I am developing a very small single-cylinder Diesel engine, looking for advice & tips...

It is a 1.84CI (30cc) two-stroke single cylinder engine of the opposed-piston type (no cyl. head, two crankshafts each driving one piston in each end of the cylinder barrel).  Yes, I know it's little! :)  The exhaust ports are 3/16" high giving an effective displacement of 1.38 CI (22.6cc).  The engine will use an oil sump and have oil control rings South of the ports at TDC to prevent oil 'eating', a forced lube oil system, and an external air pump for charging.

I've done a fair amount of research and hmmming and hawwing and am still curious...

1)At max power, say around 16 or 18 air:fuel, what is an appropriate diesel fuel injection quantity?  I really can't believe how difficult it's been getting a handle on this.  Assume 100% V.E. for 22.6cc. Volume units for fuel 'shot size' are preferred, since I have to design & build the pump myself, which I can do, but need to know the approximate Max. injection quantity first!

2)What a good starting point for compression ratio?  I know the thermo efficiency drops as cylinder size decreases, so it'll definitely be on the high side... Say around 24:1?  I want to use commercial pump Diesel fuel.

True Diesels as small as 10cc have been successfully built (as seen in Strictly I.C. Magazine a few years back) and I figure 30cc is more than achievable, but I'm aiming for a fully developed high-class little powerplant.

Looking forward to educated & insightful replies... Any questions, just ask!  And again thanks for reading!

Assuming you are naturally aspirated, you are looking at around 0.077 mm^3 per stroke for stoichiometric operation, so you will want to back off a touch from there. Maybe 0.07 mm^3 will give you 16:1. These are back of the envelope numbers, but they are in the right ballpark. Finding a pump accurate at that point may be tough, but I'm not familiar with things in that range so maybe not. As far as mass goes, diesel is a little over 80% of water, so around 0.05 mg/stroke.

I have no experience with an engine so small, so I can't tell you about what compression ratio you should use.

For what it is worth, the Tilling-Stevens TS-3 engine (3-cylinder 3.52 Liter opposed piston 2-stroke) in its lowest rating gave 117 BHP at 2,400 rev/min.  

At rated speed, and at the efficiency shown on this graph, that works out to ~62 mm3/stroke on regular diesel fuel.  Your engine will run at a [much] higher speed, but you may be able to scale your fuel delivery to piston area or similar to cross-checkvalve your calculations.

When it comes to the fuel injection, the 62 mm3/stroke would have been delivered over approx 25 crank degrees at a mean effective injection pressure of around 300 bar and a peak of ~450 bar.  The single nozzle hole diameter was ?0.55 mm with a nozzle opening pressure of ~200 bar.

The intended use is the most important of all engineering applications:  Personal entertainment ;)

I don't know much about Diesels in practice but have always held a rather deep fondness for the operating principle... So I figured the best way to get real-world experience with one of these puppies was to roll my own.

Single cylinder engines have the highest potential for fuel economy for a given displacement, so one lung it is... except they shake like a paint mixer even as mild, low-compression SI mills.  So imagine what a lightweight one-lung Diesel would be like!  The opposed piston layout makes it possible to have a one cylinder engine that can be perfectly balanced, including twin identical counter-rotating flywheels to cancel intense rotational vibration from the enormous energy exchanges on a high-compression Diesel.  She oughta be a real smoothie :)  In addition, I can play with the phasing of the two crankshafts, allowing me larger transfer ports, and the ability to supercharge the living boogers out of 'er ;)  Not to mention fuel system development, cool little lube oil pressurization system pumps/regulators, nifty little crankshaft/conrod/piston assemblies and a funky scavenging pump/supercharger to boot!

Ultimately the engine will probably end up powering the workbench for quite some time while I admire my handiwork :) The original intention was to provide ultra-low fuel consumption, vibration-free power for a mountain bike using a little powerplant that simply specs out as extremely cool.  I may end up running a high-efficiency alternator with it too, just for kicks... Guess I'm probably gonna have to build a couple :)

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