Author Topic: Engine / Flywheel mass discussion  (Read 9564 times)

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Watt

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Engine / Flywheel mass discussion
« on: May 27, 2010, 12:21:45 AM »
Peter, the bigger the flywheel the more mass and therefore the more btu required to sustain rpm....  On another note, keeping the rotating assembly as light as possible, improving efficiency and removing as much mass by way of moving components in the coupling will increase watts per power in.

Also, if that battery was so flat as to barely start the engine, my guess would be that it would not ever accept much of a charge once running and charging. 

Because we have confirmed you have an electronic ignition and I assume electronic fired injectors, install a duty meter or pulse width meter accross the injector wires to one injector.  Now start the engine and let it idle at normal operating temperature.  Then, turn on the head lights as suggested.  You'll notice the duty cycle increasing / pulse width increasing.  Now, if you have say 50 watt head lamps x2, you'll find the power required ( fuel ) will be about 300 watts equivalent running off that car engine.  Most is exiting the tail pipe and the rest is through the radiator and wiring.... 


Quote
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 but only for very short burst but none can be more of a load than that available as energy. 

Point taken. Mine is a 1998 4-banger with ecm and etc. The flattest battery I ever had in it, barely cranked it enough to start. The tach didn't show any difference. However, I was picturing a different scenario during this discussion: mainly, something that is basically running all the time without deep discharge. Much lke a stationary power plant. I take it that this isn't the case. I do wonder if enough flywheel couldn't overcome even that though; because I've never seen a car alt stay above a few amps for more than like 5 minutes. They put a bunch of power right away and then taper right off as the battery tops up.

bob g

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Engine / Flywheel mass discussion
« Reply #1 on: May 27, 2010, 01:41:54 AM »
"Peter, the bigger the flywheel the more mass and therefore the more btu required to sustain rpm....  On another note, keeping the rotating assembly as light as possible, improving efficiency and removing as much mass by way of moving components in the coupling will increase watts per power in. "


i would strongly disagree with this statement in total,
some of the most efficient engines on the planet have enormous mass!

the only thing cutting flywheel mass will do, is reduce windage losses which are so small so as to be almost unmeasurable outside of a very
well equipped test cell., removing mass from a drive coupling will be unmeasurable outside of an incredibly precision test cell

if by cutting mass on a typical 4 banger you increase the efficiency of the alternators output by even 1/10% i would be shocked.

generally speaking reduction of mass for a genset is about the last thing you want to do, unless
you plan on making a portable unit that you can backpack into a remote site. even then it is very unlikely that it will be even close to
as efficient as a very heavy high mass stationary model.

once a heavy flywheel is up to speed it takes no more btu's to keep it spinning than does a light flywheel (not accounting for windage losses
which are infinitesimal)

further efficiency has nothing to do with the btu's value of the fuel or amount of fuel put into an engine, efficiency is the measure of
how much power you get out (in btu's) vs the fuel consumed in btu's,
engine type and design, along with size (generally favoring larger high mass versions) alternator type and design (again generally favoring
larger high mass versions) are the primary factors dictating the efficiency of a genset as a system and is expressed as overall efficiency.

bottom line, there is no replacement for displacement and that goes for both engine and alternator when it comes to getting maximum efficiency.

certainly one can build up a very light weight aluminum block engine, driving a small lightweight car alternator to charge a battery bank, and
work on making it as light as possible, but

it will burn twice the fuel per kwatt/hr produced of a heavy high mass genset that might weigh over a half ton or twenty times the weight of the little fellow.

nothing wrong with small compact and lightweight, but it is not the direction to go for high efficiency.

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

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Engine / Flywheel mass discussion
« Reply #2 on: May 27, 2010, 04:38:34 AM »

So then why don't we have huge heavy gasoline engines?  Huge diesel engines exist due to the large amounts of energy in fuel oils.  Are you saying a lawn mower engine spinning a thousand pound flywheel can do the same work the same lawnmower engine does spinning just enough mass to complete its cycles?  How long does it take to use a 5hp lawn mower engine to spin up that 1,000 pounds to 3,000 rpm and then how much fuel will be required to sustain that load?  First of all, I hope you have a huge starter to get the flywheel spinning just to get the engine to start.  Try it by hand, spin that thousand pounds for an hour and tell me if you'd rather be spinning one weighing 1 pound.

Cut that 4 banger down to 1 cylinder, run that same alternator under a constant load.  At the least the energy saved will be that required to rotate the other mass in the three cylinders. 

What about friction in your no more mass statement?  Why will 1hp keep a motorized bicycle moving at 30 mph but, only move a train a inches per hour? 

And again, Power out vs power in.  MASS   Ok so you say no more power to keep a flywheel moving once up to speed, so this wouldn't burden efficiency?  What happens once the power is added to the engine with the huge flywheel?  Not only does the flywheel have to be brought back up to speed but the load has to be compensated at the same time.  Huge mass stores energy but once overcome....... Again, as stated earlier, Mass is great for starting loads. 

