Comparison of Ignition Modes to Enable Ammonia Combustion Engines: Dual Fuel, Multi-Spark and Pre-Chamber

This study presents a CFD-based evaluation of ignition strategies for enabling ammonia combustion in a light-duty internal combustion engine. The model was first validated against experimental data for both pure ammonia spark ignition and dual-fuel ammonia-diesel compression ignition cases. Upon validation, three ignition strategies were investigated: dual-fuel compression ignition with sixty percent ammonia energy fraction, and multi-spark and passive pre-chamber ignition under stoichiometric conditions. Simulations were used to assess combustion phasing, efficiency, and emissions characteristics. The dual-fuel mode enabled stable ignition but resulted in incomplete combustion, with three-dimensional contours revealing that central regions of the chamber remained largely unburned, contributing to high ammonia slip and highlighting the need for further optimization of spray targeting and combustion chamber design. The multi-spark strategy achieved the highest efficiency through rapid and distributed flame propagation but introduced significant system complexity and high nitrogen oxide emissions. The passive pre-chamber configuration produced the lowest nitrogen oxide emissions but suffered from weak ignition and high ammonia slip. An active hydrogen-enriched pre-chamber was explored to improve upon the passive configuration, increasing indicated thermal efficiency from 34.8 to 42.7 percent, advancing combustion phasing, and reducing ammonia slip by over 90 percent.