Ethanol Has Higher Lower End Torque?

[YukonCornelius]

Originally Posted by Occasionally6

I think it's worth asking why only low rpm? What's different at high rpm? Is it related to flame speed or maybe heat transfer and evaporation rates?

Low rpm is what would help the ecomodders, but the power increase is across the power band.

[niky]

If we're talking stock tunes, new cars typically run lean or ultra-lean at low rpm... at those rpm, the engines are more prone to "knock" on poor gas, which leads to the ECU pulling timing and perhaps running richer. The octane boosting from ethanol allows the engine to run leaner and stay lean.

At high rpm, the engine typically enters power enrichment, most of them sticking between 12:1 and 13:1, so you don't have that problem.

At least, this is why I think it affects low rpm more... but that would require validation.

[Allch Chcar]

Just a minor clarification on Air to Fuel ratios. New engines typically run stoichiometric at low rpm and go pig rich at high RPM. Rarely are they tuned to the otimal numbers. Factory engines are tuned for emissions and reliability.

[Occasionally6]

Not just low rpm though; low load. At least that's so with fuel introduced into the inlet manifold. There are also exceptions at constant light loads, such as used while highway cruising. I understand that the most knock resistance is required at medium type loads, where enrichment can't be used, yet the load is high enough to cause knock.

Engine speed may have some effect because the cylinder pressure will reduce faster as the piston moves away faster, while flame speed remains more constant. If there is a difference in power output between EtOH and gasoline then that may be a part of why.

Direct injection may be run globally lean because the mixture can be kept locally stoichiometric (within the cylinder). That's why there is a fuel economy benefit with DI.

[Allch Chcar]

New emissions are very strict. Engines stay in closed loop until 4k RPM and 75% load these days. A lot of tuning is to protect the catalyctic converters. But for open loop operation, yes. Flame speed and combustion stability can be a significant factor.

Now I have seen some Ford research on E85 in turbo and naturally aspirated engines. There is one where they tested the 3.5L Ecoboost and another they tested the new Coyote 5.0L. I believe they discussed these same factors.

[YukonCornelius]

Originally Posted by Allch Chcar

Just a minor clarification on Air to Fuel ratios. New engines typically run stoichiometric at low rpm and go pig rich at high RPM. Rarely are they tuned to the otimal numbers. Factory engines are tuned for emissions and reliability.

Dead on.

[niky]

Oops. Yeah. Of course, running at 16:1 or more at low rpm, my car is far from stock...

Ford's pitch for the Ecoboost 2.0 shows a wider range of rpms and loads where the BSFC is optimum versus a naturally aspirated motor.

Of course, that's all theoretical. What happens on the road, with varying gasoline quality, high temperatures and whatnot... might be different.

[Occasionally6]

Originally Posted by Allch Chcar

Engines stay in closed loop until 4k RPM and 75% load these days.

Be careful when referring to closed loop. With wide band sensors it doesn't necessarily mean stoichiometric (which is, I think, what you mean).

[Miller88]

Originally Posted by niky

Oops. Yeah. Of course, running at 16:1 or more at low rpm, my car is far from stock...

Ford's pitch for the Ecoboost 2.0 shows a wider range of rpms and loads where the BSFC is optimum versus a naturally aspirated motor.

Of course, that's all theoretical. What happens on the road, with varying gasoline quality, high temperatures and whatnot... might be different.

My parents have a 2.0 Ecoboost escape. It's geared pretty tall ("rear end" ratio of 3.07:1). It has torque everywhere.

With it's wide torqueband, it's able to cruise down the highway at 1500RPM comfortably.

If the 2.0 in my Focus were to cruise down the highway at 1500RPM, I would get HORRIBLE mileage.

My father got 32MPG on a trip out of their 2.0 Ecoboost Escape AWD!

That's the advantage of these small turob gas engine. They are fun, too ... which ends up leading people to get worse mileage with them.

But it's a small engine that, when driven lightly, can get excellent mileage. Driving it lightly with low boost, it makes good enough torque to keep the vehicle moving without playing "catch up" and by virtue of being a small engine at low speed gets better mileage.

[Allch Chcar]

Originally Posted by niky

Of course, that's all theoretical. What happens on the road, with varying gasoline quality, high temperatures and whatnot... might be different.

That's an important discussion I am having with my fellow Ethanol fans. Some pipelines are changing from 87 AKI Regular to 84 AKI BoB or Blending stock. That means Regular without Ethanol will need to be shipped in by truck, thereby increasing the price. The E10 they have been selling was labeled as 89 AKI due to mixing it with 87 AKI Gasoline. We've come to the conclusion that anyone who runs the new Regular with Ethanol will see their MPG drop. Most of them are running E85 or like me, E30-E40, so it won't affect us directly.