Diesel vs. Nitro in Cox engines.

nitroairplane Thu Aug 11, 2011 6:33 pm

Hi guys I really love running diesel model engines as they have their advantages over glow engines but they also have their disadvantages.
Advantages of diesel:
More torque
Lower RPM
Wider range of props
More controllable
More efficient (longer runs)
Lower exhaust note and less noise
No glow heads to replace
No need for glow drivers power supplies etc.
Can easily mix your own fuel
More reliable
Glow advantages:
Higher rpm (although there are exceptions)
No need for conversion heads
Less wear on parts and less premature breakages
Slightly easier to start
Lower fuel cost
Easier to buy premixed fuels.
I prefer diesel on all reed valve engines as they are then more versatile and controllable.
I tried to get a tee dee .010 to run diesel but broke 3 cranks. The project is still on going.
My pee wee .020 diesel

I do not have a video of a stock nitro pee wee i will try and upload one at a later date.
Please share your experiences and beliefs about diesel vs glow.
Thank you.

**RknRusty** Thu Aug 11, 2011 10:35 pm

How can you have enough pulling power at such low RPM? If you take a plane that flies nice and quick and responsive at 17000 RPM on glow duel, and change it to a slower turning diesel, how does it fly then? Do you have to fly lighter planes or do the bigger props compensate?

nitroairplane Fri Aug 12, 2011 4:14 am

The larger or higher pitch props mean they can creat more thrust as they don't nee to turn such high rpm to create lift.

GermanBeez Fri Aug 12, 2011 6:19 am

i'm not sure about the price advantage of nitro fuel. lets say, a liter of diesel fuel costs around 1,40 € over here, as
opposed to a liter of graupner G12 (yes, that stuff again), which costs around 12 € per liter.
nitromethane itself is a pretty pricey chemical.

nitroairplane Fri Aug 12, 2011 6:28 am

Model diesels engines like converted cox engines rubon different fuel from cars they run on a mixture of ether,kerosene,castor oil and I gnostic boosters.
Model diesel is more expensive than 1/2a fuel from most dealers.

GermanBeez Fri Aug 12, 2011 6:30 am

hm, i didn't know that. i actually saw some cox engines that were running on actual diesel fuel...

nitroairplane Fri Aug 12, 2011 6:35 am

Well you can replace kerosene with diesel but you need the oil and without ether it would have to be warmed externally or take ages to start you can rub on lots of things buy a compromised performance and reliability.

GermanBeez Fri Aug 12, 2011 6:40 am

so the engines can't produce enough heat through compression to ignite the heavy oil alone, so
you need a light and flammable substance like ether to get to ignite, did i get
that right?

nitroairplane Fri Aug 12, 2011 6:43 am

That's mostly it and ether also boosts the acetone levels but my fuel also has iso propyl nitrate to do that you don't need to worry too hard about the physics of compression ignition.

gcb Fri Aug 12, 2011 1:18 pm

Many feel that because of the difference in burn patterns between glow and diesel fuel, that a heavy duty crankshaft is preferred on Cox reedies that are converted to diesel use.

I believe both DDD and Cox International sell heavy duty crankshafts for the .049 Cox reedies, does anyone make special cranks for other sizes like the .020 Pee Wee?

George

nitroairplane Fri Aug 12, 2011 1:24 pm

No the pee wee is fine on the stock crank but I am looking into getting a few heavy duty cranks made for the cox tee dee .010.

colibriguitars Mon May 19, 2014 11:54 pm

Hi Guys, well, last week i won a Diesel Head on Ebay, the seller had sold it as 049 head with crank and disk, so... for my good look, when the mailman arrives, i noticed a very small crank and head.... Was a nice 020 head with 3 teflon seals and one crank!!!

I tried to start it last week, but my longest run was 20 seconds.... it has a lot of compression....
so. two questions, can i sand the contrapiston a little??
What is a good mix for this engines?
Aluminium soda can disc is better than teflon??

Regards,
Rodrigo from Mexico!

Surfer_kris Tue May 20, 2014 5:17 am

These heads have a too high compression setting as their lowest setting, so it is very dangerous for the crank. Just shave off about 0.15mm from the contra and you'll be fine.

