Diesel Genset Engine - Torque Speed Curve 1

[Gbawn]

Hi All,

I am analysis the performance of a Generac SD250 diesel engine (

https://www.generac.com/Industrial/products/diesel-generators/configured/250kw-diesel-generator.

Using info from the attached data sheet - including the hourly fuel consumption figures (l/hr) - I have managed to calculate and plot the engine efficiency and BSFC(g/kWhr).

What I would like to do is plot the BSFC against engine speed; however, I don't think there is enough information in the data sheet to obtain the torque vs speed characteristic of the engine. They only give the rated engine speed 1800 rpm. Any ideas on how I can find / infer this information for the diesel engine in question? What I am looking for is a plot such as the following:

Thanks

Ben

 

[genhead]

Why? The engine will always run at (or close to) 1800 RPM.
But if you really want the information, the engine manufacturer IVECO should have it.

 

[davidbeach]

Yeah, they only give 1800 rpm because that's the only speed that matters.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

I find the specs a little disappointing.
I can find no mention of UFRO as a feature of the Voltage regulator.
I see no mention of %droop.
Yes, I know that it is isochronous, but even isochronous sets typically respond to block increases in loading in droop mode and then correct back to set-point frequency.
Knowing the %droop helps anticipate the expected response when starting large motors.
Is 3% droop so common that it need not be mentioned? (5% droop for grid tied generation.)
A heads up on full consumption:
The specs don't state the SG of the fuel used for testing.
I once prepared some recommendations for a set to be used for prime power at a facility near Lake Labarge of Robert Service fame. (It was on the marge of Lake Labarge that I cremated Sam McGee).
Fuel was expensive both to buy and to deliver.
I compared fuel consumption specs for 5 or 6 sets.
All except one set were closely comparable.
One set used 10% less fuel per KWHr than all of the others.
Then I checked closer.
The supposedly more efficient set was testing with fuel that was 10% heavier than the others.
If you are someplace where winter grade diesel fuel is used, winter grade is typically 10% lighter and you may lose 10% of your power in the winter. That is you will burn the same amount of fuel for 10% less KWHrs.
Depending on how your engine is matched to the alternator, you may not be able to develop 100% output in the winter.
It depends.
It looks as if your engine has some extra capacity. That is not always the case.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

When working with small gen sets, it's hard "engineer" them correctly. Too much of the information is intended to sell the set and not accurately describe the performance. Pedigree becomes very important here. You're going to have to rely on the experience of others to properly select a generator PM.

When selecting constant speed engines you should also consider lube oil consumption as this can add up to be a significant cost factor. Lightly loaded generator sets burn a lot of lube oil. I have seen consumption rates approach 1 gallon of lube in 24 hours on underloaded 150KW sets. Fuel consumption averaged 1.5 gph.

 

[waross]

I have seen consumption rates approach 1 gallon of lube in 24 hours on underloaded 150KW sets.

I have cured excess oil consumption on several new sets by "load banking for a few days. that seats the rings and stops excess lube loss at light loads.
If it is an old, worn out set, then it is what it is.
Three options:
Overhaul.
New engine.
Keep adding oil.
That is, until someone forgets the oil. and then you may have two options.
I saw that happen with a small set. (Long stupid story.)
The cost of a complete new set was less than the estimate for repairs to the old set.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Gbawn]

Hi All,

"Why? The engine will always run at (or close to) 1800 RPM". Well not necessarily that is why I posting the question.

We are exploring the option of using the engine in a variable speed configuration whereby the synchronous alternator is decoupled from the load by a back-to-back power converter. At the moment we are just looking to develop a numerical simulation. The issue is trying to find suitably detailed info on the engine. There will be a toque speed map for the engine! It's just a question of whether or not the manufacturer wants to make it available. I was really just asking to see if anybody had come across the info for other similar engines. For obvious reasons they typically just provide the synchronous speed. Whilst I understand why they do that, providing the additional information wouldn't take much extra effort and is useful

 

[davidbeach]

In that case you may have to characterize the engine yourself or find a variable speed application where the manufacturer provided that information. Any engine driven water pump applications where that engine was used? It may also be that the engine you have was specifically optimized for operation at 1800 rpm and is somewhat different from what would have been delivered, based on the same basic block, for variable speed applications.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

Well if I was looking for that information for an Onan/Cummins set, I would check the Cummins site rather than the Onan site.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

That has been done with small sets.
The engine drives an alternator which feeds a DC bus through a rectifier bank.
The DC is then inverted to AC.
At light loads the engine runs slower to save fuel and emissions.
As the load increases, the engine speed increases to develop more power.
Google "Inverter gen Sets".

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

This is an interesting problem. All of my propulsion engines are variable speed and geared to fixed pitch propellers. We size our engines to run at maximum power when pushing against a stationary wall. This gives us a very wide range of power settings that we can operate indifferently.

Controllable pitch propellers systems typically operate the engine at maximum speed and vary pitch for power. The high speed low power time is notorious for causing wet stacking.

Being able to use variable speed for a generator set will certainly be useful to increase the turndown ratio of the generator set. I do agree that using modern inverter tech and variable speed has benefits.

BUT! Emissions regulations are going to dictate every move you make and generator sets are only rated as constant speed. This may be the reason you can't find other data. It is also illegal to operate constant speed engines as variable speed. Reach out to the manufacturer for variable speed data and I think you'll find what you need.

 

[Hoxton123]

The engine maker I worked for had different 'builds' for constant speed engines for generator drive and for mechanical drive which are usually variable speed.

The 'build' was a code number for assembly and the spare parts list. The usual differences if you compared the lists were the camshaft, turbo charger oil pump etc, perhaps pistons and some other components.

It was possible to convert one engine to the other, but no factory test sheet would exist to support the rating and (importantly) the emissions certification.

The changes are design issues which are usually not fully divulged to users.

Generator drive engines are usually optimized for full power rating, mechanical drive are usually optimized for part power operation, since that reflects what the market wants.

Once I had a similar case to the OP, there was a developer of a small gas turbine who developed this as variable speed with a dc generator and an electronic converter to AC.

Their gas turbine development was delayed and they bought some variable speed diesel engines(100 Kw class) to power their development rigs.

They then asked for a variable speed version of the gas engine which used the same crankcase etc as the diesel engine. The gas engine was 1500 or 1800 rpm, fixed speed.

The factory refused to even investigate the possibility of developing a variable speed gas engine as the market was too small.

The OP could go direct to the engine maker for a variable speed engine, but this might not meet generating set emissions regulations...

 

[genhead]

Here is the data sheet from a small Kubota engine that we use in the application you are describing. If you can get the Iveco engine model number (which, curiously, isn't mentioned in your Generac spec sheet) then you should be able to find the data sheet. There's probably enough engine information there for you to hunt it down on-line.

 

[1503-44]

Helpful hints if you have to derive it yourself,

https://www.frontierpower.com/resources/articles-and-links/make-sense-of-diesel-engine-specs/

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."