Nitrogen oxide emission calculation for post-Panamax container ships by using engine operation power probability as weighting factor: A slow-steaming case

Abstract

In this study, the nitrogen oxide (NOx) emission factors and total NOx emissions of two groups of post-Panamax container ships operating on a long-term slow-steaming basis along Euro-Asian routes were calculated using both the probability density function of engine power levels and the NOx emission function. The main engines of the five sister ships in Group I satisfied the Tier I emission limit stipulated in MARPOL (International Convention for the Prevention of Pollution from Ships) Annex VI, and those in Group II satisfied the Tier II limit. The calculated NOx emission factors of the Group I and Group II ships were 14.73 and 17.85g/kWhr, respectively. The total NOx emissions of the Group II ships were determined to be 4.4% greater than those of the Group I ships. When the Tier II certification value was used to calculate the average total NOx emissions of Group II engines, the result was lower than the actual value by 21.9%. Although fuel consumption and carbon dioxide (CO2) emissions were increased by 1.76% because of slow steaming, the NOx emissions were markedly reduced by 17.2%. The proposed method is more effective and accurate than the NOx Technical Code 2008. Furthermore, it can be more appropriately applied to determine the NOx emissions of international shipping inventory.Implications: The usage of operating power probability density function of diesel engines as the weighting factor and the NOx emission function obtained from test bed for calculating NOx emissions is more accurate and practical. The proposed method is suitable for all types and purposes of diesel engines, irrespective of their operating power level. The method can be used to effectively determine the NOx emissions of international shipping and inventory applications and should be considered in determining the carbon tax to be imposed in the future.