Super low idle - possibly OT

I know this is an academic question; would like to hear your thoughts though.

Would it be possible to idle an engine down to, say, one revolution per minute, given a large enough flywheel?
I know that the rotational inertial energy of a given flywheel increases by the square of the speed, so how would that work out at very low rpms?
(I was thinking of my 123 cubic inch, four cylinder, four stroke, Farmall Super A engine, with a normal idle speed of approx. 800 rpm.
An extra flywheel, driven at a much higher speed than the crankshaft would add a lot of rotational inertial energy...)
Typical cabin fever question ;-)
Thanks, Hendrik

Thats the idea and principal behind the hit and miss engines. I know once up to operating temp my '53 JD 60 will almost die and then fire up again just from the fly wheel keeping it turning. Its amazing to me just to sit and listen to it run like that.

I would not know why it would not work.

I grew up with a E-3 Coop, Buda engine. It idled very slow and needed new piston rings every two years. Estimated hours, under 1000 and it idled a lot because of how it was used. I now think that the reason for the ring wear was lack of oil on the cylinder walls. The oil pump pressure showed zero at idle and because it went slow, little splash would come from the crank.

60 revolutions in an hour is going to take a massive flywheel to run, don't think you'll get enough power from so few firings per hour to keep the flywheel powered?

Paul

with enough weight it is theoretically possible, as long as there is enough weight to keep the rotating mass of the engine turning until the next firing cycle motion would continue, but that being said and being done is 2 seperate things, a hit and miss engine is slow, but not 1 rpm slow, let us know if your successful,it would be really something to see, , on the other hand what are you up to that you need an engine running that slow????

take a whole lot more horsepower then that super A is gonna muster..

not sure of this but i believe there is a fine balance of engine compression and fly wheel size factored into at time of manufacture.

ohiojim
At 1 rpm the power of that engine would be around 1/100 HP; too low to compensate for frictional and other losses.
Thanks.

You are equating revolutions/RPM with fuel savings. There is ZERO relation between the two.

It all is how efficiently the fuel is converted to energy/power. Also what the BTUs/energy are in the energy source.

The old hit and miss engine where low RPM but terribly inefficient.

(quoted from post at 06:16:25 02/04/13) I know this is an academic question; would like to hear your thoughts though.

Would it be possible to idle an engine down to, say, one revolution per minute, given a large enough flywheel?
I know that the rotational inertial energy of a given flywheel increases by the square of the speed, so how would that work out at very low rpms?
(I was thinking of my 123 cubic inch, four cylinder, four stroke, Farmall Super A engine, with a normal idle speed of approx. 800 rpm.
An extra flywheel, driven at a much higher speed than the crankshaft would add a lot of rotational inertial energy...)
Typical cabin fever question ;-)
Thanks, Hendrik

Click to expand...

First you state normal idle is 800 RPM - this sounds high for a tractor, the idle spec for my 8N is 400 RPM. I am not familar with Farmalls so perhaps 800 is typical - I don't know. As you indicated energy storage is proportional to the square of the RPM. Therefore, if you reduce the idle speed from 800 to 200 flywheel energy storage decreases by a factor of 16 (800/200)^2=16. So at some point the engine will stall on the compression stroke.

Adding metal to the outer rim of a flywheel is an effective way to increase the energy storage. This method was popular for some dirt bikes (motorcycles) in years past. A ring was machined and pressed onto the OD of the flywheel.

However, I don't believe flywheel effect is always the limiting factor for idle speed. As the idle speed is reduced air flow through the carburetor venturi slows and the ability to mix gasoline with the air deteriorates. Also, the inlet passages are sized for higher speeds at very low speed the gasoline which is now poorly mixed can fall out of the air stream. As the mixture quality decreases misfire/stalling results. It has been my observation that stalling typically occurrs due to misfire prior to stalling on the compression stroke.

A smaller carburetor can maintain mixture quality however you still have the oversize inlet passages. Changing to a gaseous fuel (propane) could be used to eliminate the liquid fuel fall out problem and the resulting mixture quality issue.

Hit and miss engines use the change in RPM principle to harvest more of the flywheel energy. The engine is sped up (hit) then allowed to coast to a lower RPM (miss) before firing again. This is similar to deep cycling a storage battery. However, I don't think this large variation in RPM is what you have in mind for your Farmall.

When I worked in the JD shop I was told it was not good to idle them too slow. Poor oiling and jerking in the valve train.

Assuming this is Possible..... The Oil Pump would Not do an Adequate Job of oiling the Engine, With such LOW RPMs... Larry

There is or was a subculture in the Harley Davidson bike world. Where they had a slow idle competition.
iirc the usual tricks among others were a heavy flywheel, low compression, retarded timing , hot engine and a rich mixture.