2 Crankshafts Inverted v8

[BentRods]

Hi Fellas,

I (hopefully) attached a drawing I sketched of an inverted v8 concept that would utilize 2 crankshafts and 1 cylinder head. I'm wondering if you guys know if somebody has attempted to make this before and whether or not it worked? I'm aware of the opposed piston engines but this idea would still use a conventional cylinder head. Any ideas?

I'm still saving up to purchase machinery so in the mean time I've been sketching out ideas for fun.

Thanks
Erik

 

[Art K]

Erik,
I cant say that I have ever heard of any engine based on this concept. But there are narrow angle V6 such as the VW, or narrow angle V4 used in Lancia's. They both use a single piece head.
Art

 

[dave-in-england]

Is this an idea where the opposing pistons rise to the top at the same time ?
Share the same combustion ?

 

[Lakc]

Will it work? Certainly looks like it.
Has it been done before? Probably, but not to my limited knowledge.
Is there a reason for that? Several that I can see offhand.

You will have a rather large combustion chamber but plenty of swept volume to fill it. You are doubling the hardest and most complicated part (imho-crankshaft) and asking twice as much work from the least efficient aspect of any miniature engine. (head flow)

Those are likely two of the reasons its never been done commercially, but that does not mean it wont make for a great model. It will be unique, for sure, and just drawing it to completion will teach you a whole lot. Plenty of rotating mass should help to keep it spinning. ;D

 

[BentRods]

Art,
Are you referring to the Volkswagon VR6 motors?
http://en.wikipedia.org/wiki/VR6_engine

Dave, Yes, that was the Idea. I'm wondering if its been attempted before. I couldn't find anything searching the web so I was hoping the more knowledgeable folks on the board could help.

 

[BronxFigs]

Erik/BentRods:

"MODEL ENGINE BUILDER" ran articles and drawings for an opposed, flat, four-cylinder engine, with a similar configuration as shown in your sketch, i.e. outboard cranks, and basically, a common head towards the center of the engine. Your sketch is almost the inverted, V-version of this engine that I mentioned. Not an exact match, but close. Maybe you'll get some ideas.

This engine can be seen in Model Engine Builder, issues 19-20 "Doug Kelly's, 2 Cylinder, Opposed Piston Engine". Don't let the name of the construction article fool you. It's actually a flat-four w/ 2 pistons sharing one common cylinder but, separated by a common head. The article shows the construction a four-piston, flat version, of your engine if you were to think of your engine as flattened, and built as a four-cylinder.

I know it's a stretch, but both engines share things in common, like the crank set up, gearing, etc.

Your concept looks like an interesting build. Good luck.


Frank


EDIT: You-Tube: Dave's Twin Opposed Piston Engine....

 

[johnny1320]

I wounder if it may be hard to get high enough compression out of this engine. what would be the advantage to building it. for fun?

 

[petertha]

One challenge I forsee is the cylinders are pointing inward vs. outward. Maybe not an issue unto itself but your drawing shows them as quite close. If you sketched about a piston heights worth of 'head stuff' on top & in alignment with the piston bores (combustion chamber + rockers + cam + gear/drive...) very rapidly there is a lot of stuff competing for the same common real estate, unless you can somehow share them on a common drive line.

The vr6 cylnders look nestled & tight, but they still point 'out'.
Looks like an intersting challenge. Good luck.

 

[MCRIPPPer]

cool idea. i think if you made the pistons with a matching angle to the head surface, and made an oval shaped head dome, it would have about the same compression as a conventional engine.

 

[BentRods]

Erik/BentRods:

"MODEL ENGINE BUILDER"

I know it's a stretch, but both engines share things in common, like the crank set up, gearing, etc.

EDIT: You-Tube: Dave's Twin Opposed Piston Engine....

That's a really cool engine, I've never seen that before. It really does have the same construction just in boxer form. Kind of like an old side-valve engine with another piston in the cylinder. I'm glad it worked!

For the rest of you - I don't contain the skills to build this type of engine, nor any engine for the matter. I've got a lot to learn before I attempt anything IC related. I had a random thought for the day and am too young & stupid to think "that'll never work". So, thanks for the help and perhaps the day will come eventually and I will give this an attempt!

