Ammonia (NH3) is an emerging carbon-free fuel with the potential to
decarbonize the energy sector. However, its widespread adoption is hindered by
challenges like low flame speed, high ignition energy, elevated emissions of
nitrogen oxides (NOx), and unburned NH3. These limitations
necessitate innovative combustion strategies for efficient and stable engine
operation. This study investigates the potential of turbulent jet ignition (TJI)
to overcome these challenges through the implementation of a pre-chamber, a
small auxiliary chamber equipped with a spark plug to create hot, reactive jets
that propagate into the main chamber, promoting rapid combustion from
distributed ignition sites. In this work, TJI operation is compared to
conventional spark ignition (SI) in a diesel engine platform retrofitted for
100% ammonia operation. Experiments were conducted at 1200 and 1800 RPM across
varying loads (25%, 50%, 75%, and 100%) with equivalence ratio and spark timing
sweeps. Combustion performance, stability, and emissions (NH3, NOx,
and N2O) for both ignition systems were compared. Results demonstrate
that TJI significantly improves combustion stability, with the coefficient of
variation in indicated mean effective pressure reduced by over 50% compared to
SI at part loads. Additionally, TJI allowed operation with retarded spark
timing. Emissions analysis revealed comparable NOx levels but reduced unburned
NH3 and N2O emissions in TJI mode. These findings
highlight the ability of turbulent jet ignition to address the inherent
challenges of ammonia combustion, providing a pathway for its integration into
practical engines. Future work will focus on optimizing pre-chamber design to
further improve combustion efficiency and explore emissions control strategies
for broader applications.