Naga1337

Hi everyone!

First off, a few notes: I am not saying this would work. I'm asking if you think it would work/makes sense. Also, this isn't a debate over whether or not E-85 is cheaper/better for the economy/better for the environment than gasoline. With that being said, onto the topic...

I was driving home the other day, and for whatever reason, I started thinking about alcohol fuels. Continuing on this train of thought, I eventually got this idea in my head. For what little I have thought about it, I can see nothing wrong with the theory. Maybe someone here can. Here it is:

Tuned Port Injection is designed, for all intents and purposes, to provide gobs of low and mid range torque. In order to do this, it has extremely long, relatively narrow intake runners. These properties increase the velocity of the air entering the engine, which causes it to "pack" itself into the cylinder when the intake valve opens, because air is elastic, property-wise. However, these virtues also translate into it's breathing problems in the upper RPM range. The runners are narrow, so when the engine is begging for air up high, the intake system can't provide for it's needs. To cure these problems, some people have taken to siameseing the runners to provide more space for the air to flow through. This does indeed work, but because the air isn't moving at as high of a velocity when it goes through the now enlarged runners, it doesn't get the "packing" effect that it does when it goes through the original, narrow runners.

If you're confused, let's put my thoughts in terms that are more tangible to most people: water flowing through a hose. If you have X gallons of water (cubic feet of air) flowing through a narrow hose (the stock TPI intake system) in Y seconds, it moves at a higher velocity and has more pressure behind it, than if you put X gallons of water through a wide hose (siamesed runners, or a higher horsepower, lower torque intake system) in Y seconds.

Because the faster moving air is at a higher pressure, it "packs" itself into the cylinders, so there is more air in the cylinders, and therefore, more fuel can be burned. However, as engine RPMs increase, and the engine attempts to suck more and more air out of the atmosphere in a given amount of time, the narrow runners eventually can't keep up with the demand, and they become a bottleneck. While at low RPMs they "pack" air into the engine, at high RPMs, they don't let the engine "suck" enough air out of the atmosphere. There you have it: A high torque, low horsepower intake system.

That being said, let's get onto the topic of E-85. I will be covering E-85 specifically, because the gas station just down the street started selling it. My theory doesn't take advantage of the high octane rating (104 octane) of E-85, but rather on the fact that it requires a different air/fuel ratio than gasoline to burn optimally.

For gasoline to burn optimally, it needs a ratio of around 13 air particles to 1 fuel particle: an A/F ratio of 13:1. E-85 on the other hand, requires only around 9 air particles to 1 fuel particle: an A/F ratio of 9:1. This means that a given amount of E-85 requires less air to burn optimally than the same amount of gasoline.

As I mentioned earlier, the thing that hurts TPI is the fact that it can't flow enough air at higher RPMs to feed the engine. However, this is based on the use of gasoline, which requires stoichiometrically more air to burn than E-85. So theoretically, wouldn't the TPI's high end breathing problems be less of a burden on an E-85-fueled car, as opposed to a gasoline-fueled car, allowing it to make power further into the higher RPMs?

This is, of course, assuming you have the fuel system to supply the greater fuel demands that E-85 engines have. Higher compression heads and pistons to take advantage of the higher octane rating would help, as well.

Am I right? Wrong? Please, share your thoughts!

Guest

Doesnt really work that way. You have to include the energy produced by that reaction.

Naga1337

I had thought about that. I assumed that by taking advantage of E-85's increased octane, you could compensate for that.

royslsbry

I thought gas burned better at 14.7 to 1

Naga1337

Oops! That's right. But the same concept still stands as mentioned in the first post: Gas likes it leaner than E-85.

Rayzor32

iTrader: (1)

where is it that everyone is getting E85 from? Ive never seen a place that has it. Its gotta be possible though i mean they got funny cars that run off alcohol right

rhuarc31

Actually if I'm reading it right it does work like that - sort of. The energy contained in ethanol is like 60 or 70 % gasoline, but the mixture is so much richer that you can end up with more power when you factor in the increased density due to the cooling factor. Methanol is even better this way. Propane and Methane are not.
!! However!!! The motor requires the same amount of air at the same RPM so the intake restrictions still apply, so no you can not use E-85 to offset the RPM restrictions. Remember the motor is an AIR pump, not a fuel pump. You still have to fill those cylinders with air. Also, in general alcohol based engines like shorter intake runners, not longer. All kinds of stuff to do with heat of vaporization and stuff, though not so important in an injected application.
Thirdly if you're not gonna take advantage of the higher compression ratio's it allows, your leaving the best advantage it gives you on the table. Even just e-85 in a well tuned motor will let you hit 13 or 14 to 1 with it's increased octane and charge cooling properties.
There's a good short article on it here
http://journeytoforever.org/biofuel_...manual1-2.html.
In short a motor purpose built for ethanol or E-85 has the capability of being a great motor that has plenty of power without sacrificing too much mileage, but a mild gasoline motor, or even a compromise motor will leave you unhappy running on E-85. If GM would build a LS based motor with 13 to 1 compression to run purely on E-85 I'd just about kill to have it.

Naga1337

Get a map and put your finger in the middle of the Midwest. As you get farther away from this point, E-85 gets rarer and rarer. Here in Ohio, it's just starting to show up, and I'm fortunate enough to have a station selling it not 2 miles from where I live.