4 flywheels?

[BruceM]

Thanks Scott, they look massive, though only 20".  Alas, I am in Arizona.  If I was in the UK, I'd rebuild a SOM.

[listeroil]

This message is posted on lister power currently a 8/1 engined 4.5kw start o matic I have been running these for 8 years at first 8 hours a day and now I run from 12 noon to 12 midnight every day on WVO .

I have used both 6/1 engined startomatics and 8/1 engined startomatics over the last 8 years and the 6/1 has always flickered even though the 6/1 start o matic flywheels are much heavier being 25" diameter than the 8/1 start o matic flywheels at 23" diameter. They are the same casting but machined to a smaller diameter. Listers also fitted a very heavy pulley to the generator on both models about 3 times the mass of a standard pulley.

I have been reading posts for years about flicker on Lister (Listeroid) CS engines and it only seems to occur on the lower rpm engines. I think 650rpm is just to slow to run the engine and expect it to not slow down between power strokes. None of the 8/1 engined units that run at 850 rpm seem to flicker at all. Listers got it right with their 8/1 engined units.

Maybe a 6/1 with heavy flywheels, heavy generator pulley and AVR might cure flicker on a 6/1 engined generator.

Mick

[Wizard]

11Hz on 6/1 650rpm
14.7Hz on 8/1 850rpm.
15Hz on typical car 4 cyl engine 900rpm (just one cylinder, all 4 cylinders firing is 60Hz).

Even that only 3.7Hz difference and what keeps 8/1 gen smoother is extra momentum energy due to extra 200rpm vs 6.1 at slower rpm.  Flywheel is *excellent* dynamic energy "battery" especially that rpm is sufficient high.  PS this is another reason about dangers of any wheels/flywheel and any rotating assembly exploding due to rpm breakage limit due to enormous energy stored within mass.

10/1 is 1,000 rpm IIRC, I could be mismaken.

22Hz on a beat with firing every 540 then 180 on both cylinders (12/2?)

Cheers, Wizard

[quinnf]

Folks that have measured it report that they get about a 5.5 Hz flicker with a 6/1 because the major component is at the power stroke, which occurs only once every other revolution.  The deceleratioin at the compression stroke immediately prior to the power stroke is pretty small, comparatively.

The reason the flicker is worse on the 6/1 is the lower kinetic energy stored in the flywheel as Wizard states.  Kinetic energy increases as the square of velocity.  A flywheel spinning at 800 rpm has 51% more kinetic energy stored in it than the the same flywheel spinning at 650 rpm.  

That's about the same amount of flicker dampening you'd expect to achieve by doubling the weight of the flywheels on a 6/1.

Quinn

[Wizard]

Brain fart!  Thanks!  every other rotation.     5.5Hz is rather low and extremely noticeable especially for me who is sensitive to 60Hz on CRT monitor.

Cheers, Wizard

[Crofter]

It would be interesting to see on a chart the peak cylinder pressure, temperature, exhaust temperature and degrees of crankshaft deflection on two different setups where exact wattage was produced at the same average rpm and only difference being a much greater flywheel mass. A close study of accurate fuel consumption and heat input to the coolant would be interesting too.

I am remembering stories of certain truck engine crankshafts that could be fractured by lugging them down and wonder at what point would added flywheel weight be seen internally as lugging. 650 vs 1000 rpm would likely be a considerable difference in piston velocity relative to combustion expansion potential; also the different burning characteristics of unaltered vegetable oil could well influence the engines reaction too.

[Wizard]

When one lugs the engine, what happens is the inertia of the flywheel stored energy is too low and firing events get too far apart in time that speed get too low that pistons is hammered down on a slow flywheel, cranks twists/vibrates torsionally violently.  Evenually crank breaks.  And can hammer the gears, clutch go burning, bands/clutches (automatic) to squeak.

Cheers, Wizard

[quinnf]

It would be interesting to see on a chart the peak cylinder pressure, temperature, exhaust temperature and degrees of crankshaft deflection on two different setups where exact wattage was produced at the same average rpm and only difference being a much greater flywheel mass. A close study of accurate fuel consumption and heat input to the coolant would be interesting too.

