The fuel oil system for a diesel engine
Internal combustion engine procedure
The fuel oil system for a diesel engine can be considered in two parts—the fuel supply and the fuel injection systems. Fuel supply deals with the provision of fuel oil suitable for use by the injection system.
Fuel oil supply for a two-stroke diesel engine
A slow-speed two-stroke diesel is usually arranged to operate continuously on heavy fuel and have available a diesel oil supply for manoeuvring conditions.
In the system shown in Figure , the oil is stored in tanks in the double bottom from which it is pumped to a settling tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily service tank. From the daily service tank the oil flows through a three-way valve to a mixing tank. A flow meter is fitted into the system to indicate fuel consumption. Booster pumps are used to pump the oil through heaters and a viscosity regulator to the engine-driven fuel pumps. The fuel pumps will discharge high-pressure fuel to their respective injectors.
The viscosity regulator controls the fuel oil temperature in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, and a pre-warming bypass is used to heat up the fuel before starting the engine.
A diesel oil daily service tank may be installed and is connected to the system via a three-way valve. The engine can be started up and manoeuvred on diesel oil or even a blend of diesel and heavy fuel oil. The mixing tank is used to collect recirculated oil and also acts as a buffer or reserve tank as it will supply fuel when the daily service tank is empty.
The system includes various safety devices such as low-level alarms and remotely operated tank outlet valves which can be closed in the event of a fire.
Operation on Heavy Fuel Oil
Main engines designed to manoeuvre on heavy fuel oil are to be operated according to the manufacturer’s instructions. All other types of main engines are to be manoeuvred on diesel oil according to the manufacturers’ instructions.
In the event of problems during manoeuvring on engines using heavy oil there must be no hesitation in changing over to diesel oil irrespective of whether the engines are being operated using bridge control, or using engine room control.
It is the Chief Engineer's responsibility to inform the Master of the particular engine type’s maximum period that it can safely remain in the stopped position. He is also to inform the Master of the procedures which will have to be carried out if the particular engine type’s maximum period at standstill during manoeuvring is exceeded.
The function of the fuel injection system is to provide the right amount of fuel at the right moment and in a suitable condition for the combustion process. There must therefore be some form of measured fuel supply, a means of timing the delivery and the atomisation of the fuel. The injection of the fuel is achieved by the location of cams on a camshaft. This camshaft rotates at engine speed for a two-stroke engine and at half engine speed for a four-stroke. There are two basic systems in use, each of which employs a combination of mechanical and hydraulic operations. The most common system is the jerk pump; the other is the common rail.
Function of fuel injector for a diesel engine
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