Author Topic: reduction of rotating mass vs efficiency  (Read 16024 times)

0 Members and 1 Guest are viewing this topic.

bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
reduction of rotating mass vs efficiency
« on: May 28, 2010, 07:55:05 AM »
this is a continuation from this post

http://fieldlines.com/board/index.php/topic,143490.msg965639.html#new


where Watt and I have parted company on the his assertion that reduction of rotating mass increases power and by extension
efficiency.

watt said "Get some time on a dyno and then come back and post."

did  you not read that i have a test cell, and do active research into the area of power generation from small engine power sources?

watt said "Again, circles.  Let's really change this drastically, lets compare 1 pound and 1 million pounds. "

you can talk about theoretical conditions, but in a small engine genset, beit single cylinder or a 4 banger, there  is only so much mass you can remove, and my point being simply,,, the reduction of mass is so small that any increase in power will be almost unmeasurable.

furthermore, lister years ago built small diesel engine's, and some of which were incorporated into gensets called the "start o matic"
the engine had heavy flywheels of about 125lbs each , while the start o matic had much heavier wheels of about 175lbs each, they also put
a very heavy flywheel on the genset to increase rotating mass,  the effort was to smooth the power pulse and to reduce flicker, and
the bsfc remained the same as measured in gr/kw/hr.  clearly increasing rotating mass did not increase fuel consumption, so one could assume
that the inverse would also be true.

watt said "Yes, change wheels and tires lighter and engine hp stays the same, of course but you can't measure engine hp on a chassis dyno, only  WHEEL HP....
If the car is getting to the finish line quicker ET and faster MPH, the change ( same engine hp) made a difference right.  done."

yes this is true, however in a genset application we don't need rapid acceleration, yes it take extra power to accelerate a load but
the extra power needed to accelerate the rotating mass will also be returned to the load when surge capacity is needed. we don't need rapid acceleration because we are running generally at a fixed speed with a genset, or at the very least a narrow speed range that does not have a need for rapid acceleration of the rotating mass.

watt said "You are going off on this decreasing engine mass thing aren't you.  You must also read way too much into posts.  This subject I refer to is using the 4 banger as a power source while having no effect on the engine idling.  Go back and take a look.  Every bit of freed mass contributes to the bottom line.  Done."

i am not just talking about reducing engine mass, i am talking about reduction of rotating mass as it relates to your assertion that it will reduce fuel consumption or increase efficiency, it clearly will not! furthermore anyone that is wishing to use a 4 banger to drive an alternator to charge batteries better have a huge alternator and an even massive battery bank to work against or his overall efficiency as measured in gr/kw/hr is going to be so dreadful that removing the flywheel all together is not going to help. starting with a 4 banger and a typical alternator to charge an even more typical battery bank is just so wrong on so many levels, that worrying about efficiency is about the last consideration one would likely make.
you want to reduce rotating mass, reduce the number of cylinders by three and you will have done more to increase efficiency than any amount of reduction in rotating mass will ever accomplish.

in response to diesel efficiency statement watt said, "Never challenged this but, you already start with 10% more energy per volume than petrol.  Again, reread the thread"

apparently you don't understand that we do not test output and efficiency by fuel volume rather by fuel weight in grams,
gasoline weighs about 6.25lb per gallon while diesel about 7.15 lb per gallon, btu's are approx 115kbtu vs 138kbtu
if you test and measure using fuel weight you will find that gas and diesel work out to be very close in btu per gram, there is a slight edge
going to diesel but certainly no where near 10%

watt said, "So then, does modifying an engine to accelerate using the same BSFC increase mass?  What about adding an aluminum vs. cast iron flywheel?  We'll call it .5 percent increase in the total scope of the problem.  To go off again, using a car alternator to generate any form of electricity is insane.  Very inefficient alone.  "

in the respect to using an off the shelf automotive alternator as designed for charging a 12volt battery bank i would agree, but
to make a blanket statement that the use of an automotive alternator to generate any form of electicity is insane from an efficiency standpoint
clearly illustrates you have no idea what is possible. i have one off the shelf unit that is capable of 80% efficiency, and another that is capable of a bit better than that. they will compete very well with any other form of off the shelf generator within their output class and will out perform any
AC generator with a battery charger plugged into it.

