Confused about fuel consumption. (g/kwh and L/h)

[EzraR]

Im hoping someone can help understand something - haven't been able to research the answer.

Looking at the consumption map of a BETA Marine 30 HP Diesel engine (attached)--- I see that at 2000rpm you have a power output of approx 14KW and a stated fuel consumption of around 1L/h - and roughly this squares with our real work experience of a similarly sized engine.

Now looking at separate engine manufacturers data sheet for a 27hp engine -- I see that at 2000rpm you have a power output of around 15KW and a stated fuel consumption of approx 240g/KWH -- which by my calculation gives a L/h consumption of around 4.3L/h.

So the question is why are these figures so different? My guess is that its got something to do with "load" as I can see the BETA graph cites "theoretical propeller loading" while the second manufacturer graph cites "max loading" -- could someone clarify what this means? And if so.... is there a formula or rough calculation for "theoretical propeller loading"? -- im interested in getting some real world consumption values from that second data set.

hope this makes sense and would be very happy for anyone able to clarify

thanks

 

[earlybird]

I think the Beta fuel consumption curve is not depicted on the same basis as the power curve. The FC curve is based on a matched propellor, absorbing ~30bhp at max. rpm.The power curve, from its shape, seems to be a brake measurement at WOT, ie a lab. test. If itwas a propellor curve it would increase in gradient with increasing speed.
This means that at 2000rpm on a propellor, the Beta is not producing 15kW, but rather less, hence it appears to use less fuel than the other engine since FC graphs aren't comparable.
Hope that makes sense.