Microdiesel building plans

[boutje]

Maby a good basis to build your own small diesel engine?

http://www.practica.org/wp-content/uplo ... 051210.pdf

[realnutter]

That's an 18.5cc engine! Would need considerable scaling up to make it useful!

[realnutter]

Can be seen (and very much heard!) in action here!


http://www.youtube.com/watch?v=r3-VLNjwIsg

[Blunt Eversmoke]

That's an 18.5cc engine! Would need considerable scaling up to make it useful!

How hard would it be to use the variable compression head design to create such an engine out of some built-to-last two-stroker(preferrably around 500 cc ) instead?

[boutje]

That's an 18.5cc engine! Would need considerable scaling up to make it useful!

How hard would it be to use the variable compression head design to create such an engine out of some built-to-last two-stroker(preferrably around 500 cc ) instead?

With the right tools and enough time it is possible.
Anyone?

[skoleskibe]

try to find a single cylinder 500 cc 2 stroke engine
this type of engine is (was) common in model airplanes in the 40 - 60, running from .5cc to app 6 cc
they require ether to run fuel mixture of kerosene 25 - 30% castor oil. They could be rather difficult to start, as u had not only the fuel mixture (oil kerosene ethar) mix, the fuel to air mix and the compression to get right, also as the temperature in the innards of the engine rose the need for compression would be less ie ajust the CR a little down with temperature rise

though have a google: lohmann diesel bicycle motor, they are hard to find and rather pricey, they allso was app 18cc 2stroke diesels with variable CR. An owner told me that at morning he used a blowtorch to pre heat the head, otherwise it wouldnt start.

ilove them though

[Blunt Eversmoke]

A 300cc two-stroker would suffice, too I read that yes, they are hard to start, but, unlike model motors, they run pretty well once started. Also, there were reports on the net from people who managed to actually run them on kerosene and castor or even diesel and castor, no ether at all. Ether way, makes me wonder...

[Blunt Eversmoke]

As you all know, the Lohmann controls its compression ratio by a complete screw-in/screw-out cylinder which is also the head.
As you all also know, RC model "diesels" use a counter-piston in the cyl head for the same purpose. This is far easier to implement and makes for a generally more durable construction (Lohmann engines of certain production timespans were reported to crack their cylinders in half quite often, in contrast).
So, it was only a question of time till someone took something bigger (2.5 times bigger in this exapmle) and replicated the latter approach for shits and giggles - here's what I have stumbled upon.

Honda compression ignition scooter. Even has something akin to idle (erratic due to defect carb, the guy says.)

The basic facts:


Spark plug out, counter-piston in. Counter-piston is screwed into its own (bronze?) threaded muff which is, in turn, screwed into the (widened and re-threaded?) spark plug hole in the cylinder head. This is probably done to limit the way the counter-piston can be screwed in so as to avoid contact of piston head and counter-piston on the highest compression setting.

Highest compression ratio setting with counter-piston completely screwed in is "calcultimated" to be around 21:1, no measuring of actual compression pressure was done since compression measuring devices bring too much dead space for such a small cylinder; no info on the lowest CR possible.


Fuel is 3 parts diesel, 1 part gasoline (to lower fuel viscosity so the carb can actually disperse it?..); no mention of 2 stroke oil (still, I don't think he's running it without). NO ETHER

RPM regulation is your basic gas engine fare quantity regulation via throttled carb, controlling both fuel dosage and actual compression pressure. Apart from being easiest way to try it out, this is because, while the geometric compression ratio can be adjusted very quickly, the guy has not made any provisions to do that on the fly (in contrast to the Lohmann).
Quality regulation could probably be done the (proper) Lohmann way with one twist grip, lever or pedal for "intuitive" compression setting, turning the counter-piston via some pulley and a throttle cable, and a second twist grip for fuel dosage, but would require modifications to the intake as well to control fuel dosage (two parallel ducts to the intake port of crank case, one for just air, one with a way, way overjetted carb and a throttle (for each duct?) is the simplest solution that comes to mind; might still have its caveats).

Crankshaft and its bearings/journals are from a 70 ccm scooter while the cylinder has 50 ccm of displacement - to keep up with higher peak pressures. Conrod is probably from the 70 ccm model, as well.
No details on the piston head.
Cylinder head reported to be modified to house most of combustion space (so it can be controlled by counterpiston. Duh.).


Achievements:

10K kilometers on the clock reported so far.

MPG or liters per 100 km are not mentioned, but are probably not much better than standard, since RPM regulation is by throttle and he says he runs the carb slightly over-jetted for cooling purposes.

Power/speed gains or losses as opposed to stock: Not reported.


I am currently browsing his site and will post more info if I find anything.