watt said "You meet my challenges and I'll meet yours.  Again, you see it as a " engine mass " my post said rotating mass, from the rooter to the tooter.  Done"

i accept you are talking rotating mass, i too am referring to rotating mass

watt said"I too am no newbie, Facts are facts"

sorry my friend, but just because you call it a fact does not make it a "fact", you have presented no engineering text to support your claims
only "your" anecdotal evidence, you have not presented even one single example of a product where they reduced rotating mass and as a result increased efficiency of the unit, or reduced its BSFC numbers

watt said, "Wonder how it revved higher, faster ?  I've certainly said the same thing.  Same hp engine but now faster and quicker down the track.  For what it's worth, I build supercharged/turbocharged compound diesel engines and trucks for drag racing.  I wonder how my trucks, in excess of 7500lbs make it down the track in the 10's?  It's not because I make the engines heavier and run 40" tall tires.  Moving mass is moving mass, Why then is it easier to get a lighter flywheel to move quicker up to speed than a heavier one of the same dimensions?  Air friction loss has zero to do with it same dimensions and texture.  "

again apples to cinderblocks comparison, we are not in it to rapidly accelerate the generator, you ask how your pickup gets down the track in 10sec? largely because you are making much more hp by virtue of more turbo boost and burning more fuel, and to a much lessor extent reduction in rotating mass.  i never said you can't make the thing spin up fast with less mass, i only stated that you will not save anywhere near the amount of fuel in a fixed rpm application such as a genset as you assert.

watt said"Again, you go over board with the suggestion given.  You miss the point " remove what is not required in rotating mass ". 

agreed, no sense in powering anything unnecessary

watt said "Ummmm now you are talking alternators, not driving the alternator from a 4 banger.  What was that about tangent?"

ok, lets refocus a bit

had you stated that the use of a 4banger to drive an automotive alternator for the purposes of charging a battery bank would not be very efficient
and that the OP ought to rethink the use of such an engine, you and i would have no issues, however
to suggest that simply reducing rotating mass of the 4 banger is going to significantly improve the situation is just not responsible in my opinion
and does the OP no service as well as anyone else that should come along later and read the thread for the first time.

tag your it!

:)

bob g


research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #1 on: May 28, 2010, 11:07:25 AM »
in an effort to try and keep an open mind on my part, i will try to do the following and report back

most ever engine manufacture i know of that builds an engine that is used for other than generator use
has a lighter flywheel, and the same engine built for generator use is fitted with a heavier flywheel,

i am not aware of any reduction in efficiency, or increase in BSFC with the versions using heavy flywheels.

but i might well be wrong, god knows i have been wrong before, at least once!

lmao

seriously, if i can find a reference i will report it back and we can discuss is merits

perhaps you can also check around and see what you can find?

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #2 on: May 28, 2010, 01:37:02 PM »
Bob, the direction of the discussion was due to a comment made by driving a car alternator by means of a oem standard 4 cylinder car engine and having zero effect while running headlights from such.  I stated that fact in earlier discussion and was questioning the method and test parameters.  I believe you got off on one minor detail and clarification of such has led to this more sensible, within our realm, discussion.

On clarification, I was not asking how I get the heavy truck down the track.  I was merely stating that I did without adding mass to the engine while not running 40" tall 10,000 pound tires.  I was kinda being a smart butt...

Also, my intent was to never to say lighten, explicitly,  the engine rotating assembly.  However I did say to lighten the rotating assembly as a whole.  So, an example will be constructed with an output to drive some large spinning mass. 

I would like to give an example of one of many engines we use to drive pump jacks.

These things have similar sound as a " popping johnny ".  They are gasoline and are very large and heavy.  Huge flywheels and over 2000 pounds and gasoline or actually they run on gas produced from the well.  So, they have been converted to Vapor, not unlike the LPG systems in use. 

I'll have to wait till tonight to give the whole story. 



bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #3 on: May 28, 2010, 02:55:53 PM »
respectfully master watt

my issue was the over generalized statement of reduction of rotating mass would increase efficiency as being a fact.

only as it relates to an engine driven alternator/generator

i also over generalized with my assertion that this is not necessarily a fact, based on my experience trying to track down
oft times infinitesimal increases in efficiency.

when it comes to power generation with an engine driven alternator or generator, you rapidly reach a point where any increase
in efficiency comes at an enormous cost in time and cash, also generally speaking the largest gains in efficiency come from
engine type, operating range, optimizing the alternator, matching the load, etc.

drive components are next, moving from V belts to micro groove might improve overall efficiency a percentage points in some
application, but not all

in practice reduction of rotating mass is not desirable in an engine driven genset, most time designers are trying to increase rotating mass
(if cost is not a constraint) to improve the stability and surge capacity of unit as well as reduce flicker in 1800rpm and lower rpm engines.

none of the designers or oem's that i am aware of report an increase in fuel consumption or a reduction in efficiency with the increase in rotating mass.

therefore it is hard for me to accept that the inverse would be true, in that reducing mass is going to increase efficiency, or decrease fuel consumption?  i find nothing to support that claim.

however i would be very interested in any documentation you can provide to support your assertion.

:)

bob
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #4 on: May 28, 2010, 07:35:03 PM »
Well thanks Master Bob

Seems as if this case is being converted to money, costs and so on.  Task at hand is to prove, disprove power in added rotating mass. 

No need to continue this circle.  You have your opinions I have mine.  Thanks.

bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #5 on: May 28, 2010, 07:52:05 PM »
ok, good enough for me

we can agree to disagree, and still remain friends, right?

