Ultra Low Sulphur Fuel

Have you ever thought about marine fuel sulphur content and environmental impact of it?

January 1st 2020 MARPOL regulation came in force to minimise sulphur in marine fuels to 0,5% (previously 3,5%). It will reduce SOx pollution to the atmosphere – no doubts about it. Let’s look on the other side of the coin.

Sulphur itself is not a lubricant, but when combine with nickel they form lubricating films. When sulphur content in fuel is lower, it reduces lubricity of the fuel oil system components before it reaches combustion chamber in the engine. Maximum limit value of fuel lubricity is 520μm. Below this value fuel have ability to reduce friction between component surfaces reducing wearing process of the parts. Latest sample lab report, which I have opportunity to see, of fuel with less than 0,03% of sulphur indicates 552μm lubricity.

The simplest ship’s fuel system includes transfer pumps, HP (high pressure) pumps and injectors. More advanced system contains more components, but let’s focus on these ones only. Transfer pumps are running normally few minutes per day topping up settling tanks for daily usage. Their parts wearing progress and period between overhauls or downtimes might be difficult to proof relations to fuel oil sulphur content.

Let’s go deeper with HP pumps and injectors. Both are crucial components for engine power and efficiency. Lubrication drops, parts wearing raise, engine efficiency drop, fuel consumption raise which cause higher CO2 concentration in exhaust gases pollute the environment. HP pumps overhaul periods are between 12.000-20.000 running hours, depends on engine manufacturer and fuel type used in it. Due to the budget cuts, in many cases, it happens in upper limit of running hours. HP pump elements are manufactured as a pair (set of plunger and barrel) and cannot be mixed between different sets. It’s showing how precise those elements are and how crucial fuel oil lubricity is for their lifetime. Lack of lubrication can damage the surface between those two elements causing lower efficiency.

Fuel injectors supply fuel to combustion chamber where it’s mixed with oxygen and after ignition conversing it to power on the shaft of the engine. Lean mixture leads to lower engine efficiency, power lost, higher fuel consumption. Before new regulations I experience fuel injectors exchange, on four stroke medium size engines, every 4.000-6.000 running hours. Currently it is more often. Most of the time nozzles need to be replaced every 2.000 running hours. It might be due to fuel low lubricity. Just to be clear, this theory is not related to any of the laboratory tests or scientist publications.

These observations are just locally – on the vessel itself. Lack of sulphur reduce lubrication following shorter lifetime of the equipment.

So, let’s go further.

Shorter lifetime of the spare parts leads to more often unplanned maintenance, downtimes and what I would like to focus on, spare parts required to keep the engines running. Let the engine run for 24h, 365 days in the year. It will give 8.760 running hours per year. For better calculation let’s stick to 8.000 hrs. Instead of two exchange per year, there must be four – two times more when fuel with better lubricating properties were used. Engine manufacture needs to produce two times more spare parts which consume more energy, not always green. Those spare parts need to be delivered to the vessel by various types of transportation. Faulted parts need to be transfer to recycling facility. Most of them are not able to be reconditioned and reused, they need to be melted down and used to produce new ones. Yes, there are companies which perform their reconditions. All mentioned steps require additional energy and usage of fossil fuels which emit greenhouse gases, including sulphur oxides, to the atmosphere.

Lack of the sulphur content in marine fuels, reduce lubricating properties, causing faster wear of fuel oil system elements. Looking on the bigger picture, taking into account the whole supply, exchange and recycling or disposal process, to keep vessel fuel system in appropriate conditions, it might lead to bigger carbon footprint, when using ultra low sulphur fuels.

All above is not to deny changes made in MARPOL. Questions are: did anyone calculate carbon footprint and real impact to environment made by this change and maybe it is worth to implement minimum low level of sulphur in marine fuels or find other way to improve fuel lubricating properties.