Homebrewed Electricity > Temporary power

Generator on LPG

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waross:
An engine needs fuel to keep itself running.
There is a lot of heat rejected from the radiator and exhaust.
You have to burn fuel to produce that heat.
A loaded diesel gen-set will produce about 13 Kilo Watt Hours per gallon of standard diesel fuel.
As the load drops the ratio of load to losses drops and the efficiency drops.
We had to run our home on a small diesel set (6 KW) for a couple of months.
During the night it had to be kept on line for two reasons.
1. Power had to be available for the freezer, refrigerator, furnace and sewage pump out.
Most of the night the set ran unloaded.
2. Did I mention that the ambient was -20F to -30F.
Power had to be available for the fan in the natural gas furnace, and with no other power, if the set was left cold all night there would be no starting in the morning.
By far the most fuel consumption was during unloaded hours.
If your set is for occasional standby this may not be important.
If the set will be used frequently, fuel consumption becomes more important.
Another issue with low loading is wet stacking.
Modern diesel engines use the combustion pressure, ported to the back of the compression ring to help seal the rings.
At low load, there may not be enough combustion pressure to properly seal the rings and oil pumping or wet stacking may result.
The next step is the possibility of flaming globs of oil being expelled from the exhaust.
The other result is loss of lubricating oil.
Worst case, A new set, was started and left running with very little load a few days after I installed it.
In a few hours it pumped out all of the lube oil and shut down on low oil pressure.

Avoid a diesel set that is much oversized.
In cold weather, a radiator shutter or baffle to reduce the heat rejected from the radiator will improve fuel economy.

MattM:
I thought diesels self lubricate at low rpm's.

SparWeb:
Welcome to Fieldlines, waross!

ChrisOlson:

--- Quote from: kitestrings on September 13, 2019, 08:51:28 AM ---The fuel efficiency is lower as you say, but in our case, the generator sits for months - I haven't run ours this spring/summer at all, except to exercise it.  I do like not having to handle fuel.  Diesel I suppose long-term is better, but every time I change oil in my truck, I'm reminded how comparatively messy and expensive it is, and you do have cold-temp starting to consider.

What is your diesel unit Chris?

--- End quote ---

kitestrings, we now have a Cummins QD 10000. We have been pretty happy with this unit. It ran for 6 weeks continuous after the tornado here that took out all of our infrastructure, including our solar panels. Having the diesel during that time was very good. There was no gas stations open, could not get gasoline or LPG for 4 weeks. The natural gas infrastructure was also out due to lack of power for pumping stations.

The diesel fuel was available for construction and logging equipment that spent a month clearing roads, removing trees from buildings, and rebuilding utility power lines. Our QD 10000 burned about 14 gallons per day, running 44 days straight. We have a 500 gallon tank for it, the Cenex truck came and refilled it twice during the tornado cleanup.

Also had to pay cash for the fuel when delivered. The banks were not open. Only one bank has a standby generator and it was a natural gas unit (Generac). So no credit cards or bank cards worked during that time either, and the internet services were also down for a month.

Some people who have gas portable generators were driving 40 miles to get gas for them, and long lines at the gas pumps to fill up cans and cars. Many people who's homes survived the tornado ended up losing everything in their freezers and fridges.

Bruce S:
ChrisO;
Late to the party on this one, but good to read that you're okay.
Cheers
Bruce S

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