Optical multi-spark ammonia combustion engine: numerical analysis and validation

Ammonia (NH₃) stands out as a promising candidate for fueling internal combustion engines, owing to its high hydrogen content and well-established production and transport infrastructure. Nevertheless, its inherently low flame speed and reactivity pose a significant challenge to achieving rapid and complete combustion. One potential solution is the use of multi-spark ignition, wherein multiple spark plugs distribute ignition sites throughout the combustion chamber, thereby accelerating flame propagation across the entire charge. In this study, a three-dimensional 3D-CFD model of multi-spark, spark-ignited NH₃ internal combustion engine is developed and validated using optical engine experiments. The optical data provide critical insights into early flame kernel development, guiding refinements to two combustion submodels (SAGE and G-equation). Results underscore the importance of sufficiently refined mesh resolution—particularly near the spark plugs—and the incorporation of detailed spark plug geometries to accurately capture the early stages of ignition in low-reactivity fuels such as NH₃. Overall, the close qualitative agreement between measured flame luminosity and simulated flame evolution demonstrates the robustness of the proposed CFD framework.