Marine Engineering Basics

Engine timing refers to the relative time or position of the crank, at which each operation during the cycle is commenced and is completed. It is measured as the angle through which the crank has been rotated from a datum position such as top or bottom centre. FOUR STROKE CYCLE The majority of medium and high speed diesel engines for main or auxiliary drive operate on the four-stroke cycle, which takes place during four consecutive strokes, or two complete revolutions, of the engine.  Four stroke are: 1. Induction stroke  2. Compression stroke 3. Power or expansion stroke 4. Exhaust stroke 4 STROKE NATURALLY ASPIRATED ENGINE -:  Naturally aspirated engine, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turbocharger or a supercharger. 1   Intake valve open 10-15°  before TDC. 2   Intake valve closes at BDC. 3.  Fuel injection start at TDC. 4.  Fuel injection end 30° after TDC. 5.  Exhau

Thermodynamic cycle is either to produce power, or to produce  refrigeration/pumping of heat. Therefore, the cycles are broadly classified as follows:  (a) Heat engine or power cycles.  (b) Heat pump cycles or refrigeration cycle. The power cycles are accordingly classified into two groups as:  (1) Vapour power cycles in which the working fluid undergoes a phase change during the cyclic process. Ex- Steam Power Plant (2) Gas power cycles in which the working fluid does not undergo any phase change.Ex- ICE  An Internal combustion engine work on two baic Power thermodynamic cycle-:   1. OTTO CYCLE 2. DIESEL CYCLE AIR STANDARD  ASSUMPTION FOR IDEAL CYCLE  -: > Gas and air mixture are considered as air and an ideal gas, which   continuously circulates in a closed cycle.    > There are no intake and exhaust process. > The processes are internally reversible. > The combustion process is replaced by a heat-addition process from an     external source. > The exhaust process is

INTERNAL COMBUSTION ENGINE An internal combustion engine is one in which the fuel is burnt within the engine. It is usually of the reciprocating type. Combustion of the fuel and the conversion of the heat energy from combustion to mechanical energy takes place within the cylinders. Ex. Petrol engine, Diesel engine EXTERNAL COMBUSTION ENGINE  If the combustion of fuel place outside the engine cylinder, it is an external combustion engine. Ex: Steam turbine, Gas Turbine, Steam Turbine etc. BASIC TERMS AND DEFINITION 1. SWEPT VOLUME -: This term refers to the volume swept by the piston during one stroke and is the product of the piston area and stroke. 2. CLEARANCE VOLUME-: It   is the volume remaining in the cylinder when the piston is in the top-centre position. The difference between the total cylinder volume and the swept volume is equal to the clearance volume.  3. COMPRESSION RATIO-: This is the value obtained from dividing the total c