The effects of ammonia-methanol blending versus co-fuelling in a lean burn spark ignition engine

Ammonia has emerged as a promising renewable fuel for internal combustion engines; however, its adoption is hindered by inherent drawbacks such as high ignition energy, low burning velocities, narrow flammability range, and toxicity. Emulsifying ammonia with methanol provides a possible strategy to address these challenges and potentially improve fuel handling by maintaining the fuel in a bulk liquid state. Since emulsification may affect physicochemical properties in an unpredictable manner (even compared to co-fuelling of pure methanol and ammonia), detailed combustion analysis is a critical step towards any practical application. Employing chilled fuel storage to dissolve larger ammonia fractions (>30 %) in methanol could also help achieve improved mono-fuel operation without the need for multiple fuel storage and handling systems. The work reported here concerned an experimental investigation of the impact of ammonia–methanol emulsions on combustion, performance, and emissions in a lean-burn Spark Ignition (SI) engine. Experiments were conducted on an externally boosted thermodynamic single cylinder SI engine operated under four fuelling modes: i) pure ammonia, ii) pure methanol, iii) pure ammonia/pure methanol co-fuelling, and iv) ammonia–methanol emulsion. Results revealed that both the emulsion and co-fuelling modes achieve comparable lean-burn combustion and stability limits, with similar peak combustion pressure and pressure rise rate. Engine-out NOx emissions showed a non-linear dependence on ammonia content, with the 10 % ammonia case producing the highest NOx despite a relatively low substitution ratio. Both combustion modes exhibited similar indicated thermal efficiency (>35 %) at mid- load across all tested conditions, suggesting that the emulsion can serve as a practical single-fuel alternative with a lower carbon content than pure methanol.