Originally Posted By: Cujet
A bit off topic. Direct injection engines can, with proper design, achieve better BSFC numbers with ethanol in the gasoline. It takes very high compression, careful cam timing, downsizing and turbocharging. But they can achieve "diesel-like" efficiency when compared by BSFC methodology.
For those who don't know, BSFC is "brake specific fuel consumption" BY WEIGHT of the fuel consumed, not by volume.
For example: an engine has a BSFC of 0.5 pounds fuel per hour, per HP produced. (that's also 304 grams of fuel consumed per KWH power produced) or slightly better than a typical Chevy small block (0.55LB/HP/HR)
Stated mathematically, BSFC is fuel mass flow divided by Horsepower, and is directly related to the engine's thermal efficiency. A lower number means higher efficiency. I have tested high-performance gasoline engines that have max power BSFC's down to ~.41 lb/hp/hr. Emissions controlled engines pay a penalty in BSFC by having to be tuned over-rich to protect the catalyst from excessive exhaust temperature. Their part-power BSFC's though, are quite good, because they can be tuned to a stoichiometric mixture at road load conditions.
I can't comment on what the BSFC of modern diesels with emissions controls are, but before emissions regulations really got tight, the Detroit Diesel Series 60 was said to be achieving .32 lb/hp/hr. This was in the late 80's to early 90's.