Optical Research on Ammonia Combustion Enhancement via Gasoline Jet Ignition Generated by an Active Pre-Chamber

Ammonia is being intensively investigated due to its potential for lifecycle carbon neutrality and favorable storage and transport properties. However, its application in internal combustion engines faces critical challenges in achieving reliable ignition and rapid combustion, primarily due to high auto-ignition temperature and slow flame propagation speed. Pre-chamber turbulent jet ignition using gasoline demonstrates significant potential for enhancing ammonia combustion performance. This study employs visualization experiments in a constant volume combustion chamber to analyze the ignition and combustion processes of ammonia ignited by gasoline-fueled pre-chamber. Compared to conventional spark plug ignition, pre-chamber technology significantly reduces ignition moment and combustion duration, demonstrating superior ignition capability and accelerated combustion performance. Compared with the cases with 1.5% and 2.0% gasoline energy ratios, the 1.0% and 2.5% gasoline energy ratios are both unfavorable for the formation of thermally active jets with strong ignition capability, leading to a longer establishment of ignition moment and combustion duration in the main chamber. The condition with a 2.0% gasoline energy proportion exhibits the best rapid combustion performance, with the combustion duration reduced by 8.3% compared to the 2.5% condition. Under the 3.0 mm orifice condition, the jet velocity of thermally active material is the highest, and the combustion duration is the shortest – 20.3% shorter than that under the 6.0 mm condition. However, the 3.0 mm condition shows the weakest ignition capability, with ignition moment of 20.8 ms, more than 2.5 times that of other conditions. A higher initial temperature helps shorten both the ignition moment and combustion duration. This study aims to provide valuable insights into rapid combustion technologies for ammonia-fueled internal combustion engines, offering a new decarbonization approach for hard-to-abate transport sectors such as shipping.