Diesel versus Natural Gas Generators 1

[Cromaney]

I am a Civil Engineer looking at providing information to one of my clients on selecting a large stand-by generator for a critical water well installation (200 Hp). I would like to provide the pro's and con's to my client on selecting either a diesel powered generator versus a natural gas (NG) generator. I have gotten some input from some of the generator manufacturers (Kohler, CAT) but I would like to find out other peoples experiences in dealing with both generator types.

 

[JWaterstreet]

I am by no means an expert, that said, I would summarize it as follows:

Diesel will normally have longer life (not usually a big deal for standby use), acquistion cost will be more, running cost for fuel will be less. The provision and maintenance for diesel fuel can be a real problem, as the client will likely need a fair amount for unattended use, and it will need to be rotated/changed more often if it is not consumed for its periodic run.

Natural gas units are usually more problem free in this regard, as fuel supply & maintenance are a no brainer.

If standby power is needed often and for long periods of time, then diesel usually is the way to go.

If it is rarely off and for short periods of time, NG is much more cost effective.

 

[Cromaney]

Thanks for the input,

I am getting different answers from the generator mnfr's. They indicate that NG generators (at least in the 400 kW range) are two to three times more expensive to purchase then diesel generators becuase they are a rare breed.

As for diesel fuel going bad, I have been told that there is some type of fuel additive that can be placed in diesel fuel that will reduce the effects of age on the fuel. Are you familiar with this additive?

Currently, in comparing the energy costs of diesel fuel with that of NG the cost to ship diesel fuel to the site is consiberally more then NG. This does not include the cost to "pipe" the NG to the site.

Again JW, thanks for your input, I hope we can prompt a few more threads on this subject.

 

[reidh]

Cromaney,

If this back up generator is that much of a necessity, I think it should be a maintenance person's job to run it every once and a while to ensure it functions. This should alleviate fears that people may have of allowing a diesel engine sitting for long periods of time.

Check out this link if you are concerned about diesel storage.

http://www.ewh.ieee.org/soc/pes/centraltexas/presentations/20051025higopian.ppt

-Reidh

 

[globi5]

Natural Gas is also cleaner than Diesel (no soot and less CO2). This might not be relevant in a back up installation, but according to the laws where I live even Diesel engines in construction and agricultural machines have to be provided with particle filters.

 

[dcasto]

The natural gas generator will be more expensive because the engine will have 1650 Cubic Inch displacement vs 927 Cubic Inches for the diesel. Being in the natural gas industry I would pick the diesel over the gas for standby power. I have selected diesel myself several times. The diesel genset can be set up with a PLC cotrol from the supplier that will allow automatic starting and testing once a week to ensure it is ready to run. We always ran them for at least1 to 2 hours. This also used up fuel and allowed for "stock rotation" to minimize gelling, and other things that happen to disel.

 

[ruggedscot]

Id prefer diesel myself and this is coming from a safety point of view - If you get a gas leak then due to the way that gas is stored at pressure it will escape and could collect and form a dangerous condition. Diesel if it leaked it would be under pressure and also you could drop a lit match into it and it should not ignite.

Gas engines require a spark ignition to fire the charge in the cylinder, diesel relies on compression and as such is deemed to be a little more reliable at starting when called for.

As I said Id go for diesel. Id also be wary about setting up a routine to run your diesels off load once a week or so as well its been shown that running an engine unloaded can cause a build up in the cylinders. Its best to load them up when running them to ensure that they get a fair crack at the whip.

Ive seen diesels that have been run regularly off load fail when run under a load condition. So best to run loaded just to tempt that failure! best to fail when you dont need it rather than when you really really do need it!

Rugged

 

[ruggedscot]

sorry meant to say diesel would not be under the same pressure in the storage tanks - although would be under pressure when the engine was running in the fuel delivery lines.

Rugged

 

[rmw]

Do a search on this site for some discussions regarding distillate fuels and what can happen to them during storage.

Not withstanding that caveat, my vote is for the diesel, but I echo the recommendation to run it loaded when testing.

rmw

 

[ruggedscot]

I know diesel does deteriorate but you keep enough to run your set for 8 hours and you change that fuel or treat it on a regular basis and also you can always run your set on load.

Any critical system you will find that they will run the diesel at the very least every couple of months just to be sure that it will come in and go onto bus no problem. Peace of mind especially if it did fall over the effect could be a lot worse than using a few gallons of diesel.

Can always use a load bank to give it a good run if required and these can be made up pretty cheaply if required.

 

[MAragorn]

I have to disagree with the majority here.

My experience is that natural gas and propane engines run cleaner and longer than diesel.

Maintainance is less.

You don't have to worry about ground contamination with a leak.

I love my diesel truck, but some folks think they smell.

AND if it is critical, your fuel supply can be nearly infinite with natural gas.

 

[dicer]

Diesel power advantages
Low flamability
Higher btu content of fuel
In the old days simpler fuel system
Less maintenance

Gas Power advantages
No need for fuel tank
Cleaner exhaust
Cleaner engine (combustion process/crankcase etc)

In a bad earthquake if gas lines are disrupted that would cut off fuel supply.
To remedy the diesel degradation use #1 fuel or jet fuel.