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Simple diesel homebrew

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Old 12-10-2018, 08:24 AM
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Stuntguy13
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Default Simple diesel homebrew

Guys,
Has anyone used a simple diesel homebrew of Starter Fluid and SAE 20 wt motor oil? I know the John Deer SF works with a conventional ether/kero/oil but it seems that with other starting fluids with less ether more heptane you could just mix them with 25% mineral oil (need this to calm down the ether, castor won't work). I think you still need a SF that has ether listed as the first ingredient (this would indicate it had more ether than the next listed ingredient like heptane). In this mix the heptane replaces the kero. The important thing with this is to use mineral oil. The mineral oil calms the burn rate of the ether so it doesn't detonate. The mineral oil trick was an old Drone diesel method to get the 75/25 ether/oil mix to run in the fixed compression engines. Seems this simple mix should work for most sport flying.

Best, DennisT
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Old 12-10-2018, 01:52 PM
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The kerosene has more energy in it than Heptane does, so modern Diesels really do need or should have kerosene as that’s the fuel that’s actually burning and they would perform poorly without it. Drone Diesels used heavy mineral oil and ether only due to the fact the fuel has such a low energy density. If you run a vintage drone Diesel on modern fuel, you’d probably blow it apart due to the high energy contained in the fuel.

Don’t forget that model Diesel engines are not Diesels in the truest sense, but more of a controlled detonation engine. Ether detonates extremely easily and is the reason model Diesels actually run. Slowing the detonation rate of the ether would simply make the engine have to work harder (read higher compression settings) and likely be harder to tune/set. Correct me if I’m wrong.
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Old 12-12-2018, 05:08 PM
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GHB,
If you Google the heating value of kerosene, heptane and methanol you will find the kero is around 18500 BTU/LB, heptane is 19160 BTU/LB and methanol is 9880. Either is 13600 BTU/LB, not that bad and much better than methanol (but it is very expensive). Our engines don't like detonation (no piston engine likes it). What they like is for fuel to ignite and burn smoothly (but quickly)from one point through the charge. Detonation is all the charge going off at once. Smoothing the burn allows the pressure to build smoothly. Looking at methanol it burns very slow but doesn't detonate. This is why you have lots of spark advance when engines run methanol (like 35 deg) vs. 15 deg for gasoline (and why glow plug works so well with methanol). With the fixed compression engine like the Drone you need mostly ether for it to start and run well, but you need to smooth the fuel burn and that's were the mineral oil comes in. Kero also does the same thing in fuel for VC style diesels. This calming of the ether allows for the power to be released as the piston hits top dead center and starts the downward power stroke. As far as the Drone blowing up using standard diesel mix, this is no true. Many people have run them on DDD standard fuel, Dr. Diesels old English mix without damage, it just is much easier to start and get a setting with the Drone mix.

The Drone is a long stroke low rpm design to run around 6700 - 6800 rpm (ground). It turns an 11x10 or 12x8 prop for OTS stunt. In 1948 - 1950 the Drone won many stunt contests. People that had trouble running them didn't read the operating manual. They would try to run them like a short stroke layout. With the Drone as the engine starts you need to open the needle to smooth out the run. The ether has a very wide operating range (similar to methanol) as you richen it you do two things, First it controls the temperature and second it trims the compression. There was a VC head that works well and I have two of them that I have run my Drone on. It is a tuff, strongly build engine.

Getting back to the simple diesel of starter fluid with mineral oil, looking at the heat values we would have plenty of BTU's in this fuel. If mixed with mineral oil rather than castor should run smooth, at least for sport fuel. We know the John Deer SF works, but it is expensive. So it seems someone in diesel land should have tried some different brands of starting fluid and this mix should be lower cost.

Best, DennisT
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Old 12-12-2018, 08:57 PM
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That’s not exactly how I was taught, so I’ll have to agree to disagree for now. I will bite on the comment about mineral oil being better than castor. That couldn’t be further from the truth. 75wt mineral oil was used way back when because castor hadn’t been discovered as a suitable replacement yet. The fact is; castor oil is the best oil for model Diesels. If it wasn’t, they wouldn’t be using it nor PAG type synthetics (in a blended oil package) in modern premixed diesel fuels. Basically - if an idea is superior not only in cost to manufacture but in performance, everyone will use the same idea.

This website has a lot of great information about Diesels. AdriansModelAeroEngines.com :: Fuels for variable-compression diesels
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Old 12-13-2018, 04:01 AM
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GHB,
I agree about the castor oil being better than the mineral oil, but its not bad either (look at indy cars and NASCAR some still use it) the main reason it is not used in glow fuel is it doesn't mix with methanol. That aside for this discussion the reason for the mineral oil is to calm the ether. If you read the section for Fixed Compression diesel on the web site you posted you will see Adrian supports this (he also supports that kero is the power ingredient in modern diesel). With the simple diesel fuel proposed the power ingredient is the heptane (as it comes from the SF can) in place of the kero. Heptane doesn't calm the ether as much as the kero would so using mineral oil will do that. I think the reason kero became the main component was cost, its very inexpensive compared to ether, also very available. I'm not saying that the simple diesel mix is the best, just that it would work for most sport flying and could be easily obtained without the expensive shipping costs of commercial blends.

Best, DennisT
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Old 12-13-2018, 06:50 AM
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First I will say I have little experience with diesels. I have one that I have not tried yet, and last ran one in the 1970s. It ran great but I could never start it on my own. I did see an article on making heads for diesels from a glow engine. The guy was selling them, and simply made a brass plug that inserted into the regular plug hole. He used a very high ether content. I was going to try it, but the cost and, to a point, availability of ether held me back. I would guess that shimming the head up or down for the first couple runs would be needed.. A regular diesel head might work fine adjusted low. Another gentleman on Utube used no ether in the fuel, and just primed with ether to get it going. I think it was just an experiment and not something to use all the time. He also tried vegetable oil and other things too. (Castor oil is almost a vegetable, maybe not) Anyway, here is the MSDS for ACE starter fluid. I was going to use this, as it is available and goes on sale locally. John Deere, not so much here at least. http://www.kleenflo.com/msds/735.pdf It seems to be around 50% each heptane and ether. I thought a bit of oil was in so there would be a bit of lube for cold starts, but it doesn't seem to be the case here.

Last edited by aspeed; 12-13-2018 at 07:01 AM.
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Old 12-17-2018, 07:37 AM
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I would be comparing this space age Diesel mix against a standard kerosene-containing fuel and compare the tractability and overall ease of operation and most of all comparing power between the two fuels. For me, the fuel has to tune well, throttle well, perform equal to or better than commercial blends and the engine has to be easy to start. Also remember that throttled variable compression Diesels have slightly different needs than fixed throttle and fixed compression Diesels.
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