Study Marine Engineering Online

Marine Refrigeration System Vapour Compression System: The vapour compression cycle takes place in a closed system, comprising a compressor, a condenser, a liquid receiver, an evaporator, and a flow control or expansion valve, interconnected by discharge, liquid and suction lines. Principle of refrigeration: 1) Absorption of heat by the evaporation of a liquid refrigerant in the evaporator at a low pressure; 2) Raising the pressure ( to raise the condensing temperature ) of low pressure vapour coming from the evaporator by the compressor; 3) Removal of heat from the high pressure  vapour in the condenser so as to liquefy or condense the vapour; 4) By the use of the throttling device, reducing the pressure of the high pressure liquid ( from the condenser ) to the level of pressure needed in the evaporator. Expansion valve ( flow control ): The liquid refrigerant is stored at high pressure in the receiver. The liquid flows from the receiver through the

Cylinder Combustion in Marine Diesel Engines Fuel oil is a hydrocarbon consisting of hydrogen and carbon, together with other elements most of which are unwanted. Hydrogen has a higher calorific value than carbon, therefore, more heat may be obtained from fuels containing higher Hydrogen/Carbon ratios. The lower specific gravity of hydrogen than carbon allows a rough rule of thumb to be; the higher the Specific Gravity, the lower the Calorific Value (and quality) of the fuel. The presence of impurities clouds the issue slightly For efficient combustion an ignition source and sufficient oxygen need be present to completely oxidise the Hydrogen to water vapour and the carbon to carbon-dioxide. The combustion is required to occur in a short period of time in an internal combustion engine, there are five essential requirements to ensure this: 1. Correct Air/fuel ratio  -There must be sufficient oxygen to burn not only the hydrogen and oxygen present but also any other co