Model Forum / Radio Controlled / Air Models / September 2006

Years ago in Aeromodeller, one Robert Dulake had an article about etherless
fuel. Somewhere I still have the recipe and will post it when I discover its
whereabouts. From memeory rape oil was boiled up with a small amount of
detergent and glycerine to remove some sort of gunge. This was then mixed
with four times its volume of paraffin and then up to 5% isopropyl nitrate
added. There was no benefit adding more, but at least 2% was needed.

As you found Reg, it wasn't easy to start on this mix but a prime with
conventional fuel did the trick. I've used it quite a bit and found that the
engines run a bit hotter at higher compression and the exhaust "goo" is
very, very black. There does seem to be a gain in power and duration.

Malcolm

I've had a play but in a purely non-scientific manner (try this, try that,
try something else kind of thing) and my "measurement" of results was simply
"does it *seem* better".  It was quite a long time ago now and the details
are becoming somewhat hazy (of course I didn't make any notes!!) but here
goes.....

My first try was a mix of paraffin (bog-standard Esso Blue), 20W-50 car
engine oil and one of those cetane boosters.  It ran but, as you've
discovered, it needed starting with a drop of the real McCoy into the
inlet - "it" being an un-throttled PAW 19.  The tricky bit was getting the
compression increased to coincide with the burning of the last whiff of
commercial mix.  Power was down - quite a long way down - and the engine ran
very hard because the compression was wound in to keep it going on the
home-brew.  I concluded that the lack of an ignition agent was the culprit
and that having to run the thing so over-compressed was going to have
serious consequences for the longevity of the engine.
Mix was around: Kero 65%, Cetane stuff 5%, Oil 30%

Next attempt was to use EasyStart as an ignition agent in the mix and the
oil I used in all the mixes from now on was Castrol R-something or one of
the other castor oil based racing motorbike engine oils, Rock oil was one
such IIRC.  Incidentally, the EasyStart (or ether) is needed not only as an
ignition agent but to make the castor miscible with the burning agent -
without it the oil and the rest of the brew remain separated.  So, I
squirted out a can of EasyStart into a bottle and called that 25% of the
brew.  Then added paraffin, oil and cetane stuff to make the proportions to:
ES 25%, Kero 40%, Oil 30%, Cetane stuff 5%.  It was a transformation!  The
engine would start on the home-brew as well as run on it.  Compression was
still higher than on commercial stuff, but nowhere near as
engine-destroyingly high as with Brew-1.  I also tested it on a PAW 149, a
DC Spitfire and a DC Merlin.  All started and ran.  Result.

Suitably encouraged I played around with proportions a bit.  Best results
seemed to come with a mix of: ES 30%, Kero 40%, Oil 25%, Cetane stuff 5%.
However, the engines still ran a bit harder compared to commercial fuel.
Finally I experimented with different burning agents and mixes of such.
Instead of Kero I used straight DERV (made the engines a little bit harder
to start for some reason but ran ok once going), Kero/DERV mix (about the
same as straight Kero) and a Kero/DERV mix with the addition of about 5-10%
(of the total fuel/oil mix) four-star petrol.  This last seemed to make the
engines run very hot so I quickly abandoned that idea.  I also bought 500 ml
of proper ether from the chemist and tried that straight and cut with the
EasyStart.  The EasyStart was good stuff because there was no discernible
difference to the engine handling.  However, the Holts own-brand of
EasyStart (as opposed to the Bradex EasyStart that comes in yellow tins and
you can still buy today) was a poor performer.  It was cheaper but contained
diethyl ether (the stuff we want) and also an unspecified mix of
"Aromatics".  The real EasyStart might have had some aromatics too, although
unlike the Holts stuff it didn't say so on the side of the can, but whether
they were the same ones in different proportions or different ones that
worked better I have no idea - I just know that for me the real brand
EasyStart worked best.

I used my home brew for a long time before drifting back to glow engines,
mainly 4-strokes.  The models flew perfectly well on it so I was happy.  The
only ingredient that I never had was IPN (iso-propyl-nitrate) which would
probably have made my brews all but indistinguishable from commercial stuff.
However, it was scarce (really scarce!) and expensive which, had I bought
some, would have defeated the object of trying to make cheap home-brew!  An
alternative would be Amyl-nitrate which used to be available in small phials
on prescription for use by angina sufferers.  I never tried it (for angina
or engines!).  Amyl-nitrate is also apparently sold, or used to be sold, in
small bottles in sex shops - I've never been into one so I don't know.  What
it does I have no idea, but I can't imaging that the quantities available in
a sex shop would be enough to make a decent model diesel engine brew.  They
might also decide that you're a bit strange if you go in and buy a box
full!!

One final cautionary note here is that I broke the crank pin and bent the
connecting rod on the DC Merlin due to over-compression whilst playing with
mixes.  A brand new PAW 100 also lasted about about 10 minutes before the
connecting rod (big and and little ends) wore out.  The PAW 149 is now what
can best be described as having "a generous fit to all components" and the
Spitfire was clapped out anyway before I started.  It's had a very long
career and clatters over TDC a bit now but the PAW 19 will still run as will
a PAW 249 and  PAW 29.  The latter two had done a lot of running on
commercial fuel before they went over to home-brew.  The bottom line is,
it's not easy to make a mix that's as kind to your engines as commercial
fuel.  Longevity might be seriously impaired and the cost of some of the
ingredients added to the cost of blown engines might just add up enough to
offset the high cost of the commercial fuel.  You have been warned!!  ;-)
That said, it's fun and there's something rather nice about flying a model
that you designed and built yourself, receivs signals through a receiver
that you built yourself and the engine is running on fuel that you mixed
yourself.  Oh yes, and it's also fun to see all the more senior club members
gathering in a little knot just down-wind of you sniffing the air and
getting dewey-eyed as you refuel.

And finally finally, take care if you get real (chemist) ether and store it
in the dark and cool.  Ether is light sensitive and likes to change into
other things, mostly bad and most notably diethyl ether peroxide, which is
highly explosive.  The chemist suff *might* contain a splash of something
called BHT (butylated hydroxytoluene) which is an anti-oxidant which should
prevent nasty surprises, but you can't be sure.

Have fun!  :-)
Steve