Understanding oil stress in medium‑speed engines

There are three principal stresses that have an impact on the performance of four-stroke trunk-piston engine oils: acid stress, thermal stress and asphaltene stress. The level of oil stress in an engine depends on the operating conditions, the volume of oil that is available to absorb the stresses and the frequency with which the oil is changed.

Recent trends in the design and operation of four-stroke trunk-piston engines include higher-performing engine designs, a wider variety of operating conditions and lower-quality fuels of increasingly variable composition. Each of these changes can, if not correctly managed, contribute to increased oil stress, which has a direct influence on engine performance and operational costs. High oil stress can

  • reduce engine reliability
  • shorten oil life
  • shorten the life of your engine components
  • increase running costs.

Key to controlling oil stress is selecting a lubricant that offers the best all‑round stress management performance. Shell has used the knowledge gained from its research to develop the Shell Argina range of oils to address the challenges of acid, thermal and asphaltene stress.

Introducing the Shell Oil Life Extension Tool

Shell’s Oil Life Extension Tool uses oil stress theory to help customers who want to get the best out of Shell Argina or who are face significant challenges in the operation of their four-stroke trunk-piston engines.

Using a proven methodology, the Oil Life Extension Tool has applications across a wide range of marine settings and scenarios.

Experience gained in applying the Oil Life Extension Tool has shown that it can play a significant role in addressing the issues associated with oil stress and extending the oil-drain interval.

Benefits of the Oil Life Extension Tool

Oil stress levels are influenced by several factors, for example,

  • the power developed by the engine
  • the sulphur content of the fuel
  • the lubricating sump volume
  • the lubricating oil consumption rate.

Using values for these inputs in the Oil Life Extension Tool, Shell representatives can provide tailored lubrication advice on oil stress management in four-stroke trunk-piston engines. This helps engine operators to

  • select the grade of Shell Argina that matches the oil stress in their engines
  • achieve operational reliability
  • reduce lubrication costs
  • find greater peace of mind

When can the Oil Life Extension Tool help?

The Oil Life Extension Tool can help marine engine operators who

  • have problems maintaining the quality of their oil charge.
  • want to help ensure that they are minimising lubrication costs while maintaining the operational health of the engine.

How do operators use the oil life extension tool?

The oil change interval for trunk-piston engines is set by the equipment manufacturers’ recommendations on drain interval.

However, monitoring key indicators such as residual base number (BN) and viscosity through used oil analysis and setting the limits that trigger oil change can extend the interval. It is also known that the residual BN of an oil change in a trunk piston engine sump corresponds very closely to the build-up of oil stress factors at any given time. The Oil Life Extension Tool helps operators to identify the optimal oil-drain interval.

The Oil Life Extension Tool models the time-based decay of properties such as oil charge residual BN to assess and compare the lubrication costs of possible oil replenishment strategies over a year or more of engine operation. The options that can be modelled include

  • selecting different Shell Argina grades to predict their effect on the oil-drain interval
  • conducting complete oil changes once safe limits are triggered
  • conducting partial oil changes
  • using sweetening (draining and replenishment of small, calculated
  • amounts of oil charge at specified intervals) to delay full or partial oil changes.

The Shell Oil Life Extension Tool can help you to get the best out of Shell Argina or meet the challenges of operating your four-stroke trunk-piston engines.

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