:)

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #6 on: May 28, 2010, 09:10:44 PM »
Right on Bob.  Keep on keeping cool.

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #7 on: May 28, 2010, 09:40:02 PM »
Here is some reading, if you like and yes it's a document.  www.math.usu.edu/~bryanb/.../Rotational%20Inertia.doc




Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #8 on: May 28, 2010, 09:41:33 PM »
I'll try again, the other didn't work.  http://www.math.usu.edu/~bryanb/math 2210/Rotational Inertia.doc

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #9 on: May 28, 2010, 09:45:07 PM »
Ok, plan " ZZZ "

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: reduction of rotating mass vs efficiency
« Reply #10 on: June 03, 2010, 08:45:03 PM »
The amount of rotating mass has an effect on efficiency, etc. only if you're changing its RPM.  (Even then it's only an issue if its load affects the efficiency of the driving engine or if you're doing the slowing by wasting power in a brake, rather than consuming it in a load.)  When it's just sitting there spinning it's storing energy and not losing any noticeable fraction of it. (Just bearing and air friction.)

Further, a flywheel with more mass may make an engine run a trace more efficiently by running more smoothly.

Perhaps you're confusing flywheel mass with "unsprung mass" on a moving vehicle.  Heavier wheels lose power because, on a bumpy road, their forward motion is converted into vertical motion by bumps, then the energy of this converted motion is eaten by the shock absorbers.  The deflection is the same regardless of the mass, so the heavier the wheels the more energy is converted when some of their motion is changed from forward to upward.

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #11 on: June 03, 2010, 10:36:29 PM »
No, I'm not referring to un-sprung mass.  As you said, more power is required to increase rpm of increased mass.  Try a lighter flywheel on race engine vs a heavy flywheel which one revs faster?  Either way, the engine is supplying the power to the flywheel, the flywheel doesn't help make power.  Also change the weight of a tire/wheel combo and see what happens on a dynamo-meter.   More torque is required to increase speed of mass ( Equal mass ' in weight ' of a small diameter vs. large diameter ), just like a lever. 

I'm not sure we are on the same page here.  I never said a spinning flywheel would loose energy just spinning.  What I did say, power required to spin mass, at a constant RPM, will change as weight is either removed from said flywheel or increased to said flywheel.  It's kinetic energy will also change.  If two different mass's, of the same weight, can be continually spun at a constant speed, tell me what amount power will spin that 1 million pounds and 1,000 pounds respectively.  Both with equal dimensions. 

No, race tracks are smooth, which was used as reference.  And yes, larger diameter as well as larger width both alone or together reduce efficency of a vehicle.  Try it and check your mileage.  Whether a large difference or small, the name of the game is efficiency. 


bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #12 on: June 04, 2010, 12:15:31 AM »
Watt my friend, i think you are comparing apples to cinderblocks

you are asking for a power comparison between a million pound flywheel and a thousand pound flywheel?

there is no generator where that broad a change is even possible, and certainly has no bearing on any racecar

and you continually refer to race cars as if there is any correlation to a generator?

the only similarity between a genset and a race car is they both burn fuel, apart from that there really is no comparison
that can be made.

simple physic's and i can't remember which law it is, but
an object will continue to move in the same direction until a force of equal and opposite force acts upon it
(more or less i think i have it right)

at steady state, a generator turning 1800rpm will require the same amount of fuel to turn the reciprocating mass
whether it has a 150lb flywheel or a 200 lb flywheel (typical and available weights for a lister/oid diesel engine)

a generator turning 3600rpm will also consume the same amount of fuel whether it has a 10lb flywheel or a 12 lb flywheel
(typical weights of a briggs and stratton gas engine)

now if i were to take a lister/oid and remove the 150 lb flywheels and replace them with 1500 lb wheels then i might expect
there to be some difference, but not for the reasons you mention. the inertia of the 10x heavier wheels will alter the burn
rate/cyl pressures of the engine, and there will be higher frictional losses in the mains because they were not designed to carry
10x the weight.

before you start in about the OP and 4 bangers, i did go back and read that the OP was concerned with an alternator driven by
a 5-6hp gas engine,

in no case will you ever convince me, unless you show me the data and test results showing me that reducing the rotating mass
of a typical generator set engine results in lower fuel consumption and/or the ability to produce more electrical power.

it just isn't going to happen, i am sorry

fwiw, i took the time to run your theory past a few engineers, none of which buy into your theory
and all of which ask to see your supporting data to back up your assertion.

whatever you are witnessing with tire and wheel changes on your racecars can likely be explained in various other ways
and not by virtue of reduced mass of rotating members, such as wheels/tires, flywheels etc.

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #13 on: June 04, 2010, 06:40:52 AM »
Bob g, have your experts sign on and post away.  I could indeed tell you that NASA backs my claims and deny yours.  So, back to square one. 

