Greater flexibility in cylinder lubrication delivery required for two-stroke engines

March 2021

By Dr Rathesan Ravendran

The shipping industry’s ambitions for reducing CO2 emission are likely to follow several technological pathways, so a more flexible and modular lubrication system is now available, says Dr Rathesan Ravendran, Technology and Innovation Specialist at Hans Jensen Lubricators.

There is a paradigm shift underway that aims to make the maritime industry more environmentally friendly. As part of this, the drive towards higher efficiency has led to design changes in slow speed two-stroke marine diesel engines, the most significant being the application of the electronical-controlled, supercharged and long-stroke engine, which allows more flexible usage and higher combustion pressure.

These changes in engine design as well as the way engines are being run have led to challenges when it comes to cylinder condition and lubrication, because the lubrication systems and methods delivering cylinder oil to lubricate piston rings and cylinder liner have remained largely unchanged.

Lubrication challenges with low sulphur fuels

A large majority of the vessels made the transition to low-sulphur fuel well. However, as anticipated, a number of issues was observed on several vessels. High cylinder liner and piston ring wear, severe scuffing, heavy deposits and piston rings sticking leading to heavy blow-by/ring breakage, were some of the issues occurring just a few days after changing over.

The lower lubricity of low sulphur fuels has been made up for by cylinder lubrication oil, distributed correctly on the cylinder liner. Using a low 15-40 BN cylinder oil is currently the most widespread countermeasure adopted. However, using low BN oils creates new and other challenges, since the cleaning ability of the cylinder oil is not sufficient to keep the cylinder and piston clear of deposits, which potentially can lead to increased wear, bore polishing and scuffing.