 

[BronxFigs]

Erik...Erik...

Give yourself some credit. You came up with the concept after giving the design some thoughts, so, you are not "too young and stupid to think that your engine will never work". Success is always the child of failure. I know only enough about engines to know that I know nothing about engines!

Please don't give up. I'm sure with today's specialized, computer programs, you'll one day take your design and "build" and then animate it on the computer screen, and will be able to work out all the sordid details.

How lucky you are to be so young.


Frank

 

[Ripcrow]

Just because it ain't been done before dont mean it won't work,the first steam engine was probably doubted as well

 

[petertha]

Actually, I think I mis-interpreted your sketch so disregard my comments about cramming 2 heads worth of stuff into one spot.

If I understand it correctly, you have the left & right cylnder bores in the same section plane, so each single hole we we see on top is a common/projected silouette for both cylinder bores, right? If so, I guess that would have to be an elipse shape viewed from the top, it looked circular to me. So then the head that sits on top of this would just require a common chamber shape which is shared between cylinders? Interesting. I guess by default they would have to go up & down & boom in unison to breath through the cycles properly & not crossflow.

Kind of like this concept? except your cylinders are angled?
http://www.billzilla.org/ideas4.htm

 

[petertha]

Bentrods, I took the liberty of sketching your engine idea as a solid model. No real hard & fast dimensions, just working off your drawing & just intending to elaborate some features that were hard (for me) to visualize. Its pretty funky. Couple notes:
- the eliptical opening at top of crankcase resulting from 2 intersecting circular bores
- showing sample paired pistons at TDC & BDC positions for reference
- a head slug plopped on top with matching combustion chamber outline. But just eyeballing the resulting minimum squish volume, I think it would be difficult toget a very high CR. Maybe the head should have a 'positive' shape in the middle to raise CR as opposed to the typical recess.

Hope this helps. You should build it one day!

 

[petertha]

compression ratio 'increasing' idea.
Hmmm.. this thing gets more interesting. I'm stopping now!

 

[dman]

at first i just wanted to say "why?" but then i thought, if you changed the phasing between cranks while running you could make a variable displacement and compression engine. if you combine that with another method for variable compression like playing with the intake valve closing time you could adapt to loads and maybe get more average efficiency over a wide range of conditions.

 

[dman]

Bentrods, I took the liberty of sketching your engine idea as a solid model. No real hard & fast dimensions, just working off your drawing & just intending to elaborate some features that were hard (for me) to visualize. Its pretty funky. Couple notes:
- the eliptical opening at top of crankcase resulting from 2 intersecting circular bores
- showing sample paired pistons at TDC & BDC positions for reference
- a head slug plopped on top with matching combustion chamber outline. But just eyeballing the resulting minimum squish volume, I think it would be difficult toget a very high CR. Maybe the head should have a 'positive' shape in the middle to raise CR as opposed to the typical recess.

Hope this helps. You should build it one day!

well you could put a point on the piston, not a cone but almost like a chisel tip with a 90deg included angle then you'd have all kinds of squish area shooting from the edges and up from between the pistons.

 

[Noitoen]

A bit off topic but cool http://www.ukpapermodels.com/phpBB3/viewtopic.php?f=4&t=450&st=0&sk=t&sd=a&start=105

 

[dave-in-england]

I think this could be a good project !

The problem with having the bores at 90 degrees to each other is that it makes the base of the engine extremely wide.

If the angle was reduced to 60 degrees this makes a huge reduction in engine width.

Also the bores do not have to meet, they can be separate, the top of the pistons can be machined off at an angle to make them flat with the top of the block.

Here I have made up a model view where the bores are 50 mm diameter, the cylinder head could be made in four separate units to make things simpler.

The cranks can run in opposite directions.

I am not sure if there would be any advantages in an engine such as this, probably the reason why they are not used, but would be a good model engine that is different from the rest.


dave

 

[mu38&Bg#]

Think outside the box a bit and make the piston tops with a dome. Possibly a 90° top in a ^ with a bowl in the center. The two pistons would come together to form a squish area between each other and the head. Sort of like a high compression Hemi piston. Add clearances for valves as required. Of course compression only needs to be ~5-6:1 so squish clearances can be quite large.

Greg