I Wayan Warsita  Ocktaeck Lim

Vol. 31,  No. 4, pp. 346-354, Dec.  2025
10.7464/ksct.2025.31.4.346

Ammonia combustion Engine performance Multicoil spark ignition RCEM Zero carbon fuel

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Ammonia (NH3) is a promising carbon-free fuel, but its adoption in spark-ignition engines is hindered by a low laminar flame speed and high ignition energy requirement. This study investigates a multi-coil ignition strategy to overcome these combustion challenges in a direct-injection ammonia engine. Through CFD simulations of a Rapid Compression Expansion Machine (RCEM), the impact of increased spark energy on combustion and emissions was analyzed. The results demonstrate that the multi-coil system transforms the combustion process by generating a larger, more robust initial flame kernel. This is critical for stabilizing the flame and leads to a peak in-cylinder pressure of 5.22 MPa, which is significantly higher than conventional single-coil ignition. Consequently, indicated thermal efficiency and engine power output are substantially improved due to a more complete and accelerated combustion event. However, the higher combustion temperatures responsible for these performance gains also result in a substantial increase in nitrogen oxide (NOx) emissions. The analysis reveals that a 3 ms spark duration offers an optimal balance, minimizing NOx production without compromising combustion quality. This work concludes that a multi-coil ignition system offers a practical and effective pathway for adapting conventional engines to ammonia operation, providing a key engineering solution to the combustion limitations of this zero-carbon fuel.