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Biodiesel in a model engine

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Old 10-11-2012, 05:29 PM
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Default Biodiesel in a model engine

Hello all,

I am currently a chemical engineering student at University of Colorado - Boulder. We are competing in a competition where we need to design a vehicle the size of a shoebox which will travel a specified distance and carry a specified load.

We are looking at to use a model diesel engine which will run biodiesel produced from algae which we will grow synthesize. Our research indicates that we need to blend the fuel with castor oil and diethyl ether. However, diethyl ether is a "4" on the NFPA flammability rating, which is banned competition. Is there a less volatile chemical that we can use?

What does diethyl ether do for the engine? Our hypothesis is that the diethyl ether is a compound which will reduce the viscosity of fuel.

Thanks in advance,
Louis
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Old 10-11-2012, 05:51 PM
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Default RE: Biodiesel in a model engine

Ether lowers the ignition point of the fuel and enables the mineral based kerosene to be combined into the organic based castor oil.
(Also provides a lower % calorific rating and cooling - kerosene packs quite a few BTU's and some designs do not like the extra thump or heat)

Do a search on HCCI engines (homogenious charge compression ignition) and you will soon see that model engines are not real diesels.

P.S. If you find a suitable replacement for ether then please let us know!

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Old 10-11-2012, 05:53 PM
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Default RE: Biodiesel in a model engine

Are there real diesel engines that are similar in size as model engines?

Thanks
Louis
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Old 10-11-2012, 05:55 PM
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Default RE: Biodiesel in a model engine


Quote:
ORIGINAL: yourmightyruler

Are there real diesel engines that are similar in size as model engines?

Thanks
Louis
Ithink that some go down to the 30cc range but its the injectors that complicate things below that size.

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Old 10-11-2012, 05:55 PM
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Default RE: Biodiesel in a model engine

Louis,

Our diesel are not true diesel engines, but compression ignition two strokes. The ether is essential for the combustion process to begin.

Our usual fuel mixture is 30% Ether, 25% Castor Oil and 45% Kero.

This fuel mix is for sport use models and is often varied for specific applications. eg racing can be 30/12/58, also using some exotics like TEL and replacing Castor oil with synthetics.

Vintage engines might increase the oil content to protect frail old engines.

You might get better results from a glow engine running on ethanol mix. By choking the carb size right down you may get good consumption results although you'd give up a little power.

Good Luck

Greg
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Old 10-11-2012, 06:42 PM
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Default RE: Biodiesel in a model engine

As already indicated there is NO alternative to diethyl ether in model 2-stroke 'diesel' engines (or 4-stroke ditto-but these are so rare as to be irrelevant for this discussion)-no other chemical exists with the same combination of physical and chemical characteristics. And equally it needs to be emphasized that our engines run on kerosene as the fuel component [kerosene or a similar petroleum alkane fraction with the same characteristics-some people have used Jet A-1] The only component where you have any leeway is the lubricant-which can be mineral, castor or synthetic-but the larger majority of us prefer castor.

Now it is possible to get a model diesel to run on etherless fuel-but they won't start on it-and a higher compression setting is generally required as well-which can put additional strain on the mechanical components. In this situation-and it is not common-but has been demonstrated on this forum and elsewhere-it is normal to start the engine on a normal ether based fuel, and allow it to warm up thoroughly, before switching to an etherless fuel. So it can be done-BUT (and there are a lot of buts!) I do not recall any situation where the engine has actually been used to fly a model, as distinct to running on the bench or in a test stand.

So you have at least two major hurdles to circumvent-how to get around the need for ether in the fuel-and secondly, how to come up with a suitable biologically sourced fuel component. Do not assume that you can simply substitute 'biodiesel' for the kerosene component of model diesel fuel-even in a fuel with the normal ether component. Full size 'diesel' fuel oil does not work very well (if at all-generally it doesn't) in our model size diesels.

There are some other options-small 4-stroke model engines exist-these normally run on methanol based fuels-but are much more economical than the equivalent sized 2-stroke. The smallest commercial size is around 0.2cu ins or 3.5cc and produce about 0.25 BHP. (about 60% of the power of the same sized 2-stroke) -now only one brand is currently in production, but the OS 20 and 26 4-strokes can still be picked up second hand on places like Ebay. The HP VT-21 is still in production by MECOA, a US company, as is the slightly larger VT-25 from the same manufacturer.

Where this leads to is the option of using these very small glowplug 4-strokes running on a methanol fuel (usually with about 10% nitromethane added) for this project AND (with a bit of development work) the possibility of running these on model diesel fuel. Some 2-stroke glow engines can be persuaded to run on model diesel fuel, usually with a bit less power-but a lot more economy-than methanol fuels. The catch is combustion is not self sustaining as it is in normal glowplug operation, and the plug must be kept energised ('lit') by an on-board battery in this situation. I am not aware of anyone having attempted to run a glowplug 4-stroke on model diesel fuel-but it should be possible-if it can be done on the 2-strokes using model diesel fuel, there is no reason to think that it would not work on the 4-strokes. BUT you would be in for quite a lot of development work-especially in the area of carburrettion (and possibly compression ratio adjustment.

Anyway you now have a number of issues to consider-and a number of possible paths to take.

If you wish to gain an understanding of the economy of model diesels under extreme conditions, start reading in the area of C/L team racing-these events are where the model diesel reigns supreme-for reasons of its inherent fuel economy coupled with good power output. A modern F2C 2.5cc diesel engine represents the pinnacle of model diesel engine development. A search on 'F2C' 'team racing' and 'F2C engine(s)' will get you started.

