Specific Fuel Consumption

[tmartin125]

The senior engineer at my company uses the following estimated constants to calculate the amount of fuel used by an engine.

.0.378 lbs/hr-h
0.282 lbs/kw-h

I have been using the data from the specification sheets for example from the Cat C18 engine and when I try to get this constant I am getting numbers closer to 0.7 lbs/kw-h. Does anyone else use these constants to estimate engine fuel consumption?

 

[tmartin125]

Fuel rates are based on fuel oil of 35º API [16º C (60º F)]
gravity having an LHV of 42 780 kJ/kg (18,390 Btu/lb)
when used at 29º C (85º F) and weighing 838.9 g/liter
(7.001 lbs/U.S. gal.)

 

[pmover]

tmartin125,

please clarify/confirm the units of measurement . . .

.0.378 lbs/hr-h (i'm thinking lbs/hp-hr)
0.282 lbs/kw-h

-pmover

 

[pmover]

tmartin125,

please read the site policies. fyi, duplicate postings are not permitted.

 

[rb1957]

i wonder where a factor of 2 might've slipped in (or out) of the calc ?

 

[BrianPetersen]

VW diesels have a best-operating-point consumption around 197 g/kWh which is 0.43 lb/kWh or 0.32 lb/hp.h, and those are among the most efficient automotive engines out there. The very best extremely large diesel engines used in ships or utility power generation may be perhaps 20% better than this on account of their size (several orders of magnitude larger than the VW), but not more.

The original poster doesn't ask a question - I see only a statement and not a question. My only statement in return is that the statement that was originally made, is probably wrong, unless we are missing a critical piece of information - like what type of engine we are talking about here.

 

[pmover]

BrianPetersen,

yes, there is a question asked (a "yes/no" question) - please read the last sentence. agree in that clarification is needed.

 

[Artisi]

Back when Noah was a boy and I was involved with diesel engines, for estimates I always used 0.4lbs/ hp/ hr., but note that this changes depending on load. If you want accurate consumption you need to refer to the engine performance curve / data together with knowing what the actual or average load is over the running period.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[tmartin125]

Thank you all for your help. I used the engine performance specifications for my calculations and my supervisor used the approximations stated above however our answers for the fuel tank size were off by several thousand gallons. Turned out he miscalculated the KW approximation (muliplied 0.378 lbs/hp-h by .746 Kw/hp instead of by 1hp/0.746kw). They should read

0.378 lbs/hp-h
0.507 lbs/kw-h

Thanks again for your help