Diesel Engines

Hi Ed, Unique would have been fine but I couldn't get a thing out of the guy by mail, not so much as a single written word. All he ever did was send me different colored copies of the same instruction sheet! I was never able to did get through to him on the phone because of the shift I was working but when my wife called one morning, he hung up on her! What a jerk... Oh well, it's water under the bridge but I'd sure never do any business with the guy again. I found out a lot more about the guy when I started asking questions at the field.... I should have asked first. That darned hindsight gets you every time.

I don't have a problem with the fumes, in fact I guess it's sort of in my blood (probably literally) after spending most of my adult life at the airport. I even have a diesel Jetta although my wife gets to drive it a lot more than I do. If I ever get rich, I'm going to try out the turbine engines.

When I first set up the diesel conversions on my engines, I tried every setting imaginable and several different mixture ratios on the fuel concentrate. Like I said, not so much as a pop, which is why I suspect the concentrate was no good. Honestly, I wasn't so much disappointed in the diesel as I was ticked off at Davis (the bum!). One of these days I'll trip over all that stuff and give it another try with some properly mixed fuel. I have no doubt I'll be able to get it going then.

Prior to my personal, and very sour, experience with Davis, I'd heard nothing but good stuff from people who'd been able to get past the smell and were able to get their engines to run. Good power, long engine life, low fuel consumption, reduced engine noise.... all positive things. When I get around to it, I'll let you guys know how it works out. Cheers, jc

Hmm, I think you forgot add "rude" to that list.

Unfortunately, that seems to be an all to often reoccurring theme with this clown. I've talked to several other people that had the same opinion of him and in fact, the nicest thing I've ever heard anyone say about him is that he's "unique!" (Cregger, you should be a diplomat!) I can't imagine how he's been able to stay in business as long as he has but I guess it takes all kinds. Cheers, jc

At the time, I don't recall any engines on sale here in the US that were made for diesel, except for some that were very small. I honestly don't remember how much effort I put into searching for engines, either. It was probably a spur of the moment thing. Certainly price would be a consideration but buying a glow engine and then converting it to diesel isn't all that cheap either. Cheers, jc

"The Amazing Seismo" SNIP < I neglected to change the 2 ounce fuel tank out for

Cool beans! But if you will recall...this dumb kid once built a C/L plane for a .020 with a 1/2 fuel tank. On 15-20ft lines you fly FOREVER and then you wonder when the spinning will stop...dad still has the motor and quite possibly the red peril as well. Did rather well in all aspects, not a bad plan for S.W.A.E.G. 8^) But yes I appreciate the "Oh crap, will this thing EVER run dry?" story.

At least you don't have to worry about the airborne battery pack going dead before the engine quits, when flying control line. 8^>

Ed Cregger

Hmm, I think you forgot add "rude" to that list.

I can a few other adjectives to the list. I e-Mailed the company a couple of months ago, asking some basic questions about diesel engines. The reply I got was, "You need to call us, we don't answer by e-Mail." When I replied that all I wanted was a few answers and why couldn't they do that, I got an even more rude reply. So, I'll NEVER fly a Davis diesel conversion.

Dr1

No, all you have to worry about is the ground getting up and smiting you when you are dizzy :-)))

Malcolm

"Ed Cregger" SNIP

Uh yes you would and YES people ARE flying electric C/L. Sooooo...........NEXT!

"Malcolm Fisher" SNIP

No kidding Malcolm, that was THE ONLY C/L plane to ever make me dizzy on EVERY flight. May have to build another, you've no idea how much fun it is to grab the plane, fuel, Flight lines step out in the backyard and go in circles! Damn it was fun! Whoops hold on I'm dizzy just thinking about it, gotta sit down before I fall over.

Yes, it was, and still is fun. C/L was my first love (with i.c. power) and I still have a number of flyable models, sets of lines and handles and still enjoy connecting them up and giving them, and me, a whirl.

Malcolm

My son wants to know if anyone has tried running diesel fuel in an ordinary glow engine like an MDS .40? I think it would burn too slowly at the lower compression, but I bet someone out there has tried it.

