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
'ffkiwi'