Another so why then....  Why not have huge heavy blades on wind turbines maybe steel or hollow fiberglass filled with lead?  Forgetting fatigue and of course hoisting, the required wind speed to get heavy blades moving would be huge.  Once moving, heavy blades would store energy and none the less require a larger amount of wind than that of wood blades to keep moving.  How much energy is in wind and what's the limit...

As far as the engine block, you must be reading more into the post.  Short of reducing friction from piston and ring interference and well lighter for driven car......  Again, not part of my post so I'll quit...

Reducing heat rejection into the block / air, what ever cooling media, would most definitely increase efficiency allowing more fuel to be converted to mechanical energy.

No replacement for displacement is an old term used when naturally aspirated engines of all types were most common and charging atmospheres into an engine was brutal.  Ole turbocharged 1400cc 85ci 4 bangers in reference are making, commonly, 1000hp ( at 8,000 rpm ) where a big ole bbc at 10289cc 632 ci v8 of equal hp rating is required for equal btu rating.  work over time = hp, work = btu...  now which one is more efficient?  the 4 banger, less friction and so on.  Which one will work better as a power source for generating electricity? the bbc... which one will pump water better?  The 4 banger.  Which one will last longer, lol the bbc....

One more how come in close. 

Why are we moving away from v8's and huge SUV transportation in the U.S. and possibly else where?  It's not because we are trying to save from red light to red light, as far as getting the mass up to speed, it's because driving down the road with all the mass requires added energy. 

Single cylinder engines are at a disadvantage of sorts.   Extra mass is required to not only store energy but required to complete its cycles.  If there were no mass, all stored energy from pulling the start rope would be absorbed by the compression stroke.  So we pull harder.  Mass is required to compress the air up until the power stroke.  Once in the power stroke, too small a mass would increase rpm abruptly and cause erratic rpm fluctuation between power and compression cycles.  Even the exhaust stroke requires energy requiring the small amount of mass to over come that stroke then the intake stroke and further the compression stroke.  Not to mention torsional dampening, or the lack thereof.  So hence minimizing the mass. 

Again, what is the most efficient engines running as fuel and at what rpm?

Diesel engines, now there we go....  another topic....

"Peter, the bigger the flywheel the more mass and therefore the more btu required to sustain rpm....  On another note, keeping the rotating assembly as light as possible, improving efficiency and removing as much mass by way of moving components in the coupling will increase watts per power in. "


i would strongly disagree with this statement in total,
some of the most efficient engines on the planet have enormous mass!

the only thing cutting flywheel mass will do, is reduce windage losses which are so small so as to be almost unmeasurable outside of a very
well equipped test cell., removing mass from a drive coupling will be unmeasurable outside of an incredibly precision test cell

if by cutting mass on a typical 4 banger you increase the efficiency of the alternators output by even 1/10% i would be shocked.

generally speaking reduction of mass for a genset is about the last thing you want to do, unless
you plan on making a portable unit that you can backpack into a remote site. even then it is very unlikely that it will be even close to
as efficient as a very heavy high mass stationary model.

once a heavy flywheel is up to speed it takes no more btu's to keep it spinning than does a light flywheel (not accounting for windage losses
which are infinitesimal)

further efficiency has nothing to do with the btu's value of the fuel or amount of fuel put into an engine, efficiency is the measure of
how much power you get out (in btu's) vs the fuel consumed in btu's,
engine type and design, along with size (generally favoring larger high mass versions) alternator type and design (again generally favoring
larger high mass versions) are the primary factors dictating the efficiency of a genset as a system and is expressed as overall efficiency.

bottom line, there is no replacement for displacement and that goes for both engine and alternator when it comes to getting maximum efficiency.

certainly one can build up a very light weight aluminum block engine, driving a small lightweight car alternator to charge a battery bank, and
work on making it as light as possible, but

it will burn twice the fuel per kwatt/hr produced of a heavy high mass genset that might weigh over a half ton or twenty times the weight of the little fellow.

nothing wrong with small compact and lightweight, but it is not the direction to go for high efficiency.

bob g

Watt

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Engine / Flywheel mass discussion
« Reply #3 on: May 27, 2010, 05:02:42 AM »
http://www.physicsforums.com/showthread.php?t=201254

Just for giggles on power required to keep a given mass spinning, lol in a vacuum chamber if you wish.

Wonder what power it would take to spin a standard unsharpened pencil?  Bet it's not free... 

TomW

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Engine / Flywheel mass discussion
« Reply #4 on: May 27, 2010, 07:24:43 AM »
I am very interested in this flywheel discussion.

Not interested in getting involved as I likely suffer from some old skewl misconceptions.

