# Diesel Engine Model - run off biodiesel?



## mnbylcr2 (Dec 20, 2010)

Hi
Every year I teach about biodiesel and carry out a practical with a group of students to turn some waste vegatable oil into biodiesel. The hole process with the titration and the example of a esterification is a nice practical. I`ll be starting a new engine after Christmas, my idea was either an LTD Stirling or Elbow engine but I was thinking, could I make an engine to run off biodiesel or is this just too difficult? I`ve seen a few model diesel engines around and shown on youtube but they all seem a bit bigger than the "model" engines I`m use to. I also don`t know if they would run off biodiesel although I`d guess I could mix with some regular diesel to make sure. I`m just thinking it would give an extra edge to the practical and would give my next engine a use! I`d also need so decent plans. 

Maybe this is not possible or too difficult but I thought I would ask if anyone had any ideas or could recommend some plans.

mnbylcr2


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## shred (Dec 20, 2010)

Diesel's tough... I think there was a thread around here on the difficulties of model diesels. You should be able to get a hot-bulb or hot-tube type engine to run on it though. Now plans for those are hard to come by too, but I think more feasible in model sizes.


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## Mainer (Dec 21, 2010)

There is one here: http://www.statecollegecentral.com/metallathe/MLA-17.html


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## Dan Rowe (Dec 21, 2010)

The MLA-17 engine uses a carburetor and not the more complicated high pressure fuel pumps and injectors. Notice that it uses "model diesel fuel" which most likely has a much higher cetane rating than bio diesel. 

I doubt that bio diesel can be used with this model.

One way to eliminate the complexity and micro finishes needed on injectors and high pressure pumps is to go back to early diesel designs and use blast air injection. This of course means adding a compressor for the high pressure air. There is one advantage to blast air in that there is no need for complex head designs do induce turbulence. 

Dan


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## mu38&Bg# (Dec 21, 2010)

I get this question quite often from people who find my website. I seriously doubt it's possible to run biodiesel in a model sized engine especially without injection. Compression ratio must be high in order to achieve the in cylinder temperatures required to ignite the biodiesel. Biodidesel has a higher autoignition temperature and boiling point than petrodiesel. Add to that the heat loss of tiny cylinders and little room for the injected spray to atomize and ignite and you can see the trouble. Making a injection pump that will pump the minuscule volume for engine of model size is a problem. My lovely wife ordered "The Dux" series from SIC which is an injected 10CC four stroke diesel. It left a lot to be desired in the way of design, but I think I'll try it anyhow.

I suggest that the teachers wanting to demonstrate biodiesel try some of the Chinese import diesels which can be found in very small sizes down to 168cc. http://www.carrollstream.net I don't have any experience with these or running them on boidiesel.


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## shred (Dec 21, 2010)

As said before, the MLA-17 and other "diesel" aero engines will be entirely unsuitable for biodiesel fuel-- they are burning much different fuel.


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## Ripcrow (Aug 31, 2013)

I have thought about diesel injectors and how to make them.the only way I could come up with was to heat the tip to red hot and poke a pin through to create the injectors holes.whether the atomisation is good enough is unknown and biodiesel is known to be coarser then petrodeisel so they may block up easily.perhaps a small turbo or supercharger could raise the compression ratio enough to ignite biodiesel


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## Ripcrow (Aug 31, 2013)

Just another thought how about a glow plug hidden in the block exposed in the head to provide the extra heat required for ignition


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