My ongoing science experiment... don't know if it's ever been done before.
I did all this about a year ago but took a long break after it didn't want to start up.
Hoping to pick it back up this winter, I've got some ideas on how to improve the design.
Posting here in hopes that it'll keep me working on it.
Combustion chamber:
Super cool!!
For those of us that are slow, I can't figure out what you are doing.
maybe, some more explaining might be helpful.
Trying to whip up a two-stroke DIESEL motor.
Really the only two-stroke diesels I've heard of are some mega-huge ship engines, and the famous Detroit Diesel.
https://en.wikipedia.org/wiki/Detroit_Diesel_Series_71
Those are, of course, in a league of their own.
I'm trying to do it with piston-ported, naturally aspirated, case scavenging, carbureted Puch E50 motor.
This looks super cool. Do you need a glow plug or something to kick it off? I’m pretty diesel ignorant.
I had a QT-50 with a Malossi kit and stupid high compression that would diesel. I was pretty shocked when I pulled the plug wire and it kept running.
I think heat (or lack of heat) was my main problem when I tried to start it up last.
The piston, combustion chamber (a.k.a. "counter-piston"), and counter-piston sleeve (the thing that sits between the jug and head) are all aluminum, which sucks all the heat out.
Diesels like heat.
I have a few ideas to remedy. First I'll try using the ole' smokewrench to help preheat everything for startup. That probably won't work. So I suspect I'll end up switching to a cast-iron combustion chamber. Maybe cast-iron piston too, but I hope not; that thing took me a lot of time to make.
Surprised you didn't blow up your QT-50 motor! I've bored out the jug and case for larger top end bolts and am using a stronger race crank in hopes that I reduce the likelihood of breakage.
Also using a custom super heavy flywheel to help keep the motor spinning through the high compression. Have no need for a magneto, so it's basically just a hunk of steel, machined round.
This small model airplane motor (and motors like it) was the original inspiration. It's a 'diesel', in that it does not rely on a spark for ignition. But runs on a mixture of ether, kerosene, and mineral oil instead of true diesel fuel.
Mine has about 80x the displacement, and I'm hoping I can get it to run on pump diesel + 2T oil.
Check this out: https://cyclemaster.wordpress.com/page-44-german-cyclemotors-lohmann-hilfsmotor/
It's a variable compression diesel bicycle engine
This is really cool
This is a really cool ideal but how are you going to start this? diesels have a lot of compression unless you use a decompression valve.
> Angry Hipster Wrote:
> -------------------------------------------------------
> Check this out:
> https://cyclemaster.wordpress.com/page-44-german-cyclemotors-lohmann-hilfsmotor/
>
> It's a variable compression diesel bicycle engine
Well this is super rad. Basically exactly what I'm trying to do --- run with the throttle pretty much wide open, and adjust power with a variable compression ratio. I guess I'm just 70-odd years late to the party!
> Jeff Parr Wrote:
> -------------------------------------------------------
> This is a really cool ideal but how are you going to start this?
> diesels have a lot of compression unless you use a decompression valve.
Well for now, I'm just trying to start it with a heavy-duty electric drill.
In the meantime, maybe I'll do some squats to get my legs strong enough to kick it over. If I ever get it to work, anyway.
Least of my concerns at this point is being user friendly.
"Least of my concerns at this point is being user friendly"
Now that is the spirit of mopeds right there!
> J MR Wrote:
> -------------------------------------------------------
> This small model airplane motor (and motors like it) was the original
> inspiration. It's a 'diesel', in that it does not rely on a spark for
> ignition. But runs on a mixture of ether, kerosene, and mineral oil
> instead of true diesel fuel.
>
> Mine has about 80x the displacement, and I'm hoping I can get it to run
> on pump diesel + 2T oil
https://en.m.wikipedia.org/wiki/Carbureted_compression_ignition_model_engine
The Kreidler race bikes use a head that you can swap out the chamber size
That Lohmann motor is pretty interesting. It looks like it has a decomp valve in the head, and three piston rings. Not sure but it might be an acme thread to move the the head in and out, which would make sense. Acme threads are used on vices or other applications where you need a lot of force.
Lol those model airplane engines run on poppers:
"These 'diesels' run on a mixture of kerosene, ethanol, ether, castor oil or vegetable oil, and cetane or amyl nitrite booster."
I have thought about doing this and the real hard part seems to be fuel delivery. It has to be timed exactly so that it reaches the combustion chamber a TDC. I would think a Vespa motor would work best for timed induction. Otherwise fuel injection. What compression are you going for 25:1?
Cast iron cylinder sounds cool, do it!
And maybe weld your cases shut...
