Table of Contents
What is a Diesel engine?
Diesel engine is a machine (Internal Combustion Engine) that converts chemical energy of diesel fuel into the Mechanical energy. It was invented by Rudolf Diesel.
It is a type of Internal combustion engine which works on Diesel (fuel). In Diesel engine combustion of fuel happens due to high temperature and pressure inside the combustion chamber.
Types of Diesel engines
On the basis of number of strokes required to complete the combustion process, diesel engines can be classified into two types.
Working of Diesel engine
Diesel engine works on the Diesel cycle. Irrespective of number of strokes required to complete the combustion process, a diesel engine works in following steps.
Note: We are not particularly concerned here on two stroke or four stroke engine.
Step 1: Suction of air from environment
In this step engine sucks air from the environment and then compresses it.
Step 2: Injection of fuel
In this step fuel is injected to the engine at very high temperature and pressure.
Step 3: Combustion
Due to very high temperature and pressure inside the engine, the fuel explodes, which results in the reciprocating movement of the piston.
Step 3: Exhaust
In this step exhaust gases of combustion process are made out of the engine.
Again, fresh air is sucked and the cycle goes on and on.
Diesel Cycle explanation
A diesel engine works on diesel cycle. There are four processes in diesel cycle (as shown in diagram)
Diesel Cycle
Process 1-2
It is the isentropic compression of the air which is sucked in from environment. In this process work (Win) is done by the system to compress the air.
Process 2-3
It is where the diesel is injected. It is an isobaric process. Here fuel burns due to high temperature and pressure. In this process engine gets heat (Qin).
Process 3-4
It is the power stroke. It is an isentropic expansion process. The work obtained here is Wout.
Process 4-1
In this an isochoric process. In this step all the exhaust gases of combustion process are made out of the engine. Some heat also gets wasted with exhaust gases i.e. Qout.
Advantages of Diesel engines
There are several advantages (compared with Gasoline or petrol engines) of Diesel engines, some of them are.
- They are more efficient
- They are more durable
- They generate greater torque
- Absence of spark plugs lowers the cost
Limitations or disadvantages of Diesel engines
Some disadvantages of diesel engines (compared with Petrol or Gasoline engines) are.
- High speed performance is not that good
- Regular maintenance is required
- They are heavier
Applications of Diesel engines
There are several applications of diesel engines and some of them are.
- Diesel generators
- Locomotives
- Farming equipment
- In construction equipment
- In cargo and cruise ships
- In buses and trucks
Comparison between diesel and petrol engines
| Diesel Engines | Petrol Engines |
| They are used for heavy duty requirements | They are used for relatively light duty requirements |
| They are generally low speed engines | They are generally relatively high speed engines |
| Their maintenance cost is high | They have relatively less maintenance cost |
| Compression ratio is high (15-20) | Compression ratio is low (6-10) |
| Relatively difficult to start | Easy to start |
| Combustion happens at constant pressure | Combustion happens at constant volume |
| Combustion happen due to high compression | Charge (air and fuel mixture) is ignited by a spark |
| Fuel is injected directly into the combustion chamber with the help of fuel injection system | Carburetor is used to prepare air fuel mixture |
| Only air intake happens during suction stroke | Air-fuel mixture intake happens during suction stroke |