Things I know from experience are:

Take the blade off many vertical shaft lawnmowers and the motors don't seem to run well. Missing flywheel??

Several chain saws I replaced centrifugal clutches on would not even start without the clutch on.

I always figured the fltwheel stored power albeit small that helps the IC cycle operate smoothly and then mostly at low speeds?

Bob;

Several times you mention "not accounting for windage losses" Maybe I know this by another term? What do you mean here?

Life has been my teacher and laboratory on most stuff but I have been drawn through the keyhole of several college level physics courses at a time I was mostly just overwhelmed by the math.

As an aside I would mention modern devices are built to a cost with many corners cut and compromises made. What makes a profit may not jibe with what is mechanically "best" or "most efficient".

Thanks.

Carry on the discussion and I will leave it at that.

Tom

bj

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Engine / Flywheel mass discussion
« Reply #5 on: May 27, 2010, 08:27:48 AM »
Lots of points made in this thread, but until some common measurements are used, it will, or could continue forever.
If you rate on power produced versus engine size, there can be lots of errors. 
Trying to rate on power produced per unit of fuel might be better, but only for the same fuel.
I can build an engine that will put out 2 HP per cubic inch naturally aspirated.  Sounds good until you look
at how much fuel it took to do it.  If you want to win a race, it means nothing.  If you want to run a genset to
power your home, it means a lot.
To make any useful sense out of it, you need to compare apples to apples.
Just my opinion.
"Even a blind squirrel will find an acorn once in a while"
bj
Lamont AB Can.

bob g

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Engine / Flywheel mass discussion
« Reply #6 on: May 27, 2010, 11:23:16 AM »
lets start with the lawnmower

the reason it is built light is so you can manhandle the damn thing around the yard,


windage losses

that is the amount to drag placed upon a moving object by the air it is rotating in, presumably a high mass flywheel will be larger
if made of the same material than a low mass one, so therefore it will have more drag. but...

windage losses are very small until you start to get rediculous in comparisons, such as a lawnmower flywheel which might weigh a couple
lbs and is 8" in diameter, vs a 1000 lb unit that is 36" in diameter,, then you "might" find a measurable difference between the two.

what you would likely be measuring though would be the frictional drag on the woefully undersized main brgs

what  i am saying is this

if you take the lawnmower engine, or rather a horizontal shaft engine such as a briggs 5hp, you will find it to have a cast iron flywheel
remove and replace it with a 5hp briggs vertical shaft mower engine which uses an aluminum flywheel you will find that you have cut the
weight by well over a pound, perhaps two pounds. but
the result will be an engine that does not run smoothly and will not produce any measurable gain in efficiency outside the margins of error.

as all this pertains to reducing the size of cars,

the predominate increase in mpg from a large boxy suv and a small aerodynamic car is one of wind drag, followed by rolling resistance

i can move along pretty quickly with a sheet of plywood sitting upon my head, and do it over a considerable distance, however
if i hold it out in front of me flat to the wind, i cannot move very fast or go very far without tiring.

bottom line is this, if you want to improve charging efficiency of a small engine driven alternator, learn how best to do it
worrying about reducing mass is about the least effective means to that end that i can think of. should one persue the reduction of
mass and does so with the ability to accurately measure the overall efficiency he is likely to find that the increase in efficiency is going to
be far less than 1%, it won't even be close to one percent.

when it comes to btu content of differing fuels, that factor can be significant but plays no role in efficiency of an engine

diesel has about 138kbtu per gallon and gas has about 120kbtu, so one would think that a gas engine would have to be less efficient
than a diesel engine based on this alone, generally this is true but not because of the btu content of the fuel.

for instance the university of wisconsin has a research lab where they have tested a cat 3401 engine in dual fuel mode, where the vast majority
of the fuel consumed is gasoline and the diesel is used as pilot ignition, their reported efficiency tops 54% making it nearly the most efficient
internal combustion engine on the planet, and in dual fuel mode that engines efficiency is about 20 percent more efficient than it is running on straight diesel fuel.

another example, CSX the railroad folks have reported that they can move a ton-mile something on the order of 400plus miles per gallon of fuel
(maybe that was 200 plus miles i forget the exact number) however
here is an example of extremely high mass being able to move a ton of freight many times further than any other form of transport (land based)
per gallon of fuel consumed.  throw a ton in the back of even the best pickup truck and take off, you might get 30 miles per gallon in some highly efficient diesel pickup. throw another ton on there and forget it.

in conclusion

adding flywheel mass to a small engine is not going to generally help with battery charging, just as reducing the weight of the flywheel is not
going to increase the efficiency either.

if anyone is serious about increasing charging efficiency using an automotive alternator, pm me i will provide you with several hours of reading

this is a subject that i am intimately familiar with, i also have a test cell and actively do research and development of alternators for battery charging, and i have to tell ya...

while you are whittling away mass from your flywheels and drive trying to increase efficiency, i can increase the efficiency of an alternator twenty times more without doing anything with the mechanical systems.

anybody wanting to know, and willing to read let me know

btw, bj:

i don't rate efficiency by fuel btu, engine size, or anything other than

how many btu's of fuel are consumed to produce how many btu's of electrical power

if i burn 1000 btu of fuel (and i don't care if it is diesel, gas, alcohol, etc) and i get out 500 btu's of electrical power
then i have a system that has an overall efficiency of 50%

finally i might factor in the price of the fuel to get to the bottom line and steer me toward a particular setup
where i might well pick a less efficient system if it were to be able to use a cheaper fuel, then...

it comes down to cost per kwatt/hr produced

and we can take that analysis much further by factoring in first cost, repairs and maintenance costs, depreciation, and end of life scrap value.

in practice and considered for use to power a home, the large single cylinder slow speed diesel engine's work out to be about twice as efficient
as any gas engine driven genset. they can burn alternate fuels much easier meaning their fuel cost are fractions of a gas set, and the lifespan
is generally much higher.

and you don't see those boys taking any mass off the flywheels, if anything you see them adding mass everywhere they can.

bob g

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

bj

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Engine / Flywheel mass discussion
« Reply #7 on: May 27, 2010, 06:48:13 PM »

   I think you and I agree Bob--you just said it better.
"Even a blind squirrel will find an acorn once in a while"
bj
Lamont AB Can.

Watt

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Engine / Flywheel mass discussion
« Reply #8 on: May 28, 2010, 12:19:48 AM »

We're going in circles here Bob.


More rotating mass requires more energy than less rotating mass. 

Back to the task at hand.  Generate electricity using a lawn mower engine and an alternator ( which has mass ).  How much mass do we have and how much mass is required to start all possible loads?  Remove everything else and see how much fuel is saved doing so. 

Mass in a diesel is for obvious reasons and as stated....  Biggest obvious reason is 450 static pounds of compression and much higher dynamic pressures....  I've logged, with cylinder pressure monitor devices, over 5,000psi inside cylinders with 125mm3 fuel and 3 atmosphers at sea level charge on diesels.  Considering adiabatic, fuel only slightly increased pressure within.  3500 adiabatic air charge +1500psi fuel ignition.

I can only drag my jaw on the floor in reference to 54% efficiency in the mentioned example.  25% is what the rest of us deal with.

 




lets start with the lawnmower

the reason it is built light is so you can manhandle the damn thing around the yard,


windage losses

that is the amount to drag placed upon a moving object by the air it is rotating in, presumably a high mass flywheel will be larger
if made of the same material than a low mass one, so therefore it will have more drag. but...

windage losses are very small until you start to get rediculous in comparisons, such as a lawnmower flywheel which might weigh a couple
lbs and is 8" in diameter, vs a 1000 lb unit that is 36" in diameter,, then you "might" find a measurable difference between the two.

what you would likely be measuring though would be the frictional drag on the woefully undersized main brgs

what  i am saying is this

if you take the lawnmower engine, or rather a horizontal shaft engine such as a briggs 5hp, you will find it to have a cast iron flywheel
remove and replace it with a 5hp briggs vertical shaft mower engine which uses an aluminum flywheel you will find that you have cut the
weight by well over a pound, perhaps two pounds. but
the result will be an engine that does not run smoothly and will not produce any measurable gain in efficiency outside the margins of error.

as all this pertains to reducing the size of cars,

the predominate increase in mpg from a large boxy suv and a small aerodynamic car is one of wind drag, followed by rolling resistance

i can move along pretty quickly with a sheet of plywood sitting upon my head, and do it over a considerable distance, however
if i hold it out in front of me flat to the wind, i cannot move very fast or go very far without tiring.

bottom line is this, if you want to improve charging efficiency of a small engine driven alternator, learn how best to do it
worrying about reducing mass is about the least effective means to that end that i can think of. should one persue the reduction of
mass and does so with the ability to accurately measure the overall efficiency he is likely to find that the increase in efficiency is going to
be far less than 1%, it won't even be close to one percent.

when it comes to btu content of differing fuels, that factor can be significant but plays no role in efficiency of an engine

diesel has about 138kbtu per gallon and gas has about 120kbtu, so one would think that a gas engine would have to be less efficient
than a diesel engine based on this alone, generally this is true but not because of the btu content of the fuel.

for instance the university of wisconsin has a research lab where they have tested a cat 3401 engine in dual fuel mode, where the vast majority
of the fuel consumed is gasoline and the diesel is used as pilot ignition, their reported efficiency tops 54% making it nearly the most efficient
internal combustion engine on the planet, and in dual fuel mode that engines efficiency is about 20 percent more efficient than it is running on straight diesel fuel.

