Ship fuel consumption and emissions during low load manoeuvring conditions

Ship engine loading typically follows the propeller law, with fuel consumption models primarily using engine load as a predictor. However, this study highlights the limitations of propeller laws in accurately representing engine behaviour in port and coastal areas under transient operational conditions (e.g. manoeuvring/running under partial loading at slower speeds). This study presents a comparative analysis of on-board ship measurements and a laboratory study using a testbed diesel engine operating under a custom-designed propeller law transient cycle. Results indicate that the test engine’s measured load profile lagged during acceleration and led during deceleration, with this effect intensifying at higher ramp rates. Brake-specific fuel consumption (BSFC) peaked at low loads and decreased at higher loads in departure/arrival scenarios, highlighting the critical role of engine speed under partial loading in operational safety, asset life, and emissions. Additionally, ship EFs (g/kg of fuel) were disproportionately high at low operating loads under partial loading, reflecting increased fuel-specific emissions due to unstable operating conditions. Particle number (PN) and particulate mass (PM 1 ) EFs are over-estimation at loads <5% and <4% respectively, and underestimation for loads >5% and >4%, respectively. Low load (≤20%) correction factors overestimate NO x , CO, and PM 1 at <5% load. Above 5% load, NO x is underestimated but aligns during approaching to Port of Gladstone (POGL). CO is overestimated leaving Port of Brisbane (POB) but aligns during approaching to POGL. Testbed findings of emissions for different ramps match modelled low load correction factor values, though deceleration EFs (during 8-15% load) exceed predictions. At ≤10% load for both acceleration and deceleration states, the low load correction factors differ significantly; at higher loads, they align with the modelled predictions. Testbed engine results align with standard low load correction factors through transient cycle studies, highlighting the need to account for partial loading and dynamic conditions in emission estimates. With the aid of the propeller law drive cycle, the ship activity during the port manoeuvring demonstrated in a testbed engine. Testbed responses under acceleration-deceleration transient run, identified significance differences in specific emissions, and this study bridges a key gap in emission modelling with real-world data and empirical models. • Traditional propeller laws may misrepresent ship engine emissions in ports and coastal areas. • Measured high load (>5%) NOx/CO/PM correction factors align with emission inventory values. • Measured low load (<5%) NOx/CO/PM correction factors well below fleet emission inventory values. • Significant load profile, fuel consumption and emissions differences during acceleration and deceleration • Engine load lags during acceleration and leads during deceleration • Higher specific fuel consumption at low loads, lower at high loads