Experiment No. 02

Experiment Name: Study of Diesel Engine Power Plant

Introduction :

In a diesel engine power Plant, diesel engine is used as the prime mover. The diesel burns inside the engine and the products of this combustion act as the working fluid to produce mechanical energy. The diesel engine drives alternator which converts mechanical energy into electrical energy. As the generation cost is considerable due to high price of diesel, therefore, such power stations are only used to produce small power.

The diesel plants are more efficient than any other heat engines of comparable size. It is cheap in first cost. It can be started quickly and brought into the service. It can burn a fairly wide range of fuels. Its manufacturing periods are short and, therefore, a diesel station may be rapidly extended to keep pace with load growth by adding generating units of suitable sizes. The diesel units used for electric generation are more reliable and long-lived piece of equipment compared with other types of plants.

The diesel engine has provided the most economic means of generating electricity on small scale particularly where there is no convenient site for micro-hydro plants and cheap fuels are not available and load factors are considerably large

Objective:

At the end of this workshop, you will gain valuable know-how related to diesel generating plants on:

Combustion processes and engine operation principlesUnderstand about diesel engine power plant,

Explain fuel injection system and its functions, and

Describe various injection schemes.

Types and applicationsGenerator principles and constructionFuel and lube oil requirementsPlant layout requirements for single and multiple units

Testing and commissioning procedures• Plant performance troubleshooting techniques• Good maintenance practices• Mechanical Engineers• Instrumentation and Control Engineers• Electrical Engineers• Project Engineers• Maintenance Engineers• Power System Protection and Control Engineers• Building Service Designers• Systems Planners and Managers• Electrical and Instrumentation TechniciansPractical Operation,Maintenance & Testing ofFor Engineers & Technicians

Schematic Diagram of Diesel Engine Power Plant:

Field of use(Applications):

The diesel electric power-plants are chiefly used in the fields mentioned below.

1. Peak load plant: The diesel plants are used in combination with thermal or hydro-plants as peak load plants. This plant is particularly preferable as peak load plant as it can be started quickly and it has no standby losses as in the case of thermal plants where boilers always must be kept hot.

2. Mobile plants: Mobile diesel plants mounted on skids or trailers can be used for temporary or emergency purposes such as for supplying power to large civil engineering works for supplementing electricity supply systems that are temporarily short of power.

3. Stand-by Units: This can be used as a standby unit to supply part load when required. For example, this can be used with hydro-plant as stand-by unit. If the water available is not sufficient due to reduced rainfall, diesel stations supply power in parallel with hydro-station. The use is made temporarily till the water is available to take the full load.

4. Emergency plant: The plants used for emergency purposes are to standby units, normally idle but are used where power interruption would mean financial loss or danger in key industrial processes, tunnel lighting and operating rooms of hospitals. They are also used for telecommunication and water supply under emergency conditions.

5. Nursery station: When the diesel plant is used to supply the power to a small town in the absence of main grid and which can be moved to another area which needs power on a small scale when the main grid is available is known as "Nursery Station”. The main grid cannot extend to every corner of the country till there are enough loads. Many times the extension of grid is not possible due to the constructional difficulties as in Assam. Diesel unit of small capacity can be installed to supply the load to a small town during the process of development and it can be removed to another required place till the main grid for tapping the power is available.

6. Starting stations: The diesel units are used to run the auxiliaries for starting the large steam plants.

7. Central stations: This can be used as central station where the capacity required is small (5 to10 MW). The limit is generally decided by the cost of the plant and local conditions regarding the availability of fuel and water, space requirements and non-availability of the grid.

Types of diesel engines used for diesel power plants:

The diesels engines are generally used in diesel engine power plant are as following

1. Four-stroke Engines and2. Two-stroke Engines.

The four-stroke engine develops power after every two revolutions of crank shaft. Whereas

Two-stroke engine develops power with each revolution of crank shaft. Generally

Two-stroke engines are favored for diesel power plants for the advantages described later.

