Marine diesel engine lubricants

At present, most marine diesel engines use a single grade of cylinder lubricant almost regardless of the sulfur content of the fuel in use. Most diesel engines will cope with operating on their usual cylinder oil when burning fuels with sulfur content down to about 1%, which is the maximum sulfur content now allowed by the International Maritime Organization (IMO) for ships operating in Emission Control Areas (ECAs), and is also the limit applying in many inland markets. However, more sensitive engines may have to switch to a different cylinder oil when operating on low-sulfur fuel. In the marine context, this means that some ships may have to switch to a lower Base Number cylinder oil when entering ECAs for anything longer than a brief visit, or perhaps switch to one of the new “universal” grades of cylinder oil advocated by some lubricant suppliers.

Beyond 2015, even tighter sulfur limits from IMO both globally and in ECAs will probably mean that many ships will burn distillate fuel, rather than residual. This will almost certainly require a different type of cylinder oil from today’s widely-used 70 Base Number formulations. 

Liquefied Natural Gas (LNG) is increasingly seen as a viable alternative to conventional petroleum fuels to meet emission regulations.  LNG operation may call for different engine lubricants to those used with  residual fuel oil.  While lubricants for medium-speed engines operating on LNG are commercially available and well proven, thee is very little experience to date of operating low-speed engines on LNG.  New cylinder oil formulations will almost certainly be required for such engines.       

Liddy Associates can advise on the implications for lubricant selection of forthcoming regulations controlling fuel sulfur content, and can give guidance on how to monitor cylinder condition in diesel engines to ensure that the correct grade of cylinder lubricant is used.

Photo and schematic courtesey of MAN Diesel