Estimate BSFC at Differing Engine Loads

[jakvett]

I am looking for the estimated fuel consumption (gal/hr) of an engine at 60% load. I have the torque, horsepower, and fuel consumption curves, as well as various fuel system parameters (max fuel consumed at rated speed with full load). My issue is the fuel consumption curve is only given at 100% load. As I understand, BSFC is not scalable, and thus I cannot just scale the max fuel consumed parameter. I also don't think it's valid to say that a 60% load on the engine will equate to 60% of the power at that RPM.

Is there a way to estimate BSFC at different engine loads based off the full load consumption curve? How do I know what HP to multiply this by in order to get fuel consumed in gal/hr? Is it ever valid to assume that X% load on an engine equates to X% rated power at that RPM?

 

[SomptingGuy]

Kinda depends how you cut it back to 60%. Throttled?

- Steve

 

[jakvett]

I'm not sure how the load would be cut back. It's a diesel engine for what it's worth.

 

[ivymike]

diesel, so no throttle.. what's the BSFC at rated?

 

[jakvett]

For what it's worth, 0.395 lb/hp-hr.

I have the BSFC curve which encompasses the entire RPM range. The issue is that the values are given at 100% load for each RPM entry. BSFC is not linearly scalable to load, so I'm looking for an alternate approach to calculate it.

 

[Lou Scannon]

The BSFC at 60% load for a conventional diesel won't be a million miles away from that at full load. How accurate does your estimate need to be?


I forgot what I was going to say

 

[jakvett]

Decently accurate. I just want to be sure I'm making logical assumptions to get my estimate.

 

[ivymike]

at a given rpm, BSFC will typically be higher at part load than at full load (although it's in many cases pretty flat between 75% and 100% load. It's probably fair to say BSFC at 25% load is 20% higher than BSFC at 75% load. Knowing nothing about your engine except that it's a small-ish variable-speed diesel, I don't think you'll be too far off the mark if you take BSFC as a straight&flat line from 75% - 100% load, and a straight line from 75% to 25% load where BSFC is about 20% higher at 25% load than at 75%.

..or you could search the internet for BSFC maps for your engine.

 

[jakvett]

Thanks for the help. I'll crunch some numbers and see what kind of estimates I get.