Author Topic: Slow rpm Chang fa?  (Read 871 times)

bigbad

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Re: Slow rpm Chang fa?
« Reply #15 on: November 09, 2021, 01:59:17 PM »
Don't know if I should continue this thread or start a new one...is there an engine comparable to the Changfa that IS legal to sell in the US...that has similar reliability?  I am looking for water cooled, with an electric starter as an option...removable sleeves....
« Last Edit: November 09, 2021, 02:02:00 PM by bigbad »

guest18

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Re: Slow rpm Chang fa?
« Reply #16 on: November 09, 2021, 03:44:14 PM »
The only engine that is similar to a changfa is a Kubota EA330. The changfa is an  r175 much smaller than a s195.
The kubota is a great engine but be ready to shell out $3,200.00. Unless your lucky to find NOS (New Old Stock) The kubota EA330 likes being ran from 2400-3000 rpm. I would not recommend running a factory stock one at slow speeds. It was discussed earlier. Keep within the manufacturer's operating speed and it should run for a long time. Some people are hell bent on insisting that an engine has to run at extremely slow speeds for it to last. A matter of fact, engines that are not set up to run at Extreme slow speeds can be torn to pieces in a very short time.

Look up and study Critical Speed.

I think Kubota and some other manufacturers had done their homework. Why buck their R&D.

It's funny, some Kubota gensets have well over 20,000 hours before major overhaul.

 Did you look over and read about Veggie's work?
He did some nice work to an S195.
Yes, there are exceptions.

mobile_bob

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Re: Slow rpm Chang fa?
« Reply #17 on: November 09, 2021, 07:10:03 PM »
no problem

NOS= new old stock, or basically new still in the crate never used
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Fred8

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Re: Slow rpm Chang fa?
« Reply #18 on: November 10, 2021, 12:09:19 AM »
Lots here are hell bent on insisting that an engine has to run at extremely slow speeds for it to last. And that is far from the truth. A matter of fact. Extreme slow speeds engines can be torn to pieces in a very short time.

Whom is insisting an engine be run at EXTREMELY slow speeds? Can you provide a Link?  I have NEVER seen anyone mention let alone insist that anywhere so I'd be interested to see where you got that " a lot here" are doing that?

Running an engine at less that full speed  is NOT the same as extremely slow Speeds. Running any engine at around half speed is not either. To me extremely slow would be like Idle and I have NEVER seen anyone recommend that on any forum. The idea that an engine HAS to be loaded up and run at or near full  RPM is extremely ignorant and flies in the face of real world practical applications especially with heavier machinery where longevity due to the cost of having to virtually deconstruct the machine the engine is in to replace it is much more than the engine is worth itself.

Slowing and derating engine speed and output is extremely common in the marine, Mining, power generation agricultural and other application sectors  where oversize engines are slowed and reduced in power output for a number of reasons, Longevity, being a main one.

For the applications and engine sizes of relevance here, running an engine  extremely slow would be producing an output of 1-2 hp and I haven't seen anyone with use of that sort of low power here nor is it discussed anywhere I have seen in the home power generation groups which seems the main interest here as well.


I would think common or not so sense would tell a person that Lugging an engine would be bad for it and unless you were running something like a 3208 CAT at idle, anything in the scope of this Forum would produce useless power at very low speeds and be non viable anyway. That is a whole lot different to running something at reduced speed though.
You would most likley be well enlightened to look up how engine manufacturers rate their engines at Various RPM and see what the Military, power generation and pumping industries do as far as sizing and the speed they run different engines.

Never heard of anyone running an engine extremely slow but that's a big difference between running it under Max RPM and de rating it accordingly. 

Exaggeration of what people are saying to suit ones own proclivities however is a different matter.

guest18

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Re: Slow rpm Chang fa?
« Reply #19 on: November 10, 2021, 12:36:57 AM »
Fred8, I modified my post some. Hopefully I cleared some things up. My understanding is extremely low speed for a stock (unmodified) engine would be an engine running well under a manufactures recommended operating speed. I guess what Iím trying to convey is with a stock engine, most of the time itís best to keep an engine within the manufactures operating Parameters. We both and others understand that when an engine operates at a lower speed the engines hp has to be de-rated.
 

mobile_bob

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Re: Slow rpm Chang fa?
« Reply #20 on: November 10, 2021, 01:20:24 AM »
there are at least 3 schools of thought

1. those that operate within the manufactures recommendations, probably best for longevity.

