Page 46: of Maritime Reporter Magazine (March 1999)

LUBRICANTS REPORT

CIMAC Studies Medium Speed Lubrication Issues

The Conseil International des

Machines a Combustion, better known as CIMAC, has tackled the issue of lubrication in its recent writings, specif- ically releasing two reports on the mat- ter: Guidelines for the lubrication of medium speed diesel engines and

Guidelines for the lubrication of two- stroke cross-head diesel engines. The following will address consumption of medium speed engines.

Usually, medium speed diesel engines are lubricated through a so-called "dry sump" system. This dry sump means that the oil charge, typically 1 to 1.3 kg/kW, is set in a tank external to the engine. With such an installation, the oil flow is so that the whole charge of oil is passing the engine every five to six minutes. Usually, the specific lube oil consumption is about 1 g/kWh. In fact, in today's diesel industry, there is a ten- dency to reduce both the quantity of oil in services as well as lube oil consump- tion.

Today, it is not unusual to see oil charge at 0+3 kg/kW and a specific lube on consumption as low as 0.2 g/kWh.

In such a condition, the whole charge is going through the engine every 1.5 to 2 minutes, and the replenishment by top- ping up may not be sufficient to main- tain proper condition of the oil.

The CIMAC Lubricant Working

Groups have studied this subject in depth by examining parameters impact- ing oil consumption, and they have found these to be: engine design and conditions; oil quality; fuel quality; oil system quality; operating conditions; service effect on BN depletion; system losses; system maintenance.

Under the above-mentioned eight con- ditions, it was found that the oil is sub- ject to degradation with the following key factors: osydative and thermal stresses of the oil; product of combus- tion; metallic particles as a result of con- trolled wear at ring/liner interface; scraps left in the engine during mainte- nance; water; and corrosion.

The Working Group issued recom- mendations to carefully follow oil con- ditions by particular monitoring of the oil quality.

CIMAC Lubricant Working Group is working closely with another interna- tional body, the CEC European Council of Coordination. This body is dealing with engines including lubricants and fuels. Within this organization, there is the Working Group CEC 1L047 on "Lubrication of large diesel industrial engines." At CIMAC's request they are studying particular problems.

Some of CIMAC's main concerns in this field deal with alkalinity reserve, viscosity and insolubles. The purpose of the alkalinity reserve is to protect the engine from attacks caused by the sulfur contents of the fuel. In service, this alkalinity reserve is depleting and comes theoretically to a stabilized level.

This document studies this phenome- non, and gives guidance about initial

BN, lube oil consumption, renewal rate if needed. The group's concerns sur-

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