Effect of Sulphur Content on Bunker Fuels Performance in the Medium-Speed Engine

Sulphur limit of bunkers for ships operating inside existing four Sulphur Emission Control Areas (SECA), the Baltic Sea, the North Sea, the North American, and the United States Caribbean Sea ECA, is 0.1 mass-%. The sulphur limit outside SECAs is currently 3.5 mass-% decreasing to 0.5 mass-% on January 1st 2020. The ship owners have choices to use bunkers that complies the sulphur limits, use alternative low sulphur fuels like natural gas, or to invest on exhaust gas scrubber systems. Thus, it is predicted that starting from 2020 the variety of bunker fuels will be increasing. As heavier bunkers which comply with the tightening sulphur limits are looked for to be used as alternative to scrubbers or distillates, knowledge of performance of different fuels with reduced sulphur content in ship engines is needed. For this reason, Neste decided to test contemporary and possible future marine fuels: fuel oil based products containing 0.1 mass-% sulphur and 0.5 mass-% sulphur were tested in a medium speed engine. A commercial low sulphur marine diesel oil, Neste DMB, was used as a reference fuel containing max 0.1 mass-% of sulphur. All products were produced using components from Neste refineries. The test engine was Wärtsilä Vasa 4R32 (cylinder diameter: 320 mm, speed: 750 rpm, brake power: 1640 kW) connected to the braking generator at VTT's laboratory. The steady test cycle consisted of five loads between 90% and 10% of rated power. The engine was run from 16 to 18 hours with each fuel during the tests. Engine performance (brake power, fuel consumption, intake air mass flow, turbocharger speed, etc.) together with gaseous (NOx, CO, THC, O2, and CO2), particulate matter (PM), and smoke (FSN) emissions were measured. Exhaust gas SO2 concentrations were determined with FTIR (Fourier-transform infrared) device. PM emissions were determined using partial flow diluting method according to ISO 8178:2006. Each cylinder was equipped with in-cylinder pressure measurement for combustion analyses. Specific emissions of measured components, and engine efficiency were calculated for each fuel and load step. Rate of heat release curves were drawn, and cylinder balancing was rated by indicated power according to in-cylinder pressure data.