Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
I could use of those flywheels. I have a dinky 6A generator that won't run my fridge or my furnace blower; it drops to 90V/45Hz when trying to start either.....
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- Thread starter gar
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mivey
Senior Member
An interesting question. It is not likely that you will increased the fuel burn or reduce the vibration but you could consider capturing the heat.
The low hanging fruit would be to run the exhaust through a heat exchanger. Other measures would include a cooling blanket or even an enclosure with a circulating air loop to capture the radiant heat.
As for the vibration and similar waste, I guess you could "tune" the engine by fine-machining it like a race car to extract more energy per gallon but you would probably peak at about double the efficiency you have now.
Of course with composite materials and higher operating temperatures you could eventually get to rocket status but you might as well get a turbine to start with.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
ICE as a prime mover for a generator has always had a problem with inrush loads, this problem is more related with the response time of the governor lagging the load surge than it is a problem with the alternator handling the inrush, newer electronic speed controls are an improvement for this problem, but can not eliminate it.
I would say electronic fuel injection should have a much faster response time and might be an answer for this but I think the added cost would put a generator out of reach for most and not add that much more time response to make it worth while.
Gars idea of a flywheel would give the governor more time to respond and sounds like a good idea.
I have also notice that most natural gas/LP fueled generators seem to have a faster response time to surges but still have the lagtime just not as bad.
I would say electronic fuel injection should have a much faster response time and might be an answer for this but I think the added cost would put a generator out of reach for most and not add that much more time response to make it worth while.
Gars idea of a flywheel would give the governor more time to respond and sounds like a good idea.
I have also notice that most natural gas/LP fueled generators seem to have a faster response time to surges but still have the lagtime just not as bad.
kwired
Electron manager
- Location
- NE Nebraska
I realize that, and because of what you mention is reason why it can withstand a short duration surge of current like you might encounter with starting a motor. But the prime mover needs to be able to respond to this surge or it will stall. I may be somewhat incorrect, but I would guess the engine is most efficient somewhere near full load rating of the driven generator.
The engine is likely just as capable of providing more power than it is rated for also but also will produce excess heat when doing so. And it also can provide short duration overloads before heating becomes a problem.
As others have mentioned, it is more likely an engine control issue of being able to adjust fuel rates and ignition timing accordingly when a sudden increase in load occurs.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
121102-1117 EDT
Open Neutral:
I had responded to your post yesterday, but the response got destroyed before getting to the Forum. Internet problems and the way Internet Explorer works. So I have to recompose my thoughts.
Yes, a flywheel would probably allow your small generator to separately start the refrigerator and fan motors.
See my photos P29 and P30 at the very end at http://beta-a2.com/EE-photos.html
The large peak power inrush is probably greater than what appears in the plot because the plot data is from 1 second average data from a TED power monitor. I have not set up to get a better short time average. But is is obvious that there is a very large peak inrush. Same is true of the furnace blower motor, but it immediately drops to its steady state value.
The refrigerator peaks are probably 5 to 7 times the steady state power rather than the 3 times in photo P29.
mivey:
The heat capture is important if we can get a sufficiently efficient engine as a starting point. My electric costs have gone from about $0.12/kWh a few years ago to almost $0.16 kWh now. This is likely to rise another 25% in several years. The coal plants are being forced to change to some other fuel. There are people in the state wanting 25% from renewable sources. That is big money. There may be plans for a new large nuclear plant.
The waste heat output can probably provide more efficient use of my gas input than my present furnace and also generate electricity. I do not need heat in the summer except for hot water. So the waste heat in the summer needs to go to cooling. Capital costs become a problem in this case.
But cutting engine size down to that which is sufficient for average electrical requirements rather than peak can have a big energy impact.
The RPM issue is one relating to engine noise, and windage
losses. Vibration is part of the noise problem.
kwired:
Engine peak output is determined by air flow. Peak power and continuous power output of an ICE are about the same. Watch one of the engines on a dyno. Exhaust manifolds running red hot for days of testing, and terribly noisy. Can't run alternators red hot for very long.
The air response time, getting turbo up to speed, is more a problem than getting fuel to an ICE. On my F150 when I floor it there is a momentary lag, but then it takes off like a shot. A turbo on a generator could up efficiency on average, but it won't solve load inrush problems. That is where a flywheel is ideal.
.
Open Neutral:
I had responded to your post yesterday, but the response got destroyed before getting to the Forum. Internet problems and the way Internet Explorer works. So I have to recompose my thoughts.
Yes, a flywheel would probably allow your small generator to separately start the refrigerator and fan motors.
See my photos P29 and P30 at the very end at http://beta-a2.com/EE-photos.html
The large peak power inrush is probably greater than what appears in the plot because the plot data is from 1 second average data from a TED power monitor. I have not set up to get a better short time average. But is is obvious that there is a very large peak inrush. Same is true of the furnace blower motor, but it immediately drops to its steady state value.
The refrigerator peaks are probably 5 to 7 times the steady state power rather than the 3 times in photo P29.
mivey:
The heat capture is important if we can get a sufficiently efficient engine as a starting point. My electric costs have gone from about $0.12/kWh a few years ago to almost $0.16 kWh now. This is likely to rise another 25% in several years. The coal plants are being forced to change to some other fuel. There are people in the state wanting 25% from renewable sources. That is big money. There may be plans for a new large nuclear plant.