ChrisM
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Old 10-11-2012, 07:04 PM
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Default RE: Biodiesel in a model engine

Louis-a little more reflection on your challenge reminds me that there are now some very small-and quite refined 2-stroke petrol engines recently developed specifically for model use. [People have been using converted chain saw and other small industrial engines of about 25cc and upwards in models since the late 1970s-but in the last 2 or 3 years some of the traditional model engine manufacturers have produced small spark ignition engines of modern design in sizes as small as 9cc-see attached pictures. These generally have Hall effect ignition system, run on typical 2-stroke petrol mixtures (20:1, 25:1) rather than the typical 4:1 of methanol fueled model engines and the 3:1 of model diesels.
It may be that this approach might be compatible with biodiesel............or at least a blended fuel with some biodiesel component...........

ChrisM
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Old 10-12-2012, 01:40 PM
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Default RE: Biodiesel in a model engine

Also,
ether is required for the castor oil to mix. Diesels require castor oil to survive. Kerosene will not mix with castor, without ether. Ether provides cooling and easier running. Without ether, you can't use castor and kerosene. methanol and castor mix but that is different again. You could try your biofuel with synthetic oil and preheat the engine some how, but even then the engine won't last very long (if at all). If you mix kerosene with castor, it will separate very quickly and stay separated. There is also the ignition improver that helps the engine from beating itself up.
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Old 10-12-2012, 09:35 PM
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Default RE: Biodiesel in a model engine

While this is true-about ether being required for the castor and kerosene to mix, diesels DON'T require castor per se-we choose to use it-but mineral oil or synthetics will work quite satisfactorily. If you took the time to check any British modelling magazine of the 50's and early 60's you would find nearly every fuel brand used in diesels available in both castor and mineral oil blends, (often with several different mixes in each) with the castor based ones being considered the premium blends-and more expensive. Even in the 80s and 90s I ran diesels quite satisfactorily using Castrol 2-stroke oil as the lubricant-and for certain uses, most notably FF scale, is desirable, as castor exhaust residue has a deleterious effect on the finish that mineral oil doesn't.

ChrisM
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Old 10-16-2012, 08:26 AM
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Default RE: Biodiesel in a model engine

Hello all,

First of all, thanks for all the help. Due to the fact that diethyl ether is critical component, we won't be able to utilize biodiesel as a viable solution. I think we will synthesize our own ethanol and use that in our engine.

The forum post here: http://www.rcuniverse.com/forum/m_3219478/tm.htm indicates that a blend of castor oil and ethanol works, so I think we will try that route.

Again, thank you for all the replies, it helped greatly.

Best,
Louis
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Old 10-16-2012, 08:49 AM
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Default RE: Biodiesel in a model engine


Quote:
ORIGINAL: yourmightyruler

Hello all,

First of all, thanks for all the help. Due to the fact that diethyl ether is critical component, we won't be able to utilize biodiesel as a viable solution. I think we will synthesize our own ethanol and use that in our engine.

The forum post here: http://www.rcuniverse.com/forum/m_3219478/tm.htm indicates that a blend of castor oil and ethanol works, so I think we will try that route.

Again, thank you for all the replies, it helped greatly.

Best,
Louis
Actually, a few years ago there was a thread on one of these forums that indicated that a non ether mix could be used if the engine was pre-heated. I believe they started with regular model diesel mix then switched to a non-ether fuel. They tried several lubes but I don't remember the particulars.

George
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Old 10-21-2012, 05:53 PM
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Default RE: Biodiesel in a model engine

I think we found a source where it was possible. I think our team will go with 2 routes, 1 using bio-ethanol, and the other with bio-diesel.

R/C + biodiesel + castor + heptane: 
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Old 10-21-2012, 06:11 PM
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Default RE: Biodiesel in a model engine


Quote:
ORIGINAL: trfourtune44

Also,
ether is required for the castor oil to mix.
Not necessarily true, untreated virgin castor will not mix but polyermerized castor will.
http://www.go-cl.se/castor.html

"Castor oil is not normally soluble in ordinary petroleum oils, but if you polymerize it for several hours at 300 degrees F (149 deg C), the polymerized oil becomes soluble. Hydrogenation achieves somewhat the same effect."

Ibelieve that Klotz Benol is one of those oils.

http://www.youtube.com/watch?v=udjaMPg_wO4
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Old 10-22-2012, 07:33 AM
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Default RE: Biodiesel in a model engine

Would a glow engine do? Methanol can be made as a bio fuel. If not you can use ethanol, but will have to use a glow ignitor.
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Old 10-22-2012, 07:50 AM
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Default RE: Biodiesel in a model engine


Quote:
ORIGINAL: yourmightyruler

Hello all,

I am currently a chemical engineering student at University of Colorado - Boulder. We are competing in a competition where we need to design a vehicle the size of a shoebox which will travel a specified distance and carry a specified load.

We are looking at to use a model diesel engine which will run biodiesel produced from algae which we will grow synthesize. Our research indicates that we need to blend the fuel with castor oil and diethyl ether. However, diethyl ether is a ''4'' on the NFPA flammability rating, which is banned competition. Is there a less volatile chemical that we can use?

What does diethyl ether do for the engine? Our hypothesis is that the diethyl ether is a compound which will reduce the viscosity of fuel.

Thanks in advance,
Louis

Have you ever asked yourself what the difference is between a Sportsman and a Competitor? A sportsman reads the rules to see what the rules say. A Competitor looks at the rules to see what the rules DON'T say.

Go back and look at your rules to see the verbiage on the fuel. The way I would look at it is that if the vehicle cannot contain fuel with Ether in it, then I would start it on ether fuel from a separate tank and then switch to straight kero/castor/DII fuel once it was warm. You only need the ether to get it started.
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