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.

[NoDOHC]

Hey, that would be awesome! I have a set of 6kg scales that are accurate to 0.1g. All I need is a fuel pump in a jug and set it on the scales. I could only have about 2 gallons in the jug, but that is enough for a pretty long dyno run.

Actually, I have a gram scale that goes to 50kg +- 5g, maybe that would be better for this application. I could use a ten gallon fuel cell on that and make the dyno guy a little less nervous.

I have a second fuel pump that I could plumb in and it would be easy to install a couple of ball valves. This would not only provide accurate BSFC numbers, but also allow calculation of injector energizing time. It would also indicate the accuracy of the previous data collection technique.

The Mustang dyno I use is capable of maintaining steady-state load on the engine. There will still be a ?? loss in the drivetrain.

I really like this scale idea.

You saved me from purchasing a set of fuel flow meters (not cheap).

Thanks!

A note on accuracy: I know that this data is not exact, but I don't think that the error exceeds 10%. Even at that, the BSFC does not match the commonly posted numbers. As I pointed out earlier, the calculations that I made are worst-case - they do not account for the inertia of the fuel (assuming instantaneous acceleration of fuel into injectors). I did get flow test results on the injectors (they are rebuilt) and they were all within 3% of 460cc/min (whether that is true now is questionable).

The goal in using this method is to get an easy data source so that those who do not have precise measurement abilities can post data too.

[RICE RACING]

I like it! keep me updated