Differences between Gas and Diesel Generators

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mbrooke

mbrooke

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I'm looking at some natural gas generators and the 500kw units appear to be just as big (if not bigger) as the 1,250kw diesel units :oops: Does anyone know the size difference, weight and other noteworthy factors between natural has and diesel standby sets?
 
A good rule of thumb is that a natural gas generator requires one size larger engine than a similarly sized diesel generator.
 
I've seen NG gens be almost 2X the size of diesel due to the energy contained in NG compared to diesel.
Electrically, NG gens cannot accommodate large step loads as compared to diesels which can often pickup 0-100% with an acceptable amount of voltage and frequency drop / recovery depending on what you consider acceptable.
 
d0nut said:
A good rule of thumb is that a natural gas generator requires one size larger engine than a similarly sized diesel generator.
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Size- HP/KW is, well, HP/KW. Or do you mean physically larger? IIRC, gas has about a third the energy density of diesel- a 500HP gas engine will be physically larger than a diesel, but it's also muddy to say "one size larger" since they're different engines (compression/spark ignition).
 
ron said:
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Electrically, NG gens cannot accommodate large step loads as compared to diesels which can often pickup 0-100% with an acceptable amount of voltage and frequency drop / recovery depending on what you consider acceptable.
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Is this true for all NG units? Those that can pickup all load at once, are the engines larger?
 
mbrooke said:
I'm looking at some natural gas generators and the 500kw units appear to be just as big (if not bigger) as the 1,250kw diesel units :oops: Does anyone know the size difference, weight and other noteworthy factors between natural has and diesel standby sets?
Click to expand...
At a large hospital/ research center that I retired from they had 4 natural gas gens rated @760KW and only running at 1200 RPM due to summer peak saving use and 14 diesel generators most rated @ 2000 KW & running at 1800 RPM. The 4 Cat gas gens gave more trouble then then the 14 Cat diesel gens combined. The 760 KW Natural gas gens had a lot of problems especially in hot weather when we had to run load banks at 750 KW for a hour even after spending a millon dollars to rebuild them along with new controls. Was told by an old timer to never try to run a natural gas generator at more then 90% of rated load. Had a 800 KW natural gas gen in a new office building that had major problems with voltage regulation with only 10 to 20% of rated load.ATS swiches would not transfer back to normal piwer after 30 mintue test cycle.
 
1,200rpm? How are they getting 60Hz?

Did you or the manufacturer find the problem with the genset at the officer building?

I have to say this thread is not giving me a lot of confidence in gas.
 
You can also run a diesel engine with up to 70% natural gas, with very little modifications. Very common in the oilfield, where they are having to flareoff stranded gas.
 
Dzboyce said:
You can also run a diesel engine with up to 70% natural gas, with very little modifications. Very common in the oilfield, where they are having to flareoff stranded gas.
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I'm thinking that might be due to the very high octane of natural gas making it resistant to compression ignition too early in the cycle, but then injection and combustion of diesel fuel will ignite the natural gas with the proper timing. But that's speculation on my part.
 
synchro said:
I'm thinking that might be due to the very high octane of natural gas making it resistant to compression ignition too early in the cycle, but then injection and combustion of diesel fuel will ignite the natural gas with the proper timing. But that's speculation on my part.
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That’s correct. The compression ignition of the diesel will ignite the natural gas, with no spark plugs needed. It’s called a fumigation system. Still have to inject 30% diesel to ignite the natural gas

looking at setting up a 600-800 hp engine this way later this year.
 
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