RC Fuels Nitromethane, Castor Oil, Synthetic, heli fuel, 4 stroke, etc...Fuel Q&A is here!

Diesel Home Brew Question

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Old 03-15-2015, 02:11 PM
  #1
DaveyMo
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Thought I'd try my hand at mixing for my KMD 2.5. It's a success in that the engine actually runs, albeit not as well as I'd hoped. Here's my blend:
Castor Oil 25%
Ether 30%
Kerosene (K-1 from Home Depot) 45%
Amsoil cetane booster 2%
Note: Yields 102% for ease of mixing

After two minutes of slow sputtering, I need to increase compression a bit to get the rev's up, but it still sputters at higher speed. It finally runs smoothly at an even higher compression setting, but then the exhaust turns almost black indicating over-compression. Does anyone have an idea what might be at work here?

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Old 03-09-2016, 05:47 AM
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Try this mix 20% synthetic oil, 30% ether, 45% kerosene, 2% nitromethene. This should leave you with a cleaner aeroplane much like glow fuel. The nitromethene should stop the misfiring at the higher RPM. Good luck.
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Old 03-09-2016, 07:26 AM
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If that is an iron piston type engine, you may want to shy away from using synthetic oil only in the fuel. A mix of synthetic and castor works well as does all castor. My initial thoughts are; is the engine broken in well enough to hold a lean setting? If not, it may need to be run a little richer and under compressed for awhile until it breaks in more. Black exhaust residue usually means it's overcompressed... Perhaps you need more prop on it so you can run a lower compression setting. Another thing to consider - some smaller engines run better with a little more ether in the fuel. You could try a small batch to see if it makes a difference? Maybe do 35% ether, 20-25% oil, 40-45% kerosene, and 2-3% ignition improver. I haven't ran any purpose built diesels, but I've run a number of larger conversion engines and my experience has been that black exhaust residue happens with some engines, usually when leaned to absolute max power. Running a tad richer and under compressed has made the exhaust residue lighter in color as well, and using a bigger prop load will do so as well.

Just my thoughts.
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Old 03-09-2016, 02:31 PM
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Davey,

I have an almost new KMD-2.5 manufactured in 1990.
The engine manual suggests the following fuel mix:

- kerosene ......45%
- ether .....31%
- castor oil ......8%
- mineral oil MC-20...16% (MC-20 is a high viscosity (visc. index 89) oil used in full scale aviation).

The recommended propeller is 160x200 mm (i.e. 6x8 in.) at 14000 RPMs.


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Old 03-11-2016, 01:23 PM
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Nice to see some responses to my question. I've since gotten the KMD to run to my satisfaction in the intervening time, though you've each provided some further insight. Much appreciated!

Paul: I've basically settled on a blend similar to what you've suggested. Thee main difference is that I've added castor oil to the blend and have used cetane booster in place of the nitro.

Cottage Grove Guy: I managed to get an exhaust colored like light coffee using 25% castor, 30% ether, 45% kero, and bit of cetane booster. It turns an APC 8x4 prop at 12,000.

Houston: Glad to run into someone else who owns one of these. Mine came without a manual, so the suggestions you've provided are helpful (as well as a bit fascinating). The 6x8 prop recommendation sounds most intriguing - may have to give it a try! Oil: I can lay my hands on drug store mineral oil only, so not sure if that would work. I'll probably just stay with the castor at 25%.

Thanks all!

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Old 03-11-2016, 03:14 PM
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On MC-20 oil...
I guess the viscosity index is a SAE number.
I am going to try some gear oil (anything 80w90) next time, when I mix diesel fuel.
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Old 03-12-2016, 01:21 AM
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Quote:
Originally Posted by yyk1966 View Post
On MC-20 oil...
I guess the viscosity index is a SAE number.
I am going to try some gear oil (anything 80w90) next time, when I mix diesel fuel.
Viscosity index is a number arrived from the difference between two measured point, often 40c and 100c.
Low index number (like 89) means it changes viscosity a lot with temperature.
The MC-20 oil should be about 335cSt @40c, that's "of the chart high".
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Old 03-12-2016, 05:53 AM
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Here could one get some of this MC-20 oil and would that stuff be beneficial in modern standard issue glow engines converted to diesel? I usually use 20% castor in my diesel fuel in engines ranging from bushed .20s to BB .45s.
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Old 03-12-2016, 02:23 PM
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I found a TDS file on MS-20 (MC-20 is Cyrillic). See the attachment below, I also inserted a screenshot of the file.


Nitrovein, thank you for your remark, I was wrong mistaking VI and SAE.


[ATTACH]2152142[/IMG]
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Name:	ms-20.JPG
Views:	48
Size:	119.8 KB
ID:	2152143  
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Old 03-17-2016, 06:12 AM
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Quote:
Originally Posted by 1QwkSport2.5r View Post
Here could one get some of this MC-20 oil and would that stuff be beneficial in modern standard issue glow engines converted to diesel? ...
No idea if genuine MS-20 oil is available in USA. BTW what oil is used in Vedeneyev M14P?
But I found a document at Shell web site: "AeroShell Piston Engine Oils". The document declares Aeroshell w100 oils to meet MS-20 oil specification. Here is a screenshot of the pages:



I am going to try AeroShell as a part of the fuel mix, the main benefit I expect is easier clean-up after flights
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