gpsman1:
We'll have to watch this and see what develops.

Here's my take on your thoughts:
A) more fuel per stroke is being injected
- On an engineering basis this makes no difference.... its the energy carried into the cylinder.

B) ethanol burns slower, and thus it is said, more completely than gas
There may be something to this.
- The mechanism can also be achieved with water injection. What happens is there is more sustained push on the piston and the conversion of water to steam does just that. Go take a look, there are some websites for these and is had been used in aircraft engines to briefly increase power.

C) more fuel would mean more atomized or vaporized droplets, meaning more surface area in contact with the air during combustion, perhaps leading to more combustion, and more power per stroke.
- Once an engine is warmed up there is no benefit to the greater surface area mechanism. The reason is that all fuel is converted to a gaseous state by the engines heat.

D) ethanol has fewer btu per gallon, but if a greater % of useful energy can be extracted, then the MPG decrease will be minimized, and/or the power maximized.
- Not sure what you mean here, if you mean that the higher octane rating of ethanol makes a difference: this is true only if the engines compression ratio is setup to use that benefit of ethanol.
- If you are linking back to item B) above then possibly true but I believe this to be a very small contribution to horsepower.

I'll have to watch mine more carefully in the conditions you set out above
and see if I can replicate it and see what mechanism seems to be the cause.

With regard to rpm there is another issue: the synchronous machines inside, having a permanent magnet for the rotor, can only change their power by raising or lowering rpms respectively. So I think this is part of the picture you have. We'll have to watch.

 

I've never used E85 in my '05 or '09 FEH but I've had a ton of experience comparing straight gas to E10 in my '05. The RPM seems to run away at highway speeds and there is a big lost in power with E10. There is also a big lost of power in city driving and the RPM can get away from me while accelerating.

What is really strange is how my '09 FEH handles E10. I don't have the run away RPM or lost in power in city driving as much but highway driving MPG drops like a rock. The heat above 80F kills my '05 FEH mileage, but I'm getting much better mileage in warm weather with my '09 FEH. On this present tank with 514 miles, my Nav sys tank reading is holding a 56.4mpg average which means I may break a 54mpg tank on E10. Today it was 82F and I was getting just as good mileage as 60F which is very promising for the 90'sF I'll see this summer here in South Florida.

I don't think there is anything better than straight 87 octane gas as far as getting the most power and MPG in todays market but I keep an open mind for the future. Of course higher compression engines can produce more power, but at a reduced MPG. I can tell everyone there is not a better feeling than turning the key off in my '09 FEH and seeing 56.4mpg on my Navi when I park for the night. Maybe it's only 54mpg when I fill-up, but still I don't have to climb out of a HCH or Prius every time I stop. I'm a big man and load my FEH with anything I want and don't drive like a turtle.

GaryG

 

No, not really. It's the amount of energy extracted per stroke of each cylinder that really matters.

If 20% of the energy of gasoline is extracted, and 30% of the energy of ethanol is extracted, we have a virtual tie.

My "more fuel quantity" was meant to evoke the other possible effects of doing so. Do the injectors add 30% more E85 fuel in the same amount of time? ( as gas ) Or is the fuel metered in during a 30% longer time interval? I think it is the second.

 

Given the thermodynamics of the Atkinson cycle (or Otto Cycle) the amount of energy extracted is not dependent on the physical quantity of fuel injected. The amount of energy available in these cycles is dependent on the difference between the high temperature and the exhaust temperature (at the cylinder exhaust port).

If you get a certain peak temp on straight gasoline for the power commanded, you will get the same peak temp when enough ethanol (not quite 2x) has been injected to deliver that same commanded power level.

Thus if the engine is set up with higher compression it can extract more work from the cycle because it will have a higher peak temp. This is why octane rating makes a difference to the energy extracted. This is also why when you feed an engine octane higher than it needs you don't get more energy out of it.

Google either the otto cycle or the atkinson cycle and look at the curves associated with the intake/compression/power/exhaust parts of the cycle. There's several diagrams such as the T-S (temp-entropy) that show the work done in each phase of the cycle. Once you understand that the work extracted in the cycle is the area between the upper and lower curves, you'll see my point.

