The BSFC chart thread (post 'em if you got 'em)

[tasdrouille]

Here's the map for the 2.0 16v CR TDI found in the new 2009 Jetta TDI.

[dremd]

Prius

[Hasbro]

Originally Posted by tasdrouille

Here's the map for the 2.0 16v CR TDI found in the new 2009 Jetta TDI.

What a fascinating thread.
Am I reading this correctly that between 2-3k rpm and a fairly heavy throttle is the best for accelerating efficiently for this particular vehicle?
Where would one go to have this done- does a dyno that measures load have this kind of software? I'm seeing colored islands for each gear, does that make sense?
I'm pretty weak with math and electronics- I'm visualizing an onboard screen gizmo that shows these islands live as you shift. Does that make sense? My head hurts.

[MechEngVT]

Hasbro,

Your average speed-shop dyno probably wouldn't be able to produce this graph. The 2009 VW graph is a little different from normal in that it appears to be an iso-efficiency plot of metric-unit (g/kW-hr) brake-specific fuel consumption plotted on axes of Brake Mean Effective Pressure vs. RPM. The Prius chart is same-unit BSFC plotted on Torque vs. RPM. Since BMEP and torque can be correlated for a given engine's design it's roughly equivalent.

Wheel or chassis dynos can't really give you this graph. They typically require you to be in one of the higher gears to prevent overloading their absorber (brake) which means you can't accurately evaluate the lower engine speeds. Getting the full data set would require an engine flywheel dyno. You would also have to measure real-time fuel consumption at steady-state operation. Chassis dynos don't do steady-state operation well (depending on absorber type) and typically can not load-down without induced tire slippage.

The graphs have nothing to do with each gear. The colored islands indicate areas of efficiency between the labeled boundaries. Think of it as a topographical map of elevation where the highest elevation peaks (lowest numbers) are the peaks of efficient operation. You are correct in that it appears the most efficient acceleration would be to run the engine from 2000-3000 RPM at about 80% load.

[tasdrouille]

Originally Posted by MechEngVT

You are correct in that it appears the most efficient acceleration would be to run the engine from 2000-3000 RPM at about 80% load.

You know I'm actually not too sure about that. The cost per unit of power is in fact lower than say at 1500 rpm, but there is some additional power lost to friction at 2000-3000 rpm range. At least that's how explain what I found with my TDI. Is there's an other reason you could think of?

I did a lot of acceleration logging with vag-com in my TDI (which pretty much have the same map as the TDI ALH engine posted in a previous post). From the bsfc map I figured out lowest consumption would come accelerating in the 1500-2000 rpm range, but it in fact it was in the 1300-1800 rpm range.

[Daox]

Interesting you found it so low. I always figured the lower BSFC plateaus had something to do with piston speed, flame speed, and avaliable torque.

[cfg83]

Hello -

I keep seeing the "Engine Torque (NM)" in the vertical axis of the BSFC charts. Also, from the OBDII specification, I have access to the engine load value (the LOD parameter in the Scangauge).

Question: Can I derive the Engine Torque in NM (nanometers CORRECTION: Newton meters) from the OBDII LOD parameter?

If I can, and I know the BSFC for my engine (I do), then I should be able to figure out my approximate fuel consumption in real time.

CarloSW2

[Daox]

Very generally, yes. LOD or engine load would be the percentage of maximum torque.

[pasadena_commut]

Originally Posted by cfg83

... the Engine Torque in NM (nanometers) ...

NM = Newton meters. Torque units are force X distance.

[TEiN]

Originally Posted by Daox

Very generally, yes. LOD or engine load would be the percentage of maximum torque.

Percentage of maximum torque at the current rpm, right?