Duel Fuel Engines: In duel fuel engines, gas and oil both are used as fuels for the engines. The gas is used as main fuel and oil is used as helper for ignition.In the duel fuel engine, the air and gas are taken in during suction stroke. The pressure of the mixture is increased during compression stroke. Near the end of the compression stroke, the pilot oil is injected into the cylinder. The compression heat first ignites the pilot oil and then gas mixture. The further actions of the engine are similar to the diesel engine. The air-gas ratio is comparatively higher in duel fuel engines compared with gas engines.There is keen interest in the diesel power plants to use the duel fuel engines for better economy and proper use of available gaseous fuels in the country. The gas may be a waste product as in the case of sewage treatment installations or oil fields where the economic advantage is self-evident. With the wider availability of natural gas, the duel fuel engines may become an attractive means of utilizing gas as fuel at off-peak tariffs for the generation of electrical energy.

Operating principle of Diesel Engine:

A diesel engine has used diesel cycle principle to operate the four sequential steps. The 4 steps are done in 2 stokes or 4 stokes of piston. A stroke is the distance from top dead center to bottom dead center. The piston travels down for one stroke on intake, up for compression, down for power, and back up for exhaust. The four stoke of a diesel engine are given below:

Intake Stoke: the inlet valve opens and the piston starts to move down from top dead center. Air enters the cylinder through the inlet port. When the piston reaches bottom dead center, the cylinder is full of air. The inlet valve closes.

Compression Stroke: The compression stroke begins with the piston at bottom dead center and rising up to compress the fuel and air mixture. Since both the intake and exhaust valves are closed, there is no escape for the fuel and air mixture, and it is compressed to a fraction of its original volume. At this point, the fuel sprayed in a nice pattern and ignited automatically.

Power stoke: in this stoke both valves stay closed as the piston rises. Just before it reaches top dead center, an injector sprays fuel into the chamber. It mixes with the very hot compressed air and ignites. Combustion occurs, the temperature rises much higher and the gases expand and force the piston down in a power stroke. The piston reaches bottom dead center, the exhaust valve opens.

Exhaust Stoke: With the exhaust valve open and inlet valve closed, the piston moves up, forcing exhaust gases out of the exhaust port. The piston reaches top dead center, the exhaust valve closes, the inlet valve opens and the cycle starts again.

Fig

Essential element of diesel power plant(Short description of diesel components:

1. Diesel engine:This is the key element for a diesel power plant. It is also called compression ignition engines as they are called are generally classified as two stroke engine and four stroke engines. In diesel engine, air admitted into the cylinder is compressed, the compression ratio being 12 to 20. At the end of compression stroke, fuel is injected. It burns and the burning gases expand and do work on the position. The engine is directly coupled to the generator. The gases are then exhausted from the cylinder to atmosphere.

Figure: Diesel Engine2. Air-filter and supercharger: The function of the air filter is to remove the dust from the air which is taken by the engine.

3. Supercharger: The function of the supercharger is to increase the pressure of the air supplied to the engine to increase the power of the engine. The superchargers are generally driven by the engines.

Engine Auxiliary Systems of Diesel Power Plant:

Engine starting system:This includes air compressor and starting air tank. The function of this system is to start the engine from cold supplying compressed air.

Fuel system:Pump draws diesel from storage tank and supplies it to the small day tank through the filter. Day tank supplies the daily fuel need of engine. The day tan is usually placed high so that diesel flows to engine under gravity.Diesel is again filtered before being injected into the engine by the fuel injection pump. The fuel is supplied to the engine according to the load on the plant.

Air intake system:Air filters are used to remove dust from the incoming air. Air filters may be dry type, which is made up of felt, wool or cloth. In oil bath type filters, the sir is swept over a bath of oil so

that dust particles get coated.