> Kevin Bishop Wrote:
> -------------------------------------------------------
> I have thought about doing this and the real hard part seems to be fuel
> delivery. It has to be timed exactly so that it reaches the combustion
> chamber a TDC.
That's true for a real diesel engine, those have fuel injectors in the head.
The model airplane engines aren't true diesels. They're compression ignition engines that use a carburetor. Ignition timing is adjusted by changing the compression ratio. So timing for fuel doesn't matter, it's just like any other two stroke gas motor.
With my current aluminum combustion chamber, the compression ratio is adjustable up to about 18:1. That's the 'trapped' compression ratio after the exhaust port fully closes. The overall CR between BDC and TDC is adjustable up to about 27:1.
I suspect the 18:1 'true' CR is not high enough to burn pump diesel, so I think a new, smaller, cast-iron combustion chamber will be one of the next parts I make.
I may, alternatively (or additionally), add some diethyl ether to my diesel; the autoignition temperature for diesel is 410F, whereas it's only 320F for ether, so it should be able to run at a lower CR.
I'm a bit worried about going to a full cast-iron piston for vibration reasons. Don't really want to chop up my brand new race crank to alter the balance factor, so I'm hoping that I can get it to fire up with the changes I describe above before having to remake a piston.
Highest stressed components probably won't be the case bolts, so no need to do anything drastic like welding them shut. Pressure spikes in there won't be much different than a regular 2T motor. Thing I'm a bit worried about is the head bolts stretching, causing a leak at the head/cylinder interface. I drilled out the cases for larger bolts in hopes to mitigate some of those issues.
I know this might beyond what most can do but it's a great ideal.
Variable Compression Engine
> noah adelstein Wrote:
> -------------------------------------------------------
> The Kreidler race bikes use a head that you can swap out the chamber
> size
VHM makes an assortment of 2stroke heads with removable combustion chambers, great for tuning for short/long tracks
Hey this is pretty cool, I looked in to building one of these years ago but never cut chips. I think if you just turn the Piston flat and machine the head out for an insert with a flat bottom you'll be able to get it running. My thought was to use a glow plug from a rc airplane motor instead of adjust compression.
Doing a bunch of research into the lohman, it looks like you use the compression adjustment to get it started (high comp) then you turn it down to lower comp once it's warmed up and the rpms can then increase, controlled by the throttle. My original goal was to run on veg oil but I got cold on the idea once I realized I would have to mix it down with kerosene or something. Also you don't have to look to far for ether or methanol to cut down oil and make it light off easier, I have a torpedo heater I've had good luck running on waste oil mixed with gasoline instead of kerosene. Even 10 percent gas added to diesel or kerosene will make it light off really easy.
A guy I worked with put hydraulic oil in a Honda pressure washer once and it ran surprisingly well, in fact we couldn't figure out how to turn it off.
I somehow missed this thread until now. Reminds me of something i posted here over 13 years ago.
Please keep this thread going! There is nothing interesting being posted on MA
Without any rings on that contra-piston, you’ll never get this to run.
I don’t think straight diesel fuel will get you there either.
The smaller diesel model engines don’t have rings, but those small pistons are lapped to size, and the cylinder bores have the slightest bit of taper. At tdc, the piston may actually feel stuck before the first few break in runs.
I always ran all of mine on equal parts of ether, kerosene, and castor oil.
Regular “starting fluid” ether works fine, but be sure to read the label, as not all starting fluids are the same. It should contain at least 70% ether. They recommend 2% of some kind of “stabilizer” to the mix also, but it’s not needed, and good luck finding it anyway.
At room temperature it should fire on compression alone, but warming the cylinder will help. My Mills diesel engines run cool, slow, and amazing quiet, but the Russian diesel i have will burn your face off, and it screams like a nitro.
> Blaine- The artist formerly known as Plumber Crack "(OFMC)" Wrote:
> -------------------------------------------------------
> Without any rings on that contra-piston, you’ll never get this to run.
>
> I don’t think straight diesel fuel will get you there either.
>
> The smaller diesel model engines don’t have rings, but those small
> l pistons are lapped to size, and the cylinder bores have the slightest
> bit of taper. At tdc, the piston may actually feel stuck before the
> first few break in runs.
>
> I always ran all of mine on equal parts of ether, kerosene, and castor
> r oil.
>
> Regular “starting fluid” ether works fine, but be sure to read the
> e label, as not all starting fluids are the same. It should contain at
> least 70% ether. They recommend 2% of some kind of “stabilizer” to the
> mix also, but it’s not needed, and good luck finding it anyway.
>
> At room temperature it should fire on compression alone, but warming
> g the cylinder will help. My Mills diesel engines run cool, slow, and
> amazing quiet, but the Russian diesel i have will burn your face off,
> and it screams like a nitro.
Pics
Mills repro .75cc
Valentine .098cc
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