1. It filter the fuel insuring oil free from dirt.
2. It meters the correct quantity of fuel to be injected in each cylinder.
3. It times the injection process in relation to the crankshaft revolution.
4. It regulates the fuel supply.
5. It atomizes finely the fuel oil for better mixing with the hot air leading to efficient combustion.
6. It distributes, the atomized fuel properly in the combustion chamber.

1. Common rail injection system
2. Individual pump injection system.
3. Distributed system.

1. Needle or nozzle valve
2. A compression ring
3. A nozzle
4. Injector body

1. Single hole
2. Multi hole
3. Pintle type
4. Pintaux type

Force circulation cooling system

• Open cooling system: This 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 circulation system: The system is closed one and designed so that the water may circulate naturally because of the difference in density of water at different temperatures.It consists of water jacket, radiator and fan. When the water is heated, its density decreases and it tends to rise, while the colder molecules tend to sink. Circulation of water then is obtained as the water heated in the water jacket tends to rise and the water cooled in the radiator with the help of air over the radiator either by ram effect or by fan or jointly tends to sink. The direction of natural circulation which is slow is shown by arrows.
• Force circulation cooling system: Figure shows force circulation cooling system which is closed one. The system consists of pump, water jacket in the cylinder, radiator, fan and a thermostat. The coolant is circulated through the cylinder jacket with the help of a pump which is usually a centrifugal type, and driven by the engine. A function of thermostat which is fitted in the upper hose connection initially prevents the circulation of water below a certain temperature, usually upto 85C through the radiation so that water gets heated up quickly. Stand-by diesel power plant upto 200 kVA use this type of cooling.

Lubrication system:

5. Dry sump lubrication system: Figure shows Dry sump lubrication system. In the Dry sump, the supply of oil is carried in an external tank with the help of scavenging pump through strainer and filter, The scavenging pump is placed out of the sump. The capacity of the scavenging pump is always greater than oil feed pump. The supplied tank is usually placed behind the radiator. The dry sump is generally used in large stationary marine engine.

1. Pick load plant: Diesel plants are suitable as pick load plants in combination with  thermal or hydal plant. The pick load unit needs easy, starting and stopping and diesel plants serve this purpose.
2. Stand-by unit: There are many situations in which stand-by units are needed such as the main unit fails or cannot cope with the demand. As an example due to less rainfall in a particular year, the hydro plant cannot meet the demand. Thus diesel units are installed as stand-by unit to supply power in parallel to generate the short fall of power.
3. Central stations: Due to ease in installation starting and stopping, diesel electric plants can be used as central station where the capacity requirement is more.
4. Starting station: For starting large power plant, auxiliaries such as FD and ID fans, BFP, circulating water pump, etc can be run by installing a diesel electric power plant.
5. Energy unit: In many developing countries like India, power failure/interruption is a common feature for hours. Under this circumstances, the power to vital units such as hospitals or industrial plants can be supplied by installing diesel electric power plant.

1. Rectification of defects: The defects may or may not be urgent. If immediate repairs are needed, these may be carried out on running limits or the units should be shut down. If the repairs are not urgent, it may be carried out in planned program of future work.
2. Planned preventive maintenance on running units: A system of routine maintenance is adopted to prevent the defects and breakdowns. The planning of such system needs careful consideration in order to arrive at the optimum level of maintenance. The actual work content of each maintenance routine can only be determined after experience with the plant over a period of time. After carrying out the preventive maintenance, it is recorded on a record card with full particulars or the items attended.
3. Planned preventive maintenance on shut down units: In order to minimize the maintenance cost of shut down units, it is necessary to plan the work to be done carefully in advance so that the duration of the plant shut down is reduced to a minimum. This planning process should start some weeks or months before the shutdown is due to take place.

Steam turbine overhaul:

1. Apply the load gradually.
2. Check up the oil pressure going to the bearings and control gear.
3. Observe the oil bearing temperature.
4. Observe the turbine for any noise, vibration by watching the vibration and other indicators.

