An analysis of the energy efficiency of LNG ships powering options using the EEDI

This paper presents analyses future powering options for LNG carriers when considering the Energy Efficiency Design Index (EEDI). The IMO has recently approved amendments to MARPOL Annex 6 to extend the application of the EEDI to include LNG Carriers (LNGCs). This paper investigates the impacts of this upcoming EEDI regulation, due to be enforced from September 2015, will have on the design of future LNGCs. The study found that the current EEDI reference baseline is insufficient to stimulate improvements in the design of future LNGCs because the current Dual Fuel Diesel Electric (DFDE) propulsion proposed to be installed on majority of future LNGCs orders already achieves EEDI values that are compliant with the EEDI baseline. Analysis of EEDI values for LNGCs employing the new two-stroke gas injection diesel propulsion system also displayed similar results. However when considering unburnt methane emissions of the DFDE it was seen that the GHG emission index value could potentially rise by up to 115% meaning the EEDI is limited in its value to reduce global warming. This paper also proposes and analyses amendments to the EEDI baseline values for LNGCs as well as suggesting methods to include methane slip emissions into the current EEDI calculations. •The DFDEs offer the lowest emission index of the three propulsion systems currently in use.•The more efficient DFDEs fall way below the current IMO baseline value.•The current baseline would not appear to instigate improvements in technology for future designs of LNGCs.•The gas injection engines currently on order ordered offer a 30% improvement in EEDI values.•When methane slip is considered and analysed the efficiency gains of the DFDEs are eroded.