another example, CSX the railroad folks have reported that they can move a ton-mile something on the order of 400plus miles per gallon of fuel
(maybe that was 200 plus miles i forget the exact number) however
here is an example of extremely high mass being able to move a ton of freight many times further than any other form of transport (land based)
per gallon of fuel consumed.  throw a ton in the back of even the best pickup truck and take off, you might get 30 miles per gallon in some highly efficient diesel pickup. throw another ton on there and forget it.

in conclusion

adding flywheel mass to a small engine is not going to generally help with battery charging, just as reducing the weight of the flywheel is not
going to increase the efficiency either.

if anyone is serious about increasing charging efficiency using an automotive alternator, pm me i will provide you with several hours of reading

this is a subject that i am intimately familiar with, i also have a test cell and actively do research and development of alternators for battery charging, and i have to tell ya...

while you are whittling away mass from your flywheels and drive trying to increase efficiency, i can increase the efficiency of an alternator twenty times more without doing anything with the mechanical systems.

anybody wanting to know, and willing to read let me know

btw, bj:

i don't rate efficiency by fuel btu, engine size, or anything other than

how many btu's of fuel are consumed to produce how many btu's of electrical power

if i burn 1000 btu of fuel (and i don't care if it is diesel, gas, alcohol, etc) and i get out 500 btu's of electrical power
then i have a system that has an overall efficiency of 50%

finally i might factor in the price of the fuel to get to the bottom line and steer me toward a particular setup
where i might well pick a less efficient system if it were to be able to use a cheaper fuel, then...

it comes down to cost per kwatt/hr produced

and we can take that analysis much further by factoring in first cost, repairs and maintenance costs, depreciation, and end of life scrap value.

in practice and considered for use to power a home, the large single cylinder slow speed diesel engine's work out to be about twice as efficient
as any gas engine driven genset. they can burn alternate fuels much easier meaning their fuel cost are fractions of a gas set, and the lifespan
is generally much higher.

and you don't see those boys taking any mass off the flywheels, if anything you see them adding mass everywhere they can.

bob g

bob g

Watt

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Engine / Flywheel mass discussion
« Reply #9 on: May 28, 2010, 12:41:53 AM »
lets start with the lawnmower

the reason it is built light is so you can manhandle the damn thing around the yard,


windage losses

that is the amount to drag placed upon a moving object by the air it is rotating in, presumably a high mass flywheel will be larger
if made of the same material than a low mass one, so therefore it will have more drag. but...

windage losses are very small until you start to get rediculous in comparisons, such as a lawnmower flywheel which might weigh a couple
lbs and is 8" in diameter, vs a 1000 lb unit that is 36" in diameter,, then you "might" find a measurable difference between the two.

Try spinning something similar by hand and then reply.

what you would likely be measuring though would be the frictional drag on the woefully undersized main brgs

what  i am saying is this

if you take the lawnmower engine, or rather a horizontal shaft engine such as a briggs 5hp, you will find it to have a cast iron flywheel
remove and replace it with a 5hp briggs vertical shaft mower engine which uses an aluminum flywheel you will find that you have cut the
weight by well over a pound, perhaps two pounds. but
the result will be an engine that does not run smoothly and will not produce any measurable gain in efficiency outside the margins of error.


How much experience to you have on dynamo-meters?  Chassis or engine?  Try this, drive your vehicle on one, change only the wheel and tire weight.  Dyno stock and with the changes and see which one produces a larger wheel hp and torque.  Proven many many times.  Lighter rotating mass equals more available power to wheels. 

as all this pertains to reducing the size of cars,

the predominate increase in mpg from a large boxy suv and a small aerodynamic car is one of wind drag, followed by rolling resistance

i can move along pretty quickly with a sheet of plywood sitting upon my head, and do it over a considerable distance, however
if i hold it out in front of me flat to the wind, i cannot move very fast or go very far without tiring.

bottom line is this, if you want to improve charging efficiency of a small engine driven alternator, learn how best to do it
worrying about reducing mass is about the least effective means to that end that i can think of. should one persue the reduction of
mass and does so with the ability to accurately measure the overall efficiency he is likely to find that the increase in efficiency is going to
be far less than 1%, it won't even be close to one percent.

when it comes to btu content of differing fuels, that factor can be significant but plays no role in efficiency of an engine

diesel has about 138kbtu per gallon and gas has about 120kbtu, so one would think that a gas engine would have to be less efficient
than a diesel engine based on this alone, generally this is true but not because of the btu content of the fuel.

for instance the university of wisconsin has a research lab where they have tested a cat 3401 engine in dual fuel mode, where the vast majority
of the fuel consumed is gasoline and the diesel is used as pilot ignition, their reported efficiency tops 54% making it nearly the most efficient
internal combustion engine on the planet, and in dual fuel mode that engines efficiency is about 20 percent more efficient than it is running on straight diesel fuel.

another example, CSX the railroad folks have reported that they can move a ton-mile something on the order of 400plus miles per gallon of fuel
(maybe that was 200 plus miles i forget the exact number) however
here is an example of extremely high mass being able to move a ton of freight many times further than any other form of transport (land based)
per gallon of fuel consumed.  throw a ton in the back of even the best pickup truck and take off, you might get 30 miles per gallon in some highly efficient diesel pickup. throw another ton on there and forget it.


