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Model diesels are a little different.

Old 05-11-2005, 01:42 PM
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Default RE: Model diesels are a little different.

Has anyone tried using Coleman fuel in a model Diesel engine?

I just ran a weedwhacker on said fuel with Amzoil 100:1 synthetic lube over the weekend, just for the heck of it. Yeah, I know that others have been using Coleman fuel in gas engines for quite a while, and successfully at that. The only difference I noticed was that it made me hungry. <G>

With the much lower octane rating of Coleman Fuel than that of gasoline, I would think that it would fire easier while being squeezed than gasoline. Albeit, probably not easy enough. Any thoughts?

Ether is the nemesis of model Diesel engine operation to me. It is difficult to handle, it stinks to high heaven and it is expensive. Any way that we could eliminate or reduce its need for model applications would be a big plus.

Ed Cregger
Old 05-11-2005, 02:15 PM
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Default RE: Model diesels are a little different.

Ed,
I will be testing Coleman fuel in my .40 diesel in about a week (when the DDD head arrives).
Note these autoignition temps:
Petroleum ether/naphtha 288C
Gasoline 246C
Diesel 210C
Ethyl ether 160C
These numbers come off of MSDS sheets. Unfortunately, the Coleman Fuel MSDS does not list the autoignition temp. I have a feeling it is right in there with petroleum naphtha
What we want, of course, is low autoignition temp and slow burning. I don't think were on the right track with petroleum based distillates. Note that ethyl ether is derived from ethyl alcohol using Sulfuric Acid (among other ways).
Old 05-11-2005, 05:40 PM
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Default RE: Model diesels are a little different.

Ether are a ignitor for mainfuel as kerosene same as a gas engine has sparkplug to ignite the gasoline.

The ether has low calories (energy), therefore we need kerosene or similar fuel to add more calories to get more power out of the engine.

Richardfast, hope it is a clear text for you.

Jens Eirik
Old 05-11-2005, 07:23 PM
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Jim Thomerson
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Default RE: Model diesels are a little different.

What we need is a substance like ether which fires at a similar low temperature. We are used to running engines with a fairly low range of combustion temperatures. So if we try to use a higher temperature igniter, we have to run higher compression and higher temperature. Maybe so, but only up to a point. No use having a fuel if there are no engines which can run it and hold together. We do have a problem with availability of diesel fuel, and it would be nice if we could mix our own, using oil, kerosene or whatever, and ingredient X, all cheap and readily available. So good luck in your quest.

Jim
Old 05-11-2005, 07:35 PM
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Default RE: Model diesels are a little different.

There is no problem with availability in the US, Davis, RedMax, Ed Carlson and Eric Clutton all have fuels that are easy to get.
Old 05-11-2005, 07:39 PM
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Default RE: Model diesels are a little different.

Motorboy,
You are making things more clear for me now. I didn't fully understand before that the ether was the only "spark" even after the motor is fully warmed up. I thought as the engine warmed up the kerosene was self-igniting due to the heat of compression. And that the ether came back into play only when idling. I see now that the model motor is always using the ether as the igniter (the kindling wood) and the kerosene is the big log
Jim,
From what you are saying, we are constrained to use a low ignition temperature fuel because we have to keep the compression ratio (CR) low to avoid damage to the "fragile" glow design engine. To be able to ignite the kerosene from the heat of compression would take a much more rugged engine design with a much higher CR. Is that correct?

Thanks, Richard
Thanks,
Richard
Old 05-11-2005, 08:06 PM
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Default RE: Model diesels are a little different.

Yes, you can buy model Diesel fuel readily in the US. No doubt.

The beauty of model Diesel engines is their simplicity. A can of fuel, a squeeze bulb and you are in business.

Does anyone remember the two-stroke Diesel engines that were used in heavy equipment in the mid sixties? I can still hear them winding up as they traveled past Luke AFB in Arizona on their way to a huge construction project. IIRC, they utilized intake valve(s), a blower and exhaust ports.

Ed Cregger
Old 05-11-2005, 10:07 PM
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Default RE: Model diesels are a little different.

Yep, the blower forced air through the ports just above the piston when it was at bottom dead center and two exhaust valves let the exhaust out while the air was forced in the bottom. You needed lots of gears with them as they had little low end torque, hence the 13 Speed RoadRanger and the 16 Speed Four by Four.
Old 05-11-2005, 11:01 PM
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Default RE: Model diesels are a little different.

GM Detroit Diesels are still made, a bit improved these days , 156litre V16 2st with 2 superchargers and 4 turbo chargers around 2,000HP they are used to power heavy equipe like 200Ton capacity haul trucks.
Stewart
Old 05-11-2005, 11:21 PM
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Default RE: Model diesels are a little different.

