Exploration of ultra-low carbon heavy-duty commercial vehicle technology: Liquid ammonia-diesel dual fuel high-pressure direct injection

Abstract

Ammonia (NH₃) has attracted substantial interest as a potential carbon-free fuel source for engine applications. The high-pressure ammonia direct injection is believed a way for higher efficiency. However, only a limited number of experimental studies have been conducted on direct-injection ammonia-fueled engines. In this study, a novel ammonia-diesel dual direct-injection compression-ignition engine was constructed and tested under high-load conditions. The results demonstrated that ammonia fuel combustion was advantageous in high-load situations, achieving a high carbon reduction of 75%. The indicated thermal efficiency (ITE) could be increased to 51.6% at an indicated mean effective pressure (IMEP) of 14 bar by employing a diesel pilot-injection strategy and increasing the pilot-injection ratio to 98%. Moreover, the diesel pilot-injection strategy at high load conditions also decreased unburned ammonia and nitrous oxide emissions. The lowest NH₃ and N₂O emissions were reduced to 2.1 g/kWh and 0.67 g/kWh. Under high-load conditions of IMEP = 16 bar, employing a diesel pilot-injection strategy increased AER to 73% while maintaining high efficiency. When AER was further increased to 84%, the ITE showed a noticeable decline, and unburned ammonia emissions increased accordingly.