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General diesel question


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  #1  
Old 06-05-2017, 04:58:11 PM
Handyhiker1 Handyhiker1 is offline
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Default General diesel question

This is just a general questio. Not looking for exact amount.
If a diesel generator burns 100% fuel usage at max output, what percent is used at 3/4 liad, 1/2 load and 1/4 load and I guess no load.
Obviously it would still be running the same or basicly the same RPMs for all loads.
Again not looking for hard numbrts, just a percent of fuel used.
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  #2  
Old 06-05-2017, 05:00:17 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: General diesel question

Hard to say without knowing the engine. Some sip fuel. Some gulp it down.
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Old 06-05-2017, 05:16:50 PM
Birken Vogt Birken Vogt is offline
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Default Re: General diesel question

Without hitting the books

For a modern small 4 cylinder Japanese diesel

I would say start at 15-20% fuel no load and increase pretty linear to full load
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Old 06-05-2017, 05:20:18 PM
Steve Dawkins Steve Dawkins is offline
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Default Re: General diesel question

As a general rule, I think diesel fuel consumption is pretty much linear with the load. No load consumption is about 15-20% of full load. Of course, like Billy says, it will vary depending on the engine.

A rule of thumb I used for diesel consumption on generators is .07 gallons per hr x KW. This was usually close to the manufacturers published consumption rates.

Last edited by Steve Dawkins; 06-05-2017 at 05:30:20 PM.
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Old 06-05-2017, 09:34:44 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: General diesel question

Thanks guys. That helps.
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Old 06-05-2017, 10:27:56 PM
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Default Re: General diesel question

I'd like to see the spec sheet for a Diesel generator that hits 15% at constant-rpm, no-load.

Keep in mind that even when the electrical load is zero, the engine still has some load that's not insignificant - it's spinning a cooling fan (typically) and it's supplying the exciter power for the generator (typically).
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Old 06-05-2017, 10:37:51 PM
TLB01 TLB01 is offline
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Default Re: General diesel question

Diesel is generally best fuel economy. Decent storage life.

Gasoline is next for fuel economy, but horrible storage life.

Propane fuel economy is horrible. Forever storage life. Propane gets gobbled no matter what the load.

Nat Gas...a bit better than propane in that its just bad compared to terrible... but cheap and it comes out of a public utility pipe.

IMHO, diesel is the winner.
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Old 06-05-2017, 10:51:40 PM
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Default Re: General diesel question

Quote:
Originally Posted by TLB01 View Post
...Propane fuel economy is horrible...

Nat Gas...a bit better than propane in that its just bad compared to terrible.
Not necessarily and not always. In some parts of the country propane has, within the last few years, been as much as 1/3 the cost (per gallon) as Diesel. Yes, it has about 70% of the energy per gallon, but it still was suprisingly inexpensive for a time, and beat out Diesel.

The devil is always in the details.

Where I live natural gas, which is about $0.50 per therm, is the lowest cost fuel, even considering the lower efficiency of a spark-ignited engine vs. a Diesel. Diesel, at $2.50 per gallon works out to $1.80 per therm - 3.6 times more expensive on a per-BTU basis.

So, do the math rather than making generalizations...

Last edited by Jim McIntyre; 06-05-2017 at 11:05:35 PM.
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Old 06-05-2017, 11:00:24 PM
suntreemcanic suntreemcanic is offline
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Default Re: General diesel question

Currently propane is cheap. Diesel engines are so hard to start in cold weather. I can not think of any standby generators at remote sites that are diesel. Diesel gels up in winter, so you have to have a winter blend, have to have expensive fuel filters to keep any moisture out of it because the fuel injectors don't like water. Should rotate the diesel out after about one year and get some fresh diesel in the tank.
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Old 06-05-2017, 11:10:42 PM
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Default Re: General diesel question

When I asked for numbers here for a 12DJC (diesel) and 15JC ( gasoline) I found people generally said diesel is ~ 1/2 consumption of gasoline. I think the above 2 gens are about same displacement.

15JC gasoline is ~ 1 gal/hr @ no-load and 2.4 gal /hr full load.
7.5 JB gasoline is ~ .6 @no-load, ~ 1.2 full load

Last edited by len k; 06-06-2017 at 11:10:27 AM.
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Old 06-05-2017, 11:11:05 PM
Birken Vogt Birken Vogt is offline
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Default Re: General diesel question

I know lots of standby generators that are diesel.