We had the good and strong 2 stroke marine dieselengine made in Ruppestad, Norway, this name was "Wichman". The engine was buildet without valve and very easy started. The engine are mostly used in ship, ferryboat, fishingboat. Now they are making 4 stroke marine dieselengine named under "Wãrtsila Wichman". The other factory are making 4 stroke dieselengine "Bergen Diesel". "Bergen Diesel" has newest engine who can disassembly the complete cylinder with cylinderhead, valves, injectorpump+injectornozzle with few nuts in some minutes and replace with a ready overhauled cylinder set[X(].

Jens Eirik
Old 05-11-2005, 11:51 PM
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Default RE: Model diesels are a little different.

There you go, Hobbsy. I had the right mechanical layout, but the air moving the wrong way. <G>

Ed Cregger
Old 05-12-2005, 12:07 AM
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Default RE: Model diesels are a little different.

By substituting lamp oil for kerosene, we can eliminate part of the objectionable odor problem of model Diesel fuel. By eliminating the ether, the other part of the odor equation disappears. Or would if the replacement did not smell as bad or worse, was readily available without special licensing, was not any more toxic than ether, was not more damaging to the materials used to construct the engine and was not much more expensive than the ether we currently use. Fat chance of that happening. But, it never hurts to experiment - well, not much - maybe.

I think I'll just stick with what we have and put up with the stink.

Ed Cregger
Old 05-12-2005, 03:06 AM
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Default RE: Model diesels are a little different.

Richard,


The exact definition of a Diesel, as to whether model Diesels are true Diesel engines...
It has been discussed here in the past.

It is true that all current full-size Diesels have an injection pump(s), but does this determine the definition?
Does Rudolph Diesel's prototype run like any contemporary Diesel engine???


Dave Hobbs,


RPM relates to horsepower similarly to the way speed does.

Say, there is a car, with a standard 120 HP straight-six engine and an optional 300 HP V8 engine.
Does the stronger engine, with two-and-a-half times the power, make the car go two-and-a-half times as fast?

It actually gains 20-25 mph, compared to the base engine...

So, if your Diesel makes (just for the point) half the power of the glow engine, it will lose a bit over 20% of the RPM, on the same prop load. You should not expect a 50% RPM drop on a 50% load increase either.

And directly relating to the 12x8 Graupner props...
Given they have the same blade shapes, the 3B represents a 50% load increase.

The 2B at 11,200 RPM represents 1.45 HP actual power absorption.

The 3B at 9,400 RPM is 1.32 HP.
There is 16% RPM drop, yet HP is down by only 9%.

This means torque is up by the balance.
Old 05-12-2005, 03:21 AM
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Default RE: Model diesels are a little different.


ORIGINAL: DarZeelon

Richard,


The exact definition of a Diesel, as to whether model Diesels are true Diesel engines...
It has been discussed here in the past.

It is true that all current full-size Diesels have an injection pump(s), but does this determine the definition?
Does Rudolph Diesel's prototype run like any contemporary Diesel engine???

As i wrote in post #8 :

Rudolf Diesel never wrote it must be pump and injector to be a dieselengine. He wrote it must be hot from compressed air to ignite fuel and nothing other sources as spark or glow. Full size dieselengine and model dieselengine works same principle, they using the compression to warm up air before ignite fuel.
Jens Eirik

Old 05-12-2005, 06:52 AM
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Default RE: Model diesels are a little different.

Some of Rudolph Diesels early experiments were with running the engines on coal dust, I believe it was one of these that exploded injuring him seriously.
Old 05-12-2005, 07:07 AM
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Default RE: Model diesels are a little different.

I guess that's why some refer to them as "Diesels" and some refer to them as "Compression Ignition" engines. I guess diesel is easier to say.
Common (?) definition (as I understand it) defines a diesel as compressing the air to a high temperature then injecting fuel for ignition. The difference in two cycle operation is that the fuel and air are admitted at the same time. The air is still compressed to form heat.
Ether produces combustion at a lower temperature, ergo lower compression.
The fuel is still the fuel, be it kerosene, diesel fuel, #2 heating oil, lamp oil, etc.
The cetane improver, as I understand it, allows the fuel ingredients to work better together (OK, simplification here).
Heat in the combustion chamber metals provides a little pre-heating of the fuel/air mix, which in turn causes earlier combustion at a lower compression setting.
Does that somewhat sum it up?

BTW, diesel engines on old US submarines used opposed pistons, that is, both moving toward the center. We called them "rock crushers".

George
Old 05-12-2005, 07:30 AM
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Default RE: Model diesels are a little different.

Some insist that a true Diesel is one that has an injector pump that injects the fuel near the top of compression stroke, 33 degrees BTC in some and 8 degrees BTC and everywhere in between in others, however, Rudolph Diesels early engines took the fuel in with the air just like our two stroke RC engines do. So, thinking in logical terms we could call our two stroke conversions "Diesels" and the ones with injector pumps we could call, "Rudolph Diesels' new and improved Diesel engines." Catchy name huh.

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