DIESEL POWER PLANTS

ADVANTAGES OF DIESEL POWER PLANTThe advantages of diesel power plants are listed below.. Very simple design also simple installation.. Limited cooling water requirement.. Standby losses are less as compared to other Power plants.. Quickly started and put on load.. Smaller storage is needed for the fuel.. Layout of power plant is quite simple.. There is no problem of ash handling.. Less supervision required.. For small capacity, diesel power plant is more efficient as compared to steam power plant.. They can respond to varying loads without any difficulty. DISADVANTAGES OF DIESEL POWER PLANTThe disadvantages of diesel power plants are listed below.1. High Maintenance and operating cost.2. Fuel cost is more, since in India diesel is costly.3. The plant cost per kW is comparatively more.4. The life of diesel power plant is small due to high maintenance.5. Noise is a serious problem in diesel power plant.6. Diesel power plant cannot be constructed for large scale.

APPLICATIONS OF DIESEL POWER PLANT

Since there are many disadvantage of diesel power plant, although the plant find wide applicationin the following fields.

1. They are quite suitable for mobile power generation and are widely used in transportationsystems consisting of railroads, ships, automobiles and aeroplanes.

2. They can be used for electrical power generation in capacities from 100 to 5000 H.P.

3. They can be used as standby power plants.

4. They can be used as peak load plants for some other types of power plants.

5. Industrial concerns where power requirement are small say of the order of 500 kW, dieselpower plants become more economical due to their higher overall efficiency.

Engine ClassificationNo of strokes per cycle(Two or Four)Type of fuel burnedMethod of ignitionFiring orderReciprocating or rotaryNo of cylindersArrangement of cylindersArrangement of valves and valve trainsType of cooling

Engine?Heat engine is a device which converts heat energy (combustion of fuel) into mechanical energy.

Engine Types

External-combustionInternal-combustion

The Combustion ProcessHC + O = H2O + CO2 + HeatFuel and air compressedSpark CombustionIncomplete combustion results in Carbon Monoxide and some unburned gasolineAnother group of atmospheric pollutants from the engine is nitrogen oxides(NOx). The high temperatures in the engine cause some of the nitrogen to unite with oxygen. This forms the nitrogen oxides.

Effect of HeatPurpose of the combustion process is to produce heatHeat to do workHeat will cause most substances to expandHeat will cause air to expand

Increase in PressurePressure measured in PSI or Pounds per square inchAir pressure will increase when heated if it is in a enclosed area (air 15psi @ 32 degrees will be 17psi @100 degrees)Air pressure will increase if it is compressed (1/6 to 1/8 original volume in gasoline engines)

Increase in TemperatureAir pressure and temperature increased when compressedGasoline engine temperature is raised several hundred degreesDiesel temperature increase is even greater (more compression)

TermsThermometer measures temperature by the expansion of metalsThermostat different metals expand at different rates. This difference is used in thermostats by wielding two different metals togetherGravity is the attractive force between the earth and all other objects.

Terms cont.Atmospheric Pressure air has weight 1 cubic foot of air weighs 0.08 lbs [0.035 kg]. The blanket of air that surrounds the earth amounts to many cubic feet of air. This combined weight amounts to about 15 psi [103 kPa] at sea level.Vacuum is the absence of air.

Producing a VacuumEngines produce a partial vacuum in the cylinder by the action of the piston (this allows the air fuel mixture to be drawn into the cylinder by the force of atmospheric pressure)

Basic Parts of the S.I EngineCylinder blockPistonPiston ringsPiston pinConnecting rodCrankshaftCylinder headIntake valveExhaust valveCamshaftTiming gearsSpark plug

Cylinder BlockBasic frame of gasoline engine.Contains the cylinder.

PistonMade of aluminium alloy

Piston RingsCompression RingsOil control ringsThe rings seal the compression gases above the piston keep the oil below the piston rings.The leakage of compressed fuel-air mixture into the crankcase, through the piston clearance, is called blowby.The excessive blowby reduces the engine power, wastes fuel, and pollutes the air.

Piston PinsAlso known as the wrist pin, it connects the piston to the small end of the connecting rod.It transfers the force and allows the rod to swing back and forth.

Connecting RodConnects the piston and piston pin to the crankshaft.

CrankshaftAlong the the piston pin and connecting rod it converts the up and down motion (reciprocating) of the engine to spinning (rotary) motion.

FlywheelCarries the inertia when there is no power stroke.

Lower End Action

Intake and Exhaust ValvesDoorway that lets the gases in and out of the engine.

CamshaftThrough the use of an eccentric the cam lobes push the valves open.The valve springs close them.

Timing GearsThese gears drive the camshaft from the crankshaft.

Spark PlugElectric match used to begin the combustion process of burning air and gasoline to create heat.

Engine Related TermsTDC (top dead center)BDC (bottom dead center)StrokeBoreRevolutionCompression RatioDisplacement Cycle

Four Stroke CycleIntakeCompression PowerExhaust

Intake StrokeIntake valve opens.Piston moves down, turn of crankshaft.A vacuum is created in the cylinder.Atmospheric pressure pushes the air/fuel mixture into the cylinder.

Compression StrokeValves close.Piston moves up, turn of crankshaft.Air/fuel mixture is compressed.Fuel starts to vaporize and heat begins to build.The mixture is compressed into 1/8 or less of its original volume.

