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Old Oct 09, 2009, 03:23 PM
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Alternate fuels for nitro engines?

Hello,
A few days ago the idea just came to me about vegetable oil for nitro fuel. I know many rc engines can be successfully converted to diesel, and I know diesel engines can run on vegetable oil. So is there any chance of powering my airplanes with used vegetable oil? My main reason for asking are the environmental and economical benefits, as anyone can get hundreds of litres of used veggy oil from their local Mcdonald's.

I'm quite excited about the idea, hopefully it can work.
Tell me what you think...
Lucas
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Old Oct 09, 2009, 05:08 PM
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Not much chance really.

Model diesel engines won't run (unaided) on fuels like vegetable oil because they don't create enough heat from compression to ignite them. What's needed is a fuel with a much lower flash-point -- which is why ether is used.

You *could* use some kind of vege oil to replace some of the kerosene/paraffin that these engines usually use as the "energy component" of their fuel -- but why bother?

Diesel engines are far more fuel-efficient than glow engines and kerosene isn't that expensive in the first place.

The other problem is that the viscosity of vege-oil is *much* higher than the kerosene you'd be replacing so you may not have enough adjustment on your needle-valve(s) to cope and it probably won't vaporize adequately.

If you're contemplating replacing methanol with vege-oil it gets even worse. Glow engines require the catalytic effect that methanol brings to the party to keep the plug warm. Replacing the methanol with vege oil would mean that the engine would stop as soon as you removed the glow-heat, even if you could get it running in the first place.

And, I don't think vege-oil will mix with methanol so you can't even do a 50/50 mix :-(
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Old Oct 09, 2009, 05:12 PM
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Ah, I see. Kerosene is used in model engine fuel? What if you had a powered glow plug?
Lucas
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Old Oct 09, 2009, 06:21 PM
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Quote:
Originally Posted by lucasavaitor
Ah, I see. Kerosene is used in model engine fuel? What if you had a powered glow plug?
Lucas

Depends which model engine fuel you're referring to. Diesel engines (Some), nitro or methanol engines(Which really are kind of a diesel too) do not, usually. Though some people run gasoline/kerosene/methanol mixes in their nitro engines.
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Old Oct 09, 2009, 06:42 PM
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Model diesel engines will not burn vegetable oil at all. You can replace castor with olive oil if you want, but no oil will replace the kerosene.

It's been tried and basically we learned that only the ether in the mix was being consumed. Even if you made biodiesel from your veggie oil, little would be burned.

I recently ran a model diesel on fuel made with auto diesel and it run and burn some portion of the diesel, but there was a lot of unburned diesel in the exhaust.

Greg
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Old Oct 10, 2009, 03:48 AM
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Quote:
Originally Posted by lucasavaitor
Hello,
A few days ago the idea just came to me about vegetable oil for nitro fuel. I know many rc engines can be successfully converted to diesel, and I know diesel engines can run on vegetable oil.
Some confusion there I'm afraid. Automotive diesel engines can run on vegetable oil, though even there the extra viscosity causes some problems. Model diesel engines, despite the name, are rather different beasts and cannot run well on any heavy oil, which most definitely includes veg oils.

There are several components to both (model) diesel and glow fuels. Both include an oil used just for lubrication and vegetable oils could just about be used for that portion (about 20%). But the power and ignition promoting parts, the other 80%, can't easily be replaced.

Steve
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Old Oct 10, 2009, 06:47 AM
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Ok, so veggy oil is ruled out,
Ira NZ said that you can use a mix of kerosene, gasoline, and methanol.
For me, that would be very economical, somebody explain how it works?
Could you substitute the kerosene with jet fuel?
Lucas
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Old Oct 10, 2009, 07:53 AM
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Unfortunately the pump diesel fuel for trucks has a higher combustion temperature than kerosine does. So it doesn't work either. Kerosine and jet fuel diesel are essentially the same stuff.

The major problem you would have with vegetable oil from the resturaunts is that almost all the extablishments have contracts with vendors for disposing and recycling the veggie oils. So they very unlikely give you any. But if you own your own, maybe you could use it then, if you didn't have a contract for recycling it already.

We have had several fellows try using all sorts of things in model engines with mixed results of course. A problem with a model engine, is the scale effect, as the engine gets smaller and smaller, the air and fuel become more dense and viscous in relation to the engine size. The air and fuel density and viscosity all remain a constant while the engine size gets smaller. So veggie oil quickly becomes too thick and viscous.

Now one might have some success mixing veggie oil in small amounts with model diesel fuels. But it is a mixed bag, and a hassle too. Probably not worth the effort.
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Old Oct 10, 2009, 10:42 AM
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Jet fuel and Kerosene are virtually identical and interchangeable. Many have run Jet A in diesel fuel mixes. I have probably 15 data sheets between the two and most suppliers are similar.

The problem with veggie oil is not viscosity. It's simply that the temperatures in a model diesel engine are never high enough to ignite a heavy oil. An auto diesel will run on veggie oils and bio diesel, both of which have autoignition temperatures above 300C in most cases. The really huge ship diesels literally will run on any hydrocarbon. Small cylinders experience a lot of heat loss from the compressed air to the cylinder walls, enough that the air temperature inside the cylinder is only high enough to ignite ether when the engine is cold. Ether's autoignition temperature is 180C. Just exposing ether to that temperature without spark or flame sets it off. Kerosene is a bit higher than that at ~210C. Ether has a very high vapor pressure while kerosene doesn't. Without vapor there is no fire. Ether is essentially required for cold starting a model diesel. After the engine is warmed up it could run without ether. I've have done it with several engines.

A couple years ago a handful of diesel heads on RCU spent a lot of time and effort in research and testing to come up with fuel that didn't require the expensive and hard to get ether. We did run engines on small percentages of ether and without ether at all, but only after the engine was hot.

For reference:

Model diesel fuel: 25-33% Ether, 33-50% kerosene, 20-33% lubricant, 0-2% ignition improver (nitrate compound of some sort)

Glow fuel: 10-25% lubricant, balance methanol, 0-60% nitromethane

These are the basic fuel mixes for model engines.

Greg
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Old Oct 10, 2009, 12:13 PM
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gkamysz, you are correct, I was thinking of the pump truck diesel fuel earlier.
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Old Oct 10, 2009, 07:32 PM
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Ok, so you need ether no matter what? If so it isn't worth it.

Thanks for all the input,
Lucas
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Old Oct 10, 2009, 07:52 PM
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A normal model diesel needs ether to start cold, period. There are exceptions in existence, but they are not hobby engines.

I like diesel because it's different.

Greg
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Old Oct 10, 2009, 09:14 PM
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Darn it, oh well, there's always gas and electrics!

Lucas
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Old Oct 11, 2009, 04:10 AM
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What about ethanol? Would a glow engine run on a mix of Ethanol and oil? Would it need nitro? You can brew your own ethanol, ya know.
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Old Oct 11, 2009, 06:50 AM
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Yeah you can substitute ethanol or methanol in the glow fuel no problem. You can even run combinations that have a little gasoline in the fuel too. it isn't that far removed from using E85 gasoline and alcohol mixes either.

Yeah you can brew your own ethanol but the feds around here would take a serious interest in you when you are doing it.

The original glow fuel mix (FAI fuel as it is known today) is 80% alcohol and 20% oil. They add nitromethane to improve its performance.
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