Exhaust system:This system leads the engine exhaust gas outside the building and discharges it into atmosphere. A silencer is usually incorporated in the system to reduce the noise level. The exhaust system of a diesel engine performs three functions. First, the exhaust system routes the spent combustion gasses away from the engine, where they are diluted by the atmosphere. This keeps the area around the engine habitable. Second, the exhaust system confines and routes the gases to the turbocharger, if used. Third, the exhaust system allows mufflers to be used to reduce the engine noise.

Engine cooling system:The temperature of burning gases in the engine cylinder is the order of 1500 to 2000’C. To keep the temperature at the reasonable level, water is circulated inside the engine in water jackets which are passage around the cylinder, piston, combustion chamber etc. hot water leaving the jacket is sent to heat exchanger. Raw water is made to flow through the heat exchanger, where it takes up the heat of jacket water. It is then cooled in the cooling tower and re-circulates again.

Engine lubrication system:It includes lubricating oil tank, oil pump and cooler. Lubrication is essential to reduce friction and wear of engine parts such as cylinder walls and piston.Lubricating oil which gets heated due to friction of moving parts is cooled before recirculation. The cooling water used in the engine is used for cooling the lubricant also.

Governing system: The governing of diesel engine is done by varying the quantity of fuel supplied to the engine. Generally constant stroke with variable suction or variable bypass method is used to control the quantity oil fuel supplied according to load. Centrifugal type governor is used to control the suction or bypass of the fuel.

Installation of Diesel Power Plant:

Site selection of diesel power plant:The following Factors should be considered while selecting the site for a diesel power plant:

• Foundation sub-soil condition: the condition of sub-soil should be such that a foundation at a reasonable depth should be capable of providing a strong support to the engine.

•Access to the site: the site should be so selected that it is accessible through rail and road.

•Distance from that load centre: the location of the plant should be near the load centre. This reduces the cost of transmission lines and maintenance cost. The power loss is minimized.

•Availability of water: Sufficient quantity of water should be available at the site selected.

•Fuel transportation: The site selected should be near to the source of fuel supply so that transportation charges are low.

Engine construction:

Operation and Maintenance:

Diesel engines comprise the vast majority of prime movers for standby power generators because of their reliability, durability and performance under load. Diesel powered generators are depended on for back-up power systems in the most critical locations: hospitals, airports, government buildings, telecommunications facilities, and even nuclear power plants. In standby power applications, diesel generators can start and assume full-rated load in less than 10 seconds, and they typically can go 30,000 hours or more between major overhauls. This remarkable set of credentials is unique to diesel engines, but like any mechanical device, maintenance is critical for ensuring that a diesel powered standby generator will start and run when needed. Facilities with qualified in-house technical personnel can often perform required preventive maintenance on diesel generators. Other facility managers prefer to contract with a local service provider or power system distributor for regular maintenance service—especially if they have generators in multiple locations. (For unplanned maintenance, engine repairs or overhauls, it is always best to use qualified diesel service technicians.)

Preventive maintenance:

Because of the durability of diesel engines, most maintenance is preventive in nature. Preventive diesel engine maintenance consists of the following operations:• General inspection• Lubrication service• Cooling system service• Fuel system service• Servicing and testing starting batteries• Regular engine exerciseIt is generally a good idea to establish and adhere to a schedule of maintenance and service based on the specific power application and the severity of the environment. For example, if the generator set will be used frequently or subjected to extreme operating conditions, the recommended service intervals should be reduced accordingly. Some of the factors that can affect the maintenance schedule include:• Using the diesel generator set for continuous duty(Prime power)• Extreme ambient temperatures• Exposure to weather• Exposure to salt water• Exposure to dust, sand or other airborne contaminatesIf the generator set will be subjected to some or all of these extreme operating conditions, it is best to consult with the engine manufacturer to develop an appropriate maintenance schedule. The best way to keep track of maintenance intervals are to use the running time meter on the generator set to keep an accurate log of all service performed. This log will also be important for warranty support.

