There are several ways of injecting water into the diesel engines to reduce NOx, PM and some claim to save fuel.
One of the methods is to inject water droplets to the combustion air before the cylinder heads. Following is what I have had a few years ago:
When I joined ship, the ship had already passed the first phase of an “onboard trial” of the WIS. “Filtered” water, using nozzles, was injected into the turbo compressor and before the air cooler of a diesel generator. Data were collected on the exhaust. I was very doubtful of the arrangement as I never had water injected into the turbo compressor almost continuously; the company conducting the trial did not appear to me to be very professional; their equipmnt were very primitive and the documents were very vague and poorly presented. Too bad the project was sponsored by the regualting authority and approved by the management.
Second phase was on the diesel main engine with one additional point of injection, after the air cooler.
-Due to higher than normal exhaust temperatures of the diesel generator, OEM technicians found the turbo compressor suffered damage due to the water mist impingement and the air cooler was fouled. Both had to be replaced.
-Main engine turbo exhuast casing cracked, leaking JW. Although it could not be identify as related to WIS, it was the first time this happened to me in my decades of seatime.
In the final report, they even could not get the NOx unit same as IMO one. When this was pointed out, they had to “convert” the results to be in line with IMO.
Of course, the conclusions were: +20% reduction in NOx, lower exhaust temperatures, reduction in PM and 1% fuel saved. (My memory only.)
Although the internet can provide some info, I would like to hear more first hand experiences regarding this subject. Thank you.