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Old 12-10-2007, 07:36 AM   #1 (permalink)
EcoModding Apprentice
Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
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Pulse and Glide Fuel Economy Calculator 4 valve / Cylinder

Attached is my updated fuel economy calculator for generic 4 valve EFI engines. I've tidied it up a bit, and automated it so that most people here should be able to figure out how it works - I've really dumbed it down this time, no looking up BSFC values, you don't even have to google an air density chart, all you need is temperature and altitude. I assume dry air, but I did the calculations to adjust density for humidity and decided not to bother. Even at 30 deg C, and 100 degrees C, the difference is only 1.6% in air density. At 25 degrees, it's only 1.1%.

Note that it is available either as an ODS file in a nod to open formats, or in reverse engineered xls (MS Excel format). Either should work. Created in Ubuntu using Openoffice. Note that EVERYONE can use this spreadsheet for free, whether they have Windows, Mac or Linux. I suggest trying either gnumeric or openoffice.

Figures you will need to know:
Average speed during pulse and glide (assumes constant acceleration)
Total drop in speed until the next pulse starts
Max Power of your car (just google it)
Drag Coefficient (google it, or do a coast down test)
Frontal Area
Coefficient of Rolling Resistance (use 0.06 for heavily pumped tyres)
Total Mass of Car (include driver etc)
Altitude above sea level
Displacement of engine (or the idle fuel burn rate)

Note that you can unhide the rows to see my workings out and verify my equations, which I'd strongly encourage. Read my provisos as well.

Attached Files
File Type: zip (60.6 KB, 127 views)
File Type: zip (54.3 KB, 133 views)
"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

Last edited by newtonsfirstlaw; 12-11-2007 at 05:27 PM..
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