2. those that operate well under the manufactures recommendations, with added flywheel mass, changes in timing, etc.  nothing wrong with that, so long as you know something about what you are doing and accept some level of risk

3. those that operate at the bleeding edge, flat out max load, with arguable reduced lifespan, and ok if you accept the risks involved and know what you are doing.

me?  with a changfa in a co-gen plant?  i fit comfortably within #3 group!  short runs, full load, flat out.  i accept the risks, also i think i have a pretty good idea what i am doing, with tightly controlled coolant temperatures, monitoring systems, emergency shutdowns, and limited run times.

why?  because i have proven to my satisfaction that peak efficiency comes at full load operation, with an enclosed cooling system (pressurized) operating within 205-214F.  this is where max. efficiency of the engine is attained, max heat recovery from both exhaust and coolant,  and peak power.

results?  yes there will be a reduction is lifespan, in hours, but
the operation calls for a max run time of 2 one hour runs/day, so the engine while running fewer hours before overhaul will last several years.

i figure cost per kw/hr and btu/hr recovered

bottom line is this, every application has its own goals, concerns and risks involved.

i think to hwew' point
you should be aware of the engine's critical speed, that is a valid point.  no engine should be operated at critical speed that is if you want it to last and not have some form of premature failure, some of which can be quite catastrophic like broken crankshafts or engine cases, or mounts.

all you have to do is ride a ferry boat or be anywhere around a diesel locomotive
you can feel the boat vibrate like hell as the throttle opens and the rpm passes through critical speed... and you will note the man with the throttle in his hand does not allow the engine to operate at that speed any longer than is necessary. 

it can be felt in the ground around the train yards, as they throttle up.

small engine's may not demonstrate this effect so plainly, but the thing also has a critical speed that should be avoided.

bob g
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Fred8

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Re: Slow rpm Chang fa?
« Reply #21 on: November 10, 2021, 01:24:00 AM »

Fred8, I modified my post some. Hopefully I cleared some things up.

Well no, you haven't cleared anything up. The points I addressed are unchanged

Quote
Some here are hell bent on insisting that an engine has to run at extremely slow speeds for it to last.   

Please Clarify who these " some are"  with links to where they "insist" The engines be Run at extremely slow Speed and exactly what that is.  Best to  clear up any ambiguity and be accurate don't you think?  The only "Insistence" I can see here is your own in that engines have to be run full tilt.  That notion is completely undermined in industry as I mentioned.


[/quote]A matter of fact at Extreme slow speeds, engines can be torn to pieces in a very short time. Unless lots of modifications are done to an engine.
[/quote]

Again, can you specify and give an example of what an extremely slow speed is ( and a link to those insisting on them and what they are specifying as an example would be best)  and can you explain what those Modifications are?

I haven't read every thread here but I'd be real interested to see what those insisting on extremely slow speeds are saying over all and in context.

As for Critical speed,

"The critical speed of a shaft occurs when the shaft rotational speed is at or close to resonant conditions. In this condition the torsional vibration of the shaft increases greatly, and will impose very high shear stress on the crankshaft. These levels of stress could even cause crankshaft failure."

It is A speed, not every speed below maximum speed on an engine.  Most engines have a speed at which they vibrate at a greater degree, harmonics dictate that an engine cannot be balanced at  Every speed.
Furthermore, the load an engine is driving either direct or by belt will also have it's own harmonics and imbalances and transmit those to the engine and change the speed at which it's natural frequency occurs.

"Extremely slow speed" which again without specification can only be taken to mean at or slightly above idle is more likely to be a product of lugging the engine than anything to do with Critical speed.

If running an engine at lower than full speed was such an inherent danger, one would have to wonder why the Transmissions in modern Vehicles are not set up to run the engine high in the rev range as to lower down and use the torque the engine supplies. 
Many vehicles have gone to larger engines  that produce more torque and rev lower for Fuel economy for one thing.

If this Critical speed you speak of is such an issue. There is no way the engine in my vehicle would have a redline of 7000 RPM but cruise at highway speed at less than 1600 RPM and do it literally all day long nor would it be able to idle for hours in traffic Driving the AC and alternator.

I think it would be pretty clear to most interested in facts rather than pushing an agenda to be seen to be right that running an engine at lower than max speed is not going to tear it up and  running the thing near idle which would be extremely slow is stupid and nonsensical in the first place.  Running any engine at half speed is far from extremely slow not is it going to cause the thing to detonate as you infer.

Again, to clear up any misunderstanding, please specify what you believe is " extremely Slow Speed" and give links to examples where people are insisting this.