This why those fuel additives that say they'll improve mileage by doing things like "aligning the molecules" really don't work.

They set up the fuel system with a constant pressure on the fuel injector header, so the amount of fuel injected is dependent on the open time sent to the injector. They could use a variable pressure along with times but that makes the fuel system more complicated.

The timing is dependent on what the computer is sensing as the concentration of ethanol in the fuel.

 

I have noticed for years, running gas or presumably E10 ( not always labeled ) that my engine water temperature is always in the 184-186'F range.

Running more than "normal" ethanol ( and I don't have specific data based on ethanol content ) my engine water temperarure is always in the 190-191 range.

The volume inside each cylinder is of course, constant.*
*If the valve timimg is constant.
The temperature can rise, and thus, the pressure during the power stroke.

Since the engine block is a huge heat sink, a small cylinder ( x4) could have a pretty large temperaure rise internally to raise the block and associated water 5 degrees.

However, the lower RPM when running ethanol help to mask this effect, making it almost invisble to the driver.

So why do you think the RPM's are lower when running high proof?

 

More torque

 

There are only two things that could allow as much or slightly more power from ethanol fuels vis-a-vis straight gasoline in the FEH engine with its fixed valve timing and fuel pressure:

1. Heat of vaporization of ethanol fuels vs. gasoline. Much greater cooling effect when the fuel is atomized through the injectors. This results in cooler, denser mixtures and occurs after the MAF/IAT.

2. Increase in BMEP due to an increase in the total ignition timing. One would have to observe the amount of advance to determine if this is indeed happening. The higher octane of ethanol combined with the cooling effect listed above makes it possible to have much greater advance before the onset of pinging.

An engine producing the same power at a lower RPM is working harder and thus more efficiently.

Flex-fuel vehicles generally have variable pressure regulators and larger injectors/fuel pumps in addition to the other changes required to operate on high ethanol content fuel without slowly (or quickly) destroying the engine.

Back when I was an EE undergrad, classical thermodynamics was still required for EEs. The thermodynamic analysis of the otto cycle is a classical spherical cow exercise and reveals that the thermodynamic efficiency depends only on the compression ratio. Although in my textbook, the authors mention how this is not the case in reality.

 

First we have to remember that the computer controller is controlling three machines. I recall from the manuals that even when there is no battery charge/discharge the two electric machines trade power (input from the ICE). The computer is setting the engine at what is its programmed most efficient operating point.

Second synchronous electric machines have two ways of increasing power: rpm and excitation. Since these use permanent magnet rotors there remains only one way to change power input/output: changing rpm.

I'll have to look up in the shop manuals just how the system handles this when cruising with no net battery current. As mentioned above the computer can set three different rpms for each machine to maximize fuel efficiency.

The issue of slower burn rate has some merit, but I don't believe it is a major contributor in the lower power range engine these run.

The valve timing is constant on the earlier ICEs. I understand that they have introduced a variable intake cam timing capability recently. This regulates the charge taken into the cylinder and "sort of" regulates the compression ratio.

The beauty of the atkinson cycle is that it has a different compression vs expansion ratio enabling it to extract more energy from a given charge.

I've got some homework to do.

 

Highly likely to be #2. How does the FEH control maximum advance? Is there a knock sensor? Can it map a higher advanced curve? I know that the Highlander does this. The manual actually states that increased performance is possible with higher octane fuels.

 

Yes, the Knock Sensor (KS) is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and retard spark timing.

After FL mandated E10 my Son came to visit from NY with four friends. They borrowed my '05 FEH to go to Miami and when they got back said the engine RPM was very high and they could not get much over 70mph on the turnpike.

Of course they did not know I could review their trip data with my SGII. The Max RPM was something like 5,900 and their Max speed was 80mph. I don't normally drive that fast but I have been to 80mph a few times with straight gas but never with E10. No problems with straight gas getting to 80mph.

I took the '05 FEH out on I-95 and it was true I was having a hard time accelerating above 70mph without backing off the RPM and slowly accelerating again to reduce RPM. I tried to get up to 80mph and at 5,900 RPM I was getting bad engine knock and had to back off accelerating. To this day I still think it was the E10 causing the lost of power and high RPM.

GaryG