Dan

Dan_Thomas snipped-for-privacy@yahoo.com wrote:

If you are talking about diesel fuel used in automobiles and trucks then it actually burns too fast. In a true diesel the fuel is injected at a steady rate to cause nearly even pressure on the down stroke, as apposed to gas, glow, and model diesel engines where it explodes and has a pressure spike. Since the fuel is injected at a steady rate it doesn't need to burn slowly so there is no anti knock additive as there is with gasoline. Model diesel engines are not true diesel engines, the compression is higher but the fuel (either) is used with an extremly low ignition temperature (not the same as the flast point). The either is mixed with kerosene so that it has more power than with pure either. To convert the model engine to a true diesel you would have to increase the compression ratio to about 16 to one to get the required ignition temperature, then add a constant pressue injector. Then you would have a two stroke diesel engine. To do the injector without electronics you would have to have a very small piston pump to pump in the correct volume of fuel. The pump would be connected to the crank shaft and the pump piston would be timed to be somewhere around bottom dead center just before the engine piston is near top dead center. The throttle is esentially a diverting valve which diverts fuel from the pump to the fuel tank. All of this is difficult to do with small model engines. Still I would like to see this done, maybe on a larger engine of around 30 cc?

Agreed that model "diesels" are not true diesels, but the name stuck as both rely on compression for ignition.

In a model diesel, the ether is largely responsible for the ignition and does little for the power which comes from the kerosene plus whatever of the lubricating oil is burned.

It is possible to run such an engine on a mixture of kerosene and oil with a small amount (up to 5% max) of Isopropyl Nitrate to help with the ignition. In my experience this produces more power than conventional model diesel fuel and is considereably cheaper. However a higher compression is needed and the exhaust emission is much, much blacker i.e. dirty.

When I use this fuel I usually start up with a prime of normal ether bearing fuel and then don't need to "back off" the compression as I would if using ether based fuel.

Malcolm

Where did you learn of this alternate fuel formula, Malcom? I have never heard of it before.

One of the things that turns me off to normal model diesel operation is the volatility of the fuel and its rapid decline into an unusable quantity of toxic mess. Your formula does not sound as though it would suffer the same fate.

Ed Cregger

injected

Kerosene-type fuels such as diesel have a flame-front spread rate of about 30 feet per second, compared to gasoline's 100 fps. Diesels use the high-pressure injector to get the fuel into the cylinder directly because of the high compression and to get best atomization of the fuel, and injection time length controls power. An "explosion" of fuel is detonation and destroys engines. In gasoline detonation the flame front speed is 5000 fps or more. In jet engines the compressed air has to be slowed in the combustor can to 5 or 6 fps to get proper burn, since kerosene is so slow.

Dan

Not sure about flame front spread but it still will not ignite without an extremly high compression ratio. Look at a pressure chart of a gasoline engine VS a diesel. The gasoline engine has a pressure spike shortly after ignition. The diesel engine has a nearly even pressure flow, at least at full throttle, at part throttle with the electronic injectors there is high pressure during injection and drops off afterward. In thermodynamics a Desiel engine is described as a constant pressue system. Explosion is relative, I should not have used that term but the gas engine does come closer to that than a diesel.

When a gasoline engine runs properly, you do not hear the cracking sound of the connecting rods being slammed onto the crankpins when the fuel charge ignites. When a Diesel engine runs properly...?

Ed Cregger

Big Snip>

There was an article in Aeromodeller many years ago. The author was, IIRC, an organic chemist as well as a modeller.

He did a considerable amount of research and came up with a formula using "modified" rape seed oil and kerosene (paraffin to British readers) with IPN.

I have used it for a number of years - not recently as I now mostly fly using glow engines. It isn't easy to get a start with a cold engine, hence the prime with conventional ether based fuel.

I can find the details if anyone is interested in having a go.

As said, the exhaust "goo" is very black, but I found an increase in speed with 1.5cc engines in C/L models and, subjectively, slightly longer run time on the same tank - I never actually timed it but seem to remember more laps per tank and a quicker rate of rotation with the handle.

Malcolm

You really only hear that at idle, I thought it was the high compression they have to work against. It cannot be during the power stroke because the connecting rod is already pushed against the crankpin on the upstroke. But I do not understand what differance it makes.