BSFC Numbers for Rotary

[RICE RACING]

Originally Posted by NoDOHC

If I can afford the dyno time, I would love to document a full BSFC curve. This issue with this is that drivetrain loss is a little funny at lower throttles (manifold pressures), as some of it drops with load (bearing and gear resistance) and some is fixed (windage and oil displacement). Still, this curve would be more useful than an actual engine BSFC curve to develop optimal mileage gearing....


More data would be awesome here, as I would not consider the number from a single engine a representative sample.

The data is easy to get, simply datalog injector on-time and engine speed during a dyno run and compare the graphs. You should have fuel pressure and manifold pressure to be really accurate.

With enough data, we could develop compression ratio comparisons (which should show lower BSFC with higher compression). Porting comparisons, aspiration comparisions, AFR comparisons (mostly done already by Kenichi Yamamoto) and ignition timing comparisons.

I wish I owned a dyno sometimes, I would get a lot more data if it didn't cost me $60 per hour to collect it.

What you really need is an engine dyno and a super accurate fast acting lab (not Leb!) spec scales) I did BSFC testing on our FSAE car engine and simple effective way to measure fuel flow was to have the whole fuel system sitting on the scales! this negated the need to have $20,000 worth of calibrated fuel flow sensors in both supply and return line to determine the exact fuel flow into the engine. these sensors are still only as good as the data they are calibrated too and only work on certain fuel types!

With 3 reference meters we could see air fuel ratio and thus determine air flow rate in the said engine, from this data we could then along with power on the brake (on equilibrium!) establish that correct output less intertial variances! (very important). The output fuel usage (by mass) was feed into a data logger and all the collections automated.

Seen all kinds of set ups, there are many ways to do it, but as anything in life lots of ways to do it incorrectly! Dealing in an Aeronautical and Mechanical Engineering lab even 4th year Thesis students tended to make some very fundamental mistakes and ASSumptions that they think would cut it in doing up a proper report.