Why diesels get good economy - application to petrol engines

[GasSavers_Brock]

Your correct I was assuming that gasoline engines had a higher BSFC then diesel. I have seen them specificaly for the TDI and they are right about 1900-2000, which is where I cruise. I did assume from past knowledge that gas engines were higher like in the 3k range, mabye not so anymore?

[GasSavers_Erik]

I have heard that higher ICE compression ratios are more efficient- perhaps the diesel 22:1 compression ratio helps.

As mentioned in the opening thread, diesels automatically have a respectable 12% advantage. A gallon of diesel has 112% of the btu's in a gallon of gasoline. If we all adjusted our mpg up 12%, that would definitely help to bridge the divide.

1 gallon of gasoline = 124,000 Btu

1 gallon of diesel fuel = 139,000 Btu


Source:
http://www.eia.doe.gov/kids/energyfa...alculator.html

[omgwtfbyobbq]

Originally Posted by Brock

I did assume from past knowledge that gas engines were higher like in the 3k range, mabye not so anymore?

It probably depends on the engine, but imle most are around the 2-3,000rpm range. For instance, minimal BSFC for the TDI from 2-3k rpm is ~200-215g/kwh, but low load (most driving) BSFC is still good in the 230-250g/kwh range. Gassers have the same minimal BSFC (when taking into account the difference in energy density) from ~2-3k rpm of ~230-240g/kwh, but at anything less than full load, the efficiency starts dropping like a rock, and tends to bottom out at something like 500-600g/kwh from 2-3k rpm for most driving.