gigneil
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Ethanol/biofuel For The Piston Market

Tue Jun 30, 2009 8:38 pm

Certainly the topic of synthetic, vegetable based kerosene additives, blends, or total replacements is well discussed in the industry as a whole.

What I'm unclear on is the viability of ethanol blends or some other biofuel I haven't heard of being used in piston aircraft. Clearly, ethanol burns just fine in gasoline engines on the ground with about $100 worth of parts and voiding most warranties.

So, what would the technical feasibility of burning E10, E15, or even E85 or 100 be in most of your GA aircraft?

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PPVRA
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RE: Ethanol/biofuel For The Piston Market

Tue Jun 30, 2009 8:50 pm

http://en.wikipedia.org/wiki/Embraer_EMB_202_Ipanema

From what I've read over the years, the ethanol-powered version is quite a popular choice in Brazil. Seems like it is a bit more expensive, though.

Technically it shouldn't be a problem. Supposedly you get a boost in power too, though that is offset by reduced range.
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KELPkid
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RE: Ethanol/biofuel For The Piston Market

Wed Jul 01, 2009 6:05 am

Most autofuel STC's for existing gasoline engines specifically prohibit operation with ethanol fuel blends. There are good reasons for this. In most updraft carburetors, gasoline blended with ethanol creates prime carburetor icing conditions over a broader temperature range than straight gasoline. Also, the alcohol in the fuel can attack parts in the aircraft's fuel system. Finally, gasoline mixed with alcohol has a lower vapor point than straight gasoline, which can cause vapor lock in the fuel system.
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rwessel
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RE: Ethanol/biofuel For The Piston Market

Tue Jul 07, 2009 3:28 am

As KelpKid pointed out, for most GA aircraft, water absorption and component incompatibility are big issues for ethanol/gasoline blends.

And that could be dealt with if there was some point - change some parts, and use fuel injection, and you're good.

The problem is that ethanol has a much lower energy density than avgas. Gasoline contains about 46MJ/kg and 34MJ/l. Ethanol does 30MJ/kg and 24MJ/l. So on a weight basis (and most small airplanes are pretty weight limited as is), you're taking a 35% hit on range, and on a volume basis a 29% hit on range (the latter being a limit imposed by the physical size of the fuel tanks, even if weight is not an issue).

On a car, which typically has much less fuel on board, and much looser performance limits when it comes to weight and range, it makes little difference and ethanol is quite practical.

Now you *could* design airplanes to run on ethanol, but they'd have to be bigger, and more expensive.

That being said, for the tiny, tiny volume of avgas consumed in the world, it's just not worth it.

Going diesel is in many ways a much better idea. First, you can burn Jet-A (which is widely available*, and produced in vastly larger quantities than avgas), and while the potential energy in Jet-A is slightly less than gasoline on both a mass and volume basis, the efficiency of the engine is higher so that you actually get more useful energy out of a given mass and volume of fuel.



*And remember that outside of the US, Canada, Brazil, Australia and South Africa, there are only a handful of countries where avgas is commonly available, and then only at considerable expense.
 
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SEPilot
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RE: Ethanol/biofuel For The Piston Market

Tue Jul 07, 2009 11:49 am



Quoting Rwessel (Reply 3):
and while the potential energy in Jet-A is slightly less than gasoline on both a mass and volume basis,

Do you have figures? I had always thought that kerosene had more energy per unit of volume than gasoline. I used to have an old John Deere two cylinder all fuel tractor; it would burn either gas or kerosene; on kerosene it used less than half as much fuel per hour as gasoline to do the same work. And I was also under the impression that jets have so much more range than piston engines did because the fuel contained more energy.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
rwessel
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RE: Ethanol/biofuel For The Piston Market

Tue Jul 07, 2009 8:31 pm



Quoting SEPilot (Reply 4):
Do you have figures? I had always thought that kerosene had more energy per unit of volume than gasoline. I used to have an old John Deere two cylinder all fuel tractor; it would burn either gas or kerosene; on kerosene it used less than half as much fuel per hour as gasoline to do the same work. And I was also under the impression that jets have so much more range than piston engines did because the fuel contained more energy.

In raw terms, kerosene and Jet-A is about 43MJ/kg and 33MJ/l. Typical biodiesel is right there too. "Real" diesel is a bit better at 46MJ/kg and 37MJ/l (a hair less dense on a mass basis than gasoline, a bit better on a volume basis). A nice set of charts summarizing this things:

http://en.wikipedia.org/wiki/Energy_density

But it's important to remember than diesel engines typically manage to extract a fair chuck more useful energy from the fuel (35-40% vs. 25-30%). That's largely due to the much higher compression ratios.

I don't know much about the sort of engine you described, but I've heard of them (although I though they were intended to use some other distillate usually called "tractor fuel," which was not actually kerosene). It might not be a valid comparison though - that sort of thing is often optimized for one thing (diesel/kerosene in this case), and might be “able” to run on gasoline, but with lower efficiency.
 
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SEPilot
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RE: Ethanol/biofuel For The Piston Market

Wed Jul 08, 2009 3:08 pm



Quoting Rwessel (Reply 5):
But it's important to remember than diesel engines typically manage to extract a fair chuck more useful energy from the fuel (35-40% vs. 25-30%). That's largely due to the much higher compression ratios.

I realize that; that is why I brought up the John Deere tractor. It has exactly the same compression ratio whether burning gas or kerosene, yet does more than twice the work with kerosene. Do you have an explanation for that? By the way, I am speaking from personal experience, and what I used was kerosene. The "distillate" you refer to is no longer available; I do not know what it is, but it ran on kerosene just fine. The main problem was it would not start on it, as it did not vaporize as readily; you had an auxiliary tank for gasoline; you would start it on gas and wait until it warmed up before switching to kerosene. You would then switch it back to gas before shutting down, so as to leave the carburetor full of gas. The main differences between the all fuel engine and a straight gas engine were the compression ratio was much lower (about 4:1) and the intake manifold was heated by the exhaust. Your point about being optimized for distillate is valid; obviously the compression ratio is much too low to get the best efficiency, but it still brings up the question as to how it was able to get so much efficiency out of kerosene at that low compression ratio?
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
TheSonntag
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RE: Ethanol/biofuel For The Piston Market

Wed Jul 08, 2009 4:33 pm



Quoting SEPilot (Reply 6):

Maybe the engine is more efficient working as a Diesel?
 
XT6Wagon
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RE: Ethanol/biofuel For The Piston Market

Wed Jul 08, 2009 5:25 pm

yah, people used to use kerosene in thier cars too. Start on a small ammount of gas then switch to kerosene. This went away when kerosene dropped in useage, gasoline usage increased and kerosene became more expensive than gasoline.
 
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SEPilot
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RE: Ethanol/biofuel For The Piston Market

Thu Jul 09, 2009 1:04 pm



Quoting TheSonntag (Reply 7):
Maybe the engine is more efficient working as a Diesel?

It does not work as a diesel; it is spark ignition whether running on gas or kerosene. The carburetor and spark plugs are used for both; the only thing that has occurred to me is that the carburetor may give a leaner mixture for kerosene than for gas, as you do not adjust it when you change. But if this were the case it should give evidence of running excessively rich on gas, such as black smoke at high power or black spark plugs, and it did not.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler

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