Power StrokeValves remain closed.Spark plug fires igniting fuel mixture.Piston moves down, turn of crankshaft.Heat is converted to mechanical energy.

Exhaust StrokeExhaust valve opens.Piston move up, crankshaft makes turn.Exhaust gases are pushed out polluting the atmosphere.

Four Stroke Cycle Animation

Diesel Four Stroke Animation

Diesel 2 stroke

General cycleAll the gas engines and oil engines operate in the same general way. The working fluid undergoes repeated cycles. A thermodynamic cycle is composed of a series of sequential events in a closed loop on P-V or T-S diagram. A typical cycle has following distinct operations1. Cylinder is charged2. Cylinder contents are compressed3. Combustion (Burning) of charge, creation of high pressure pushing the piston and expansionof products of combustion.4. Exhaust of spent products of combustion to atmosphere.

*AN OVERVIEW OF RECIPROCATING ENGINESNomenclature for reciprocating engines.Spark-ignition (SI) enginesCompression-ignition (CI) enginesCompression ratioMean effective pressure

*DIESEL CYCLE: THE IDEAL CYCLEFOR COMPRESSION-IGNITION ENGINESIn diesel engines, the spark plug is replaced by a fuel injector, and only air is compressed during the compression process.In diesel engines, only air is compressed during the compression stroke, eliminating the possibility of autoignition (engine knock). Therefore, diesel engines can be designed to operate at much higher compression ratios than SI engines, typically between 12 and 24.1-2 isentropic compression 2-3 constant-pressure heat addition 3-4 isentropic expansion 4-1 constant-volume heat rejection.

DIESEL ENGINES/HEAVY OIL ENGINES

In diesel engines air is compressed as the compression stroke begins and the fuel enters the cylinder at the end of compression stroke. Heat of compression is used for ignition of fuel.In a typical diesel engine, air is compressed to about 30 bars, which increases the temperature when finely atomised diesel fuel oil is sprayed into the heated air, it ignites and burns. High compression ratio is therefore essential for reliable combustion and high efficiency. The pressure ratio depends on engine speed, cylinder size and design factors. Typical compression pressures in diesel engines range from 30 bar to 42 bar.

*Thermal efficiency of the ideal Diesel cycle as a function of compression and cutoff ratios (k=1.4).Cutoff ratiofor the same compression ratio

Components of diesel power plant

EngineAir intake systemExhaust systemFuel systemCooling systemLubrication systemEngine starting systemGoverning system

Components of diesel power plant

1.Engine- generates the power and is directly coupled to the generator2.Air intake system- conveys fresh air through pipes or ducts.

Exhaust system:- Diesel engine exhaust manifold- expansion joint- silencer- gas out. Fuel system :- The five essential functions of a fuel injection system are:1. To deliver oil from the storage to the fuel injector.2. To raise the fuel pressure to the level required for atomization.3. To measure and control the amount of fuel admitted in each cycle.4. To control time of injection.5.To spray fuel into the cylinder in atomized form for thorough mixing and burning.

It incorporates a pump with built in pressure regulation, which adjusts pumping rate to maintain the desired injection pressure. The function of the pressure relief and timing valves is to regulate the injection time and amount. Spring-loaded spray valve acts merely as a check. When injection valve lifts to admit high-pressure fuel to spray valve, its needle rises against the spring. When the pressure is vented to the atmosphere, the spring shuts the valve.1. COMMON RAIL INJECTION2.INDIVIDUAL PUMP INJECTIONeach fuel nozzle is connected to a separate injection pump. T he pump itself does the measuring of the fuel charge and control of the injection timing. The delivery valve in thenozzle is actuated by fuel-oil pressure.

3. DISTRIBUTOR SYSTEM In this system, the fuel is metered at a central point i.e., the pump that pressurizes, meters the fuel and times the injection. From here, the fuel is distributed to cylinders in correct firing order by cam operated poppet valves, which open to admit fuel to nozzles.

COOLING SYSTEM OF DIESEL POWER PLANTBased on cooling medium two types of cooling systems are in general use. They are(a) Air as direct cooling system.(b) Liquid or indirect cooling system.Air-cooling is used in small engines and portable engines by providing fins on the cylinder. Bigdiesel engines are always liquid (water/special liquid) cooled.Liquid cooling system is further classified as(1) Open cooling system(2) Natural circulation (Thermo-system)(3) Forced circulation system(4) Evaporation cooling system.

OPEN COOLING SYSTEMThis system is applicable only where plenty of water is available. The water from the storage tank is directly supplied through an inlet valve to the engine cooling water jacket. The hot water coming out of the engine is not cooled for reuse but it is discharged.

Natural and forced cooling systemNatural forced

Lubrication system:-The main function of lubricant is to,1. To reduce friction and wear between the parts having relative motion by minimizing the forceof friction and ensures smooth running of parts.2. To seal a space adjoining the surfaces such as piston rings and cylinder liner.3. To clean the surface by carrying away the carbon and metal particles caused by wear.4. To absorb shock between bearings and other parts and consequently reduce noise.5. To cool the surfaces by carrying away heat generated due to friction.6. It helps the piston ring to seal the gases in the cylinder.7. It removes the heat generated due to friction and keeps the parts cool.

Semi pressure(Splash) and full pressure systemSemi pressure full pressure

By Pass Type Wet sump lubrication System