C. Sequence when shutting the turbine down:

1. Application of controlled power illuminates all of the malfunction lights. This provides a check of the malfunction lights before starting the turbines.
2. Reset malfunction circuit by operating a reset switch. Malfunction lights go off and all control devices assume the condition for starting.
3. Inspect the governor mechanism, till all grease cups and oil where necessary.
4. Open the boiler stop valve to permit heating of the line and avoid condensation in the line.
5. Open header, separator, throttle and turbine casing drills.
6. Start auxiliary oil pump. This has to be stopped when the main oil pump starts delivering oil at normal pressure.
7. Adjust middle valve to secure required oil pressure for the bearing.
8. Start the circulating water pumps and dry vacuum pumps of the condenser. Operate the condensate extraction pumps as found necessary to remove water during the warming up period.
9. Turn on the turbine steam or water seal.
10. Turn on the water to the generator oil cooler and other water requiring parts.
11. Keep open all the drains ahead of the throttle valve untill all water of condensation has been removed.
12. Open the throttle or governor valve quickly to set the rotor in motion.
13. In order to check up whether the tripping mechanism operates properly or not and to prevent the turbine from accelerating too rapidly, operate the overspeeed trip valve by using the hand lever as soon as turbine starts rolling.
14. Reset the emergency overspeed valve and before the turbine comes to rest, adjust the throttle so that the turbine wheel operates between 200 and 300 rpm.
15. While the rotor is in slow motion, observe any rubbing or mechanical difficulty by using a metal rod or listening device.
16. As soon as the temperature of the oil leaving the bearing reaches about 40-48 C, start the circulating water through the oil coolers to maintain bearing oil temperature.
17. Increase the speed gradually following the manufacturer's instructions.
18. Adjust the water seal on the turbine and the atmospheric relief valve.
19. Once the machine comes under the control of governor, test the emergency governor by opening the valve in the oil line to it. See that all valves controlled by this tripping mechanism close promptly. Reset open throttle valve and restore speed to normal.
20. Close all drains.
21. Open leak off from H.P. side gland in order to flow any excess steam to the filled water heater or to one of the lower stage of the turbine.
22. Synchronize the generator and tie it in the line.
23. The speed is now under the control of governor. The turbine is now ready for load and is regulated from the turbine control panel.

1. The built-up rotor
2. The integral rotor
3. The hollow drum rotor
4. The solid drum rotor
5. The welded disc rotor

1. The Built-up Rotor:

It consists of forged steel shaft on which separate forged steel discs are shrunk and keyed. It is cheaper since the disc and shaft are relatively easy to forge and inspect for flaws and machining of these components can be carried out concurrently. Its shaft is machined with a series of stepped diameters ending with central collar. Each disc is heated and assembled on the shaft in turn, each being held in position by a form of circlip.  Relative rotation is prevented either by keys, or by hub dowels known as buttons, which locate the hubs one to another to the central collar. The number of discs depend upon the number of stages which in turn depends upon the turbine output.

2. The Integral Rotor:

The shaft and wheels of this type of rotors are formed from one solid forging. Integral rotors are expensive and difficult to forge, and there is a high incidence of rejects. Over and above, a large amount of machining time and waste material are involved.

• There is no chance of disc to become loose, particularly at high temperature end where at times the wheels may be hot and the shaft pull as found in the built-up rotor.
• This rotor is also free from the effect of creep which may cause the shrink fit of built-up rotor to disappear after a large number of running hours.
• The hoop stress is of lower magnitude as it contains a small hole meant for inspecting the forging.
• There is saving in axial length and reduction in spindle diameter over the built-up type.

3. Hollow Drum Rotor:

This type of rotor promotes even temperature distribution because it is designed with the same thickness of material as the casing.

4. Solid Drum Rotor:

This type of rotors are suitable for cylinders where there are lower temperatures but large diameters, as in I.P. cylinders without re-heat.

5. Welded Disc Rotor:

The last stage disc is the most heavily stressed part of the turbine and this is one of the main problem of L.P. rotor. The centrifugal load of the large rotating blades set up a tensile stress in the rim of disc, and this stress increases with decreasing radius, its maximum value being at the bore of the hub. If the bore is exceedingly small, the hoop stress becomes very less but of there is no hole, the hoop stresses throughout the disc are theoretically halved. Since there is no central hole in welded disc rotor, it suitable for L.P. rotors. It has two main advantages: It is less stressed and no need for large shaft forgings which are expensive and difficult to manufacture. The welding process and subsequent heat treatment should be performed with great attention. 

