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    Unit II

    Internal Combustion(Diesel) PowerPlant

    By

    Mq. K. Obula ReddyAsst. Pqof. Dept. of Mech.Gitam Univeqsity Hydeqabad

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    Diesel power plants produce power in the range of 2 to

    50 MW.

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    Classification of Engines

    Engines can be classified in many different ways, asthey have many attributes, whereby making them

    capable of meeting a variety of needs and

    requirements.

    vcylinder numbers & arrangement

    vengine cycles

    vvalve position & location

    vmethod of air supply

    vmethod of fuel supply

    vcooling system

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    Cylinder numbers & Arrangement

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    Engine CyclesIn four-stroke engine the cycle of operation is completed in four strokes of the piston or

    two revolution of the crank shaft.

    In two-stroke engine the cycle is completed in two strokes, i.e. one revolution of the

    crank shaft.The difference between two-stroke and four stroke engines is in the method of filling the

    cylinder with the fresh charge and removing the products of combustion.

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    valve position & location

    A - valve in block (L)

    B - valve in head (I)

    C - one in head and

    one in block (F)

    D - on opposite sides

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    Method of Air Supply

    1. Naturally aspirated engine:Admission of charge at near atmospheric pressure

    2. Supercharged engine:Admission of charge at a pressure above atmospheric

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    Method of fuel supply

    2.Multi-port fuel injection

    consists of an injector for each cylinder

    in the engine. This injector sprays fuel

    directly through the intake valve or

    valves into the combustion chamber.

    Each injector is activated separately bywire

    1. Direct and Indirect Injection

    In an indirect injection (abbreviated

    IDI) diesel engine, fuel is injected

    into a small prechamber, which is

    connected to the cylinder by a narrow

    opening.2

    1

    3

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    Cooling System

    Liquid Cooling Air Cooling

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    Layout of a Diesel power plant

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    The essential components of a Diesel Electric Plant are:

    (1) Engine

    (2) Engine air intake system

    (3) Engine fuel system

    (4) Engine exhaust system

    (5) Engine cooling system

    (6) Engine lubrication system

    (7) Engine starting system

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    Diesel Engine

    This is the main component of the plant which develops power.

    Generally engine is coupled directly to the generator

    Diesel engine may be a four stroke or a two stroke engine

    Four stroke engine is generally preferred as it has higher efficiency,lower specific fuel consumption and more effective lubrication than a

    two stroke engine

    Other things which may be specified in diesel engines are: arrangement

    and number of cylinders used, simple aspiration or supercharging,efficiency and economical fuel consumption

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    Engine air intake systemThis includes air filters, ducts and supercharger (an integral part of the

    engine). The system supplies the required quantity of air for combustion. Air

    requirements for large diesel plants are considerable, around 4-8 m3 per kwh.

    Air is drawn from outside the engine room and delivered to the intake

    manifold through the air filters which remove the dust and other suspended

    impurities from air.

    The purpose of the filter is to catch any air borne dirt as it otherwise may

    cause the wear and tear of the engine. The filter should be cleaned

    periodically.

    Filters may be of dry type (made up of cloth, felt, glass wool etc) or oil bathtype. In oil bath types filter the air is swept over or through a bath of oil in

    order that the particles of dust get coated.

    The supercharger increases the pressure of air supplied to the engine so that it

    could develop an increased power output. Superchargers are generally driven

    by the engine.

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    Engine fuel system

    This include fuel storage tanks, fuel transfer pumps, strainers, heaters

    and connecting pipe work. Fuel transfer pumps are required totransfer fuel from delivery point to storage tanks and from storage

    tanks to engine. Strainers (filters) are needed to ensure clean fuel.

    Heaters for oil may be required especially during winter.

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    Engine exhaust systemThe function of the exhaust system is to discharge the engine exhaust to the

    atmosphere outside the building. This includes silencers (muffler) andconnecting ducts/ pipes. A good exhaust system should keep the noise at a

    low level, exhaust well above the ground level to reduce the air pollution at

    breathing level and should isolate the engine vibrations from the building

    by using a flexible selection of exhaust pipe. The exhaust pipe is provided

    with a muffler to reduce pressure in the exhaust line and reduces the noiselevel.

    Engine cooling system

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    Engine cooling system This includes coolant pumps, spray ponds, water treatment or

    filtration plant and connecting pipe work. The purpose of the

    cooling system is to carry heat from engine cylinder to keep thetemperature of the cylinder within safe limits.

    There are three system for the re cooling of water for continuous

    use:

    1. Open system or direct evaporation.

    2. Closed system including heat exchangers with a secondary

    water circulation.

    3. Radiators.

    Engine cooling system

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    Engine cooling system

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    Engine lubrication system

    The life of the engine and the efficiency depend largely on the

    lubrication system.

    The main functions of the lubricating oil are: to lubricate the moving

    parts, to remove the heat from the cylinders and the bearings, to help thepiston rings to seal the gases in the cylinder and to carry away the solid

    dirt particles from the rubbing parts.

    The parts of the engine, which need lubrication include piston and

    cylinders, gears, crankshaft, and connecting rod, bearing etc. Piston andcylinder need special-lubricating oil.

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    Engine Starting system.

    Because of the high compression pressure, even a small diesel

    engine in a power plant can not be started by hand cranking.

    The various methods used for starting are:

    (1) Compressed air starting for medium and large capacitystationary and mobile units

    (2) Electric-motor starting for small high-speed gasoline and

    diesel engine

    (3) Auxiliary-engine starting for medium capacity mobile units

    SUPERCHARGING OF DIESEL ENGINES

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    It is a known fact that the power output of the engine increases with an increase in amount of air

    in the cylinder at the beginning of compression stroke because it allows to burn more quantity of

    fuel.

    Supercharging is a term used to a process which helps to increase the suction pressure of the

    engine above atmospheric pressure and the equipment used for this purpose is known as

    supercharge

    Supercharging an engine performs the same function as turbo charging an engine. The difference

    is the source of power used to drive the device that compresses the incoming fresh air. In a

    supercharged engine, the air is commonly compressed in a device called a blower.

    The blower is driven through gears directly from the engines crankshaft. The most common typeof blower uses two rotating rotors to compress the air.

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    Supercharger Vs Turbocharger

    The advantages of supercharged engines are listed below :

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    The advantages of supercharged engines are listed below :

    1. Power increase. By supercharging the engine, the engine output can be increased

    by 30 to 50%at the same speed of the engine.

    2. Fuel Economy. The combustion in supercharged engine is better as it provides

    better mixing of the air and fuel than unsupercharged engine. Therefore, the specific fuel

    consumption of a supercharged engine in less than natural aspirated engine. The thermal

    efficiency of supercharged engine is also higher.

    3. Mechanical efficiency. The mechanical efficiency of a supercharged engine is betterthan natural aspirated engine at the same speed. This is because, the power increase due

    to supercharging increases faster than the rate of increase in friction losses.

    4. Scavenging. The scavenging action is better in two-stroke supercharged engines

    than naturally aspirated engines because the quantity of residual gases is reduced with the

    increase in supercharged pressure.

    5. Knocking. Supercharging reduces the possibility of knocking in diesel engines

    because delay period is red