Have the particulars for success?  Didn't they also reclaim energy that was otherwise wasted? 
in conclusion


adding flywheel mass to a small engine is not going to generally help with battery charging, just as reducing the weight of the flywheel is not
going to increase the efficiency either.

if anyone is serious about increasing charging efficiency using an automotive alternator, pm me i will provide you with several hours of reading

this is a subject that i am intimately familiar with, i also have a test cell and actively do research and development of alternators for battery charging, and i have to tell ya...

while you are whittling away mass from your flywheels and drive trying to increase efficiency, i can increase the efficiency of an alternator twenty times more without doing anything with the mechanical systems.

anybody wanting to know, and willing to read let me know

btw, bj:

i don't rate efficiency by fuel btu, engine size, or anything other than

how many btu's of fuel are consumed to produce how many btu's of electrical power

if i burn 1000 btu of fuel (and i don't care if it is diesel, gas, alcohol, etc) and i get out 500 btu's of electrical power
then i have a system that has an overall efficiency of 50%

finally i might factor in the price of the fuel to get to the bottom line and steer me toward a particular setup
where i might well pick a less efficient system if it were to be able to use a cheaper fuel, then...

it comes down to cost per kwatt/hr produced

and we can take that analysis much further by factoring in first cost, repairs and maintenance costs, depreciation, and end of life scrap value.

in practice and considered for use to power a home, the large single cylinder slow speed diesel engine's work out to be about twice as efficient
as any gas engine driven genset. they can burn alternate fuels much easier meaning their fuel cost are fractions of a gas set, and the lifespan
is generally much higher.

and you don't see those boys taking any mass off the flywheels, if anything you see them adding mass everywhere they can.

bob g

bob g

On with efficiency, why are exhaust gas temperatures of a diesel engine lower idling, no load, compared to exhaust gas temperatures of a gasoline engine idling, no load?  Again, mass requried for complete cycle on both.   A diesel idles at 50 to 1 air fuel ratio, where a gas engine idles at 14 to 1 ratio.  Same rpm for both and same displacement for both.  You won't find it is because the extra mass is helping the diesel, but you will find the amount of fuel rejected into the cooling and exhaust system is greater in a gas engine than that of a diesel.  Simple explanation is this, more fuel is being converted into mechanical energy in that diesel.  Try it, I have handy infrared devices that tell the tale.  As mentioned, more  btu available in fuel oil than gasoline.  So, volume is not a great indication or measure.  And yes, propane and other fuels as catalysts are common..

bob g

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Engine / Flywheel mass discussion
« Reply #10 on: May 28, 2010, 01:36:23 AM »
if all you change is the flywheel mass in a car, and place it on a dyno there will be no measurable difference in hp
changing to lighter wheels but using the same tires will also not increase hp to those wheels

its really simply physics, and what you are describing is measured in fractions of a percentage point, at best
and beyond the means to be able to measure by any common dyno on the planet.

as for turning a shaft by hand

a well conditioned man can produce approx 1/2 hp, that is with his legs predominately, and of this total amount of power
his ability to produce hp by "hand" might well be measured in hundredths of a hp.

properly mounted a heavy flywheel will not require measurably more hp to turn it than a light flywheel, even though you might
feel like you actually feel it, remember it is unlikely you can produce even 1/100th hp spinning a shaft by hand. this is not to say if
the difference in weights is taken to extremes that this might not be the case, but it will come down to predominately windage losses
and some brg friction "if" one were to change from perhaps a 10lb flywheel to a 500lb flywheel, but that is an exception and not the rule

generally we have a relatively narrow range to work within when it comes to flywheels, taking even a lb off of a 10lb flywheel is generally pretty hard to do without causing issues with strength. we certainly are not going to reduce the flywheel weight by half?? and even if we did
the engine is likely going to exhibit operational problems because of it, and it will not become a more efficient producer of power.  it just isn't going to happen.

there is only one reason folks reduce rotating mass with cars in relation to dyno's, that is to reduce the reaction time of the engine. in other words
a lighter rotating mass will accelerate quicker than a heavy rotating mass, the hp will remain the same. drag racers and circle track boys reduce flywheel weight so that the engine can rapidly gain rpm, providing fast times and a bit quicker out of corners, they give up a bit of instantaneous torque in the process and also usually end up with an even rougher running engine at lower speeds.

as for exhaust temps and the differences between the otto and diesel cycle, that is a tangent apart from you assertion that reduction in rotating mass will increase efficiency.

