Comparing modelled and measured exhaust gas components from two LNG-powered ships

Mikko Heikkilä*, Niina Kuittinen, Tiia Grönholm

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Bottom-up modelling is used frequently to estimate emissions produced by seagoing vessels, and the accuracy of modelling is dependent on the data the model is trained with. Observational studies can be used to increase the model accuracy. Here we compared data from two measuring campaigns conducted on board ships that use Liquefied Natural Gas (LNG) as primary fuel in internal combustion engines (ICE) in a diesel-electric setup with values obtained from the Ship Traffic Emission Assessment Model (STEAM). The power demand for propulsion calculated using Automatic Identification System (AIS) data matched observations reasonably. The root mean square error between the modelled and observed power demand was 759–914 kW (28.6–34.5%) for the measured ropax vessel and 1869–1916 kW (16.7–17.1%) for the large cruise vessel over four voyages while the ships were underway. The discrepancy is largely explained by the auxiliary power demand, which was 4 times higher on the large cruise vessel than the model prediction. Using meteorological data to estimate the increase of resistance did not improve the goodness of fit between modelled and observed engine power demand. STEAM model's base-specific fuel consumption calculation method fits observed values reasonably when the engine load is over 50%, but ICEs used in constant speed mode have increased consumption at lower engine loads compared to variable speed ICEs. The share of pilot fuel of total energy consumption was found to play a significant role in the emission factors for measured exhaust gas compounds. More accurate functions to model fuel consumption and emissions were derived using the observed data.

Original languageEnglish
Article number100275
JournalAtmospheric Environment: X
Volume23
DOIs
Publication statusPublished - Aug 2024
MoE publication typeA1 Journal article-refereed

Funding

This research is a part of the European Union project GREEN RAY which has received funding from the European Union's Horizon 2020 \u2013 Research and Innovation Framework Programme action under grant agreement No 101056642.

Keywords

  • Liquefied natural gas
  • Modelling
  • Shipping emissions

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