I'm sure stan would have consider ignition by pressure in cylinder, its an interesting aspect to consider, there seems to be quite a few people have tried hho on small motors, they might have some insights on that.
Thanks firepinto for info on solenoids and water pressure, I wan't aware of that,
Since fuel injectors are lower pressure it still might be feasible to use the fuel injectors with some adapter, the lower pressure will simplify the build, I'm guessing his high pressure waterplugs are high pressure to match the engine, rather than being related to the water splitting process.
Also since valyonpz has shown step charging can occur without direct contact of the water to the stainless steel, that might open up the possiblity of simplifying the electrodes i.e. being located outside of the voltage zone, that also means other materials apart from stainless could be used for the electrodes.
It might even mean its possible to use a 3d printer to make an adapter to go onto a fuel injector, if the electrodes can be on the outside of the voltage zone, the whole adapter could be plastic ( some of level of heat resistance necessary though).