the largest engine's on the planet are those used in ocean going container ships, there rotating mass is measured in tons and their efficiency is second to no other engine.

on the other end of the spectrum are small displacement single cylinder diesel engine's that do well to make upper 20's in efficiency, cutting rotating mass is not going to improve the efficiency or the manufactures would have done so.

something a bit more common around my quarters is the changfa s195 idi diesel engine, it weighs approx 350lbs, is rated at 12hp continous
at 2000rpm, and is dyno good at 32% thermal efficiency. with an appropriately sized genhead of 7.5kwatt capacity the engine will make 7kwatts continuously and return an overall efficiency of approx 25.6%

no gas engine in this class will even come close, most will be doing good to return 15% overall efficiency and none will make 7kwatts continuous
with a 12hp rating.
i don't care how much rotating mass you remove the efficiency is not going to change in a measurable way, i know this because i have a test cell
where i can actually measure the difference in bsfc when switching in a 40 watt light bulb.

the same engine driving a 12kwatt head (typically thought of as a bad match, because of higher windage losses) works out to actually be more efficient overall by returning an overall efficiency of approx 27% and will make 8kwatts continuous

same engine, same drive but one head is 50% larger physically, heavier and much higher rotating mass, but it returns a higher overall efficiency?
and makes more power? obviously the bigger head is more efficient to start with, because we know that the windage losses are higher with the larger head, as well as excitation power.

i would challenge you to go ahead and build up a small genset, and do some serious testing, then do your reduction of rotating mass, and then
come back and report your findings. you will find that documenting that supposed increase in efficiency is going to be extremely difficult if not impossible.

my basic point is there are countless other ways to increase efficiency that are easier to do, cheaper to implement, and will return measurable and significant result. all of which should be done and exhausted long before worrying about reduction of rotating mass.

i am no newbie when it comes to this sort of thing, i have a test cell, complete with all the requisite tools to measure just about everything one wants to know, i am also anal about tracking down every last percentage point in efficiency gains and am known for it and often derided for it as well.

the simple and basic gensets that are typical here are those put together often times with small gas engine's belt driving salvaged car alternators
with simple reostat control, made to charge a 12volt battery bank when the wind doesn't blow or the sun doesn't shine.
in my opinion none of them ever get to 15% overall efficiency, and none of them will make any gains by reducing rotating mass, if no other reason than there just isn't much mass to trim away at to start with.

when i mentioned replacing the cast iron flywheel from a horizontal briggs 5hp with an aluminum flywheel from a vertical briggs, it was from experience, i used to build race karts 40 years ago that ran on nitro additive using such modified engine's. there was only one reason to make the change, that was to reduce kart weight and to allow for faster engine acceleration, but
the tradeoff was a pair of engine's that were very hard to start, ran irratically at lower speeds, and were just more finicky than they were with cast iron flywheels.
the difference in weight between iron and aluminum was not much, iirc about 2 lbs tops.

one thing for sure is this, making such a modification for a small genset would be setting yourself up for a very hard to start, erratic running engine, that would be downright miserable to maintain operation of.

but by all means do as you please, don't let me stop ya

:)

bob g

btw, when you get your alternator up close to 80% efficient, from the more typical 45-50% come talk to me about reducing rotating mass

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

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Engine / Flywheel mass discussion
« Reply #11 on: May 28, 2010, 02:45:53 AM »

One note in an earlier post.  As far as the plywood and the wind, try a simialar size piece of foam, same resistance in the wind but now you don't have to hold the same weight.  Easier.

if all you change is the flywheel mass in a car, and place it on a dyno there will be no measurable difference in hp
changing to lighter wheels but using the same tires will also not increase hp to those wheels

What?  If added/freed hp/torque is not being made available to the rear wheels then why on earth are we using aluminum SFI flywheels down the track.  It's not because the extra few pounds reduction in total car weight.

its really simply physics, and what you are describing is measured in fractions of a percentage point, at best
and beyond the means to be able to measure by any common dyno on the planet.

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

as for turning a shaft by hand

a well conditioned man can produce approx 1/2 hp, that is with his legs predominately, and of this total amount of power
his ability to produce hp by "hand" might well be measured in hundredths of a hp.

properly mounted a heavy flywheel will not require measurably more hp to turn it than a light flywheel, even though you might
feel like you actually feel it, remember it is unlikely you can produce even 1/100th hp spinning a shaft by hand. this is not to say if
the difference in weights is taken to extremes that this might not be the case, but it will come down to predominately windage losses
and some brg friction "if" one were to change from perhaps a 10lb flywheel to a 500lb flywheel, but that is an exception and not the rule

generally we have a relatively narrow range to work within when it comes to flywheels, taking even a lb off of a 10lb flywheel is generally pretty hard to do without causing issues with strength. we certainly are not going to reduce the flywheel weight by half?? and even if we did
the engine is likely going to exhibit operational problems because of it, and it will not become a more efficient producer of power.  it just isn't going to happen.

