Diesel Power Plants Working Principle

Diesel power plants are standby power plants. Whereas a diesel engine is used as the prime mover to generate electrical energy is called a diesel power plant. To generate mechanical energy diesel burns inside the diesel engine, and the products of this combustion act as the working fluid. The diesel engines are coupled with an alternator if the diesel engine or prime mover rotates alternator also rotates and then produces electrical energy.

It means the alternator converts mechanical energy into electrical energy. Diesel power plants are very costly due to the high price of diesel. The diesel power plant is used to generate a small amount of electrical power.

We know that thermal power plants, and hydroelectric power plants are used to generate bulk electrical energy due to the cheap cost of fuel and simple construction. Diesel power plants run when load demand becomes more high than the base load and it is also called peak load power plant because it is used as a peak period (5 pm to 12 am).

What do you mean by diesel-fired power plant?

Prime mover is one of the most essential devices for electrical power plants. But in a diesel power plant, the diesel engine is used as a prime mover to generate electricity. In a diesel power plant, diesel is fired by using a diesel engine and generates mechanical energy that is converted into electrical energy by using an alternator.

Indeed, diesel plants or diesel engine power stations are used to meet the peak demand that certainly occurs in the power system. It is noted that the diesel engine power plant is not used to generate bulk electricity due to its huge per-unit cost.

Working principle of diesel power plant

Working of the diesel power plant is not the same as some other electrical power plants like a nuclear power plant, coal power plant hydroelectric power plant, etc. The working of diesel power plant or basic working principle of diesel power plant is that thermal energy is converted into mechanical energy.

This mechanical energy is converted into electrical energy to generate electricity using generators or alternators. A diesel power plant works on four main stages such as compression, combustion, expansion, and cooling.

A diesel engine works as a prime mover diesel is burned inside these combustion engines and products act as working fluids for the production of mechanical energy. Diesel engines run an alternative that converts mechanical power into electrical power. 


Since the cost of production is significant due to the high cost of diesel, such power plants are used only for small power generation. Although steam power plants and hydropower plants are always used to generate bulk power at a cheap cost, diesel power plants are favored in places where electricity demand is low, adequate coal and water are not available and transportation facilities are inadequate.

To start a diesel engine one has to rotate between 150 to 250 rpm. The purpose of the initial system is to provide the required torque to achieve the required minimum cranking speed. The crankshaft is turned on when the starter motor starts to rotate the flywheel, which then starts the piston movement. There are two types of diesel power plants stationary diesel power plants and mobile diesel power plants.

Stationary diesel power plant

The four-stroke diesel engines used in stationary diesel power plants use power ratings of 110, 220, 330, 440, and 735 kW (kW). The advantages of diesel power plants are optimal economy of operation, stable operating features, and easy and fast start.

The main disadvantage is the relatively short spacing between large overhauls. Diesel power plants are mainly used to serve transmission lines or areas where water supply sources are limited and where it is not possible to build steam power plants or hydropower plants. Fixed-type diesel is usually equipped with a synchronous generator.

The economic efficiency of a diesel power plant is significantly improved if the engine waste heat (55 to 60 percent of the total heat release the engine currently has available) can be used to preheat fuel and oil or for internal heating of the power station building or adjacent premises. In diesel power plants with a high power rating (above 750 kW), waste heat can be used in a heating system that serves an entire block or an entire city area near the power plant.

Mobile diesel power plant

Mobile diesel power plants are widely used in agriculture forestry and geological exploration. In these applications, diesel power plants can be used as power sources for power or lighting networks; these can be used as main, auxiliary, or standby power sources.

In transportation, diesel power plants are a basic energy source (for example, diesel-electric locomotives and diesel ships). In mobile diesel power plants, high-speed diesel acts as a prime mover.

A mobile diesel power plant includes a diesel-electric unit itself, spare parts, appliances and accessories, a set of wires to connect to the load, and firefighting equipment. Power plants rated at 20 kW or more are usually installed in two-axis, covered trailers.

Such a mobile station has not only diesel-electric units but also power distribution cabinets (or panels), cabinets with automatic controls, remote control consoles, heating and ventilation equipment, rectifiers, and storage batteries that automatically control the feeding system.

Diesel power plant components

There are different types of essential diesel power plant components. Each component plays an important role in the generation of electricity.

  • Diesel Engine
  • Fuel Supply System
  • Engine Air Intake System
  • Diesel engine Exhaust System
  • Diesel engine Cooling System
  • Engine Lubrication System

Diesel engine

Diesel engines are the main component used in diesel-electric power plants to develop mechanical power. This mechanical energy we use to run generators and to generate electrical energy. Diesel engines are mechanically connected to a generator to produce electrical power. When diesel fuel is burning inside the engine, it starts to generate mechanical power.

The combustion of diesel fuel increases the temperature and pressure inside the engine. Due to this pressure, gas is formed, this gas pushes the piston inside the diesel engine and then mechanical energy is generated. With the use of this mechanical power, the shaft of the diesel engine begins to rotate.

Fuel supply system

Diesel power plants include fuel storage tanks, fuel filters or strainers, fuel transfer pumps, day tanks, heaters, and connecting pipes. First of all diesel fuel is stored in storage tanks with the help of transport facilities (road, rail, etc.). This diesel fuel is then transferred to the day tank; the job of the day tank is to determine how much diesel the store needs for 24 hours.

