfield.com/Pages/HenryFordfirstengine.aspx

Chuck

 

[OrangeAlpine]

Thanks all, especially Chuck. I was aware that Henry made a long stroke engine, but was unable to find any specs.

In general, I understand the comments (sort of) about the power generating ability of the long stroke, but there is one fact that sticks in my mind: The engine I put in the Alpine has a 3.7" stroke and will rev effectively to 7,000. Why is the 4.0" stroke restrictive at the 500 (max) rpm I hope to run my engine?

The overall purpose of the engine will be to make an engine that is unusual, so a crosshead and overhung construction was kind of baked into the concept.

I had considered making a double action engine, but incorporating the auxiliary exhaust with the long stoke would result in an incredibly long piston and engine. Then this morning, I had a a thought (or possibly a brain fart). How about a double acting engine and instead of ported auxiliary exhaust, use either a slide or poppet valve? Each end of the engine would have two exhaust valves, one to serve each combustion chamber.

Bill

 

[Till]

Hello Bill

The engine I put in the Alpine has a 3.7" stroke and will rev effectively to 7,000. Why is the 4.0" stroke restrictive at the 500 (max) rpm I hope to run my engine?

You got the term wrong. Long stroke refers to the ratio of bore and stroke. longstroke = Bigger stroke way than bore size.
It has nothing to do with the absolute way swept by the piston.


Difficulties with very long stroke engines (=very long stroke compared to bore size):
-inefficient combustion chamber geometry (this is will be even more important with very small displacements, as the swept volume rises linear with stroke, wereas the volume of a hemispherical chamber only rises with third power, which ist very very small at small sizes!!!)
-small valves = bad gasflow at high rpm = low torque at high rpm = low outputpower
(-huge valve angles)
-difficult balancing for a wide range of rpm

As long as you don't need outputpower or efficiency, a very long stroke isn't a problem for your modell engine.

 

[mu38&Bg#]

When you look at all the variables of engine design, it basically comes down to "that's how you make power". The obvious point you've already mentioned is the limited valve area for breathing. Limiting bore diameter of a four stroke cycle engine makes for small valves. The extreme oppposite of your design is a Formula 1 engine. where bore exceeds twice the stroke! F1 engines are designed to operate at 18,000 RPM (well this past season anyway) so they take advantage of the greater valve area to make power at that speed. An F1 Engine wouldn't be the ideal engine for highway cruising either, so cars have bore/stroke ratios that they do.

For display engines, virtually anything works. Your engine will likely run. Efficiency doesn't matter, so I wouldn't worry about it. If making a 1" bore over 5" deep isn't a problem, I'd give it a try

 

[aonemarine]

How about a non compression engine?
[ame]http://www.youtube.com/watch?v=fiVbeyoUmuA[/ame]

 

[MuellerNick]

In general, I understand the comments (sort of) about the power generating ability of the long stroke,

But you shouldn't understand it, because it is wrong. You won't pull any vacuum.
A bore:stroke ratio of 1:4 is quite uncommon, so you won't find that much real examples.
A ratio of 1:2 is very common on ship Diesels and these are the top notch efficient engines.
There is a valid remark (or drawback) of long strokes that huge as you want it: A huge flywheel (but that looks attractive to me) and a very long pushrod (or it would hit the cylinder walls). So, the longer the stroke, the more you run out of (esthetic) proportions, as this engine will become quite long and skinny.

You could take any design that you like, change bore:stroke as you want and keep the CR and displacement. And it will run.


Nick

 

[aonemarine]

heres a good one too
[ame]http://www.youtube.com/watch?v=9W875WV0v90[/ame]

 

[MuellerNick]

heres a good one too

The Otto & Langen is a really nice engine. But absolutely nothing for a starter. The ratchet-mechanism is intriguing, and it is really hard to get here running.


Nick

 

[cfellows]

I've really liked the Henry Ford engine from the first time I saw it running. A fellow had a 1/2 scale version running at the PRIME show a number of years ago and it was a delight to watch, ticking over at around 300 RPM all day long.

Unfortunately, from what I hear, it's a bit tricky to get running as designed. There is too much space in the combustion chamber so packing material has to be added to get a decent compression ratio. Also, the exhaust valve assembly is such that it's hard to get a good compression seal. The drip carburetion is also tricky to get adjusted right.

However, with all that said, it's quite an attention getter. I've seen it at several different shows. If you are inclined to incorporate some of your own designs, you can take my appoach and change the things you don't like and make improvements. As you can see from the videos, my version is quite different than the original.

Chuck

 

[cfellows]

This is another engine I found kind of interesting.

[ame]http://www.youtube.com/watch?v=WFabrN8zT0g[/ame]

Here is the fellow's website. I believe he has plans and perhaps some rudimentary castings for this engine.

http://rmcscratchbuilt.20megsfree.com/photo.html

Chuck

 

[Wagon173]

I honestly think it could be done but you would have to find something very very slow, hot and consistantly burning that isn't too thick. And even then you would have several head scratching sessions trying to get it to run. And on top of it I doubt it would have enough power to run anything but itself. Unless maybe you had an abnormally large combustion chamber maybe? If you go forward with this thing I'm very very anxious to see it! Best of luck!

 

[MuellerNick]

Unless maybe you had an abnormally large combustion chamber maybe?

Or "maybe" just keep the compression ratio within reasonable limits? 1:6 for a slow running engine, and no wild guesses of maybe abnormal maybes.


Nick

 

[OrangeAlpine]

Or "maybe" just keep the compression ratio within reasonable limits? 1:6 for a slow running engine, and no wild guesses of maybe abnormal maybes.


Nick

Nick, that was going to be my next question.

The number that you have expressed makes me wonder. 1:6 Just what does that mean? My interpretation is that compression would be less than atmospheric. I have aways seen compression ratios written just the opposite, or 6:1. Would you write the ratio for a modern engine as 1:10?

Regardless of the notation employed, I would probably be using Coleman fuel. Would that ratio be good for that fuel?

Bill

 

[MuellerNick]

1:6 Just what does that mean?

Sorry, read it from right to left.
I always confuse the order of the numbers for CR and scale. It's like being unable to properly use left and right (I can do THAT!).
I meant 6:1


Nick