Usable RPM range of modern engines

[Jens]

I don't remember if this has been discussed already but what is the usable rpm range on a modern diesel engine.
We know the top speed from the spec's, let's say 2800 rpm and we know that the published hp vs rpm graph stops at say 1400 rpm. We also know that we will want to run the engine with veggy oil and at 75% power. Let's say it's a 4 cyl engine so we have a power stroke every turn of the crank for relatively even rpm's.
The engine would be set up for generator duty and load would be dynamically adjusted to within a fairly small range so that we wouldn't see wild power demand fluctuations.
Let us assume that the engine oil pressure will not be a limitation in this example. I guess all we are concerned with is that we don't get the combustion chamber all plugged up with veggy goo.
Let's say the engine idles at 800 rpm as supplied by the factory

What can we expect for minimum usable engine rpm while still achieving extended engine life from slowing the rpm's way down ? Would the power graph that is published pretty much give the rasnge of suitable engine rpm's or can we go lower ?

[Henry W]

Hi Jens,

My guess is you will get multiple answers here.

From what I understand the most effeciant operating RPM range for a modern diesel engine is at or just above peak torque. A Kubota Z482 peak torque is at 2600 RPM's. And from what I learned is the Z482 loves to be ran at 2600-2800 RPM. The engine is very smooth at this RPM range.

There are some engines that are speced to run at 1800. I would imagine the camshaft profile is differant and injector pump and timing is set up differant also.

No modern diesel engine likes to be worked at below specifed RPM's. Lots of R and D have been put into modern designed engines. If you want a diesel engine to last try to run it at peak torque RPM range with a load.

Bob G. can probably give more info here.

Henry

[Crofter]

Jens, it does not put out 20 HP at 1400 rpm unless you load it to that amount. At 1400 rpm and no load it produces 0 HP. (it only has the potential for 20) The fuel consumption will be relative to the actual load with it probably being more efficient just a bit higher rpm. As far as wear you have to remember that for a given horsepower output the torque must be higher if the rpm is lower so some of the stresses will be higher in the engine if you lower the rpm and belt it up. My bet is that engine will produce more lifetime work direct coupled to a gen. head at 1800 rpm and use less fuel than it would belted to run at 12 or 14 hundred. They are sweet engines; a friend has one on a welder that I have put a few hours on but I dont know the rpm it runs at.

[mobile_bob]

Jens:

the following for what its worth

you have now amassed a bunch of data that is pertinent to your exact needs, this is a huge help in designing a
future cogen plant in my opinion. lessons learned on the listeroid twin should not be lost, but used to make version 2
much better.

as for your choice of engine, i am not familiar with it, however
take a look around and see who uses it to drive a genset at 1800rpm, if there are those that do
then i would expect the engine to be good at 1800rpm for your use, 1400 might be a little low but probably doable

if on the other hand you don't find any direct drive 1800rpm applications using this engine, i would not expect it to be
a good choice at 1400, in my opinion.

i would think most modern stationary engine's are made with the idea of them being used in gensets, and if so
perhaps the kubota was too?  if it was it stands to reason that they are also made to drive gensets at 1500rpm
for 50hz for a large part of the world.

so i guess if the unit is used on gensets then it ought to be good for 1400rpm operation i would think, unless it is some
derivative engine that was designed and optimized for higher rpm operation, such as a mower, or some variable speed application?
if that is the case you may end up having to change an internal spring or some other internal adjustment to the injection pump
to optimize it for generator use.  i know the C201 isuzu has that option where an internal adjustment is made to set the injection
pump up for 1800rpm generator use as opposed to dual speed 1300/2300rpm refrigeration use (with inline injection pumps) and
there is also a rotary pump that was used for vehicle application (it generally is not a good candidate for generator use)

this doesn't mean the engine is unsuitable, just that the fuel system either has to be setup properly if it has the right injection system
or have it replaced if it has a rotary injection pump.

probably the best bet is get the engine s/n and call kubota, and find out how and what this specific engine was setup to do, and if
it is not setup properly find out if it is something as simple as changing out an internal spring or some other simple adjustment/calibration.

bob g

[Henry W]

Hi Jens,

Make sure it is a BG series engine from Kubota. They are set up to run at 1500 and 1800 RPM's for generator use.

This link should help. http://www.kubotaengine.com/products/bg/index.html

The engine you are looking at is set up to run at 2800 RPM's.

Be carefull, We hate to see you make a costly mistake.

Henry

[Henry W]

I guess I good question I would like to ask is why run a modern Diesel Engine at 1400 rpm's? This means you would have to run a belt setup. Why not get an engine that is set up to run a single bearing generator head, run it at 1800 RPM's and be done with it.

I talk to some people I know that made and sold thousands of  Kubota Generators since they started and I hear from them at times that they go out on a service call and finding that some of these engines having well over 40,000 hours on them and still running fine. What is wrong with that?

One thing you do not want to do is oversize an engine for a genset and never being able to get it loaded properly when in use.

Another thing is I would not even think of running WVO in any modern Kubota engine.

