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Diesel Engines
How difference in displacement of engines affects its performance

We have a 1000kVA DG Set with 38 litre (16 cylinder Vee) displacement. We have another 1000kVA DG Set with 28 Litre (8 cylinder Inline) displacement.

The operators are telling that the 38 litre engine is performing better. Noise at high loads is much lesser and smoother. What could be the reason for this?

Is it advisable to specify the displacement of the engine along with kVA for procurement?

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sangeetha_ma,

>We have a 1000kVA DG Set with 38 litre (16 cylinder Vee)
>displacement. We have another 1000kVA DG Set with 28 Litre
>(8 cylinder Inline) displacement.

What is the generator output of each diesel generator set when the operators are making these comments? Is the generator output of the two generator sets equal when the operators are making these observations? For example, are both generator sets running at 1000 kW, or at 800 kW? Or is one running at 950 kW and the other running at 875 kW?

What is the maximum output of each generator set--not the generator nameplate rating, but the nameplate rating of the generator set (the combined diesel engine AND generator)?

A diesel generator set uses the diesel engine as the prime mover (the "driver") for the generator. Every generator prime mover has its own power rating--independent of the generator rating.

What is the horsepower (or equivalent) ratings of EACH of the two diesel engines?

It is very common for generator set packagers to use prime movers that are rated higher or lower than the generator nameplate rating (many diesels are rated in horsepower and/or kilowatts, or some equivalent value that can be converted to other engineering units). There are various reasons for doing this, but one of them is that it's customary for generator set packagers to use generators that are rated slightly higher than the prime mover--so that the prime mover can provide it's maximum power to the generator. (This means the rated output of the generator set (the combined prime mover and generator) will be LESS THAN the nameplate rating of the generator, and most likely equal to the nameplate rating of the prime mover (the diesel engine in your case.)

If the prime mover output was rated higher than the generator output then it would be necessary to limit the diesel engine's power output in order to protect the generator from excessive load (and the heat that causes in the generator).

Also, sometimes the coupling used between the prime mover and the generator can be the limiting factor--it might be rated for less than either the prime mover's output or the generator's output, and in that case the prime mover's output would have to again be limited to protect, in this case, the load coupling.

Using prime movers that are rated for more than the load coupling or the generator means that the full capability of the prime mover can't be utilized without possibly damaging the load coupling or the generator (depending on the ratings of the two). So, that's generally not done--but is does happen on occasion.

Displacement is important, but it's not the only factor to be considered when analyzing the power output of a diesel generator set. The exact same engine (by displacement), equipped with different intake and exhaust equipment, can produce more or less power (be more or less efficient).

It's likely you will find--and hopefully share with us--that the ratings of the two diesels are different, AND that the ratings of the two generator sets (the combined diesel engine AND generator) are also different--even if the nameplate ratings of the two generators are identical.

Please write back to let us know what you find.

It turns out that the old engine is Cummins KTA3067 (This model no. is not being followed now -but identical engine with different model no. exists) which has 50 litre displacement and is rated 1000kW. It is coupled to a 1000kVA alternator. So when the people concerned wanted to buy a standby to this one, they simply gave the requirement as 1000kVA without any data on the load profile etc. They got a Perkins 4008 from the market against this specification.

However, the abnormal noise was being caused by some reason which has nothing to do with the capacity etc. Air was being sucked in the fuel line and this was causing the abnormal noise. Once the fuel line was fixed, noise became normal.

sangeetha_ma,

Thank you very much for the feedback and information!!!

The brief answer to your question above is the V configuration allows half of the pistons to cycle along a plane which is roughly 90 degree different from the other half of the pistons which allows significant cancelling out of forces and a smoother longer lasting engine.

>The operators are telling that the 38 litre engine is
>performing better. Noise at high loads is much lesser and
>smoother. What could be the reason for this?

Hope that helps,
Jerrod