General inspection:

When the generator set is running, operators need to be alert for mechanical problems that could create unsafe or hazardous conditions. Following are several areas that should be inspected frequently to maintain safe and reliable operation.• Exhaust system: With the generator set operating, inspect the entire exhaust system including the exhaust manifold, muffler and exhaust pipe. Check for leaks at all connections, welds, gaskets and joints, and make sure that the exhaust pipes are not heating surrounding areas excessively. Repair any leaks immediately.• Fuel system: With the generator set operating, inspect the fuel supply lines, return lines, filters and fittings for cracks or abrasions. Make sure the lines are not rubbing against anything that could cause an eventual breakage. Repair any leaks or alter line routing to eliminate wear immediately.• DC electrical system: Check the terminals on the starting batteries for clean and tight connections. Loose or corroded connections create resistance which can hinder starting.• Engine: Monitor fluid levels, oil pressure and coolant temperatures frequently. Most engine problems give an early warning. Look and listen for changes in engine performance, sound, or appearance that will indicate that service or repair is needed. Be alert for misfires, vibration, excessive exhaust smoke, loss of power or increases in oil or fuel consumption.

Lubrication service:

Check the engine oil level when the engine is shut down at the interval specified in FIGURE 1. For accurate readings on the engine’s dipstick, shut off the engine and wait approximately

10 minutes to allow the oil in the upper portions of the engine to drain back into the crankcase. Follow the engine manufacturer’s recommendations for API oil classification and oil viscosity.Keep the oil level as near as possible to the “full” mark on the dipstick by adding the same quality and brand of oil.

Fuel system service:

Diesel fuel is subject to contamination and deterioration over time, and one reason for regular generator set exercise is to use up stored fuel over the course of a year before it degrades. In additional to other fuel system service recommended by the engine manufacturer, the fuel filters should be drained at the interval indicated in FIGURE 1. Water vapor accumulates and condenses in the fuel tank and must also be periodically drained from the tank along with any sediment present.

Generator set exercise:

Generator sets on continuous standby must be able to go from a cold start to being fully operational in a matter of seconds. This can impose a severe burden on engine parts. However, regular exercising keeps engine parts lubricated, prevents oxidation of electrical contacts, uses up fuel before it deteriorates, and, in general, helps provide reliable engine starting. Exercise the generator set at least once a month for a minimum of 30 minutes loaded to no less than one-third of the nameplate rating. Periods of no-load operation should be held to a minimum, because unburned fuel tends to accumulate in the exhaust system. If connecting to the normal load is not convenient for test purposes, the best engine performance and longevity will be obtained by connecting it to a load bank of at least one-third the nameplate rating.

Preventive maintenance for diesel engine generators plays a critical role in maximizing reliability, minimizing repairs and reducing long term costs. By following generally recognized diesel maintenance procedures and specific manufacturer recommendations for your application, you’ll be assured that your standby power system will start and run when you need it most.

Performance Testing of Diesel Engine Power Plant:

The performance of the diesel engine focuses on the power and efficiency. The engine varies with parameters of the engine like piston speed, air-fuel ratio, compression ratio inlet air-pressure and temperature. The two usual conditions under which I.C. engines are operated are: (a) Constant speed with variable load, and

(b) Variable speed with variable load.

The first situation is found in a.c. generator drives and the second one in automobiles, railway engines and tractors etc. A series of tests are carried out on the engine to determine its performance characteristics, such as: indicated power (I.P.), Brake power (B.P.), Frictional

Power (F.P.), Mechanical efficiency (ηm), thermal efficiency, fuel consumption and also specific fuel consumption etc. The measurement of these quantities is discussed below. Indicated Mean Effective Pressure (IMRP) In order to determine the power developed by the engine, the indicator diagram of engine should be available. From the area of indicator diagram it is possible to find an average gas pressure which, while acting on piston throughout one stroke, would account for the network done. This pressure is called indicated mean effective pressure (IMEP).

