this is a continuation from this post
http://fieldlines.com/board/index.php/topic,143490.msg965639.html#newwhere 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