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. In addition, they also have a 9.4L engine modular engine based on the the Ford 7.5L (460 CID) 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 had a prototype engine running on NH3, which operated for extended periods providing clean power to irrigate a walnut grove and to provide water for a cattle ranch. The HEC NH3 press release didn't mention if other fuels were co-fired with the NH3. HEC announced a hydrogen/ammonia tractor in a November 2014 press release.
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: