Definition

Specific Cylinder Lubricating Oil Consumption (SCLOC) is the quantity of cylinder lubricating oil consumed by the engine to produce a unit of power over a specified period.

It is normally expressed in:

g/kWh (grams per kilowatt-hour).

SCLOC is an important parameter for assessing the effectiveness and efficiency of the cylinder lubrication system. It helps ensure that sufficient oil is supplied for proper lubrication and acid neutralization without causing excessive cylinder oil consumption.

Formula and Derivation

Let:

• m_oil = cylinder oil consumption, kg/h
• P = engine brake power, kW

The specific cylinder oil consumption is the oil consumed per unit of engine power:

$$SCLOC=\frac{\dot{m}_{oil}}{P}$$

Since the above value is in kg/kWh, it is converted into g/kWh by multiplying by 1000:

$$SCLOC=\frac{\dot{m}_{oil}\times1000}{P}$$

Therefore:

$$\boxed{SCLOC=\frac{\dot{m}_{oil}\times1000}{P}\ g/kWh}$$

When Oil Consumption Is Measured Over a Period

If cylinder oil consumption is measured over a specific period:

• M = mass of cylinder oil consumed during the period, kg
• P_avg = average engine power during the period, kW
• t = operating time, h

The total energy produced during the period is:

$$Energy=P_{avg}\times t$$

Therefore:

$$SCLOC=\frac{M}{P_{avg}\times t}$$

Converting kg to grams:

$$SCLOC=\frac{M\times1000}{P_{avg}\times t}\ g/kWh$$

Hence:

$$\boxed{SCLOC=\frac{M\times1000}{P_{avg}\times t}\ g/kWh}$$

If Cylinder Oil Is Measured by Volume

If cylinder oil consumption is measured in litres:

• (V) = cylinder oil volume consumed, litres
• (\rho) = cylinder oil density, kg/L

The mass of oil consumed is:

$$M=V\times\rho$$

Therefore:

$$SCLOC=\frac{V\times\rho\times1000}{P_{avg}\times t}\ g/kWh$$

Hence:

$$\boxed{SCLOC=\frac{V\times\rho\times1000}{P_{avg}\times t}\ g/kWh}$$

Onboard Procedure to Optimize Engine Operation

The following procedures are normally adopted onboard to achieve and maintain the optimum SCLOC:

1. Determine the actual cylinder oil consumption by monitoring cylinder-oil tank levels, measuring oil flow, or using the flow/consumption data provided by the cylinder lubrication system.
2. Calculate the actual SCLOC using the quantity of cylinder oil consumed and the engine's average power output.
3. Compare the calculated SCLOC with the cylinder oil feed rate or consumption recommended by the engine manufacturer.
4. Check cylinder lubrication at different engine loads, because the optimum cylinder oil feed rate depends on engine load and other operating conditions.
5. Adjust the cylinder oil feed rate according to engine load and speed using the electronic or mechanical cylinder lubrication system, as fitted.
6. Ensure correct timing of cylinder oil injection. Oil should be injected at the correct crank angle and piston position as specified by the engine manufacturer.
7. Regularly inspect cylinder liners and piston rings for excessive wear, scuffing, corrosion, deposits or other abnormal conditions.
8. Carry out scrape-down oil analysis to monitor the condition of the cylinders. Important parameters include:
   • Iron content
   • Residual BN (Base Number)
   • Wear indicators
   • Signs of corrosive wear
9. Adjust the cylinder oil feed rate based on actual condition monitoring, including scrape-down oil analysis, cylinder liner and piston-ring condition, fuel sulphur content and engine load.

The objective should not simply be to reduce cylinder oil consumption. The feed rate should be optimized to maintain adequate lubrication and acid neutralization while avoiding unnecessary oil consumption.

Factors Affecting SCLOC

1. Engine Load

Engine load has a significant effect on cylinder lubrication requirements. Low-load operation generally requires different lubrication settings from high-load operation, and the cylinder oil feed rate should be adjusted accordingly.

2. Engine Speed

Engine speed affects the number and timing of cylinder lubrication events and therefore influences the quantity and distribution of cylinder oil supplied to the cylinder liner.

3. Cylinder Oil BN

The Base Number (BN) of the cylinder oil must be suitable for the fuel being used. Adequate BN is required to neutralize the acidic products formed during combustion.

4. Fuel Sulphur Content

Higher fuel sulphur content can produce more acidic combustion products. Therefore, adequate alkaline cylinder lubrication is required to neutralize these acids and prevent corrosive wear.

5. Cylinder Liner Condition

The condition of the cylinder liner, including its wear, honing condition and surface temperature, affects the quantity of oil required for effective lubrication.

6. Piston-Ring Condition

Worn, damaged or sticking piston rings can increase oil consumption and cylinder wear. Proper piston-ring condition is therefore essential for maintaining optimum SCLOC.

7. Cylinder Liner Temperature

Excessive liner temperature can promote oil degradation and deposit formation, affecting lubrication quality and cylinder oil consumption.

8. Lubricator Condition and Calibration

The condition and correct calibration of the cylinder lubricator are important. Faulty lubricator pumps, quills, non-return valves or associated components can result in incorrect or uneven cylinder oil delivery.

9. Engine Condition and Combustion Quality

Poor combustion can increase carbon deposits, corrosive wear and abnormal cylinder conditions, which may increase the cylinder oil requirement.

Methods of Monitoring and Adjustment

1. Cylinder Oil Flow and Consumption Monitoring

Regularly record cylinder-oil tank levels or use a flowmeter/flow-monitoring system to determine the actual cylinder oil consumption.

The measured consumption is then used together with engine power output and operating hours to calculate SCLOC.

2. Scrape-Down Oil Analysis

Samples of scrape-down oil are analysed for:

• Iron content
• Residual BN
• Other wear and combustion indicators

A high iron content may indicate increased cylinder liner or piston-ring wear. Excessive residual BN may indicate that more alkaline oil is being supplied than required and may therefore indicate over-lubrication.

3. Cylinder Inspection

Regularly inspect the:

• Cylinder liner
• Piston rings
• Piston crown

The inspection should look for:

• Scuffing
• Corrosion
• Excessive deposits
• Abnormal wear
• Piston-ring sticking

4. Load-Dependent Lubrication

The cylinder lubricator should be adjusted according to:

• Engine load
• Engine speed
• Manufacturer's recommended feed-rate curve
• Actual cylinder condition

Where an electronic lubrication system is fitted, the feed rate can be automatically adjusted according to the engine's operating condition.

5. Fuel-Dependent Adjustment

Cylinder oil BN and feed rate should be selected and adjusted according to the fuel sulphur content and actual operating conditions.

Adequate alkalinity must be maintained to neutralize acidic combustion products and prevent corrosive wear.

6. Avoid Over-Lubrication and Under-Lubrication

The cylinder lubrication system must be maintained within the optimum operating range.

Under-Lubrication

Insufficient cylinder oil can result in:

• Corrosive wear
• Scuffing
• Cylinder liner damage
• Piston-ring damage
• Increased wear

Over-Lubrication

Excessive cylinder oil can result in:

• Excessive deposits
• Piston-ring sticking
• Exhaust-valve deposits
• Increased maintenance requirements
• Unnecessary cylinder oil consumption and increased operating cost