Marine engine oils have evolved significantly the past couple years due to implementation of the IMO 2020 fuel regulations. Panelists at a recent shipping industry webinar said the trend should continue in coming years as fuels used by ocean-going vessels keep evolving.
Like many other industries, the shipping industry is grappling with demands that reduce levels of pollution that it generates. While greenhouse gas emissions hold most of the world’s attention, the IMO 2020 regulation implemented last year by Marpol, International Convention for the Prevention of Pollution from Ships, focused on sulfur dioxide, which can harm human respiratory systems and contributes to acid rain.
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IMO 2020 required ships operating in most ocean waters to be equipped with exhaust scrubbers that caption SO2 or to use fuel with no more than 0.5% sulfur – much less than the previous limit of 3.5%. Operators of ships without scrubbers could choose from three categories of fuel – very-low-sulfur fuel oil, distillates such as vacuum gas oil or liquid natural gas.
Cylinder oils that lubricate large marine engines are mixed with fuel, so the different categories of fuel exert different formulation requirements for oils, as explained by Total Lubmarine Technical Director Nikolaos Kotakis June 8 in a webinar hosted by Riviera Maritime Media and titled, “Four-stroke lubrication options post-IMO 2020.”
One of the main differences is the base number of the oil formulation, which represents its ability to neutralize acids formed in the cylinder environment. Very-low-sulfur fuel oil requires a base number between 20 and 30, while marine diesel oil or gas oil require base number of only 12-15 and LNG just 4-7. Scrubber-equipped vessels that continue to use high or intermediate sulfur fuel oils require cylinder oils with base number of 30-55, Kotakis said.
During the first year of IMO 2020, 59% of vessels used very-low-sulfur fuel oil, while 31% used distillates and 2% opted for ultra-low-sulfur fuel oil, said Ram Vis, CEO of consulting firm Viswa. Eight percent ran on high-sulfur fuel oil, but that portion should rise to 11% as scrubbers are installed on more ships.
Lubricant requirements can vary even within the main fuel categories, Vis added. For example, very-low-sulfur fuel oils made from crude oils that are high in aromatic molecules tend to have higher levels of asphaltenes, which generate soot, leading to formation of slude and sediments that can choke fuel purifiers. On the other hand, very-low-sulfur fuel oils made from paraffinic crudes tend to have higher Estimated Cetane Numbers, which can increase the likelihood of damage to pistons and ring packs, leading to increased blowby.
Fuel oils from paraffinic sources are also more susceptible to microbial and fungal contamination when stored for more than six months, particularly in high-moisture environments. This contamination causes other problems for the fuel-lubricant mix.
Formulas are still developing in other ways as lubricant companies seek to optimize performance, Vis said. A growing number of products are being blended with API Group II base stocks instead of Group I as suppliers seek the greater oxidative stability that comes from higher portions of saturated molecules.
“Of course, the additive package needs to change as the base stock changes,” he noted. Chemical additives account for 30% of cylinder oils by volume, compared to 70% for base stocks.
The shipping industry is also facing demands to reduce carbon dioxide emissions, and these could bring additional requirements for marine lubricants. Marpol this month will consider a proposal to phase in fuel economy mandates beginning later this decade, and lubricant formulators are already working on products that could help.
Kotakis said Total Lubmarine began five years ago to develop a product that employs a new detergent mix and new friction modifier chemistry. It has not yet been approved by engine original equipment manufacturers, but Kotakis said field trials demonstrated that it can boost fuel economy by 4.7%.