The optimization for the combustion and emissions performance of a multi-cylinder ammonia-diesel dual fuel engine in both steady-state and transient operating conditions

The utilization of ammonia as carbon-free fuels holds significant potential for various applications in energy systems. To enhance the ammonia-diesel dual-fuel (ADDF) engine performance, it is necessary to blend a highly reactive fuel due to its inherent difficulty in igniting and lower combustion speed. This study systematically investigates the combustion and emission performance of a multi-cylinder ADDF engine with a displacement of 13 L, where ammonia is injected into manifold using low-pressure injection and direct injection of diesel into the cylinders. Experiments were conducted under both steady-state (World Harmonized Stationary Cycle, WHSC) and transient (World Harmonized Transient Cycle, WHTC) conditions. A coordinated optimization strategy is proposed, integrating in-cylinder combustion control with aftertreatment system (ATS) management. Under WHSC, through active regulation of the ammonia-to-nitrogen oxides molar ratio and optimized diesel injection strategy, the engine achieved a maximum ammonia energy ratio (AER) of 59% while maintaining original power and torque. The effective thermal efficiency reached 48.8%—3% higher than the baseline diesel engine, with NOx and NH 3 emissions as low as 0.089 g/(kW·h) and 0.62 ppm, respectively. Extending the strategy to WHTC operation, a cyclic AER of 53% was attained together with a 2% reduction in fuel consumption. At the ATS outlet, NOx and NH 3 emissions were controlled to 0.22 g/(kW·h) and 7.18 ppm. All measured pollutants comply with China’s Stage VI emission standards in both steady and transient cycles. This work demonstrates a viable systematic methodology for enabling efficient, low-emission ADDF engine operation, providing critical insights for future commercial implementation.