Analyzing the Carbon Footprint of an LNG Tanker Using Real Operational Data: Quantifying Methane Slip Effects

This paper presents an exploratory operational assessment of the carbon footprint of an LNG tanker using real operational data collected by a continuous emission monitoring system over a ten-month period of vessel operation. The analysis included carbon dioxide (CO2) and methane (CH4) emissions from the main engines and diesel generators, the calculation of CO2-equivalent using the GWP100 and GWP20 global warming potential factors, and a comparison with a hypothetical heavy fuel oil (HFO) operating scenario. The methodology is based on a Tier III approach, that is, on real operational data, which allows a more realistic assessment of emissions than approaches based on standard emission factors. The results show that CO2 emissions make up the largest share of total emissions, but including methane emissions significantly increases the ship’s overall climate impact. Total methane slip was 3.62%, with diesel generators exhibiting higher slip than the main engines. When GWP20 was applied, total emissions expressed as CO2-equivalent were, in some periods, comparable to or higher than those estimated for the HFO scenario, despite lower direct CO2 emissions. The emission distribution indicated that the main engines dominated CO2 emissions, while methane emissions were more evenly distributed between the main engines and the auxiliary generators, with generators making a significant contribution to total CO2-equivalent emissions due to their higher methane slip. The results confirm that any assessment of the climate performance of LNG-fueled operation must include methane emissions and should be based on real operational data; otherwise, the overall climate impact may be underestimated.