A new engine design is being put forward by a New Zealand firm. They state that "The Pivotal engine is the ideal CNG/hydrogen internal combustion engine design" a further quote from them is :- "The Pivotal engine is a new mechanical means of harnessing the power from combustion fuels. It is an internal combustion engine (ICE) that overcomes inherent limitations of the conventional device. It delivers the potential for a significant advantage in power density and thermal efficiency on a wide range of fuels. With full thermal control of the combustion chamber environment it is a clear choice for hydrogen and will become the ubiquitous hydrogen engine of the future. The Pivotal engine will successfully adapt to a wide range of alternative fuels and is particularly suited to gaseous fuel blends."
see www.pivotalengine.com