Another Engine design question

[borna]

Hello all,
I’m planning to build a vertical 4 cycle single cylinder slow running engine (500 – 1200 RPM) with usable power.
This is what I came up with. Would you please let me know what I have so far gives me the result I want?
1" Bore x 1.5" Stroke
Piston length: 1"
Piston Center pin: 0.5" below top (right at center of piston)
Cylinder length: 2.56"
Rod length: 2.5"
Compression Ratio: 5:1

At TDC, the piston is .25” below the top of the bore
At BDC, the piston skirt is .1875” below the bore
Flywheel: 5.5” diameter

Thanks
Borna

 

[kuhncw]

How much power are you expecting and what will the enigne be used for?

Regards,

Chuck

 

[borna]

Mostly will run as model engine, with no load. Main purpose is to run very slow and reliable. maybe drive a 12V generator.

Thanks
Borna

 

[gbritnell]

Another thing you will have to consider is the size of the combustion chamber (compression ratio). This will have a great impact on the running speed of the engine.
gbritnell

 

[borna]

Yes as I mentioned, the compression ratio is about 5:1
Now should I go lower or higher?

Thanks
Borna

 

[flatbelter]

Hi Borna,
First off, good luck with your engine.
Second, I'm more of a high speed engine kinda guy so you may want to double check my opinions.

What fuel will you be running on?
Is this a hit 'n miss engine? If so you should have no problem hitting your target RPM.

If not, how will you be governing the speed?

Is this a fuel burning engine? (as opposed to compressed air, or steam)

If fuel, what are you using for carburation?

For a gas or alcohol motor, I would shoot more for 8:1 as it would still work even after you get some wear. (keeps the exhaust cooler too) It will start easier too.

Can you lengthen the piston to reduce the distance below the deck height? (then you could trim it back latter if needed.)

We get the 2 stroke model airplane engines to idle down to ~1600 RPM at 8+:1 compression and only a prop for a flywheel. With a good stout flywheel you should be able to do much better.

5.5" flywheel, yea that sounds perfect.

I would worry more about getting the carb and governor setup correctly than the compression ratio, but I like more compression than less in the general scheme of things.

Your mileage may vary.

FB

 

[borna]

looks like 2.5" rod will not have enough clearance at 45 deg. at 90 deg barely will make it.
Need to go with 3" rod.
FB, to answer your questions,
This will be a gas engine running mostly on camp fuel, and not planning to make it a hit and miss engine.
For carb, I'm thinking to use a RC engine carb size 10?

Thanks
Borna