In this study operating characteristics of a compression-ignition engine using mixtures of ammonia and dimethyl ether (DME) are investigated. Ammonia can be regarded as a carbon-free fuel that can help mitigate greenhouse gas emissions. Ammonia is one of the world's most synthesized chemicals and its infrastructure is well established. Recent technological advances also show that ammonia can be produced from renewable resources, making it an attractive energy carrier.

In the present study, a high-pressure mixing system is developed to blending liquid ammonia with DME that serves to initiate combustion. The engine uses a modified injection system without fuel return to prevent fuel mixture from vaporizing in the return line. Results using different mixture quantities of ammonia and DME show that ammonia causes longer ignition delays and limits the engine load conditions due to its high autoignition temperature and low flame speed. The inclusion of ammonia in the fuel mixture also decreases combustion temperature, resulting in higher CO and HC emissions. NOx emissions increase due to the formation of fuel NOx when ammonia is used. However, improvements for the same operating conditions were made by increasing the injection pressure using 40%NH3-60%DME. Exhaust ammonia emissions is on the order of hundreds of ppm under the conditions tested. Soot emissions are extremely low for all cases. Double injection schemes using 20%NH3-80%DME are also employed and found not to extend engine performance. Its effects on the exhaust emissions vary with operating conditions.