After H2O ...
You ask of vacuum, etc... Some threads ago you have posted an youtube video link about engine that theorically work to water.. This work in this way.. First charge water with temperature at 90°C, chambre combustion is different and air compressed with piston (high temperaure is reached) is accumulate with specific valve inside chambre combustion, after piston oes down and create vacuum.. in this condition is injected water atomized 90°C and electric arc HV is created.. result (to verify) is creation of hydrogen into combustion chambre.. after hot air is released and burn hydrogen.. This is an best scenario but in fact must be verified and engine must be modified in some parts.. Our real scenario is different .. we have an standard 4 stroke engine and we have to work on it.. If you have run with success an 4 stroke engine you are great but you can share with us your video and explain pratically and not with theory as you have reach this success.. no more words are needed .. I don't want your project but only an scheme to blocks ..