Brickley Engine: BSFC comparisons

[boonebucker]

Below are a couple of links to BSFC numbers for engines with similar technology criteria and displacement per cylinder. Does anyone have any numbers that would indicate for this type and size engine that these numbers are incorrect? The first link shows a sweet spot of about 440g/kW hr.for 179cc engine. The Brickley Engine is 173cc per cylinder and I am obtaining 350g/kW hr. The other link indicates numbers much higher than 440 g/kW hr and they will have to be converted from lb/Hp hr. I used the 3/4 throttle numbers. Your thoughts?

https://online.tugraz.at/tug_online/voe_main2.getVollText?pDocumentNr=488002&pCurrPk=73453

https://www.arb.ca.gov/msprog/offroad/sore/swri-final-report.pdf

 

[boonebucker]

 

[BrianPetersen]

I believe the other engines you are comparing to, are all air-cooled engines with integral cooling fan whose power demand would be incorporated in those measurements. Is yours the same situation?

 

[boonebucker]

Not exactly. Air cooled, similar carbs and mufflers, yes, but my engine does not have a cooling fan. Why do I think they can still be comparable? The work of the cooling fan is replaced by the work necessary to drive the two preloaded tapered Timken roller bearings and hub seal that support the two caliper disk brake for the prony brake. As I had mentioned previously, a small crank-speed oil pump adds a small drag that I don't believe any of the other engines have as well. I would not be surprised if my setup actually has more drag on the system than a fan. Something more to test.

 

[boonebucker]

The cooling fan on the stock 173cc engine is 6.5" in diameter and the fin height is slightly under 1". A comparable Fasco A118 has a 5.75" fan and a 1.125" wide fan and is driven @3000rpm with a 1/15 Hp motor. 746/15= 49.7watts. I'm working on way to figure the hub friction.

 

[boonebucker]

Being limited by Covid quarantine resources, I clamped a 24” piece of ¾” X ¾ maple across the disconnected hub and added weights until it began to barely move: 375 – 400 grams @ 1 ft. Being that it would be difficult to imagine maintaining 2600 or 3000 rpm without needing to add more mass to offset anticipated additional torque, I think using 375 grams would be on the conservative side of a reasonable number to use for estimating torque. Accordingly: 375/454 = .826 ft lbs >>> .826/.737 = 1.12 Nm

(1.12)(2600)/9.549 = 305 watts. >>> 305/4 = 76 watts per cylinder (power loss through hub @2600rpm).

(1.12)(3000)/9.549 = 351 watts >>> 351/4 = 87 watts per cylinder (power loss through hub @3000rpm).

What do you think?