Comparative analysis of injection rate and spray characteristics of ammonia and diesel from multi-hole diesel injector

• Ammonia has a higher injection quantity and discharge coefficient than diesel. • Ammonia shows a larger spray angle and lower penetration rate than diesel. • Flash boiling amplifies the differences in ammonia and diesel spray structure. • Ammonia and diesel spray can be predicted and scaled using Naber & Siebers model. Ammonia is attracting attention as an alternative fuel for internal combustion engines to achieve carbon neutrality. For marine engines, ammonia has been introduced as the primary fuel in ammonia/diesel dual-fuel engines, with diesel acting as a pilot fuel for ignition. In dual-fuel engines, the ratio of ammonia to diesel injection amount and the spatial distribution of each fuel’s spray dominate ignition and combustion characteristics. A detailed analysis and comparison of the fuel injection rate and spray characteristics of ammonia and diesel are necessary to establish injection strategies for optimized engine combustion. In the first stage of this study, the transient injection rate characteristics of ammonia and diesel injected from an 8-hole diesel injector are compared using a Bosch long-tube injection rate meter. The results showed that ammonia had a 0.016 ms advanced start-of-injection timing but a 0.6 ms delayed end-of-injection timing compared to diesel. A quasi-steady Injection rate of ammonia is higher than diesel due to 0.22 higher flow discharge coefficients. The ammonia spray has a 4.78° larger spray angle and a lower penetration rate than that of diesel. The spray penetration of ammonia was longer in the early stage but was overtaken by that of diesel later. The mechanisms behind these results were discussed based on fuel properties. It was further found that the spray penetration of ammonia and diesel can be scaled and predicted based on a conventional momentum-conservation-based spray penetration model.