Effects of ammonia energy ratio and hydrogen addition on the performance of ammonia-diesel dual-fuel engine

Ammonia is recognized as an important carrier for hydrogen storage and transportation, distinguished by its high hydrogen storage density, ease of liquefaction, cost-effectiveness, safe storage and transportation, and well-established infrastructure. However, the extensive utilization of ammonia in internal combustion engines is restricted by its physical and chemical properties. Currently, ammonia-diesel dual-fuel (ADDF) engines have a strong capability to reduce carbon dioxide emission while maintaining the indicated thermal efficiency (ITE). However, the wide operating range imposes stricter requirements on the combustion stability of the ADDF engine. Therefore, this paper further experimentally investigates the ADDF engine under the operating condition of 1500 rpm and a load of 7.8 MPa. Then, the simulation model is built and used to study the effects of ammonia energy ratios (AER) on the performance of ADDF engine. In addition, hydrogen addition strategy is adopted to improve the combustion process of ADDF engine under high AER conditions. The results show that 20 % AER in ADDF engine can achieve a peak of 44.2 % ITE and reduce CO2 emission by 19 %. The combustion, performance, and emission characteristics are observed to decrease when the AER exceeds 20 %. When the AER reaches 80 %, the combustion process is further deteriorated, resulting in the ITE decreasing to 10.7 %. Additionally, adding 10 % hydrogen energy ratio (HER) in 80 % AER can optimize the performance of ADDF engine, yielding 40.1 % ITE and greatly reducing unburned ammonia and carbon emissions. However, with further increasing HER, the combustion efficiency of ADDF engine is decreased.