Assigning machinery power values for estimating ship exhaust emissions: Comparison of auxiliary power schemes

While ship exhaust emissions can be calculated at both large scales and fine resolutions due to the availability of activity data from the Automatic Identification System, there are still uncertainties in the assignment of ship engine and boiler power, which then leads to uncertainties in the estimated emissions. Reliable information is usually available for main engines, including engine type and installed power, and physical models exist for estimating propulsive power requirements. However, similar models are not available for estimating auxiliary power requirements. This study examines methods for calculating the actual operating power of auxiliary engines and auxiliary boilers. Earlier approaches assumed that installed auxiliary engine power increased in proportion to installed main engine power. Auxiliary-to-main engine power ratios were specified by ship type, and load factors were specified by ship type and operating mode. Auxiliary boiler power was generally not differentiated by ship size. More recent approaches are based on extensive ship survey data, and give tables of auxiliary engine and auxiliary boiler power binned against ship type, ship size and operating mode. These surveys show that auxiliary power does not necessarily increase with ship size or main engine power. A revised approach based on the recent data sources is adopted and applied to a case study of four ports in southeast Australia. The revised approach is informed by a local survey of ships to investigate auxiliary power demand. Comparisons are made of the impact of the different approaches on the magnitude and spatial distribution of the emissions.