The Teflon disks are also very dangerous for the crank, they always leak a little and fools you into raising the compression ratio, and when/if they fire the engine is overcompressed. Soda can material (Al) can be used but the lifetime is only a few runs. I have hade much better results with thin a brass sheet (0.1-0.15mm). This will last for more than 10 runs at least.

Prime the side of the piston only and they fire right up each time (if you have a good seal to the head). Regular fuel works fine: 33-35% ether, 25% castor and 1.5% IPN

Here is a little video of mine on a 6x3 prop:

Here is the cub that it pulls around with authority:

Diesel vs. Nitro in Cox engines. Img_1215

Diesel vs. Nitro in Cox engines. Img_1215

colibriguitars Sun May 25, 2014 1:57 pm

Hi Guys!
Well, my engine does not want to run for more than 20 seconds, i had reduced the contra piston from 3.16 mm to 3.02 mm.... i´m using soda can discs, and 35% ether, 25% castor oil, and 45 Diesel from car pump.

Here a video,

https://www.youtube.com/watch?v=ZJgk-JAz5cY

**Cribbs74** Sun May 25, 2014 3:03 pm

I know nothing of diesel operation, but I did notice one thing, it only fires off after being primed.

So have you gone through the tank? If it runs off prime and then quits it's not feeding itself.

Surfer_kris Sun May 25, 2014 3:51 pm

Try a larger prop, a 6x3 is more suitable for diesel fuel.
You should only prime the side of the piston and it should fire on each prime. There really shouldn't be any need for a spring starter...

Can you get some commercial fuel instead?
I have never tried with car diesel instead of kerosene, and you do need an ignition improver too.

ian1954 Sun May 25, 2014 4:03 pm

colibriguitars wrote:Hi Guys!
Well, my engine does not want to run for more than 20 seconds, i had reduced the contra piston from 3.16 mm to 3.02 mm.... i´m using soda can discs, and 35% ether, 25% castor oil, and 45 Diesel from car pump.

Here a video,

https://www.youtube.com/watch?v=ZJgk-JAz5cY

The traditional recipe is 33% ether, 33% paraffin (kerosene) and 33% castor oil. Car diesel fuel is not a good substitute for paraffin.

I have only managed to get larger diesels 7cc plus to run with car diesel and they didn't run well.

I only use ignition improver for competition fuel mixes - my smaller diesels run quite happily on 40% ether, 30% paraffin and 30% castor oil. (and I mean small engines!)

JPvelo Sun Jun 01, 2014 7:00 pm

How many runs will the Teflon disc last? I'm thinking of buying a conversion head for an .049. What size prop for a 110 square inch control line model?
Thanks,
Jim

**Cribbs74** Sun Jun 01, 2014 7:55 pm

Jim,

I have a NIP Davis Diesel head if you want it.

batjac Sun Jun 01, 2014 8:25 pm

After seeing this video, I thought it was very interesting. I'd even try it if there was a local source for diesel fuel. I'm not interested enough to go to the trouble of mixing my own or mail ordering just to satisfy my curiosity.

The Mildly Curious Mark

JPvelo Sun Jun 01, 2014 10:24 pm

Cribbs74 wrote:Jim,

I have a NIP Davis Diesel head if you want it.

How does the Davis differ from the one Bernie sells? I was going to use my gift certificate. Very Happy

**Cribbs74** Sun Jun 01, 2014 10:53 pm

It's the same in appearance. Sending you a PM

Surfer_kris Mon Jun 02, 2014 8:00 am

The DDD and the Bernie heads, both used the teflon gasket. This, to me, is a very strange solution as teflon is not suited as a gasket material, especially with the creep that comes from elevated temperatures and different materials. The head will effectively pinch through the gasket, giving you small leaks. This will then trick you to increase the compression ratio further and if/when the engine fires it breaks the crank...

The RJL heads (sold by Mecoa) are much better. That gives you a traditional copper gasket seal between head and cylinder, and a counter piston with an o-ring seal.

Diesel vs. Nitro in Cox engines. Rjl_he10

Diesel vs. Nitro in Cox engines. Rjl_he10

JPvelo Tue Jun 03, 2014 6:47 am

Does anyone know if I can use a surgical tubing bladder with diesel?

Thank you,
Jim

**Cribbs74** Tue Jun 03, 2014 2:25 pm

Figured someone would have answered by now, but it may be best to just try and see.

My guess is it can't be any worse than high nitro.

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