They are typically used in larger applications above 100 kw where power needs are more critical and larger.

Diesels start way faster in a standby application for two reasons

1. Large diesels are generally direct injection with no glow plugs necessary nor provided
2. They typically also have engine heaters in the kilowatt range keeping them around 100F at all times ($$$) but the money the company stands to lose from downtime is much worse.

A properly situated diesel begins to fire on the first or second compression stroke and will be up to speed within seconds. It also responds much quicker to load transients.

Also, if anything should go wrong with a diesel there should be more mechanics available familiar with it.

A gaseous fueled engine takes some seconds of cranking a dead engine just to prime and purge the fuel system and arrive at a burnable mixture. Sometimes I wonder that some of them start at all.

And conversely to above, gaseous engines are generally foreign to run-of-the-mill equipment mechanics.

Anything can be made to work, just stating my observations.
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Old 06-05-2017, 11:24:39 PM
suntreemcanic suntreemcanic is offline
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Default Re: General diesel question

I agree all big standby generators are probably diesel. I am referring to smaller standby generators 5 to 7 KW that are on mountain tops powering up emergency radios in the event of loosing commercial power. The kind the highway dept. and state police rely on.
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Old 06-06-2017, 12:11:58 AM
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Default Re: General diesel question

I have not seen any that size. Unless it is a little Kohler air cooled or something. Most mountaintop repeater sites here run Ford V10, Chevy 350 or John Deere or Cummins 6 cylinder because they have some pretty large buildings to back up.
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Old 06-06-2017, 01:05:04 AM
Wayne 440 Wayne 440 is online now
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Default Re: General diesel question

Quote:
Originally Posted by suntreemcanic View Post
I agree all big standby generators are probably diesel. I am referring to smaller standby generators 5 to 7 KW that are on mountain tops powering up emergency radios in the event of loosing commercial power. The kind the highway dept. and state police rely on.
I have 35+ years of experience in the mentioned field, and here the days of a 2 cylinder JB for communications site standby are long gone, our sets are 35 to 350kW.

Diesel is my choice when it has to run no matter what. All you need to transport diesel fuel is a liquid tight container and a way to move same. When you can put propane in a plastic trash can and haul it up to a tower site, I'll reconsider it.

My home standby is diesel, and starts quickly in winter or summer, thanks to a water jacket heater. The fuel filters for it cost about $4 annually and my fuel supplier gladly delivers winter blend fuel on request. I have not had, nor do I anticipate problems with water, algae or "stale" fuel.

My point is that every situation is different, one cannot always say X fuel is best, particularly from behind a distant keyboard.
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Old 06-06-2017, 11:15:18 AM
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Default Re: General diesel question

For starting diesel engines in winter it surprises me someone doesn't sell a propane powered air intake mini-heater ( heat exchanger). Seems would be easy to have it make ~ 140 deg air.
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Old 06-06-2017, 11:18:26 AM
nothingbutdarts nothingbutdarts is offline
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Default Re: General diesel question

Cummins and MACK/Volvo both have electric grid style intake manifold heaters for starting in cold and also to help with cold engine emissions.

Last edited by nothingbutdarts; 06-06-2017 at 11:18:56 AM. Reason: added info.
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Old 06-06-2017, 11:36:49 AM
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Default Re: General diesel question

There are Espar and Webasto diesel heaters which can heat up the engine in cold weather. Cheers Dan
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Old 06-06-2017, 12:50:42 PM
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Default Re: General diesel question

I like idea of 1 pound propane cans instead of electric. Takes lot of bat power to make heat, and bats get weak with age. Propane heater would likely be cheaper to build than diesel one. Easy and cheap have a couple 1# tanks.
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Old 06-06-2017, 05:23:23 PM
Wayne 440 Wayne 440 is online now
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Default Re: General diesel question

For a set of any kind in an even slightly critical standby application, an electric water jacket heater is generally installed. Keeping the block at 100+ degrees goes a long way toward making the engine happy when it is called on to go from stop to rated RPM immediately and pick up a load in a few seconds.
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Old 06-06-2017, 05:42:12 PM
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Default Re: General diesel question

On some of the NH Cummins I have owned, they had a glow plug and an injector in the intake manifold. Fuel was supplied to the injector via a hand pump. None of mine were operable when I got them, but the idea was to start a fire in the intake manifold during cranking. Big enough to heat the air, but not enough to consume too much O2.

Keith
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