Comparative visualization study of turbulent jet ignition for zero carbon ammonia-hydrogen pre-chamber engines: focus on pre-chamber parameters optimization and hydrogen blending ratio

Abstract

Ammonia, a carbon-free fuel, holds significant potential for clean combustion applications, but challenges like ignition difficulties and slow combustion rates limit its practical use. This study aims to improve the ignition and combustion of ammonia-hydrogen mixtures using turbulent jet ignition, with experiments conducted in an optical constant volume combustion chamber. The investigation focuses on optimizing three key parameters: the equivalence ratio of hydrogen injected into the pre-chamber (Φp,h), the pre-chamber nozzle diameter (DN), and the volume ratio of hydrogen mixed in the main chamber (VH). Results indicate that adjusting Φp,h and DN can significantly increase ignition energy, leading to a stronger hot jet flame and a faster combustion process. A DN of 3 mm achieves a balance between ignition stability and combustion duration, while a larger DN (4 mm) reduces pressure buildup, resulting in slower flame ejection. In contrast, a smaller DN (2 mm) extends ignition delay due to re-ignition effects. Increasing VH to 0.1 shortens ignition delay by 7.6 % and reduces combustion duration by 10.4 %. The optimal configuration—DN = 3 mm, Φp,h = 1.0, and VH = 0.1—achieves an 80.7 % reduction in ignition delay and a 35.0 % decrease in combustion duration compared to the passive pre-chamber.