A process and apparatus is provided for burning liquid ammonia in an energy device such as a diesel engine, boiler or gas turbine. In particular, the process and apparatus include mixing a renewable fuel with a low flame speed and high ignition temperature, e.g., ammonia, with a combustible liquid fossil or bio-fuel and supplying the mixture into a closed fuel loop where part is efficiently burned in an engine combustion chamber, and part is used to cool the engine and returned by the loop for mixture with fresh incoming fuel mixture. The invention provides for the mixing and emulsifying in such a way that vapor lock is avoided. In the loop, the mixture is emulsified into a disperse distribution of fuel droplets such that upon injection of a portion into the combustion chamber, the renewable fuel in an emulsified droplet evaporates, mixes with the air and forms a small combustion cell surrounding the liquid fuel droplet. The fuel droplet burns and then serves as an ignition kernel for the gas mixture in the small combustion cell producing efficient and rapid combustion of the renewable fuel. The fuel loop allows the fuel system to automatically scale for engines varying in power output from 1 to 35,000 horsepower.