E85 Fuel

[troppo loungo]

Corvette GT1 announced they will be using E85 (85% ethanol) fuel for this season. E85 has a higher octane rating and therefore the engine will be more resistant to knock. This should allow them and others using this fuel to run higher compression and more aggressive tuning (timing..etc). However, there is roughly a 30% degredation in fuel economy. I wonder how they will account for this ? Will larger fuel tanks be allowed or just more pit stops and make up for it with the extra power ? A dilema for endurance racing.

[wmcot]

Will they run E85 at LeMans, too?

[BobbyC]

Higher compression means if you're running 10:1, and you can go to 16:1, you use 10 litres of air per litre of fuel. In 16:1, you use 16 litres of air per litre of fuel.

[BoilerIMS]

Higher compression means if you're running 10:1, and you can go to 16:1, you use 10 litres of air per litre of fuel. In 16:1, you use 16 litres of air per litre of fuel.

Check your facts on that:

1. Compression refers to the reduction in cylinder volume during the compression stroke. 10:1 means that the full air charge into the cylinder is compressed to 1/10 its volume during compression. It has nothing to do with the fuel/air mixture.

2. An engine needs to maintain a proper fuel/air mixture (in chemistry we call this the stoichiometric ratio) so raising the compression actually requires the engine to use more fuel. If the compression increases from 10:1 to 15:1 and you maintained one unit of fuel per 10 units air (it doesn't matter what those units are) in the 15:1 cycle, there would be a drastic reduction in the fuel/air mixture which would lead to a less powerful engine. The fuel/air mixture must rise with compression, though it is not a perfect 1 to 1 scaling.

[call_me_andrew]

Since when does stoich change with compression? I've been taught that stoichiometric (with pure gasoline) is 14.7:1 at 6:1 compression and at 14:1 compression.

[BoilerIMS]

Since when does stoich change with compression? I've been taught that stoichiometric (with pure gasoline) is 14.7:1 at 6:1 compression and at 14:1 compression.

Now that I re-read my post, comment 2 is way off. What I intended to say is that if you stuff more air in the cylinder, you have to add more fuel to keep the right stoichiometric balance. So if you just raise the compression, but keep the initial air charge constant, you don't need more fuel. On the other hand, if you add a turbo or supercharger, the air charge increases so extra fuel is needed. That said, there is subtle tuning of the fuel/air mix that may make an engine more or less efficient at different compression ratios. Remember that an engine runs with excess air, and that excess is just one tuning variable.

[CDN_Wolf_eh]

I was talking to Ron Fellows last Thursday, and he was telling me that AMLS allowed Corvette Racing to increase their fuel cell size, due to the reduced fuel efficiency.

They will run the regular race fuel, not the E85 at Le Man.

One last thing he told me that I found interesting ... the weight of the fuel ... E85 is heavier than the regular racing fuel.


Mark

[wmcot]

I was talking to Ron Fellows last Thursday, and he was telling me that AMLS allowed Corvette Racing to increase their fuel cell size, due to the reduced fuel efficiency.

They will run the regular race fuel, not the E85 at Le Man.

One last thing he told me that I found interesting ... the weight of the fuel ... E85 is heavier than the regular racing fuel.


Mark

Since the E85 is heavier, are the cars allowed to be lighter? Not that it matters much without any other close competition...