These 5 types of rotors are also used in gas turbines.

Also read: Balancing of Rotors

1. Rolling - Sections are rolled to the finished size and used in conjunction with packing pieces. Blades manufactured by this method do not fail under combined bending and centrifugal force.
2. Machining - Blades are also machined from rectangular bars. This method has more or less same advantage as that of rolling. Impulse bladings are manufactured by this technique.
3. Forging - Blade and vane surfaces having air foil sections are manufactured by specialist techniques. The simplest way is to determine the profiles required at the hub and tip, and join them by straight, ruled lines. For more accuracy, a profile, at middle to each end separately is obtained. Once the geometry of the family of the ruled lines is established they may be machined in turn by milling machine, rest carefully for each line to generate the shape required in a master blog from which the forging die may be copy-machined. This method ensures the accurate forging of blades to their finished size, requiring only fletting and polishing. The machining of the fir-tree root is often done by broaching, and electrochemical machining may be used in some parts to avoid the conventional cutting processes. In advance method, computers are used to determine the blade shape required by aerodynamic and stress criteria. The computer may then instruct a numerically controlled milling machine to prepare the dies.
4. Extrusion - Blades are sometimes extruded and the roots are left on for subsequent machining. This method is not as reliable as rolled section, because of narrow limits imposed on the composition of the blade material.
5. Cold Drawing - Blades are also cold drawn.

• LP stage blading
• Hollow Blades
• Shrouding

• The design of nozzle should be such as to permit easy manufacturing and finishing and allow accurate channel sections to be obtained specially at the high pressure end of the turbine.
• The inlet of the nozzle should be so designed as to utilize the carry over energy from the previous stage to the largest possible extend.
• There should not be any sudden change in the direction of flowing steam, specially at high velocity.
• The shape and finish of the nozzle should be designed so that the conversion of thermal energy into kinetic energy should take place with greatest possible efficiency.
• In order to reduce friction, specially when the steam velocity is high, the valve surface should be as smooth as possible.

Construction of convergent nozzle:

First Stage Convergent Nozzle:

A segment of convergent nozzle suitable for the first stage of an impulse turbine of medium power is shown in figure:

Built-up construction is shown in figure.

It provides an accurate nozzle segment. It consists of a number of vanes 'a', which are machined all over, and placed between curved angles 'b', likewise machined all over. The ends of segments are closed by pieces c of suitable shape. Through the rivets 'd' the guide vanes are attached to the angles. A small spigot 'e' is riveted over it.

Diaphragm Nozzle:

A different type of built-up construction for high pressure diaphragm is shown in figure.

Each diaphragm contains a steel centre 'a', in halfes to which several nozzle elements 'b' are riveted as shown in figure. Each nozzle elements are machined all over to a fine finish.

Construction Of Convergent-Divergent Nozzles:

De-Laval Nozzle:

It is a convergent-divergent type of nozzle made of gun metal as shown in figure.

 The nozzle is fitted with a valve arrangement 'c' which opens or closes it to a steam chest 'a'. It is mostly used in experimental type of impulse turbine.

Cast -in Type:

Cast-in type is shown in figure.

It is largely used in marine impulse turbine. Guide blades are rolled to the section shown by dotted lines in the upper part of figure, and then cut to shape and cast into the nozzle segment in the usual manner.

Built-up Nozzle:

Built-up nozzle is shown in figure.

It is made of steel to B.S.En 58B and is readily replaceable at any time. It consists of two parts- lower and upper forming rectangular cross-section. It is machined from a bar by employing jigs and fixtures to the required shape. It is used in many impulse turbines and another form of built up nozzles is also shown in figure.

It consists of 3 parts segment strips 'a' in which the nozzle passages are machined, a covering segment 'b' and a wedge piece 'c'. The locking screws 'd' on the ring 'c' causes the strips 'a' and 'b' to be forced against the steam chest. The cap nut 'e' covers the set screw 'd' so that there should not be any leakage. It is used in so many turbines.

1. Construction of nozzles and diaphragm.
2. Construction of turbine blades.
3. Rotor construction.