Race cars, car tires, Millions of pounds and fwiw some of your examples are also comparing apples and deep space black holes.

You are saying the 50lbs difference is being spun free.  I am saying if 50lbs is free then 1 Million must also be free.  How else can I get it through that nothing is free.  You, my friend, have excluded windage and bearing loss.  I did not exclude these facts so......  Also not saying windage and bearing friction is the only losses, I AM SAYING MASS ( WEIGHT ) is another added loss.

If cylinder pressure is being increased, more work is being done.  EXACTLY......  Now, hook up your cylinder pressure monitor, as I have hooked up mine, test away......   

You are so hooked on this flywheel thing, LET ME REPEAT.  COMPLETE ROTATING ASSEMBLY AS SUGGESTED BY OP< should have spelled out, my original post to the person I quoted in that post >  CAR 4 CYLINDER ENGINE TURNING A 60AMP ALTERNATOR, WHICH I SHOULD ADD WAS FREE POWER PRODUCTION AS IT DID NOT REQUIRE MORE FUEL TO LOAD THAN THAT REQUIRING THE ENGINE TO RUN AT IDLE.  MY ORIGINAL POST RELATED TO TRIMMING THE ENGINE DOWN TO ONE CYLINDER AND SAVING THE FUEL WHICH WOULD HAVE BEEN REQUIRED TO SUSTAIN THE THREE EXTRA CYLINDERS AND RELATED MASS and so on in coupling and so on and so forth.   I also noted somewhere " that which is not required " and gave my reason for needed mass to at minimum complete the 4 cycles.  This thread is related to reducing rotating assembly mass.  So, get off the flywheel as a whole.  My example was given to show the lighter flywheel allowed the engine to rev quicker and therefore deliver more power to the wheels, true, not a race generator.  However, Newtons laws of motion, law three

Third Law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear. This means that whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction. This law is sometimes referred to as the action-reaction law, with F called the "action" and −F the "reaction" 


So, that 50lbs can't be free....  IF more energy is required to accelerate that 200lbs flywheel than the 150lbs flywheel we first must realize as load increases to the engine, rpm will drop because the stored kinetic energy has been used.  For every action, there is an equal but opposite reaction.  Increased load = release of kinetic energy -> Engine cylinder pressure increase to regain rpm + load + friction losses and windage so on.  If I understand what you are saying, that extra 50lbs of rotating weight has no bearing on what an engine can ultimately deliver beyond that flywheel to a load before stall?  correct?  We have an action, 50lbs extra to be spun up and sustained at 3600rpm, now what is the reaction?  Also, what is the torque requirements per watt generated and further power if it's being done for any real length of time?  So what does this mean as far as added power requirements?  Bob, how about you tell me what the diameter is of the mass, also tell me what the density of the mass is close to the center of the flywheel, between the middle and the outer edge and also the density of the outer portion.  Let's get some constants here we can work with.  My examples seem to be to outlandish and ridiculous for your realization.   Let's go on to the generator, watts being generated or free spinning.  What type of engine will this be?  Again, I'm calling it rotating mass as a whole, flywheel included of course but no limited to.

What is the difference between a flywheel and a tire and wheel?  Do they both store kinetic energy?  Are they both harder to stop the heavier they get?  Are they both harder to accelerate than lighter and smaller diameter ones?  If you say a flywheel of 50lbs would require more cylinder pressure to accelerate at the same velocity then the same has certainly got to be said about heavy tires and wheels and ones which are bigger in diameter.   I only brought up the race car, and elaborated, because you say you have XX years of racing experience.  One more black hole.  Why are strictly racing wheels and slicks feather weights compared to oem road worthy units?  Not only do you have to move the tire wheel weight forward, but you also have to spin them.  Total weight loss, if you must, has an end result, quicker times and fast mph.

I'm not sure how you could not follow my replies?  My Original Post in the thread, replied to Peters Post.  AS follows.


Newbie
*
Posts: 39


View Profile Personal Message (Online)
   
   
Re: Small(est) engine powered auto alternator
« Reply #31 on: May 04, 2010, 11:56:15 PM »
   Reply with quote
Quote from: Peter- on April 22, 2010, 03:33:17 PM
Quote

What you want is not that hard to get, if you scrap the car alt and the concepts related to a car alt.
I am working on one now, and it is pretty simple.

"that I could bolt into my car and just leave it idling"
Careful.  Idling cars are not a lot different than idling 3.5 B&S.
Turn on your car head lights, with a warmed up motor, and watch the tach.
All power comes from somewhere.
Thinking a turning car alt makes power with no effect on an idling 200HP motor is a pipe dream.



You are wrong, period and full stop.
Cars idling are very much different: They have much more mass as expressed by the flywheel rim.
I have turned on my car headlights with both a cold and a warm motor. There is *zero* difference at the tachometer.

