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Old 07-19-2009, 09:56 AM   #1 (permalink)
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Alternate BSFC views

Hello
I have just developed a spreadsheet to display different views of BSFC contour charts. It converts the Y axis values of torque or BMEP to kw and, with vehicle details specified, also to speed.
It then goes one step further and calculates and plots the possible fuel consumptions for a vehicle at different speeds.
These are the charts produced for the Geo/Swift.


There are another 10 BSFC charts in the spreadsheet.
The spreadsheet can be downloaded from http://megametrelitre.com/BSFC-GlennThorpe.xls.
Please note: 1 - It is 3.5 mb so can be uploaded to ecomodder; and 2 - a macro is needed in the spreadsheet to calculate vehicle speed from power.

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Old 07-19-2009, 11:10 AM   #2 (permalink)
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Hi,

I downloaded the spreadsheet but am confused by the source of 'fuel consumption.' I didn't see a fuel consumption input. Did I miss something?

It looks like the "contour #" defines which curve is drawn. But the logic that applies a value of "0, 1, 2, ... n" to a data point isn't clear. Is this data in the worksheets or was it copied from other BSFC charts?

The reason I ask is another model based upon drag and fixed engine efficiency and overhead gives the following fuel consumption vs speed:


I've long suspected engine efficiency, the BSFC variance, is responsible for the outliers in the data measurements. Field measurements of BSFC supports this hypothesis.

What I noticed is the "Toyota" tab shows the 1.6L engine BSFC rpm limits. Actually the limits for the 2001-03 Prius with a maximum 4,500 rpm. But field data suggests the actual BSFC is different than the published BSFC chart. There is something called the "operating line" that defines the targeted operational region for the engine.

Understand, I appreciate the effort and like the contour plots. You've given me some ideas that may allow me to combine the field BSFC data and drag function into a more accurate plot of expected MPG vs speed.

GOOD JOB!
Bob Wilson
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Old 07-19-2009, 05:00 PM   #3 (permalink)
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Bob, where do you put your brake? BSFC maps are produced with the engine on the dyno. You work off road load. Results will obviously be different since there is a whole lot of stuff between the road and the crank, and this load is not a linear function of rpm.
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Old 07-19-2009, 06:15 PM   #4 (permalink)
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Hello Bob
The y values for each contour are separate columns. The curve # values separates them into columns.
The consumption lines in the second chart are actually contours, they just end up squashed flat.
Their y values are calculated in the cells starting in column AA.
These values are calculated as KwGross/SpeedKmh*BSFCinGrams/1000*0.74*100).
As in 1 hour @ 100 km/hr @ 50 kw gross = usage of 50kwh/100 km and 1 kwh = BSFCinKg/0.74 kg/litre fuel weight.
The theoretic minimum fuel consumption would be a curve joining the end points of the lines.
The code that calculates speed from power input is in the macro module. Please feel free to use that elsewhere. It needs to solve a quartic (power 4) equation and is a pain to have to recreate.

Last edited by thorpie; 07-19-2009 at 06:19 PM.. Reason: added
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Old 07-19-2009, 10:13 PM   #5 (permalink)
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Quote:
Originally Posted by tasdrouille View Post
Bob, where do you put your brake? BSFC maps are produced with the engine on the dyno. You work off road load. Results will obviously be different since there is a whole lot of stuff between the road and the crank, and this load is not a linear function of rpm.
I have a Graham miniscanner and it reports MG1 torque. There is a fixed ratio of 28:100 between the ICE and MG1 so I can calculate ICE torque. With ICE rpm, I have the operational power and combined with injector timing, I have everything needed. <grins>

Bob Wilson
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Old 07-19-2009, 10:23 PM   #6 (permalink)
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Quote:
Originally Posted by thorpie View Post
The y values for each contour are separate columns. The curve # values separates them into columns.
The consumption lines in the second chart are actually contours, they just end up squashed flat.
Thanks! This is a good plotting technique but my BSFC numbers are part of a scatter plot.

Quote:
Originally Posted by thorpie View Post
. . .
These values are calculated as KwGross/SpeedKmh*BSFCinGrams/1000*0.74*100).
As in 1 hour @ 100 km/hr @ 50 kw gross = usage of 50kwh/100 km and 1 kwh = BSFCinKg/0.74 kg/litre fuel weight.
The theoretic minimum fuel consumption would be a curve joining the end points of the lines.
I thought that was one of the clever parts of the spreadsheet. I'm not ready to go there until I'm happier with my BSFC data from the field.
Quote:
Originally Posted by thorpie View Post
. . .The code that calculates speed from power input is in the macro module. Please feel free to use that elsewhere. It needs to solve a quartic (power 4) equation and is a pain to have to recreate.
Interesting. I recently came across the EPA drag formula from SAE 2009-01-1322:

A*(v**2) + B*(v) + C

A - coefficient proportional to aerodynamic drag
B - coefficient proportional to a linear drag function
C - fixed, typically rolling drag
v - velocity

I briefly saw a table of these values used by the EPA to calculate some the EPA mileage numbers.

Thanks, excellent work.

Bob Wilson

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