what about a heat exchanger loop wrapped around the exhaust manifold, the downpipe, or wherever, and a regular old WI system (shurflo pump, nozzle, solenoid, etc) that injects HOT water pre-turbo? The "superheated", high pressure water (T>100C) will flash to vapor as soon as it leaves the nozzle due to the pressure drop. You the run the watery mix through the turbo, through the intercooler (yes some will condense, deal with it appropriately), and into the engine...

EDIT: My vote is still for a "IDI" water injection system where the glowplugs are replaced with injectors (like those found on your average FI gasser) and supplied with high-pressure water. A crank position sensor (like the RPM sensor?) provides timing info for a little computer which times your water injection event at some point ATDC (ideally when the diesel fuel injection event has terminated).. Think it will work? It doesn't sound too expensive if using parts from a junk gasser motor...

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99 E300 Turbodiesel 100k