You need to remember that HP is a product of both torque and RPM. The car alt is only a very tiny fraction of what is available at the flywheel of a 4-cylinder in my case.

What kind of car do you have?  Is it a 70's vintage or is it late 80's or 90's or newer with fuel injection and computer controls?

You imply idling that gas engine is nearly free and so is the wattage used by electrical accessories and such.  First, is you alternator so new as it is field controlled by your ecm?  Is the alternator driven by resistance from a load such as a bulb?  Or, has your alternator fully charged you battery and now at float stage?  Or, the more relevant the question, have you started your vehicle and swapped the battery for a very low charge state battery and then watched the tach?  A WATT is a WATT.  Once your engines mass has delivered in the way of energy, to the load, it's mass is no longer usable.  meaning for every action, there is an equal but opposite reaction.  That engine now has to deliver the power to sustain the new load.

If that is not a good enough explanation, put a vacuum gauge on your engine.  Put a load on that engine and watch the vacuum gauge when it starts towards zero, that is your throttle delivering more air and therefor fuel.   That car engine idling is very inefficiency, just to keep it idling takes a huge amount of energy.

Seems you need to remember HP is a product of BTU.  Huge mass is great for getting a load moving or the initial start of huge energy requirements ( should have added the Kinetic energy bit here )but only for very short burst but none can be more of a load than that available as energy.


 


On other point which should have been brought up regarding the above.  HP is ' calculated ' HP = torque * RPM / 5252rpm 



Bob, you are saying something is free and I love you for it.  Problem is, last bit of property I got for free is worthless and I can't even get rid of it without paying someone to take it.  It was never free.  I suggest you get your mind off of the tiny benefit of reduced rotating mass relating to .000000000001 hp engines and reread my posts in relation to peters reply to someone he posted a response to ( peters response was to the thread starter, not the thread starters original post ' if I can ever remember now ' ).  I could care less to convince you otherwise Bob, that is not my point, my point is to explain my views and back up my statements.  When I feel I have done so, I will be done.  How about this, before you pitch your next set of bald tires, fill them with a hardening tire gel, hardening so as to keep your wits instead of putting up with a dangerously shaking vehicle with a liquid filler, and go for a cruise in the city, track or dyno. 

bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #14 on: June 04, 2010, 07:33:33 AM »
i am not saying that increasing rotating mass is free, what i am saying is this and this alone

at a fixed rpm, and a fixed load, driven by a specific engine, the difference in efficiency or reduced fuel consumption
or increase in the available amount of power per unit of fuel consumed is damn near unmeasurable save for some
incredibly accurate test cell, and even then the results are going to be suspect because they are likely within the margins of error.

i repeat you will not ever increase the efficiency or the power of "any" genset "if" the only variable you change is the rotating mass

it just isn't going to happen, never has happened, and even if you can prove it so,,, it likely will be an increase of less than a tenth or two
in percent, which likely could be explained by other means.

i would also like to clear this factor as well

50 lbs or million lbs in theory is all well and good, we can argue theory till the cows come home, but
this is not in keeping with reality,

there is no generator set that one is likely to be able to change the weight by reduction as you report to anywhere near that scale anyway
so discussing that is going out on a tangent in my opinion.

but if you would like to go there, how about considering this planet as a flywheel
it is what 4.5 billion years old, and has been spinning on basically frictionless brgs, and has no windage losses, but
if i were to buy into your theory i would have expected the old girl to have long since quit turning billions of years ago.

yes planet earths rotation is decaying, but it is so because of external forces working against her, such as gravitational forces
from other planets and our sun, not because of a lack of hp being put into her.

going back to subject at hand
and using your example of a 4 banger driving an alternator

how much weight can your reduce the rotating mass by? maybe 10lbs? 20?  certainly you aren't going to tell me 1000 or a million?

you see i build gensets, i test them as well, and do so to a remarkable degree of accuracy, and there is just no way that reducing
the flywheel and coupleing mass by 10-20lbs is going to increase the amount of available steady state power or reduce the amount
of fuel consumed as measured in grams/kwatt/hour

going back to the OP and his 5-6hp engine driven alternator, how much weight can you trim from it?  i will tell you this much it won't be over
5 lbs at most, and that weight will not return higher efficiency or more power from the alternator as measured in grams/kwatt/hour.
what it will do is make for a unit with poor surge capacity, hard to start, rough running and finicky as hell in operation.

how do i know this? because i have built my share of 5-6hp gas engines as well, and trimming rotating mass does nothing for more power
or increased efficiency, it just reduces weight that something like a gokart might have to carry, but it will not do anything beneficial for a genset.

in conclusion

reducing the amount of rotating mass in as much as it is possible with a small engine driven generator is not going to return a measurable increase in overall efficiency or reduce the amount of fuel used as measured in grams/kwatt/hr.

now increasing rotating mass by a factor of 1000 or more, may well cause a measurable change in efficiency and/or measurable change in fuel consumption, but .. no one is contemplating doing such a thing to start with, and even your assertion was in relation to reducing rotating mass not increasing it.

