The Hydrogen Engine Center (HEC) was founded on May 19, 2003 and has been developing hydrogen and anhydrous ammonia (NH3) fuel systems for their engines.

HEC seems to be primarily concerned with agricultural and stationary engine applications for their technology.  HEC has a line of power plants based on the Ford 4.9L (300 CID) inline six-cylinder engine.  From this basic engine, they have 0.8L 1-cylinder, 1.6L 2-cylinder, and 2.4L 3-cylinder variants.  In addition, they are developing a modular engine based on their proprietary design.  This could be their 7.5L engine.

NH3 is very difficult to ignite and HEC has been able to run anhydrous ammonia in their engines by using combustion enhancers such as LPG.  To accomplish this, they have developed their own simultaneous NH3 and LPG injection system using their Oxx Boxx™ control system.  HEC has a prototype engine running on NH3, which operates for extended periods providing clean power to irrigate a walnut grove and provide water for a cattle ranch.  The HEC NH3 press release doesn't mention if other fuels are co-fired with the NH3.

Although HEC does not currently have engines running on 100% anhydrous ammonia, they are working towards this goal. 

The Hydrogen Engine Center has provided updates of their progress to the Ammonia Fuel Conferences:

Internal Combustion Engines and Ammonia - 2004

Internal Combustion Engines and Ammonia (Second Report) - 2005

Performance of a Commercial Internal Combustion Engine on Ammonia Fuel - 2006