Viscosity is an essential property of marine fuels. Due to the high viscosity of HFO at low temperatures, it must be heated prior to being supplied to the engine.
This device measures and controls the viscosity of fuel oils used in the marine fuel systems. It provides a continuous reading and helps to ensure the correct viscosity by controlling the heating process. This device is commonly used in fuel oil systems of main and auxiliary engines. Keeping the correct viscosity ensures correct fuel injection, efficient combustion and correct engine performance.
A Viscotherm is an automated fuel viscosity measuring and control system. The main function of the device is to measure the viscosity of heated fuel oil and control the fuel oil heater to ensure the correct viscosity. This device helps measure the viscosity of the fuel oil rather than just the temperature. Different grades and batches of fuel will have varying viscosities.
The system will heat the fuel oil to a higher temperature if the viscosity is higher than the required level. If the viscosity is too low it will reduce the amount of heating.
A standard capillary type Viscotherm contains the following components;
A standard Viscotherm works using a principle of measuring the differential pressure of a capillary tube.
When a liquid is passed through a narrow capillary tube under laminar flow conditions there will be a relationship between the pressure drop and the dynamic viscosity. The higher the viscosity the greater the differential pressure.
This will happen automatically.
Marine diesel engines require fuel oil of the correct viscosity to ensure correct fuel injection.
Keeping the correct viscosity will help ensure correct performance of the fuel injection equipment and the engine.
The correct viscosity for injection will depend on the recommendation of the engine manufacturer and the fuel characteristics.
The temperature of marine fuel will have a direct impact on the viscosity. The higher the temperature the lower the viscosity of most liquid fuels. Similarly, the lower the temperature the higher the viscosity.
For example;
The Viscotherm will help keep the viscosity to the correct level by automatically controlling the heating of the fuel oil.
Like any instrumentation, issues can occur with a Viscotherm due to contamination of fuel, wear and tear and electrical fault.
Causes could be;
The gear pump may be worn, blocked or the motor fails. This can cause incorrect viscosity readings.
The steam control valve may become stuck causing incorrect temperatures.
Impurities and sludge in the fuel can block the narrow measuring area. This will affect the differential pressure and create incorrect readings.
Ensure the device is isolated and safely locked out before opening the measuring unit. Follow permit to work procedures on the ship and those outlined by the manufacturer.
A Viscotherm is an important device in the fuel oil systems of a ship. It helps to ensure the correct fuel viscosity is maintained before injection into the engine. The device passes a controlled flow of fuel through the measuring capillary and measures the differential pressure. The controller then adjusts the control valve to control the fuel oil heater to keep the correct viscosity. Correct operation and regular maintenance will help to improve fuel injection conditions, quality of combustion and reliability of the engine.
To measure and control the viscosity of the fuel oil supplied to the marine diesel engines.
The differential pressure is proportional to the dynamic viscosity of the fuel oil. This is done by controlling the flow rate and other measuring parameters.
To ensure a continuous and controlled flow of fuel.
To measure the differential pressure and convert it into an electrical signal.
The controller will increase the amount of heating going to the heater. This will increase the fuel temperature and decrease the viscosity.
No. The main purpose of this device is to measure and control the viscosity of the fuel oil. The pressure is controlled by the fuel supply system.
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