Minh
I have been following this discussion with some interest and there have been some useful comments so I will add my ten cents worth.
When building a model diesel say 6th scale or less, there are some aspects of the combustion cycle that are difficult to replicate in terms of the real thing. Firstly, the pipe work from the injector pump to the injector must have a very small diameter typically 0.5mm or less. In theory you can't compress diesel fuel however in this case you are talking about significantly less than half of a single drop of fuel. If the internal diameter of the tube is large say 6mm the tube simply expands with each pulse of fuel. I used 1.5mm OD (0.25mm ID) stainless steel capillary tube via ebay and tig welded the joints. This worked out well. The other problem you have is, that you can't get the cylinder and cylinder head hot enough to ignite the fuel air mix using just standard diesel. One of the reasons some diesels need glow plugs to get started. The information is on the net re the compression pressure for different types of liquid fuels.
You will find kerosene is significantly less than diesel and further, ether is significantly less again. For a miniature diesel, a mix of kero 70% and ether 30% makes it quite easy to start. If you want, after the engine is hot, you can switch to straight kero.
As for injection pressure, my testing showed that 1800 to 2000 psi was sufficient to atomise the fuel. You can't see it as such but put some paper in front of the injector. If you can see the spray, it not atomized as such.
I used parts from a cheap commercial pump eg the barrel and plunger for my pump and it would pump up to 3000 psi with out any trouble. For the injector, I used a small commercial pintal type nozzle fitted into a steel body. The best I could ever achieve making my own was about 1200 psi for the pump and a dripping injector at about the same pressure. I tried many variations and they ranged from a total failure to just not good enough.
Just my thoughts from building a miniature diesel.
Bruce