Monday, August 18, 2008

Variable Compression for better fuel economy on ethanol

With a high compression engine to take advantage of high octane, fuel economy on ethanol can be near that of fuel economy on gasoline. But most flex fuel engines are designed for optimum fuel economy on gasoline. That's why they get much worse fuel economy on E85. A variable compression engine like the research model described below could run with optimum efficiency on ethanol and gasoline. This would be huge for motorists, reducing cost per mile driven and making ethanol much more competitive with gasoline. 
Lotus developing efficient two-stroke OMNIVORE engine - Autoblog: "This engine design is expected to significantly increase fuel efficiency for sustainable bio alcohol fuels. The architecture features an innovative variable compression ratio system and uses a two-stroke operating cycle with direct fuel injection."


Chief said...

I suspect this is the reason for anecdotal evidence of massive fuel economy hits with E10...along with the large tank-to-tank variability of gas mileage due to the wide range of factors that affect it. Perhaps vehicles designed from the start for higher octane fuels will improve this.

Jeff Goettemoeller said...

I think you are excactly right, Chief. It's frustrating to me when I hear about people who have written off ethanol altogether because they find E10 hurts their fuel economy substantially. They don't seem to realize the variability from one engine to another. It would be very helpful for reducing fuel consumption if car makers would design for greater efficiency at higher octane, taking better advantage of ethanol. Currently, even most Flex-Fuel vehicles are not designed to take advantage of ethanol's high octane. That just seems ridiculous.