I've been interested in HHO for a long time but the main problem with HHO as I can see, it is inconsistent HHO flow. Since hho flow depends on temperature and amount of KOH. It might work great for a month and after a month hho flow might drop or increase. The best way to always know how much flow you are getting because if cell would stop producing hho or decrease the flow then you are damaging your engine by over leaning. Since I couldn't find anyone selling or making such sensor to public for cheap here is an idea and I'd like to know your opinion.

It should consist of a pipe such as PVC with a propeller inside. See the picture. When HHO flowing thru the pipe, prop would rotate. Using IR leds we can easily count rotation of the prop and figure it out average prop rotation requires for 1 liter per minute. I can easily get the result on a small 16x2 Character LCD display.

Now I'd like to hear your ideas and what parts would be the best to use. In regards to electronics that's the easiest part for me.