I did a google search using: introduction of hydrogen to enhance combustion
There is a wikipedia article, "Hydrogen fuel enhancement".
https://en.wikipedia.org/wiki/Hydrogen_fuel_enhancement
I have included some articles from the search results below:
Effect of hydrogen-diesel fuel co-combustion on exhaust emissions with verification using an in–cylinder gas sampling technique.
Effect of hydrogen-diesel fuel co-combustion on exhaust emissions with verification using an in?cylinder gas sampling technique
Use of Hydrogen-Methane Blends in Internal Combustion Engines
http://cdn.intechopen.com/pdfs-wm/40243.pdf
Effect of Hydrogen Enriched Hydrocarbon Combustion on Emissions and Performance (The author, Jacob Wall, is an hho true believer and internet advocate)
http://pesn.com/2009/01/17/9501513_1...Combustion.pdf