26 ms·

I've mentioned the theoretical energy density, and notice that this is what the EIA uses to derive the 3% efficiency loss. This is a highly theoretical value; c

I've mentioned the theoretical energy density, and notice that this is what the EIA uses to derive the 3% efficiency loss. This is a highly theoretical value; combustion engines are very complex beasts and theoretical energy density is a poor predictor of their efficiency, but what is known is that higher octane ratings are beneficial for fuel efficiency. Since ethanol has a high (>=100) octane rating, it might actually improve fuel consumption despite being less energy dense. Also, E15 and higher fuel blends have been in widespread use in the US for 10+ years now. I don't think car engines die quicker in the US.

bri3d 11y ago
http://feerc.ornl.gov/pdfs/pub_int_blends_rpt1_updated.pdf http://feerc.ornl.gov/pdfs/pub_int_blends_rpt1_updated.pdf Here are some fairly extensive test cycles applied to real-world engines, which found that the effect closely mirrors the theoretical reduction in energy density (3-4% for E10, ~7% for E20). Higher octane ratings are not generally beneficial for fuel efficiency unless the engine has been designed for them (compression ratio, cam profile, timing, tune). Dropping higher-octane fuel into an engine designed for a lower-octane fuel will generally not affect economy.