Comprehensive study on the effects of initial parameters and pre-chamber structure on the combustion characteristics of ammonia/air mixture

• The coupling effects of ambient and pre-chamber structure parameters are conducted. • High ambient temperature can improve the ignition delay of large pre-chamber. • The ignition position is mainly related to the volume of the pre-chamber. • The small orifice shortens the combustion duration but prolongs the ignition delay. • Double orifice is a strategy for optimizing ignition and combustion performance. Ammonia is a promising clean and carbon free fuel. The use of pre-chamber ignition technology is one of the effective ways to realize the application of ammonia in internal combustion engines. However, there is currently limited research on the coupling effects of pre-chamber structural parameters and initial parameters on jet, flame propagation, and combustion characteristics. Therefore, a visualization study on the effects of various parameters on ignition and combustion characteristics of ammonia/air has been conducted under high initial temperature and pressure. The results show that the large-volume pre-chamber can obtain higher maximum pressure rising rate and shorter combustion duration, but the ignition delay of the large-volume pre-chamber is long at low initial temperature, and increasing the initial temperature can reduce the ignition delay of the large-volume pre-chamber. In addition, a 1 mm orifice is unable to ignite the mixture. A 2 mm orifice has a longer ignition delay and a higher maximum pressure rise rate compared to 3 mm orifice. Therefore, an optimization strategy for the double orifice structure is proposed, so that both shorter ignition delay and higher maximum pressure rise rate are obtained.