The droplet size in a combustion chamber depends on several factors such as injection pressure, distant from spary orfices, and angle of spary. The higher the injection pressure, the smaller they are in size. spray pattern is also important. The spray trajectory (called a ploom) is produced by each orfice in the nozzle (in diesel). If one lags or angle of sparay changes, the plooms will hit each other and higher droplet size will occur. You will need a high speed camera (about $100K), a laser beam, and a pressure chamber to accurately see the spary pattern. There is no uniform droplet size out of an injector. You would have to look at a droplet size distribution. Usually ranges between 30-250 microns in a gas injector. In a diesel engine, injection pressure is a major and important factor effecting diesel droplet size and hence particulate matter (Soot) size distribution that ranges from 3 to about 1000 microns in diameter in newer engines and from about 300-3000 microns in older engines.
I think in a 124 260e, the pressure to open the injector is about 3 bar (~45 psi) and it's dependent on the fuel pump pressure.
To get fuel flow in Gallons/hour you need to do a volumetric flow rate measurement. It different and I believe is depends on pump pressure. If you let the injector (or pump) spary for 30 seconds into a container and you get 1 Liter/1 minute, you can convert this quantity into gallons/hour. I think it would be difficult to do this at home with electronic injectors, however, the injectors in a 260e can be tested by energizing the fuel pump and pushing the sensor plate down by hand (linear relation). The injector will spray. The spray is very flamable. Be careful if you try this.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer