BASIC MARINE DIESEL ENGINES

                                                

BASIC MARINE DIESEL ENGINES

IC (INTERNAL COMBUSTION)  ENGINES:

         Internal combustion engine : Combustion of fuel takes place inside the cylinder of the engine. e.g. - PETROL ENGINE - DIESEL ENGINE

External combustion Engine :  Combustion of fuel takes place outside the cylinder of the engine.   e.g. STEAM ENGINE.

DIESEL ENGINES or COMPRESSION IGNITION ENGINES:

                           The diesel engine was first patented in 1892 by Rudolph Diesel

As  the name implies,the engine using diesel oil as the fuel, to produce power by combustion process.

The fuel is burnt inside the combustion chamber by means of compressing atmospheric air(compression ignition engine).

The combustion of fuel taking place inside the combustion chamber by increasing the temperature of air.At the point of auto ignition temperature(self ignition temperature) of  fuel reaches,the fuel catches fire without any external sources of heat such as spark plug.

it can be either 2 stroke diesel engine or four stroke diesel engine or etc.but concept is same.only stroke is the difference.

PETROL ENGINES or SPARK IGNITION ENGINE:

The burning of fuel (petrol) occurs by the spark generated by the spark plug located in the cylinder head. 

Auto ignition temperature        

                  The auto ignition temperature or self ignition temperature of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark .                                                                                                                                                                                                                                                                                Diesel oil auto ignition temperature- 256 °C (493 °F) varies upto 300°C depending upon grade.


2 STROKE DIESEL ENGINES:

1. The crankshaft is revolving clockwise and the piston is moving up the cylinder, compressing the charge of air from pressure 2 bar and the temperature 40°C  .Because energy is being transferred into the air, its pressure and temperature increase. By the time the piston is approaching the top of the cylinder (known as Top Dead Center or TDC) the pressure is over 100 bar and the temperature over 500°C

2. Just before TDC fuel is injected into the cylinder by the fuel injector. The  fuel is "atomised" into tiny droplets. Because they are very small these droplets heat up very quickly and start to burn as the piston passes over TDC. The expanding gas from the fuel burning in the oxygen forces the piston down the cylinder, turning the crankshaft. It is during this stroke that work energy is being put into the engine; during the upward stroke of the piston, the engine is having to do the work.

3. As the piston moves down the cylinder, the useful energy from the burning fuel is expended. At about 110° after TDC the exhaust valve opens and the hot exhaust gas at 600°C,pressure 4 bar   (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen)  begin to leave the cylinder.

4. At about 140º after TDC the piston uncovers a set of ports known as scavenge ports. Pressurised air enters the cylinder via these ports and pushes the remaining exhaust gas from the cylinder in a process known as "scavenging". The piston now goes past Bottom Dead Centre and starts moving up the cylinder, closing off the scavenge ports. The exhaust valve then closes and compression begins

2 STROKE VALVE TIMING DIAGRAM:

1 -2 Compression 2 - 3 Fuel Injection 3 - 4 Power 4 - 5 Exhaust Blowdown 5 - 6 Scavenging 6 - 1 Post Scavenging

1. approx 110º BTDC 2. approx 10º BTDC 3. approx 12º ATDC 4. approx 110º ATDC 5. approx 140º ATDC 6. approx 140º BTDC

4 STROKE DIESEL ENGINES:

1. INDUCTION: The crankshaft is rotating clockwise and the piston is moving down the cylinder. The inlet valve is open and a fresh charge of air is being drawn or pushed into the cylinder by the turbocharger

2. COMPRESSION: The inlet valve has closed and the charge of air is being compressed by the piston as it moves up the cylinder. Because energy is being transferred into the air, its pressure and temperature increase. By the time the piston is approaching the top of the cylinder (known as Top Dead Centre or TDC) the pressure is over 100 bar and the temperature over 500°C

3. POWER: Just before TDC fuel is injected into the cylinder by the fuel injector. The  fuel is "atomised" into tiny droplets. Because they are very small these droplets heat up very quickly and start to burn as the piston passes over TDC. The expanding gas from the fuel burning in the oxygen forces the piston down the cylinder, turning the crankshaft. It is during this stroke that work energy is being put into the engine; during the other 3 strokes of the piston, the engine is having to do the work.

4. EXHAUST: As the piston approaches the bottom of the cylinder (known as Bottom Dead Centre or BDC) the exhaust valve starts to open. As the piston now moves up the cylinder, the hot gases (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen)  are expelled  from the cylinder. As the Piston approaches TDC again the inlet valve starts to open and the cycle repeats itself.

4 STROKE ENGINE VALVE TIMING DIAGRAM