Several pdf links on that page for further explanations.
A couple changes I see from current engines are the addition of EGR to lower the combustion temperature and a redesigned fuel injection system of some sort. The claim is reduced NOx. What about the other contaminants such as particulates, hydocarbons, CO, etc? http://www.epa.gov/otaq/technology/420f04023.pdf states aftertreatment still being used.
OT: I found the "Hydraulic Hybrid Research" of interest. Reminded me of having done a little DD on Shep Technologies (STLOF.OB). http://www.shepinc.com/