Diesel engines run lean & #2 diesel is an oil as opposed to a solvent as gasoline is a solvent. Gasoline will vaporize quickly which is why carborators have worked for years & years. When diesel is injected into the cylinders the injectors attempt to atomize the fuel as much as posible but it is still oil so it is important that there is excess oxygen for combustion to take place.
For more that 10 years propane injection has been on the market & has been proven to add horsepower, torque, & fuel efficentcy by taking advantage of the extra space in the cylinder to burn propane. As a bonus the combustion is more uniform, quicker, & more robust causing more complete burning of the diesel resulting in lower emisions.
Thre is no reason to think that a legitimate onboard HHO producer (from the electrolysis of water) would not work the same as they claim to produce about 5 liters of uncompressed HHO per minute for about 20 amps. I would have to see that demonstrated.
