When an engine begins to work,a charge of fresh air is drawn or pumped into its cylinder and is then compressed by the moving piston to very high pressure.When the air is compressed,its temperature rises so that it ignites the fine spray of fuel which is being injected into the cylinder.The burning of the fuel adds more heat to the air charge  and causes it to expand and force the piston to do work on the crankshaft which in turn drives the ship's propellers.

The air pressure in the cylinder is always changing by means of the_____.

As a heat engine,heat energy is the source of power by which the diesel engine can be operated.But excessive heat will cause damage to the engine.It is therefore necessary to constantly cool the components of the machinery  so that the engine can work properly.A separate cooling system is designed for this purpose.The principal function  of the cooling system is to dispose of the heat transferred from the burning fuel to the metal adjacent to the  combustion chamber.But this system is usually extended and put to other uses,such as cooling the compressed air,  the lubricating oil,the exhaust gases and the cross head guides.

Diesel engine is called "heat engine"because

The ballast system is arranged to ensure that water can be drawn from any tank or the sea and discharged to any other tank or the sea as required to trim the vessel.Combined or separate mains for suction and discharge may be provided.Where a tank or cargo space can be used for ballast or dry cargo then either a ballast or bilge connection will be required.The system must therefore be arranged so that only the appropriate pipeline is in service;the other must be securely blanked or closed off.Where tanks are arranged for either oil or ballast a change-over chest must be fitted in the pipeline so that only the ballast main or the oil transfer main is connected to the tank.

According to the passage,the function of the ballast system is_____.

The basic function of the fuel systems is to deliver the fuel in accurately metered quantities into the cylinders at the right time in the cycle,in a finely atomized state and so distribute it throughout the combustion chamber that it will mix with the air and thus obtain the oxygen necessary for complete combustion.

Fuel oil is injected into the cylinders in_____.

In the impeller pumps,the rotating impeller does work on the liquid.It throws the liquid by centrifugal force from the center to the periphery of the impeller and discharges it through the delivery outlet.Under the impeller pumps,there are the centrifugal pumps,the axial-flow pumps and the volute pumps.The impeller pumps have the advantages of simple construction and smooth,constant,non-pulsating discharge.They are often used for large-quantity of liquids at low pressure.Sometimes,a number of impeller pumps are builtin series to attain a higher final delivery pressure.

When working,the impeller_____in the pump.

The centrifugal  separation of two liquids,such as oil and water,results in the formation of a cylindrical interface between the two.The position of this interface within the centrifuge is very important for correct operation. The setting or positioning of the interface is achieved by the use of dam ring or gravity discs at the outlet of the centrifuge.Various diameter rings are available for each machine when different densities of oil are used.

What is important to the correct operation of a purifier?