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #15 on: June 04, 2010, 02:43:03 PM »
i am not saying that increasing rotating mass is free, what i am saying is this and this alone
  You have said so.
at a fixed rpm, and a fixed load, driven by a specific engine, the difference in efficiency or reduced fuel consumption
or increase in the available amount of power per unit of fuel consumed is damn near unmeasurable save for some
incredibly accurate test cell, and even then the results are going to be suspect because they are likely within the margins of error.
  What is " the margin of error "?

i repeat you will not ever increase the efficiency or the power of "any" genset "if" the only variable you change is the rotating mass  You said above extra mass in not free to rotate

it just isn't going to happen, never has happened, and even if you can prove it so,,, it likely will be an increase of less than a tenth or two
in percent, which likely could be explained by other means.
   That is an increase of efficiency. 
i would also like to clear this factor as well

50 lbs or million lbs in theory is all well and good, we can argue theory till the cows come home, but
this is not in keeping with reality,
   You are again justifying your biased views. 

there is no generator set that one is likely to be able to change the weight by reduction as you report to anywhere near that scale anyway
so discussing that is going out on a tangent in my opinion.
   Again, running a 1kw alternator with a 150hp vs. running the same 1kw with a 3 or 4 hp engine is the point of the my original post. 

but if you would like to go there, how about considering this planet as a flywheel
it is what 4.5 billion years old, and has been spinning on basically frictionless brgs, and has no windage losses, but
if i were to buy into your theory i would have expected the old girl to have long since quit turning billions of years ago. 
  Duhh, apples to black holes again.  You must think windage and gravity have no relation on earth? 

yes planet earths rotation is decaying, but it is so because of external forces working against her, such as gravitational forces
from other planets and our sun, not because of a lack of hp being put into her.

going back to subject at hand
and using your example of a 4 banger driving an alternator

how much weight can your reduce the rotating mass by? maybe 10lbs? 20?  certainly you aren't going to tell me 1000 or a million?

you see i build gensets, i test them as well, and do so to a remarkable degree of accuracy, and there is just no way that reducing
the flywheel and coupleing mass by 10-20lbs is going to increase the amount of available steady state power or reduce the amount
of fuel consumed as measured in grams/kwatt/hour

going back to the OP and his 5-6hp engine driven alternator, how much weight can you trim from it?  i will tell you this much it won't be over
5 lbs at most, and that weight will not return higher efficiency or more power from the alternator as measured in grams/kwatt/hour.
what it will do is make for a unit with poor surge capacity, hard to start, rough running and finicky as hell in operation.


Are trying to save face here Bob?  I never mentioned a 5 - 6 hp engine exclusively, however Yes that 5 to 6 lbs has merit.  You've said it yourself. 


how do i know this? because i have built my share of 5-6hp gas engines as well, and trimming rotating mass does nothing for more power
or increased efficiency, it just reduces weight that something like a gokart might have to carry, but it will not do anything beneficial for a genset.

in conclusion

reducing the amount of rotating mass in as much as it is possible with a small engine driven generator is not going to return a measurable increase in overall efficiency or reduce the amount of fuel used as measured in grams/kwatt/hr.


In CONCLUSION?  You are completely avoiding the point to the topic, and ALL relevant questions which would make measurements and calculations possible.  You have a self proclaimed state of the art test cell with nothing to substantiate its accuracy.  ONLY YOUR opinions as to its perfection.  Explain how you come to your conclusions.  What are you using a bathroom scale and a lever for torque measurements?  Your margin of error may in fact be due to YOUR test cell and understanding of such.  Let's get some facts on the table.

now increasing rotating mass by a factor of 1000 or more, may well cause a measurable change in efficiency and/or measurable change in fuel consumption, but .. no one is contemplating doing such a thing to start with, and even your assertion was in relation to reducing rotating mass not increasing it. 
  AGAIN, my post is in response to powering an alternator from a 4 BANGER............

My reason for such a drastic increase in mass, in my examples, is to point out a change makes a difference.  You said no they don't so I say lets go to an extreme.....  Just as current through a wire, drastically increasing wire size when not needed may still help to some degree, but only so much till the costs exceed the benefit.  Just as weight on your Lister, once enough mass is determined to dampen combustion ( keep a smooth cycle ) as well as start loads, the rest of the weight is a waste.  As small as the increase may be, an increase is just that.  Just as you increasing the efficiency of your alternators, every little bit helps.   
bob g



Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #16 on: June 04, 2010, 03:12:59 PM »
On final point.  Spin two flywheels on their own bearings, 200lbs and one 150lbs.  Remove the power from them, they loose speed right. So, power is required to sustain speed.  Now which one stops first?  The 150lbs flywheel meaning more energy is stored in that 200lbs flywheel.  Where did the kinetic energy come from?  Has to be the engine.  RIGHT! 

DamonHD

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 4125
  • Country: gb
    • Earth Notes
Re: reduction of rotating mass vs efficiency
« Reply #17 on: June 04, 2010, 03:42:18 PM »
Watt, I hate to wade in at this stage, but no.

The Ancient Greeks thought (arguably because they'd never had the pleasure of a decent low-friction bearing) that a sustained force was required to maintain speed, but as Newton's formula F=ma indicates, in the absence of friction sustained input is only necessary to maintain *acceleration*.

Rgds

Damon
« Last Edit: June 04, 2010, 04:22:51 PM by DamonHD »
Podcast: https://www.earth.org.uk/SECTION_podcast.html

@DamonHD@mastodon.social

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: reduction of rotating mass vs efficiency
« Reply #18 on: June 04, 2010, 04:47:01 PM »
No, I'm not referring to un-sprung mass.  As you said, more power is required to increase rpm of increased mass.  Try a lighter flywheel on race engine vs a heavy flywheel which one revs faster?

They both rev to the same speed.  The one with the heavier flywheel just takes longer to get there.

A flywheel is not an energy CONSUMING device.  It is an energy STORAGE device.

It takes twice as long for ten charging amps to bring a 100 AmpHour battery from half to full charge as it does to bring a 50 AmpHour battery from half to full charge.  And it takes twice as long for ten horsepower to bring a 100 pound flywheel from 1800 RPM to 3600 RPM as it does for ten horsepower to bring a 50 pound flywheel (of the same geometry) from 1800 RPM to 3600 RPM.  That's because the 100 pound flywheel has twice as much stored energy at a given RPM as the 50 pound flywheel.

But you were asking about how much power is CONSUMED by the flywheel.  Answer:  NONE!  Once it's up to speed it just spins, and all that stored energy is available to KEEP it spinning for a while (and driving a load, until all that stored energy is gone) after you turn off the fuel to the motor.  Meanwhile, once you're running at a constant RPM, all those engine horsepower drive the generator.  The flywheel is just along for the ride (and to transfer a little energy from the more powerful to the less powerful parts of the engine rotation, keeping the RPM more constant).

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #19 on: June 04, 2010, 06:33:03 PM »
If a flywheel is not an energy consuming device, how then did it gain it's kinetic energy?  Really, how long does it take two equal size engines with different weight flywheels to come to rest once fuel has been removed?  The heavier flywheel will continue after the lighter one has stopped. 

Not consumed by the the flywheel but consumed keeping the flywheel at a constant speed. 

Exactly Damon, Ours today is not perfect either, but the best available today. 

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #20 on: June 04, 2010, 06:58:33 PM »
No, I'm not referring to un-sprung mass.  As you said, more power is required to increase rpm of increased mass.  Try a lighter flywheel on race engine vs a heavy flywheel which one revs faster?


Ok then " faster " how about " quicker " to a given rpm.

How about try this with that faster statement?  What is the highest rpm 1 hp can spin 150 pounds?  Now, what is the highest rpm 10 hp can spin that same 150lbs?  Use all the gearing required.  Now use 1hp to spin 150lbs and then 200lbs. 

Without any power applied to rotating an object, no rotation occurs.  Without sustained power of some quantity, the rotation will slow and eventually stop. 

Jack up your car and spin the wheel with your finger, how long can you keep a constant speed of say 30 rotations a minute, now try 60 rotations a minute.   

ghurd

  • Super Hero Member Plus
  • *******
  • Posts: 8059
Re: reduction of rotating mass vs efficiency
« Reply #21 on: June 04, 2010, 07:32:59 PM »
Mike,
All of the forces being discussed so far are basic Newtonian physics.
The mathematical equations known.

Converting the issues into Units of "Joule" is the missing link?

"What is the highest rpm 1 hp can spin 150 pounds?"
The RPM limit of a 150 pound flywheel powered by 1HP or 10HP prime mover is unlimited.  Infinity.
The practical limit is defined by the structural integrity of the material and the diameter.

Pretty hard to spin 150 pounds of Jell-O 3600RPM.
G-
www.ghurd.info<<<-----Information on my Controller

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #22 on: June 04, 2010, 10:44:36 PM »
Wow, again the practical purpose of the post is being derailed. 

Start at .000000001 hp and spin that flywheel of 150lbs.  How many rpm can be reached before the power produced will no longer allow for any further rpm.  That is the required power to spin that mass at that velocity.  Start adding incremental power, by any means, until the next rpm limit is met. 

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #23 on: June 04, 2010, 10:55:51 PM »
Mike,
All of the forces being discussed so far are basic Newtonian physics.
The mathematical equations known.

Converting the issues into Units of "Joule" is the missing link?

