No gas mileage figures are given. One key question is, does this optimized E85 engine make up for the mpg penalty from using E85. On a 2007 Silverado 1500 2wd vehicle, the EPA penalty in gas mileage is 23.5%.

Also, the gas only SAAB 9-3 Sport Sedan 2.0T is rated at 210 hp. So, it appears this article fails to point out that you still may have a power penalty with an optimized E85 vs a gasoline E85. To just point out that an optimized E85 using E85 is better than the same engine using gasoline seems pretty meaningless.

While interesting, this article appears to have been written in such a way as to hide the performance and mpg penalties associated with E85, even if optimized.
Now, of course, the figures I have given for the 9-3 could be for the American version and the European version would paint a different picture. If so, I stand corrected.

Comparing MPG numbers across fuel types is totally meaningless, except wrt operating range on a full tank of the same volume.

Numerical comparisons of volumetric fuel consumption across different fuel types is totally misleading. There are meaningful ways to compare fuels, based on gravimetric energy density (for thermodynamic efficiency), on CO2 emissions (for global warming impact) or on $/mi (for cost of operation).

Comparing the performance of one and the same engine on gasoline vs. E85 does make sense for anyone interested in buying it. Saab's optimization means that filling this variant up on E85 makes it more fun to drive, which in addition to the warm fuzzies on how green you are, may compensate for the higher purchase price, the higher fuel cost per unit of energy and the shorter operating range.

If raw power is all you care about, a single fuel vehicles will likely give you better value for money.

tom,

If they took the same engine and optimized it for Gasoline it would have less power than the E85 optimized engine. There is no performance penalty (only the mpg penalty).

Even if you took a car NOT optimized for E85 but turbocharged and you calibrated the fuel settings yourself (ignoring the ignition timing changes) you could still put down more horsepower than with the same engine running on gasoline.

"Also, the gas only SAAB 9-3 Sport Sedan 2.0T is rated at 210 hp. So, it appears this article fails to point out that you still may have a power penalty with an optimized E85 vs a gasoline E85"

Not a good comparison. The Euro spec 1.8 is more comperable to the 2003-2005 2.0t, which only had 175HP, due to it's lower boost pressure.

BSFC is always lower on a turbocharged engine.

So undoubtedly, running higher boost with E85 which it's self has a horrible BSFC... the BSFC is probably pretty wreched, I'd wager near .8 or worse.

Hi everybody,
no doubt that ethanol has less energy content per litre, but since most of the energy is converted in heat and not necessarily in power for the engine. Still, fuel consumption is higher. In addition to environmental reasons, a higher fuel consumption from renewable sources is still better than burning oil - even for local industries. To catch consumer interest you must compensate the higher fuel consumption with lower prices at the gas station which means lower taxes. Example Sweden: Gas sell for 97p while E85 is 53p. Regardless of the exchange rate you talk a discount of 40%. You can easily compensate the extra consumption.

Michael

Ash -

it is true that a turbocharged gasoline engine has to designed with a slightly lower internal compression ratio (e.g. 9.5-10 instead of 11-11.5) to avoid engine knock. Since the thermodynamic efficiency of the Otto cycle is related to this ratio, this is undesirable. Moreover, near rated power the mixture has to be enriched to avoid damaging the turbocharger.

However, that is not the whole story, for three reasons:

First, boosting an engine means you can deliver the required power with a lighter power plant featuring lower displacement (aka downsizing). There are secondary weight savings in the engine points, suspension, firewall etc. Reducing vehicle weight improves performance or fuel consumption, depending on the design priority.

Second, the fuel economy of a *vehicle* depends not only on the BSFC map of the engine but critically on its duty cycle as well. Passenger cars are almost never operated at rated power, so one with a t/c gasoline engine almost never has to be run rich. Diesels run lean even at nominal power so their exhaust gas is cooler, permitting the use of efficient variable geometry turbos without a water jacket and made from non-exotic materials.

Third, any real drivetrain will not get close to the theoretical efficiency anyhow because of fluid dynamic losses during gas exchange, imperfect combustion, heat transfer to the coolant, friction in the crank train and its peripherals and friction in the transmission.

If the engine and turbocharger are designed primarily to deliver low-end torque rather than increase rated power, all of these losses can be reduced by letting the engine run at lower RPM by using longer gear ratios (aka downspeeding).

The sum total of these advantages overcompensates for the lower theoretical efficiency discussed above, so a vehicle with a turbocharged engine *should* feature better fuel economy than one with a naturally aspirated one. Indeed, this is the case with many recent European designs.

In the US, turbochargers are apparently still thought of primarily as a way to increase rated engine power.

"E85 reduces fossil carbon dioxide up to 80%." John Schreiber

Making ethanol from grass (grass being much more productive per acre than corn, BTW) will remove last year's CO2 emissions from the air within one growing season. So, the only CO2 added to the atmosphere would be from fossil fuels used in transport, production and processing of ethanol. Crude oil, BTW, also uses intensive transport, production and processing infrastructure that uses fossil fuels. Doh!

"All else being equal", E85 would cut CO2 emissions by 85% when measured over 12 months time. When measured at the end of a 5 month growing season, CO2 will appear to have dropped about 204%. This means that global warming will be reduced most dramatically in late Summer and early Autumn (or whenever the second half of the growing season occurs).

This depends on the added miles people drive during Summer. That figure of 204% might drop to something a little less amazing, like 180%.

But, every number here is way better than burning 500 million years worth of fossil fuels in 500 years time.

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