DaveyMo

Hello All:

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 maybe an over-compression. I did not diddle the needle setting at all so it's identical to the previous commercial fuel runs. Does anyone have an idea what might be at work here?

FYI, this has been cross-posted to the RC Fuels board also.

Davey Mo....

fiery

My Feedback: (2)

Fuel composition sounds fine.

Correct setting for any modern (non fixed compression) diesel requires adjustment of fuel-air mix (needle valve) and compression. Without checking your needle setting you will never an achieve the optimum.

Once adjustments are correct a KMD 2.5 in sound condition will run very well indeed. You did not specify a propeller. I suggest an 8 x 4.

DaveyMo

Ah, so I do need to go back to balancing out the needle vale and compression setting with a change in fuel! It seems obvious now that you mention it, Fiery. Many thanks!

Dave Mo...

123Cat

Thats the fun of diesels you twiddle everything and nothing changes

and you take the comp screw out and throw it in the toolbox ,

and that doesnt change anything

so you takeoff straight up ,


and crash down in a million pieces

steve111

Dave, it sounds like you might have been more reluctant to adjust the needle setting than the comp, when it should really be the other way around. You really want to mess with the comp as little as necessary - too much fiddling (especially when running) and they can wear and become sloppy. (Unlike a needle valve.) Ideally you'll just find the right compression setting and then pretty much leave it alone. There'll be a bit of variation with different fuels and prop sizes, but not too much. Remember that a misfire could be due to too little compression, mixture too lean, or the engine just not being warmed up. Quite possibly your KMD could've just done with the needle open a turn or so for starting, a bit of a warm-up, and no need to touch the comp at all.

Sorry if this is telling you (or anyone else) to suck eggs!

DaveyMo

Thanks, Steve. I didn't know that it's best to adjust the comp screw as little as possible. The learning curve is kind of steep for this ol' bird!

As for your fine words Mr. cat123, I'll gladly take them under advisement! Ha!

steve111

No worries Dave, it's natural to think that if something's adjustable, then you can adjust it to your heart's content. I didn't know better either, until I started flying with people like David Owen.

Although the learning curve might seem a bit steep, if you can leave the comp alone at a good running setting, it actually makes things easier, because you're removing one of the variables. The trick then is working out what will convince the thing to start. It varies from engine to engine, but mostly I can richen the needle a turn or so, choke it once or twice, maybe prime the side of the piston, and it'll fire up. It'll probably be misfiring initially, but as you slowly lean it out, the engine will heat up and the misfire will clear. Easy! Of course sometimes you have no choice but to mess about with the comp - the engine may be flooded, the presence of a muffler might stop you priming through the exhaust port, or the engine may be just plain perverse. I also think that the better an engine is, the less the comp needs to be fiddled with to get a good run. Things like my R320 and T2.5 barely have the compression touched from one year to another.

Steve

123Cat

Thats why you should fly down by the old steel mill ,

cause the grass is long there

greggles47

Since I changed to using Amsoil, warm ups are a lot slower than with IPN.

DaveyMo

Again Steve, some top-notch follow-up advice on your part. Will shoot for a good run setting and then tackle the starting challenge from there. Much obliged.

Quite the fair point, Greg, concerning warm-up and Amsoil. I'll have to figure that into the behavioral parameters. Thanks!

And last but not least, Mr. 123Cat: I heard by the grapevine that chlorophyll makes an excellent cetane booster!

Until we meet again...

Dave Mo

DaveyMo

Greetings Again:

I just returned from a bench run if the KMD 2.5 taking all of the above into consideration (no, Mr. Cat123). My preliminary conclusion: methinks somebody goofed up on the fuel mix, and I shan't say who that might be!

Running it last fall on the 8x4 prop and commercial fuel, I easily got 12,000 RPM. Today with the same prop, the same contra and needle settings, I got a sputtering 6,500 tops. Maybe I should bite the bullet for the commercial fuel and use my own mix for wood-stove fire starter? Or, should I try goosing my mix with more ether or Amsoil?

Either way, this KMD is a lovely little engine and I'm willing to figure things out to keep it happy! Thanks.