Economy of diesel power plant:

The diesel engine (also known as a compression-ignition or 'CI' engine) is an internal

combustion engine in which ignition of the fuelthat has been injected into the combustion

chamber is initiated by the high temperature which a gas achieves when greatly compressed

(adiabatic compression). This contrasts with spark-ignition engines such as a petrol

engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which

use a spark plug to ignite an air-fuel mixture.

A Diesel engine built by MAN AG in 1906

The diesel engine has the highest thermal efficiency of any standard internal or external

combustion engine due to its very high compression ratio and inherent lean burn which

enables heat dissipation by the excess air. A small efficiency loss is also avoided compared to

two-stroke non-direct-injection gasoline engines since unburnt fuel is not present at valve

overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-

speed diesel engines (as used in ships and other applications where overall engine weight is

relatively unimportant) can have a thermal efficiency that exceeds 50%.

Diesel engines are manufactured in two-stroke and four-stroke versions. They were originally

used as a more efficient replacement for stationary steam engines. Since the 1910s they have

been used in submarines and ships. Use in locomotives, trucks, heavy equipment and

electricity generation plants followed later. In the 1930s, they slowly began to be used in a

few automobiles. Since the 1970s, the use of diesel engines in larger on-road and off-road

vehicles in the USA increased. According to the British Society of Motor Manufacturing and

Traders, the EU average for diesel cars account for 50% of the total sold, including 70% in

France and 38% in the UK.

The world's largest diesel engine is currently a Wärtsilä-Sulzer RTA96-C Common Rail

marine diesel, which produces a peak power output of 84.42 MW (113,210 hp) at 102 rpm.

Advantages and disadvantages of diesel power plant over thermal plants:

Advantages of Diesel Power Station:

1. This is simple in design point of view.

2. Required very small space.

3. It can also be designed for portable use.

4. It has quick starting facility, the small diesel generator set can be started within few

seconds.

5. It can also be stopped as when required stopping small size diesel power station, even

easier than it’s starting

6. As these machines can easily be started and stopped as when required, there may not be

any standby loss in the system.

7. Cooling is easy and required smaller quantity of water in this type power station.

8. Initial cost is less than other types of power station.

9. Thermal efficiency of diesel is quite higher than of coal.

10. Small involvement is less than steam power station.

Disadvantages of Diesel Power Station:

1. As we have already mentioned, the cost of diesel is very high compared to coal. This is

the main reason for which a diesel power plant is not getting popularity over other means

of generating power. In other words the running cost of this plant is higher compared to

steam and hydro power plants.

2. The plant generally used to produce small power requirement.

3. Cost of lubricants is high.

4. Maintenance is quite complex and costs high.

Present trends in diesel research:

The present research work in the diesel engines development is directed towards higher operation speeds, lower specific fuel consumption (kg/kW-hr), lower specific weight (kg/kW) and higher unit size. An air-fuel ratio of 25 : 1 is required for the combustion of diesel fuels. The power developed in the engine is proportional to the weight of fuel burnt in unit time. Therefore, the power developed by the engine can be increased by increasing the weight of air present in the cylinder at each cycle or by increasing the number of cycles per unit time (r.p.m.) or using both. So long the necessary weight of air can be provided in an engine cylinder of given size, theoretically there is no limit to the weight of fuel burnt in unit time and hence to the power which can be developed. The increased weight of fuel burnt creates

lot of mechanical and thermal problems. The solution of these problems can be expected to be major lines of continuing research work.

Discussion and conclusion:

In this unit, we have learnt the functioning of diesel power plant. The diesel engine drives alternator, which converts mechanical energy in to electrical energy. In this unit, we have also studied the concept of fuel injection system and its functioning. The unit, also elaborated on various types of injection schemes. The diesel engine plants are mainly utilised to generate small power output. Which are mostly utilised as standby modes, when power not takes place? Its cost is high.