You're talking about a research engine there.  It's pretty amazing when you read about just how sophisticated Dr. Diesel and others were in their measurements of engine performance more than 100 years ago.  Diesel had several specially built research engines in the 1890s that recorded instantaneous cylinder pressure on a paper-covered drum by means of an ink stylus protruding from the combustion chamber.  When you think of all the things that could go wrong with such a gadget, you have to be impressed by how sharp those folks were back then. 

Diesel was trying to design an engine that would maintain constant cylinder temperature and pressure throughout the power stroke.  At least, that's the way he wrote his first patent for the engine in 1892.  He was never able to achieve that goal.

Quinn

[Wizard]

I was thinking more about the lugging... a stover flywheels (spokes) on a 5/1 and 6/1 is marginal inertia means engine is just at point of lugging, good thing that engine was way overbuilt for bearings to take the beating.

Well, Put SoM style flywheels on 8/1 or 10/1 provides much less light flicker and less belt flapping.  Would that be ideal?

Cheers, Wizard

[Crofter]

I am sure that the additional flywheel mass would be less disturbing to the crankshaft at the higher rpm. Flicker is already much less than on the 6-1 at 650.

The rotating mass must be accellerated to absorb energy (other than heat) and must decellerate to transfer the energy to the load. The crank and piston are only in position to absorb the energy efficiently through a limited portion of the power stroke; because there is no favorable crank angularity early in the combustion event little fuel can be burned then without excellive pressure rise, then beyond a certain point the combustion chamber is expanding too rapidly to effiently capture the energy of combustion.

If combustion were to occur against a locked piston that was unable to accellerate away from the pressure, (infinitely heavy flywheel) pressures would rise extremely high but the total energy of the event would go into heat lost into combustion surfaces and since there was no accelleration, no useable force would been imparted to the rotating mass.  The conversion of the potential chemical energy of the fuel into mechanical energy of the flywheel would have been zero. Running heavier flywheels and resulting higher cylinder pressures is not a free lunch since more force due to rod angularity gets converted to friction. Making bearing surfaces larger to bring pressure per square inch back within supportable levels, eventuall would create other problems to compensate for.

I think there is a limit to how much can practically be done to reduce flicker by adding mass to the system.  Personally I feel that a minute amount of cyclic belt slip at peak crank accelleration is easier on things than forcing more of the forces to be absorbed and wasted where it is more expensive to compensate for (internal wear, fatigue and conversion losses)

No question that a certain minimum  flywheel inertia is necessary for hand starting and getting up to speed but I think there is an optimum amount that is arrived at with a lot of different tradeoffs considered.

[Dail R H]

   Let me chime in with my vast un scientific knowledge. Spent most of my working life around sawmills,some small n way underpowered. One constant of these mills was a balance wheel,just a big flywheel that was belted indirectly to the saw shaft. The purpose of these was to keep the saw speed up in the cut. You could watch the slack change sides of the belt as the wheels took on the load,and hear the change in engine exhaust sound.
   I said all that to say this . IMHO,the extra flywheel mass would be better added on a lay shaft . Reason being,it would serve as a buffer between the driver, n the driven. I have an old haybaler flywheel ,and the plan is to flatbelt drive a lay shaft with the wheel on it,then drive the genhead off the lay shaft. Hopefully, the belt strech / slip n correct pulley sizing will take care of the flicker ,as the genhead will run at a more constant speed.
   That's the plan anyway, reality may be different. 12/2 Metro here

[Crofter]

I agree entirely with that use of additional mass to store energy.  When an energy source is inherently pulsating it is no easy task to prevent surges from transferring to the load. The heavy inertermediate shaft set up to allow some peak slippage of the engine, but belted firmly to the generator (or saw blade) would keep the most severe pulses from showing up on the load. Also its weight would not be born by either the gernerator or engine bearings.In electrical terms I think it would be something like the equivalent of an impedance matching transformer.