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Old 09-17-2016, 08:59 AM   #21
twistedtree's Avatar
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Originally Posted by psneeld View Post
Back to the engine...

From my marine engineering source.....

Concerning energy content.....

The engine only cares about the weight of the fuel, that is what specific fuel consumption is about. That is why BSFC is given in g/kWh or lb/hph All this talk about gallons is nonsense. Since petroleum volume changes considerably with temperature and a gallon is not the same volume in all countries it is not used to measure power production.

Also a slight correction.....

"BTU/lb of that heavy fuel is probably a good bit higher than diesel, so that would have some effect."

It has a BTU content of between around 18500 to a bit less than 20000 BTU/LB which is the same as ULSD and maybe a bit less than gasoline.

That engine typically burns what is called IFO 380, an "intermediate fuel oil" which is a mix of heavy fuel oil and a distillate like diesel fuel.

It is thick at room temperature but will usually flow like lube oil. It has a maximum pour point around 30*C or about 85*F and a minimum of around 0*C or 32*F. It is warmed to transfer more easily and is heated to around 250*F to reach about the same viscosity as SAE 40 motor oil just before being delivered to the injectors.

It is most certainly not full of sand, rocks, and pebbles.
Very cool. Thanks for the research.

So does that mean that all the efficiency gain is from the engine's design? And if so, where does it come from?

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Old 09-17-2016, 10:39 AM   #22
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Thanks but not my research... RickB tutors me on a lot of things so I pass useful tidbits along....

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Old 09-17-2016, 11:10 AM   #23
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Mr. ps. "...RickB tutors me..." WHO??? Ohhhh, the paint scraper...

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Old 09-17-2016, 11:22 AM   #24
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Yep, BSFC uses terms of weight, so density and gallons does not come into play. I just put it in terms of hp/gph as the magic 20hp/gph is the benchmark for our little engines. Serious engineers stick with g/kWh.

20hp/gph is about 213g/kWh, the big beast is 171g/kWh. My little VW car at absolute best sweet spot on BSFC chart is 196g/kWh.

As engines get larger, it is easier to get better efficiency. As cylinder gets bigger, displacement increases faster than metal surface area, so a smaller fraction of the combustion heat is lost to heat transfer to relatively cooler metal. Flow losses less due to having more time to move gasses around.

Also, the design goals focus on longevity and efficiency, on little engines cost and performance are more primary.

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