Hybrid

Vote no on HHO.

Actual hydrogen boosting on a Diesel engine tend to work similar to propane boosting.

Every engine will have its ideal peak level it can handle so I don't think that there is an exact answer to your question other than yes it does work and it does provide both power gains and lowers diesel fuel consumption.

Yes, but where are you producing this hydrogen? How does the cost of hydrogen production compare with fuel savings? Generally speaking it takes quite a bit of power to produce hydrogen, that in turn only holds a fraction of the power it took to produce. If the hydrogen is being produced on-board the vehicle using electrolysis, it is consuming more power to produce than it is adding back into the system. If you are buying the hydrogen from an external source, IE in tank form, how does the cost of that tank of hydrogen compare to the cost of fuel saved. Also, I'm not aware of any long term studies (please point me to them if available) that discuss the issue of hydrogen embrittlement on the engine components over time. Not saying it might not seem to work, but I would like to see the actual numbers. and for the OP, it will completely depend on the engine's stoichiometric mix, compression ratios etc.

Was there a second part to this question I did not see or are you reading between the lines of posters actual question.

Hydrogen boosting research is not new and it has been studied in detail and like every other fuel its cost and production are relative to what resources you have available.

As far as my understandings go hydrogen embrittlement is not a major concern or issue with typical engine components being the cast iron, hardened steels, and aluminum alloys that engines are built out of are quite forgiving.

Propane boosting has been done for about as long as the modern diesel engine has existed so hydrogen boosting is just a logical follow up to it.

I hadn't considered it before, but that sounds accurate. Propane is, after all, mostly hydrogen:

C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + heat, otherwise said as

propane + oxygen → carbon dioxide + water

However, this reaction will deny available oxygen that would otherwise be available to combust the diesel. Turbo, anybody?

You get an "A" for stoichiometry!