I always always relish the opportunity to lean something new as I am sure do others.    :)

mobile_bob

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Re: Slow rpm Chang fa?
« Reply #22 on: November 10, 2021, 01:53:57 AM »
Damn Glort, take a chill pill man!

;)

bob g
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guest18

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Re: Slow rpm Chang fa?
« Reply #23 on: November 10, 2021, 02:09:48 AM »
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Fred8

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Re: Slow rpm Chang fa?
« Reply #24 on: November 10, 2021, 02:11:50 AM »

1. those that operate within the manufactures recommendations, probably best for longevity.

This brings up an interesting point......

I have NEVER seen a manufacturer recommend ANY engine speed.
What I do see is a power output figure at a specific RPM. Sorry to anyone that thinks otherwise but that is NOT a recommendation to operate at that speed, it's a RATED power figure at what that engine will do, normally a MAXIMUM  output figure, still below max RPM, NOT what you should run the engine at.


This is why industrial engines often come with power curve charts to show what they will do at specific  speeds. I am amazed people are not aware of those.
If the Max HP/ RPM figure was a recommendation, why isn't everyone, especially those so concerned with critical speed problems not driving their vehicles round at the Figure given for it's maximum power output which is what these Numbers are, NOT an engine operation speed recommendation. 

The numbers merely tell you what the engine will do at that speed.  That is all.

Perhaps I have missed something and if so I'd sure like to be educated if someone could show me where any manufacturer says something akin to "This is the recommended speed to operate this engine".
That is nothing like a MAX power figure at a certain RPM manufactures specify.

Further more, there is also a max Torque figure specified which is regarded as the sweet spot and where vehicle manufacturers, especially Trucks and things like locomotives try to gear their equipment to.  Cruising speed in a vehicle in top gear is always closer to the much slower max torque figure than it is the max power figure which is far higher up. And again, if Operating the engine slower was going to grenade it, how do city cars especially manage to put around for a couple of decades without snapping cranks or falling apart.

Here is a power output Chart of a Cummins engine.


Engine Model    Max. Power HP (kW)     Peak Torque lb-ft (Nm) @ RPM     Governed Speed (RPM)
X12 500            500 (373)                 1700 (2305) @ 1000                         2000
X12 455           455 (339)                        1700 (2305) @ 1000                        2000

We see here that the peak torque is at half the RPM of the peak power.
Would someone like to ring Cummins  ( or Cat, Kubota, JBC, Yanmar, Detroit, Volvo, Mercedes, Ford, Deutz, MTW, Perkins, Isuzu, Honda, GM or any other manufacturer) and ask if operating their engine at 1000 RPM ( or whatever is)  in the peak torque range, going to cause issues with critical speed failure or damage the engine operating at that speed?

I think we all know what the answer is going to be and that for mine shoots down any of this idea that an engine operated below max power rating will destroy it.  It's simply  maligned fantasy to suggest that as is the idea people would operate an engine at " extremely low speed".

I also looked at the Changfa site being a recognised small engine Builder and while they don't specify Torque Figures I could find,  They do only give RATED HP/ speed figures. No where could I find anything that even alluded to as much as " Engine recommended operating speed. " If anyone can, please link to it because i'd like to see where I missed it.

As such I can dismiss the position of " Manufacturers recommendation" for engine speed as a fallacy and contortion of the truth.
It's not even a Recommended RPM speed, that where specified, is usually listed separately and is higher again.

Calling a manufacturers power output rating as the recommended operating speed is simply wrong and ignorant of what is actually being specified by those whom don't understand what they are reading.   


Quote
you should be aware of the engine's critical speed, that is a valid point.  no engine should be operated at critical speed that is if you want it to last and not have some form of premature failure, some of which can be quite catastrophic like broken crankshafts or engine cases, or mounts.

I agree.
I wonder how many people know that or manufacturers that could even be found from?
Again, it is a Single speed or very narrow range, it's not any speed under the max power rating of an engine.

Quote
all you have to do is ride a ferry boat or be anywhere around a diesel locomotive
you can feel the boat vibrate like hell as the throttle opens and the rpm passes through critical speed... and you will note the man with the throttle in his hand does not allow the engine to operate at that speed any longer than is necessary. 

A great example.  I would say though that a lot of this is in the drive train however that is just as important to avoid.

Quote

small engine's may not demonstrate this effect so plainly, but the thing also has a critical speed that should be avoided.

I'd suggest with a little observation it is discernable and it is at very low speed where anyone with any mechanical sympathy or common sense would not operate an engine and on a small engine would be at a point where the power output would be near useless anyway.
It's also dependent on load.