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

On subject, one percent is better than zero percent.  1 cylinder engine to generate 5kw is better than 100 cylinder engines to produce 5kw electricity.


there is only one reason folks reduce rotating mass with cars in relation to dyno's, that is to reduce the reaction time of the engine. in other words
a lighter rotating mass will accelerate quicker than a heavy rotating mass, the hp will remain the same. drag racers and circle track boys reduce flywheel weight so that the engine can rapidly gain rpm, providing fast times and a bit quicker out of corners, they give up a bit of instantaneous torque in the process and also usually end up with an even rougher running engine at lower speeds.

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.

as for exhaust temps and the differences between the otto and diesel cycle, that is a tangent apart from you assertion that reduction in rotating mass will increase efficiency. 

Umm reply to your tangent. 

the largest engine's on the planet are those used in ocean going container ships, there rotating mass is measured in tons and their efficiency is second to no other engine.

Yes, with fuel btu ratings up and beyond 150,000 btu per/gallon. Guess rotating there crankshaft with a lawn mower engine is possible.  

on the other end of the spectrum are small displacement single cylinder diesel engine's that do well to make upper 20's in efficiency, cutting rotating mass is not going to improve the efficiency or the manufactures would have done so.

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.

something a bit more common around my quarters is the changfa s195 idi diesel engine, it weighs approx 350lbs, is rated at 12hp continous
at 2000rpm, and is dyno good at 32% thermal efficiency. with an appropriately sized genhead of 7.5kwatt capacity the engine will make 7kwatts continuously and return an overall efficiency of approx 25.6%

Never challenged this but, you already start with 10% more energy per volume than petrol.  Again, reread the thread.

no gas engine in this class will even come close, most will be doing good to return 15% overall efficiency and none will make 7kwatts continuous
with a 12hp rating.


i don't care how much rotating mass you remove the efficiency is not going to change in a measurable way, i know this because i have a test cell
where i can actually measure the difference in bsfc when switching in a 40 watt light bulb. 

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. 


the same engine driving a 12kwatt head (typically thought of as a bad match, because of higher windage losses) works out to actually be more efficient overall by returning an overall efficiency of approx 27% and will make 8kwatts continuous

same engine, same drive but one head is 50% larger physically, heavier and much higher rotating mass, but it returns a higher overall efficiency?
and makes more power? obviously the bigger head is more efficient to start with, because we know that the windage losses are higher with the larger head, as well as excitation power.

i would challenge you to go ahead and build up a small genset, and do some serious testing, then do your reduction of rotating mass, and then
come back and report your findings. you will find that documenting that supposed increase in efficiency is going to be extremely difficult if not impossible.

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

my basic point is there are countless other ways to increase efficiency that are easier to do, cheaper to implement, and will return measurable and significant result. all of which should be done and exhausted long before worrying about reduction of rotating mass.

i am no newbie when it comes to this sort of thing, i have a test cell, complete with all the requisite tools to measure just about everything one wants to know, i am also anal about tracking down every last percentage point in efficiency gains and am known for it and often derided for it as well.

I too am no newbie, Facts are facts.


the simple and basic gensets that are typical here are those put together often times with small gas engine's belt driving salvaged car alternators
with simple reostat control, made to charge a 12volt battery bank when the wind doesn't blow or the sun doesn't shine.
in my opinion none of them ever get to 15% overall efficiency, and none of them will make any gains by reducing rotating mass, if no other reason than there just isn't much mass to trim away at to start with.

when i mentioned replacing the cast iron flywheel from a horizontal briggs 5hp with an aluminum flywheel from a vertical briggs, it was from experience, i used to build race karts 40 years ago that ran on nitro additive using such modified engine's. there was only one reason to make the change, that was to reduce kart weight and to allow for faster engine acceleration, but
the tradeoff was a pair of engine's that were very hard to start, ran irratically at lower speeds, and were just more finicky than they were with cast iron flywheels.
the difference in weight between iron and aluminum was not much, iirc about 2 lbs tops.

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. 

one thing for sure is this, making such a modification for a small genset would be setting yourself up for a very hard to start, erratic running engine, that would be downright miserable to maintain operation of.

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

but by all means do as you please, don't let me stop ya

:)

bob g

btw, when you get your alternator up close to 80% efficient, from the more typical 45-50% come talk to me about reducing rotating mass

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



My comments in red.  Thanks Mike

TomW

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Engine / Flywheel mass discussion
« Reply #12 on: May 28, 2010, 05:19:38 AM »
bob and watt;

I think you guys should open a fresh thread on this.

You have taken it way beyond the original posters question.

It is interesting so that would be my suggestion.

Maybe I will split it off into its own topic if I have time.

Tom