NOx emission reduction in tugboats with SCR systems: Real-world impact of AdBlue

• Real-world NOx and CO emissions on tugboats under dynamic load conditions. • SCR with AdBlue reduced NOx by over 60 % during short maneuvers. • Increased CO emissions observed as a trade-off during load transitions. • Annual NOx reduced by nearly 50 % using SCR systems in harbor operations. • Study offers field-based insights into tugboat emissions and SCR performance.. This study evaluates the real-world performance of a Selective Catalytic Reduction (SCR) system with AdBlue injection on a tugboat operating at Mersin Port, Turkey. The objective was to assess SCR effectiveness in reducing nitrogen oxides (NOx) under dynamic load conditions. Emission measurements were conducted on two main engines: one with SCR inactive (portside) and the other with it active (starboard). Under SCR passive conditions, the portside engine emitted 654.4 ppm NOx and 384.9 ppm CO on average. In contrast, the SCR-active engine achieved NOx reductions of 60.1 % during short maneuvers and 50.1 % during long maneuvers, while CO emissions increased by 83.8 %, indicating the NOx–CO trade-off. SCR performed best under stable loads and optimal exhaust temperatures (250–400 °C), while lower loads reduced its efficiency and required more AdBlue. Annual NOx emissions were reduced from 282.47 tons (SCR passive) to 99.31 tons (SCR active – short) and 139.83 tons (SCR active – long). These results highlight SCR’s effectiveness in marine applications and the importance of optimized AdBlue dosing. Adaptive injection strategies based on real-time exhaust conditions may further improve performance and minimize consumption, supporting regulatory efforts for cleaner port operations.