Just for clarity, please note I am not trying to attack you Bob or what you said personally, your comment just sparked a thought  of a good point that seems to have been missed/ maligned till now and which I wanted to address and clarify.

guest18

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Re: Slow rpm Chang fa?
« Reply #25 on: November 10, 2021, 03:42:23 AM »
Fred8,

Here is some stuff that might be of interest. It shows some of the info your requesting.

1A08 Military Standard Engine:
http://everyspec.com/MIL-STD/MIL-STD-1100-1299/download.php?spec=MIL-STD-1226A.013509.pdf
Page 8 shows speed range for continuous operation.
Page 29 shows operating speed range.
Page 23 Critical speeds for directly attached end item.
Page 24 Vibratory torque at critical speeds for directly attached end item.

Iím doing a build with one of the two I have. Should be done some time next year.


Kubota EB series engines:
https://www.sv-zanshin.com/r/manuals/kubotaebseriesbrochure.pdf

For my application 2600 rpmís works best with my EB300 genset.

I would like to add that the EA300 and EB300 are pretty much the same engine. I believe the differenceís are: injector pump timing, injector pump and injector calibration, fuel limiter calibration and Governor speed. The EA300 is set to run up to 3000 rpm, and, the EB300 is set to run up to 2600 rpm.


Honda GX390 Tech Manual:
https://www.trictools.com/wp-content/uploads/2015/07/HONDA-GX-390-TECH-MANUAL.pdf
Pages 3 and 4 shows recommended engine speeds.
Page 10 Resonance Check (critical speed)

Used a GX390 on a build about a year ago.
Engine had a vibration problem at just under 2600 up to over 3000 rpm. This was with the engine mounted on the pad. Engine running without drive pulley attached. I was surprised that a Honda could have such bad vibration at the speeds mentioned. Packed it up and returned it.

38ac

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Re: Slow rpm Chang fa?
« Reply #26 on: November 10, 2021, 03:51:16 AM »
NOS = New Old Stock.
Collector and horder of about anything diesel

guest18

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Re: Slow rpm Chang fa?
« Reply #27 on: November 10, 2021, 07:33:57 AM »
Don't know if I should continue this thread or start a new one...is there an engine comparable to the Changfa that IS legal to sell in the US...that has similar reliability?  I am looking for water cooled, with an electric starter as an option...removable sleeves....



bigdad,

There is possibility that you might be able to get a Changfa engine.
Here is the link: http://www.pelletmasters.com/products/index.html#dieselpower
If they still are available you would have to purchase a complete pellet mill in order to get one.

mobile_bob

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Re: Slow rpm Chang fa?
« Reply #28 on: November 10, 2021, 11:53:38 AM »
(i typed the following late last evening, but forgot to hit "post" so it is probably out of sequence)


i have been guilty in the past of getting into the weeds, and over time found it to be non productive for myself and for the members of the forum.

we can argue fine points, and believe me i can do that as well as anyone
but what is to be gained?

when i mention the oem recommendations on operating speed, i should have expanded on that a bit perhaps, and related it as  recommended "operating range", rather than speed.

i think most folks understand that.

most all stationary engine manufactures, or those that build for that purpose, and for purposes of heavy loading in particular do recommend an operating range.  by that it is meant  that this is the range of speeds that the oem recommends the use of their engine under load.  stationary engines are likely far more heavily loaded than the typical automotive engine which can get by quite nicely operating over anywhere from idle to redline (which btw is a recommended don't go over line)

lets take hwew' kubota single cylinder diesel, iirc it is rated for 2600-2800rpm at rated load, and the power curve stops at something just over 2200rpm or so, its not that the engine won't run under 2200, its just that it vibrates badly at around that speed.  likely one of the critical speeds that they don't recommend running at, especially under load.

(my  bet is hwew has talked to the kubota engineers about this issue.)

it is apparent to the user that this is not a good speed to operate at, because the thing shakes and vibrates so bad that it works parts loose, which generally is not a good thing, unless you want a asphalt packer or concrete screed vibrator ?

getting back to automobiles and critical speeds, these engines are generally very stiff, compact, well balanced, well engineered, with serious attention to things like harmonic balancers, and engineered mounting systems, along with the decoupling effect of the almost ubiquitous automatic transmission.

go back to the 40's and early 50's and the 6cyl stick shift transmission cars and trucks, one could certainly determine by feel what he might not understand as a critical speed but knows that "hey, i don't want to drive in this gear, this thing vibrates my teeth out"
its doubtful that the oem's had to make a recommendation on what engine speed to operate under, they left it to the user who figured it out within the first few blocks of leaving the dealership, or....

he was like some of those old farts that lugged the crap out of their car or truck and you could hear every part of the vehicle vibrating like mad, gears clatter, driveline ringing a horrible tune, and the old deaf guy oblivious to what was happening, or he was driving down the road in first gear at 55mph turning 6 grand! (that was my poor dad, he couldn't hear a thing)

as for your point on industrial engines and power curves, and folks not aware of such, i think you are sadly misinformed.  while there might be some newbie that doesn't know about such things, it is doubtful that you will find but a tiny percentage of the members on this and other forums that are unaware.

(skipping down a bit to your cummins reference)

if we go back to the 60's and early 70's cummins made a taper nose ntc335 engine
it had a critical speed problem in that if you loaded the engine at a certain speed you ended up with a broken crankshaft

ford tractors, 50's with the 4cyl diesel had a similar problem, recommendation was to not load the tractor at some specific rpm, i don't recall what it was either, but broken cranks were not uncommon.

the reason that cummins is now able to get max torque down to 1000rpm is they have built the engine massively stronger than it has ever been.  you can build any engine heavy enough to stand up to about any critical speed issue you like, but almost without exception, the bean counters don't want an oz. of extra iron or expense put into a design without very good reason.

car and pickup reference again

the engine in the typical 5k lb suv has what? 300hp or more these days?
what does it take to in hp to move a 5k lb suv at highway speeds, maybe 100hp?
what does it take to plug around town at 30mph? maybe 25 or 30 if the a/c is on?
the typical car engine is asked to deliver on average probably a quarter of its capacity
and likely half of that driving around town, with brief excursions.  so maybe you are lugging around at some critical speed in your car, putting around town, however because the engine is built to make upward of 300hp it is over built for the need required to putt around at that speed, it is decoupled and isolated so the driver has no feel that it is even happening, and yes it is not a problem.  don't feel it therefore it doesn't exist?  ya right.

every engineering book ever written on internal combustion engines, beit for cars, trucks, planes,  trains, boats, or anything else has a chapter on critical speeds and what is done to deal with them..  you either overbuild and isolate the engine, or if you can't you instruct the operator on where not to run the engine under load.

i mentioned the ferry boat
they are an interesting case study in critical speed

the engines are generally very rigidly mounted to the boat superstructure, and as such engine vibration is transmitted through the hull and around the boat.

when the captain leaves the dock and starts to throttle up he does so , increasing rpm slowly, sometimes remaining at a lower rpm while he clears the dock and/or other obstructions, but as he increases the rpm the engine will enter critical speed, at that precise moment you can feel the boat start to violently vibrate and you can also feel the surge as the captain shoves the throttle open so he can quickly pass through that rpm.

it is actually very interesting to witness having studied the phenomenon, to actually feel the process from before, during and after.  its not something most of us would think about, but that captain sure does.

after witnessing that i went looking for other examples, and came across a railroad yard, and found the same thing taking place, they start to slowly throttle up, then at some rpm the ground starts to vibrate and the engineer cracks up the throttle and he gets through that rpm quickly.  again very interesting.

if you would like i can refer you to a two volume set of engineering books from MIT on engine design, believe me critical speed is a very real thing that must be dealt with one way or another.


its been a very long day, i will part with you for now
and time willing,  pick up where we left off tomorrow.

fair enough?

bob g


« Last Edit: November 10, 2021, 11:57:42 AM by mobile_bob »
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sirpedrosa

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Re: Slow rpm Chang fa?
« Reply #29 on: November 10, 2021, 03:04:13 PM »
Hi Gentles,

Bob G, please, Glort is no longer here! maybe... maybe a clone of him, perhaps an ancient good person whom answers by name David.

Remember king David from scriptures?

I know, a horse is a horse... and a wolf will never be a sheep , but with some discreet rant, not wearing out keyboards, letting others make their point of view, etc, etc.....

Everyone can have a 2nd chance, but.... but the water will never run twice under same bridge.

If, and only if we have a reborned David... maybe he can stand along.

My very deep thoughts.

Cheers
VP
By order of firing up:
Bernard 18A - 1968 (mama's water pump - year of my birth)
Petter PAZ1 - Jun 1967, 3HP, sn 416xxxx
Petter PAZ1 - Nov 1979, 3HP, sn 425xxxx
Lister 12/2 - 12651227, the pearl!