Dave Mo...

steve111

Dave, I'm not sure it's possible for you to have goofed on the fuel mix enough to cause that sort of drop in performance, unless maybe you reversed the kero and castor proportions. (You are measuring by volume not weight, aren't you?) If what you've got is even remotely similar to the proportions stated at the start of the thread, it should run fine. I don't know about 'goosing' the mix, either, since adding an arbitrary amount to an uncertain quantity is reallly just stabbing in the dark and may just be a waste of good ether and Amsoil. Even if it worked, you'd have no idea of the actual composition that was now working for you. In any case, a shortage of ether or DII isn't ever going to cut rpms by nearly 50%. If it started ok, you've probably got a sufficient amount of ether.

While it's hard to say without being there, 'sputtering at low rpm' sounds like it might be very rich (regardless of what the needle setting was last time). If it starts ok and isn't labouring, leave the comp where it is for now, and see if you can lean it out slowly.

What sort of 8x4 is it? Just curious, since 12000 is still on the low side for a decent 2.5 on that size prop.

Steve

123Cat

There is a paper from Moscow state uni

Entitled Hydrogen peroxide Oxidative Desulphurization of Model Diesel Mixture using Azacrown Ethers

Maybe that would do it

greggles47

You can discover the mixture of your fuel by the simple evaporation method.

Measure out a specific amount of your fuel in a graduated cylinder. 100ml is a good amount, but not necessary although you must record the amount in the cylinder.

Now place the cylinder where the fuel can evaporate, but no foreign matter can enter.

Once the ether evaporates off, the oil & kero will separate - giving you the two major fuel components, and the full mixture by calculation.

Your sputtering run - if the fuel was close to described - could be due to being undercompressed, or lean/rich.

Keep on mate.

DaveyMo

Gents:

My apologies, but I'm a bit slow on the uptake to a very nifty set of responses here. Long story short: my better half, Jen, has come down with a rather serious health problem. As you'd imagine, my attention has to be hijacked in that direction for a little while. I'll pick this up again in the near future. Thanks for your thoughts and patience.

Davey Mo...

Recycled Flyer

[QUOTE=steve111;12005641
What sort of 8x4 is it? Just curious, since 12000 is still on the low side for a decent 2.5 on that size prop.
Steve[/QUOTE]
Low side is putting it very diplomatically Steve!

http://www.clamf.aerosports.net.au/n...LN/Issue81.pdf

This test by a well respected modern day engine tester says that the engine aint happy at all at 12 000 rpm.
"No self-respecting racing engine is happy at sloggingspeeds and the KMD was rather unhappy below 12,000RPM."

Is this a brand spanking un-run engine that 'could' be fossilized in cosmoline engine preservative causing your black exhaust?

paw080

Hi Davey, at this point, I have to say; bite the bullet and get commercial model diesel fuel. Your KMD should turn an 8" X 4"

close to 14K.

Tony

DaveyMo

Hello All:

Back to this board between running around to help my wife. Last season, the 12,000 with the APC 8x4 prop wasn't an attempt to maximize performance. I'd hoped to do that this season with my own fuel. I'll try not to stay on hiatus too long before I fire it up again. Will get back to you ASAP. Thanks!

Davey Mo...

steve111

Hope everything goes well with your wife, Dave.

Hobbsy

My Feedback: (102)

Davey, I'm another Davey, my grandmothers called me that my whole young life. In his instructions for Davis Diesel conversions Mr. Davis advocates running Diesels as near the peak as you can get away with and the compression just below the egg frying noise which I call the "secondary rattle". 25% castor is never going to allow the engine to be under lubed and when leaned too far Diesels don't go into the pre ignition mode, they just quit.

DaveyMo

Good Gents:

All I can say is "carrumba" but I've been getting some excellent advice here! This diesel thing sure brings out the generosity in my fellow oil burners. I'll read through and try all of this advice in one form or the other and let you know the results. But for the time being, I'd like to thank Steve for his thoughts. And because it was done easily enough, I took Greg's advice and set out some fuel in graduated container. Neat trick there! The results confirmed my original percentage mix of ether (30), oil (25), and K-1 (45).

Much obliged.

Davey Mo...

DaveyMo

Howdy All:

Yes indeed, the KMD was under compressed as I finally got 14,000 on the APC 8x4 prop today. Will not monkey with the contra screw setting unless I want to fry some hen fruit a la Hobbsy!

Davey Mo...