Combustion and emissions characteristics of a compression-ignition engine using ammonia (NH3) and dimethyl ether (DME) mixtures were investigated in this study. The experiments were conducted using three different mixtures, including 100%DME, 60%DME-40%NH3, and 40%DME-60%NH3 (by weight). The injection pressure was maintained at approximately 20.6 MPa and engine combustion and exhaust emissions were measured in order to analyze and compare the performance of different mixture compositions. Results show that engine performance decreases as ammonia concentration in the fuel mixture increases. Significant cycle-to-cycle variations are observed when 40%DME-60%NH3 is used. The injection timing for best torque needs to be advanced with increased ammonia concentration in the fuel mixture due to the high resistance to autoignition of ammonia. Moreover, with the increase in ammonia concentration, both engine speed and engine power exhibit limitations relative to 100%DME cases. For 40%DME-60%NH3, the appropriate injection timing was found to range from 90 to 340 BTDC and the engine exhibits homogeneous charge compression ignition (HCCI) combustion characteristics due to the highly advanced injection timing. 40%DME-60%NH3 conditions also results in higher CO and HC emissions due to the low combustion temperature of ammonia. Soot emissions for 40%DME-60%NH3 remain extremely low. When ammonia is used, NOx emissions are increased due to the formation of fuel NOx. Exhaust ammonia emissions also increase as ammonia concentration in the fuel mixture increases from 40% to 60%. Overall, in this study appropriate strategies are developed to enable the use of ammonia in direct-injection compression-ignition engines and the corresponding engine performance is evaluated. (C) 2013 Elsevier Ltd. All rights reserved.