The modern engine you should be looking at is the Lister-Petter LPWSB series engines. They are designed to run on 100% bio diesel. (B100)

Here is a link to the Lister-Petter LPWSB:  http://construction.lister-petter.com/products_browse.php

Henry

[Henry W]

Hi Jens,

Just trying to help here. If you will be thinking of running WVO I would not purchase a New Modern Engine. Kubota engines and others are great and run for a very long time. But,the injector pumps are well over 1,000.00 for replacement. You ran into many problems with WVO gumming things up on your Listeroid. Do you think it would be much differant with a new modern engine?

I would look for a used Isuzu C201 like Bob mentioned and rebuild it.

Another option if you want new is to purchase a Laidong KM385D 3 Cylinder 21 Hp. @ 1800 RPM Chinese Diesel engine. This is a complete Power Pack, Key Start Ready!!! They go for around $2,562.00. The quality is much better than the earlier ones imported.

Spare injector pump is under $250.00 for the KM385D. Price a spare injector pump for an engine made in Japan
At least you can purchase injector pumps cheap when one gets trashed

About the 2 bearing generator head you have. You can always sell it and than buy a single bearing. In the long run you will be ahead. Just think how much you will save on fabricating. All you would have to make is a frame for the assembled unit to sit on. Simple, clean looking, safer and less maintenance.

If you want to keep the 2 bearing genhead you have than just buy a coupling like this. http://www.guardiancouplings.com/productline/guardexFH.htm

A matter of fact, I think you can get a complete genset kit for around $3500.00 all you would have to do is bolt it on a frame. I feel this would be a winning combination for you.


Henry

[Henry W]

Hi Gens,

Here is what the Kubota V2203 engine is capable of doing when set up to run 1800 RPM gen-heads.

It is used to drive 19.6 Kw cont.

Henry

[mobile_bob]

you might look into the new lister/petter water cooled 3 cylinder that Tom at Georgia generator has

i really like the looks of that critter, comes with a nice sae bellhousing, and looks very cleanly built
first world, nice engine.

a single brg head, and a three point mounting system,and bob's your uncle (another bob) 

the injection pump looks like it should be easy to deal with, as it uses seperate pumps for each cylinder iirc

they should be good for 25 plus thousand hours i would think with good maintenance, at least it uses a real oil pump
and full flow filtration.

i think it is also epa compliant as well.

bob g

[Geno]

http://cgi.ebay.com/Lister-Petter-LPSW3-New-Diesel-Engine-/160470642530?pt=BI_Generators

The project hasn't even started yet but after a few hundred hours I'll probably try heated WVO in my Kubota with a lot of oversight. I won't count on it working to well and a tear down on it would be way harder than the Roid. There's little doubt in my mind I'll be learning how to make B100 from my WVO stock. Luckily I have a mentor who will get me over the curve.

Thanks, Geno

[Henry W]

you might look into the new lister/petter water cooled 3 cylinder that Tom at Georgia generator has

i really like the looks of that critter, comes with a nice sae bellhousing, and looks very cleanly built
first world, nice engine.

a single brg head, and a three point mounting system,and bob's your uncle (another bob)  

the injection pump looks like it should be easy to deal with, as it uses seperate pumps for each cylinder iirc

they should be good for 25 plus thousand hours i would think with good maintenance, at least it uses a real oil pump
and full flow filtration.

i think it is also epa compliant as well.

bob g

Gens,

The lister-petter I wrote obout is the one that tom can get for people outside of the US. A matter of fact I spoke to Tom before I posted about it and ask if he can get some prices. I will let you know what they go for. I will also get a price on  the lister-petter LPWS3  this morning.
He has one in stock.

Henry

[Henry W]

Hi Gens,

Henry's quote:  Another option if you want new is to purchase a Laidong KM385D 3 Cylinder 21 Hp. @ 1800 RPM Chinese Diesel engine. This is a complete Power Pack, Key Start Ready!!! They go for around $2,562.00. The quality is much better than the earlier ones imported.


Jens quote:  I found a parts breakdown but nobody that actually sells these units. Got a source in mind ? BTW, the engine seems to be rated for 10k hours. That is ok but I was impressed with the Kubota 40k hours which seems to be mentioned a lot.


Tom has 2 in stock.

Henry

[Henry W]

you might look into the new lister/petter water cooled 3 cylinder that Tom at Georgia generator has

i really like the looks of that critter, comes with a nice sae bellhousing, and looks very cleanly built
first world, nice engine.

His web site doesn't show the engine. Have you got a URL where you saw the engine ?

I have some pictures of it at home. I will try to remember.

Henry

[Henry W]

http://cgi.ebay.com/Lister-Petter-LPSW3-New-Diesel-Engine-/160470642530?pt=BI_Generators

The project hasn't even started yet but after a few hundred hours I'll probably try heated WVO in my Kubota with a lot of oversight. I won't count on it working to well and a tear down on it would be way harder than the Roid. There's little doubt in my mind I'll be learning how to make B100 from my WVO stock. Luckily I have a mentor who will get me over the curve.

Thanks, Geno

That is the same engine when I visit Tom 3 months ago. Yes Tom has it on Ebay. Very nice Engine!!!


Henry

[Henry W]

Henry's Quote:  A matter of fact, I think you can get a complete genset kit for around $3500.00 all you would have to do is bolt it on a frame. I feel this would be a winning combination for you.

Jens Quote:  What make are you referring to, the Laidong ?
Thanks for all your input !!!



Henry's Quote:  Yes this is the price of a Laidong Engine with a Gen-head. Complete drop on frame setup.

Henry