ICCT paper: Newer marine engines have ‘significantly higher’ emission rates than older engines

The International Council on Clean Transportation on Wednesday (11 October) released a new working paper that analysed 615 samples of real-world NOx emissions from 545 ships operating in Danish waters between the North Sea and the Baltic Sea in 2019. 

Measurements for the Real-world NOX emissions from ships and implications for future regulations working paper were obtained using sniffers attached to helicopters flown into exhaust plumes. The data includes measurements from ships covering all engine age categories (tiers).

The results were eye-opening: Newer Tier II engines had significantly higher NOx emission rates than older Tier I engines. Moreover, there was no statistical difference in NOx emission rates between unregulated Tier 0 engines and Tier II engines.

The greatest mean NOx emission rates were found at main engine loads below 25%, with emissions averaging 12 g/kWh across all vessel types and engine tiers. Emission rates decrease as main engine loads increase, with mean emission rates of 8.1 g/kWh at loads greater than 75%. Existing NOx test cycles assume that marine engines most often operate at higher engine loads; however, this study finds that engines typically operate at lower engine loads.

NOx regulations could be revised to make them more effective at reducing air pollution. Rather than relying on weighted emissions limits, the International Maritime Organization could consider implementing not-to-exceed (NTE) standards for new and existing ships, particularly focusing on operations at low loads, and including a test point below 25% load.

Note: The full Real-world NOX emissions from ships and implications for future regulations can be downloaded here.

Photo credit: International Council on Clean Transportation
Published: 13 October, 2023