is electrical load on generator equal to higher fuel consumation? 2

[15ant60]

Relationship between generator load and fuel consumation on ships auxiliary engine.
How´s this relantionship?..since the engines run on fast rpm, i still assumme that teh generator torque influences the fuel feeding,,,or not?
Thanks in advance

 

[rbulsara]

Energy in= Energy out + losses. Regardless of the rpm. Plus in a given set up rpm is a fixed quantity.

Rafiq Bulsara

http://www.srengineersct.com

 

[15ant60]

thanks;-)...so, re-chaptering..no matter how big( in kWh) the electrical load imposed on generator is, the diesel motor fuel consumation will remain the same, right?
.....now i´m a simple mechanic studying marine engineering and I know for af fact that car generators electrical load has an influence on fuel feeding..cuz of the torque required when extra el. load..windowshiels washers for instance..that´s the the reason why i asked.
....best regards....

 

[rasevskii]

for 15ant60:

No, you have got it all wrong. The diesel will have a governor that keeps the speed (nearly) constant so that you get the 60 or 50Hz generator output tha the set is designed for. As you increase the load on the generator, (your consumers) the drag will increase so that the engine governor will have to open up more fuel to the injectors to keep the speed (nearly) at set RPM. So therefore the fuel consumption will go up as load increases.

rasevskii

 

[15ant60]

,,yes..that´s what made sense to me..even though i might have expressed me otherwise,-)...it´s a fact that as refered that Energy indput= Energy ouput+losses..but nevertheless the extra electrical load will alter the torque within generator..and that will force the diesel engine to maintain rotations that match the frequency,right?...meaning: more fuel........the issue is that i´m working on a chiller project on bord a vessel..the marine engineers on bord don´t seem to b worried about electric consumation, since as they say, the diesel generator motors are due to run anyway...my point is less el. load = less fuel consumation...
-------as soon as i know for a fact that the el. load in kWh costs them the equivalent in tons fuel I´ll kind of smile;-)

 

[rbulsara]

Substitute "Energy in" with Fuel and "Energy out" with load in the equation!

There is no free lunch. Fuel provides the energy and load consumes the energy. You figure out the relationship.

Rafiq Bulsara

http://www.srengineersct.com

 

[15ant60]

..no free lunch-exactly;-)..so let´s say the el. load is for instance 1000 kWh and the specific fuel consumation is for instance 100 g/kWh..that´s will lead us to
1000* 100/1000 = 100 Kg fuel
--------that will be the relationship, i believe..please correct if i´m wrong.

 

[waross]

You will get about 13 Kilo Watt Hours of energy for every US gallon of fuel that you burn, plus.
The more efficient engines may get near 14 KWHrs per Gallon.
Caveats:
This is based on an engine working in it's most efficient range. Less than a full load results in less than the optimum KWHrs per gallon.
This is based on test fuel at a given specific gravity. Lighter fuel will produce less KWHrs per gallon and heavier fuels will produce more KWHrs per gallon. This effect is fairly linear.
But the answer to your question is yes, more load always uses more fuel.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Just a side, what would run the chillers on board the vessel if not the diesel gens?

Rafiq Bulsara

http://www.srengineersct.com

 

[jraef]

The thing that changes with load is the relative efficiency of the system. There are a certain amount of losses in the generator (and engine for that matter) that will remain constant regardless of loading. At higher loading on the generator, those fixed losses become a lower percentage of the total fuel consumption, but at light loading (or even no load), they are still the same so they represent more (or all) of the fuel consumption. that's why you should know your optimal load point of the genset and try to keep it there. Over sizing it without good cause can end up increasing your fuel costs.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[15ant60]

thanks to u all by the enlightning answers---the engines in question are Wartsilla(swedish) and run on light fuel(gasoil).I observed that they share the existing load when the vessel is manoeuvring..otherwise it´s only one of them taking up most of consummers.
Actually i´m only calculating how the chiller retrofit (from R22 to 134a) will act in terms compressor efficiency, since that´s an older screw one...but i allowed myself to amplify the picture, since the el-motor driving the compressor is rather big (I n = 720 A )...according to the crew the second engine (AE) is a back up..running for safety reasons cuz we r talking of a passenger-ship (2000 PAX).
...anyway I guess I should take a closer look to fuel consumption in different conditions(loads) and see if i´m able to come up with some results...instead of assumptions;-)
..........cheers......

 

[waross]

Divide your normal running kilo-Watts by 14. You will probably use about that much extra fuel in gallons per hour.
Example; A 150 kW motor will cause an increase in fuel consumption of 150/14 = 10.7 Estimate that you will use an extra 10.7 gallons per hour of standard specific gravity diesel fuel.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[15ant60]

Hi Bill..since i´m european i´ve will rather think it over in SI units..so u writte I should multipie my el kW usage by 14 US gallons/h = more or less 53 liters/h....where do this fuel quantity comes from (we forgett all about different densities)?
..as far as i remember fuel comsuption is a product of effective engine power and fuel specific heat value-----i´m really curious concerning the 14 gallons/h...........cheers

 

[rbulsara]

Look up data sheets of diesel generators on some of the mfrs' website. They all list their fuel consumption at 100%, 75% and 50% rated loads.

The numbers suggested here, by Bill, are for #2 diesel oil, the most common in North America. You may want to check out units that run on the fuel you are interested in.

Rafiq Bulsara

http://www.srengineersct.com

 

[15ant60]

...cool..thanks..shall do.

 

[waross]

Thanks Rafiq. Right on.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

A slight mistake. I was intending a conservative figure, I should have rounded down to 13 instead of rounding up to 14.
Please use a factor of 13.

Bill
--------------------
"Why not the best?"
Jimmy Carter