If the day tank is full or excess flow occurs, the excess diesel is returned to the storage tank. Filters or strainers are used to purify diesel. The fuel is transferred to the diesel tank with the help of a transfer pump.

Diesel engine air intake system

Diesel engine air intake systems include air filters, air tanks, compressors, and connecting pipes. Air filters are used to supply fresh air to diesel engines for combustion purposes. The engine needs fresh air because the entry of dust particles into the air in the engine will have a devastating effect on the valves, cylinders, and pistons. A valve is used to increase the air pressure supplied to the compressor or supercharged engine. This will help increase the output power.

Diesel engine exhaust system

The diesel engine exhaust system consists of a silencer and connecting duct. Since the temperature of the exhaust gas is high enough, it is used to heat the air supplied to the fuel oil or diesel engine. Exhaust gases are removed from the engine into the atmosphere through the exhaust system. A silencer is usually used in this system to reduce the noise level of the engine.

Diesel engine cooling system

The diesel engine cooling system consists of a coolant pump, water cooling tower, and connecting pipe work. The heat generated due to internal combustion drives the engine. However, some of this heat raises the temperature of different parts of the engine. High temperatures can cause permanent damage to the machine. Therefore, it is essential to maintain the overall temperature of the engine. The cooling system of the diesel power station works the same way.

The cooling system is required to carry heat from the diesel engine so that its temperature is within safe limits. The water pump conducts water to the cylinders of the diesel engine to carry heat. Cooling towers are used to reuse the same water. The cooling system requires a water source, a water pump, and a cooling tower.

The pump conducts water through the cylinder and the head jacket. Water removes heat from the engine and it heats up. The hot water is cooled through the cooling tower and re-circulated for cooling. The cooling system can be divided into two types: open cooling system and closed cooling system.

Engine lubrication system

The diesel engine lubrication system includes oil pumps, oil tanks, filters, coolers, purifiers, and connecting pipes. This system provides lubricating oil to the running parts of the system to reduce wear and tear between engine parts. This system reduces the amount of water rubbing on the surface of the engine. Here the oil is stored in the main oil tank.

The oil then goes through the oil filter to remove impurities. From the filtering point, this clean oil is distributed to different points of the machine where lubrication is required. The oil is supplied to the system to keep the oil temperature as low as possible. It is then cooled through cold water through a heat exchanger and then it is fed to the engine.

Operating cost of diesel power plant

Electricity can be generated in various ways. Coal, oil, gas, nuclear energy, and water are the major electricity generation sources. But oil is one of the most expensive fuels to generate electricity. The per-unit generation cost of diesel power plants is much higher than some other conventional energy source power plants. We know well diesel is a very costly fuel. For this reason, the generation cost is higher than others.  


Statistics show that the per-unit cost of diesel power plants is $0.15 to $0.32 but rental power plants per unit cost is $0.23 to $0.33 which is comparatively high. The power plant’s cost is divided into three, such as initial cost, fixed cost, and running cost. The operating cost of diesel power plants is indeed more due to the high price of diesel. Due to the higher operating cost diesel power plants are operated for the peak load. We have given a chart that can give the assumption about the per-unit operating cost.

Coal-fired combustion turbine$0.02 – $0.04  per unit operating cost
Coal gasification combined-cycle$0.04 – $0.08
Natural gas combustion turbine$0.04 – $0.10
Natural gas combined-cycle$0.04 – $0.10
Wind turbine (includes offshore wind)Less than $0.01
Solar energy$0.02 – $0.05
Hydro electric energyLess than $0.01
Nuclear energy$0.02 – $0.05

Diesel power plant advantages and disadvantages

The diesel engine is used as the prime mover for the diesel power plant. Diesel is ignited inside the engine and these combustion products act as working liquids in the production of mechanical energy. Diesel engines run an alternative that converts mechanical power into electrical power. There are lots of advantages and disadvantages of diesel power plants. The advantages are given below:

  • The layout of the diesel power plants is very simple. 
  • The diesel power plant occupies a small place.
  • It can be started quickly and picked load within a very short time.
  • The diesel power plant has no standby losses.
  • It requires a small quantity of water to cool.
  • Diesel power plant requires less staff.
  • The thermal efficiency is higher than the steam power plants.


  • Diesel power plants have higher running costs than hydroelectric power plants.
  • The diesel power plant does not work successfully to meet the overload condition for a longer period, due to higher fuel costs and low generation power.
  • It generates a small amount of electrical energy.
  • The operating cost is very high.
  • Maintenance costs are also very high.

Diesel power plant’s efficiency

The actual heat efficiency of a modern thermal power plant usually ranges from 35% to 49%. 2.3 Generator Damage Modern generators achieve an efficiency of 96% -99%. Most of the energy losses occur in thermal power plants from boiler heat loss, pipe heat loss, cold source loss, mechanical loss, generator loss, etc. Diesel power plants efficiency is about 35% and this plant has low standby losses.

Why Diesel Power Plant is not used as a Base Load Power Plant?

Indeed, the diesel power plant is not used as baseload power plants. Basically, a diesel power plant is used for the peak period (5 pm to 12 am). Because diesel power plants have high running costs due to their fuel. For this reason, whenever load demand is increased then diesel power plants are operated. For this reason, the diesel power plant is also called a standby power plant.

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