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Deisel Genrator set overview
Engine Operation : 4 Stroke Diesel Engine
1. The intake stroke starts at TDC and ends at BDC. The intake valve opens during this stroke to admit fresh air into the combustion chamber. The intake valve closes at BDC.
2. The compression stroke starts at BDC and ends at TDC. The air is compressed to a small fraction of its initial volume. Compression ratio is about 17:1. Due to high compression, the air temp. increases.
3. Fuel is injected into the combustion chamber in the form of a fine spray. This ignites by the hot compressed air in the chamber. The energy released by combustion forces the piston down to the BDC.
4. The exhaust valve opens at BDC and upward movement of the piston drives the exhaust gases out. The exhaust valve closes at TDC. This is followed by the next intake stroke.
Direct Injection Diesel Engines
In a direct-injection diesel the fuel is injected directly onto top of the cylinder. The piston is dished to form the combustion chamber.
Diesel Engines of this design have a high performance,high efficiency and good fuel economy.
Turbocharged Diesel Engines
A Turbocharger uses waste exhaust gas energy to compress and supply more air. With more air, more fuel can be burned to get more power.
Air System Operation
Air System
Function
• To supply air for complete combustion of fuel
• To take exhaust gases out of engine
Hence divided into two parts
- Air Intake system
- Exhaust system
Air Intake System
• Sufficient air ?
1 liter of of fuel needs 12,500 liters of air for complete burning
Oxygen in air is essential for burning
• Clean air - dust in air is harmful for engine
• Cool air - Air at high temp will ignite fuel early
Air at high temp is thin and has less oxygen
• Dry air - Air with moisture will have less oxygen
Moisture in combustion chamber is harmful to engine
Exhaust system operation
Requirements of exhaust system operation
• Exhaust back pressure within limits ( 3 inches of Hg )
• Noise reduction
• Prevent rain water entry into cylinder
• Exhaust pipings support
• Lagging
Lubrication System Operation
• Lubrication system
• Lubricates all moving parts by providing thin protective coating
• between all moving parts during engine operation
• Cools the parts by absorbing heat generated by friction & combustion
• Cleans the engine by picking up the foreign particles
• formed during combustion
Functions of Lubricating oil
• Seals combustion chamber from crankcase by forminga thin film between piston rings & liner wall
• Provides a cushioning between contacting surfacesof components & dampens the shocks
• Provides a protective barrier, isolating non - like metals to prevent corrosion
Understand Lubricating oil
Physical property modifiers
Viscosity improvers
Maintain more uniform viscosity over a wide range of operating temperature
Detergent / dispersants
Hold contaminants in suspensions in dispersed state
These contaminants are trapped by filter to prevent damage to engine parts
Extreme pressure agents
Prevent destructive metal to metal contact in highly loaded components
Anti-foam
control foaming & prevent air bubbles