Generator efficiency

 

There are about 140,000 BTUs in a gallon of Diesel fuel, and 3415 BTU
per kilowatt hour.  So at 1005 efficiency you would get about 41
kilowatt hours per gallon of fuel.  Anyone got any idea what a little
unit like this would do?

http://www.allworlddieselgen.com/adg_kubota_Marine.htm

I would assume that a low rpm model would be more efficient than a high
rpm model, but that may not be true.  I notice for these nearly
identical units the power outputs are 4.5/2000 vs 7/2800.  So for a 40%
increase in rpm you get a 55% increase in power.  Of course there is
nothing saying that the fuel used is directly proportional to the rpm.

Anyone got any links to sites where they give specific info on fuel
useage at a given power output?

In the automotive world turbo Diesels not only put out more power for a
given size engine, they also get better fuel mileage.  Anyone know of
any small (under 10 KW) turbo Diesel generators?

Thanks, Bruce

 

Bruce Richmond wrote:

==================================
Power is torque x speed, so same cylinder firing more often gives more
power. Usually longevity is important in a generator, so slower is
better. Weight of generator is less important for non mobile use. You
want to use this out behind the barn, or in your car?
I think the idea of 'super tuning' the intake and exhaust to run at
exactly one speed is interesting... I calculated that the time between
'bangs' at 1800 rpm traveling down an exhaust pipe that was 1/4 of a
wvelength of the bang frequency needed a 19' exhaust pipe. Maybe rig up
a telescoping pipe and a fuel flow gauge and 'tune' it for min fuel
consumption like a trombone.

 


BobG wrote:

The efficiency I was interested in was getting the most KW hours out of
a gallon of fuel, which is not the same as getting the most power out
of the engine.  Running slower means less internal pumping losses, less
friction, more time for complete combustion.  The cam timing, injector
timing and manifold lengths can be optimised for the chosen rpm.

What I have in mind is using a liquid cooled generator to heat a house.
 The electrical power could be used to run a geothermal heat pump.  All
the heat dumped into the cooling system would heat the house.  The
exhaust could be run through a heat exchanger for the heating system,
then a heat exchanger to warm the intake air for the Diesel, then
through a heat pump coil to get it down to or slightly below the
outside air temp.

If the engine/generator is 40% efficient, and the heat pump has a COP
of 8, then it would pump .4*8=3.2 times as much heat into the house as
was contained in the fuel used.  Add to that the remaining 60% of the
energy that was given off as heat from the engine/generator.  Since no
heat is allowed to leave the house from the cooling system or exhaust
it must all be going to heat the house.  That means a total of 3.8
times the fuel energy  would be available.

Looked at another way, heating fuel consumption could be cut by 76%.

 

wrote:


You won't be able to get a geothermal heat pump with a COP of 8. The
highest "marketing numbers" today are around 5, the best real-world
results about 4.

 


Jens Kr. Kirkebø wrote:

Thanks for the info.  It was easy to find info on the theoretical COP
but not the real world numbers.

Bruce