The waste heat output can probably provide more efficient use of my gas input than my present furnace and also generate electricity. I do not need heat in the summer except for hot water. So the waste heat in the summer needs to go to cooling. Capital costs become a problem in this case.
But cutting engine size down to that which is sufficient for average electrical requirements rather than peak can have a big energy impact.
The RPM issue is one relating to engine noise, and windage
losses. Vibration is part of the noise problem.
kwired:
Engine peak output is determined by air flow. Peak power and continuous power output of an ICE are about the same. Watch one of the engines on a dyno. Exhaust manifolds running red hot for days of testing, and terribly noisy. Can't run alternators red hot for very long.
The air response time, getting turbo up to speed, is more a problem than getting fuel to an ICE. On my F150 when I floor it there is a momentary lag, but then it takes off like a shot. A turbo on a generator could up efficiency on average, but it won't solve load inrush problems. That is where a flywheel is ideal.
.
JoeStillman
Senior Member
- Location
- West Chester, PA
A diesel engine has higher thermal efficiency due to the higher compression ratio.
I don't know why there aren't more small generators (5-10 kW) with diesel engines. I wanted to use one recently for a small sewage pump installation but I couldn't find one. I wanted diesel because of my own experience with poor fuel stability of gasoline.
I don't know why there aren't more small generators (5-10 kW) with diesel engines. I wanted to use one recently for a small sewage pump installation but I couldn't find one. I wanted diesel because of my own experience with poor fuel stability of gasoline.
Must be limited in your area. Here are some: http://www.generatorjoe.net/subcat.asp?0=541
Availability may be limited due to higher cost also.
K8MHZ
Senior Member
- Occupation
- Electrician
A couple reasons. First, have you ever tried to pull start a diesel? They have 16:1 compression. I doubt it would be possible to pull start a 10-20 hp diesel engine.
Then, there is the fuel blend issue. You have to use winter blend in the winter and summer blend in the summer or the engine will gum up. That would mean either two tanks or two fuel swaps per year.
They are also pretty loud. It's not the exhaust you hear in a diesel engine, it's the engine block resonating.
K8MHZ
Senior Member
- Occupation
- Electrician
I went to the site and now have questions.....
They list 3600 rpm engine speed. For a diesel? Good luck!
Also, electric/recoil start. Again, for a diesel?
Wiki diesel and check out the max rpm for even a turbocharged diesel with electronic controls.
kwired
Electron manager
- Location
- NE Nebraska
I didn't look real hard, nor have I seen any of these units. It is possible the engine speed is slower and increased via gears to drive the generator at 3600.
Recoil start may need larger diameter pulley to keep from needing to pull so hard but likely can be done.
I can still see problems with cold starting, especially if using recoil starting method.
- Location
- Massachusetts
That is not a problem at all, it just depends on how the engine was designed. Stroke being the biggest issue.
My Duramax diesel runs the same RPMs as any standard automotive engine. On the other hand I have driven gas powered tractors that red lined under 2000 RPM.
I understand Diesel engines. The technology is advancing everyday. I will admit that most of the chinese made diesels are throwaway. Yanmar has good luck with their 3600 RPM engines. I have personally started a yanmar diesel with recoil start. (8 kW model) It ain't that bad. They are just twice the price of a gas burner.
I saw for high speed engines >1000 on wiki. Didn't see a max speed. Some passenger car diesels are rated max power @4000 RPM.
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Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
Fuel source
Fuel source
I've looked long & hard at the Diesel vs. propane question on a ~20KW unit. {If you have piped natural gas, the same issues apply...}
Unless you use the Diesel fuel continuously, it's a PITA; it has a definite lifetime, needs stirring & bug-a-cide.
Diesel engines need far more frequent oil changes.
Propane always burns clean, it's vapor. It stores forever. It does need ignition to start. The EPA does not freak re: underground storage in a watershed.
The big issue with propane is can you get refilled when you need it?
Fuel source
I've looked long & hard at the Diesel vs. propane question on a ~20KW unit. {If you have piped natural gas, the same issues apply...}
Unless you use the Diesel fuel continuously, it's a PITA; it has a definite lifetime, needs stirring & bug-a-cide.
Diesel engines need far more frequent oil changes.
Propane always burns clean, it's vapor. It stores forever. It does need ignition to start. The EPA does not freak re: underground storage in a watershed.
The big issue with propane is can you get refilled when you need it?
Yes. But it is one of the big issues. Others are
- Pressurized cylinder of flammable gas.
- Fuel system is more complicated (increased possibility of failure).
- Propane can become very dangerous if lines are broken.
- More expensive to operate by as much as 3-times the fuel consumption compared to diesels.
- Shorter life expectancy by a factor or 10 to 1for air-cooled models and 3 to 1 for water-cooled models compared to diesel powered GenSets.
- Shorter life than diesel engines.
kwired
Electron manager
- Location
- NE Nebraska
I guess that may depend on where you are at and how much propane is used in your area. Where I am at, propane delivery trucks are about as common as diesel delivery trucks, and most are operated by same fuel companies as the diesel anyway. Most of farm fuel tanks anymore have monitoring devices on them, that automatically orders more fuel when it is needed.
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