"What is the highest rpm 1 hp can spin 150 pounds?"
The RPM limit of a 150 pound flywheel powered by 1HP or 10HP prime mover is unlimited.  Infinity.
The practical limit is defined by the structural integrity of the material and the diameter.

Pretty hard to spin 150 pounds of Jell-O 3600RPM.


Tell me how you determined your infinite answer? 

Sure and no problem, 150lbs of jello in an appropriate container.  Why not.

dualsport54

  • Newbie
  • *
  • Posts: 13
Re: reduction of rotating mass vs efficiency
« Reply #24 on: June 05, 2010, 02:33:08 AM »
Wow, again the practical purpose of the post is being derailed. 

Start at .000000001 hp and spin that flywheel of 150lbs.  How many rpm can be reached before the power produced will no longer allow for any further rpm.  That is the required power to spin that mass at that velocity.  Start adding incremental power, by any means, until the next rpm limit is met. 

Given a 150 lb flywheel (or any weight) and accelerated by a .000000001 hp source of power (or any input power), assuming the flywheel exists in a totally frictionless environment (no air, perfect bearings, no influencing fields, etc.), the flywheel will accelerate continuously until it looses structural integrity and self destructs. The incremental power you speak of to reach, what you refer to as "the next rpm limit" is the power required to come into equilibrium with the frictional losses of your specific situation (bearing efficiency, atmospheric influences surrounding flywheel, eddy currents generated by flywheel movement in ambient magnetic fields, etc.). It is these losses that cause your flywheel to decelerate to a stop when a driving influence is removed. A flywheel is an energy storage device. Given a "perfect" environment... once spinning a flywheel would continue to spin forever until acted on by some outside influence.

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #25 on: June 05, 2010, 04:51:47 AM »
So you are saying exactly what I have said in so many posts.  Thank you. 

bob g

  • Hero Member
  • *****
  • Posts: 1107
  • 8.8kwatt idi diesel thermal conversion unit
    • microcogen.info
Re: reduction of rotating mass vs efficiency
« Reply #26 on: June 05, 2010, 07:27:56 AM »
AMAZING!

 ::)


glad we got that settled

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Watt

  • Guest
Re: reduction of rotating mass vs efficiency
« Reply #27 on: June 05, 2010, 01:33:45 PM »
AMAZING!

 ::)


glad we got that settled

bob g


 ::)   

Nicest thing you've posted yet. 

 :-*

Peter-

  • Newbie
  • *
  • Posts: 13
Re: reduction of rotating mass vs efficiency
« Reply #28 on: June 09, 2010, 07:18:38 PM »
Sorry 'bout that, Tom. Re-posting in the other thread here so people can follow it..

I felt the need to clarify my viewpoint instead of simply giving up on it.

Here is what I have so far to work with: an older Tecumseh 5-horse in good condition, and collecting mags at the moment. Rather powerful, I already got a blood blister from 2 mags. Also some decent electonic equipment incl. a expensive DMM and a surplus scope which I had for years. I still want a scale to measure fuel weight and a non-contact (IR) thermometer.

For the most part I'm stuck with accepting a range of values from most engineering manuals, such as BTU's per gallon, etc.

I have to offer my real-world experience and commentary about this, though.
In the steel and welding shop where I worked, there was a very antique machine which basically ran on flywheel power. It would punch holes, cut and notch steel plate, etc. It was built in the late 1800's or early 1900's.

It would punch a 1 inch hole through 1/2 inch plate as fast as you could feed it. It has a cast iron flywheel 9 inches thick by 4 feet in diameter, driven by a 3-horse electric motor. It was geared down so the wheel was only at a few hundred RPM. The manufacturer advertised an 80-ton force through a 2-inch stroke length.

Nobody cared how fast it accelerated; you only had to start the machine once, in the morning. Every hole punched became cheaper to do after that. It lost perhaps less than a dozen RPM after each hole. The electric motor only had to supply enough power to keep the RPM within working range.

I apply the same idea to a stationary genset. Regardless if it's diesel or gas, I assume you want a fairly constant RPM, to be achieved with both governors and flywheels. Constant RPM for years on end equals money saved. Especially for AC. The savings are gained by not having to accelerate much except when there are peak demands. Also less "wear and tear" and not having to re-start.
This doesn't even get into re-using the "waste heat" from water jackets and exhaust.

I view it as the mechanical equivalent of large capacitors and inductors. Sure you are going to lose some due to friction or resistance. But the losses are tiny compared to what is available through something over-sized, in order to over-ride both the internal losses and the actual surges in demand. The wind and solar guys have exactly the right idea in this regard, using batteries.

A car alt on a mower engine is a whole different ball of wax: there isn't much concern for efficiency there, but rather dump a bunch of power ASAP.

Overall, I do not deny that it's gonna cost you and energy isn't free; rather I argue that such things could be *way* more efficient, and IMHO a heavy flywheel and engine governor is the way to go for constant-speed applications.