Content Writer
The difference between petrol and diesel engines relies on compressed air. In the case of diesel engines, they rely on heavily compressed air without any spark plugs, while petrol engines use spark plugs to ignite the air-fuel mixture.
- The difference between petrol and diesel engines depends upon the working cycle.
- Working of a diesel engine depends upon the diesel cycle.
- The working of the petrol engine depends upon the Otto cycle.
- It is determined that most of the transport uses either petrol engine or diesel engine.
- They are widely used engines available in the market.
- Another type of engine works on the principle of heat transfer.
- Fuel is used as a parameter of classification for various types of engines.
Read More: Two Stroke Engines
Key Terms: Diesel Engine, Petrol Engine, Power Cycle, Otto Cycle, Diesel Cycle, Compression Ratio, Ignition of Fuel, Heat Transfer, Fuel, Heat, Pressure, Engine
Diesel Engine
[Click Here for Sample Questions]
In diesel engines, the fuel is put into a combustion chamber, and then the air inside the chamber undergoes adiabatic compression. It results in so much heat that the fuel is ignited. The compression ratio is very high in the case of diesel engines.
- In diesel engines, the fuel is ignited by compressed air.
- The air-fuel mixture is compressed to 23 to 24 times its original volume.
- No spark plugs are used.
- It uses the diesel cycle, which consists of a constant pressure process, a constant volume process and two isentropic processes.
- Diesel engines have a low rpm (revolutions per minute), which results in a greater torque.
- It is used to push the vehicle uphill and tow or carry a heavy load. That’s why it is used in heavier vehicles.
- These engines use 15-20% less fuel comparatively.
- The fixing and repairing costs of these engines are more expensive.
- Diesel engines are known to produce lower CO2 emissions than petrol engines.
Diesel Engine
Read More:
Petrol Engine
[Click Here for Sample Questions]
In a petrol engine, both the air and fuel undergo compression. The air-fuel mixture is put into the carburettor after compression. The compression ratio is comparatively lower.
- In petrol engines, the air-fuel mixture is ignited by using spark plugs.
- Petrol, being highly volatile and inflammable, immediately burns with a spark.
- Petrol engines work on the Otto cycle, mainly consisting of two isochoric and two isentropic processes.
- They have a higher rpm, which provides great pick-up speed to the vehicles; hence, they are mostly used in lighter vehicles.
- Petrol engines consume more fuel, hence quite expensive running costs.
- The manufacturing and maintenance cost is comparatively lower than diesel engines.
- Such engines have a greater rate of CO2 emissions but do not emit soot-like particles.
Petrol Engine
Read More: Reversible and Irreversible Processes
Power Cycle
[Click Here for Sample Questions]
In the intake process, the air is introduced into the cylinder via the opening intake valve. In the compression process, the intake wall is closed, and then the air is compressed with the fuel. With the proceeding compression, the air and fuel are ignited, causing an explosion.
- It is this explosion that causes the piston to move downwards and moves the crankshaft to produce motion.
- This is the power process that immediately follows the compression process.
- The last phase of the power cycle is the exhaust process.
- In this, the exhausting air-fuel mixture is expelled out of the cylinder via the opening exhaust valve, allowing a new cycle to begin.
- The basic processes of the power cycle in both engines are the same.
- There are certain variations in terms of fuel consumed, fuel combustion process, and work efficiency.
Power Cycle
Read More: Joule Thomson Effect
Differences between Petrol and Diesel Engine
[Click Here for Sample Questions]
Key differences between petrol and diesel engine are given below:
| Diesel Engine | Petrol Engine |
|---|---|
| Diesel engines have a higher Compression ratio. | Petrol engines have a lower Compression ratio. |
| The fuel is ignited by adiabatic compression of the air mixed with the fuel. | The fuel is ignited by a spark from the spark plugs. |
| Diesel engines work on the Diesel cycle. | Petrol engines work on the Otto cycle. |
| Diesel engines provide a greater torque because of which they are used in heavier vehicles. | Petrol engines provide a lower torque and so is used in lighter vehicles. |
| The running cost is lower as it consumes less fuel, but the initial and maintenance cost is comparatively higher. | The running cost is more as it consumes more fuel, but the initial and maintenance cost is comparatively lower. |
| Produces less amount of carbon dioxide. | Produces a greater amount of carbon dioxide. |
Read More:
Things To Remember
- The difference between petrol and diesel engine depends upon the value of torque.
- Diesel engines ignite the fuel using adiabatic compression, while petrol engines ignite the fuel using a spark.
- The reason behind the use of petrol engines in lighter vehicles is that they come at cheaper prices.
- SUVs and bigger, heavier vehicles use diesel engines.
- Sports cars have great pick-up speed and use petrol engines.
- It has been determined that petrol engines emit more carbon dioxide than diesel engines.
Read More: Born-Haber Cycle
Sample Questions
Ques: What is the difference between petrol and diesel engine? (5 marks)
Ans: The basic difference between petrol and diesel engine are as follows:
| Diesel Engine | Petrol Engine |
|---|---|
| Diesel engines have a higher compression ratio. | Petrol engines have a lower compression ratio. |
| The fuel is ignited by adiabatic compression of the air mixed with the fuel. | The fuel is ignited by a spark from the spark plugs. |
| Diesel engines work on the diesel cycle. | Petrol engines work on the otto cycle. |
| Diesel engines provide a greater torque because of which they are used in heavier vehicles. | Petrol engines provide a lower torque and so is used in lighter vehicles. |
| The running cost is lower as it consumes less fuel, but the initial and maintenance cost is comparatively higher. | The running cost is more as it consumes more fuel, but the initial and maintenance cost is comparatively lower. |
Ques: Name the four processes of the power cycle used in both types of engines? (4 marks)
Ans: The four processes of the power cycle are as follows:
- Intake: The air and fuel are introduced into the cylinder.
- Compression: The air and fuel mixture is compressed.
- Power: The fuel is burned to produced energy.
- Exhaust: Removal of the burnt exhaust fuel.
Ques: Which can be considered better, diesel engine or petrol engine? (2 marks)
Ans: Diesel engines and petrol engines, both have their own advantages and disadvantages. It is difficult to determine which one is better, but when it comes to providing a greater toque (which is needed in heavier vehicles) diesel engines are suitable while petrol engines are efficient in providing high speed and are cost-effective, so used in lighter vehicles. The power cycles involved in diesel and petrol engines are different. Diesel engines work on the diesel cycle whereas petrol engines work on the Otto cycle.
Ques: What is the difference between the Diesel cycle and Otto cycle? (4 marks)
Ans: The difference between diesel cycle and otto cycle are as follows:
| Diesel Cycle | Otto Cycle |
|---|---|
| Diesel cycle was introduced by Dr. Rudolph Diesel in 1897. | Otto cycle was introduced by Nicolas Otto in 1876 |
| It will condense the mixture at 22.1 ratios. | It will condense the mixture at 11.1 ratios. |
| Diesel cycle start with adiabatic process. | Otto cycle start with intake stroke. |
| It produces less amount of carbon dioxide. | It produces a greater amount of carbon dioxide. |
Ques: What is meant by diesel engine? (3 marks)
Ans: In diesel engines, the fuel is put into a combustion chamber and then the air inside the chamber undergoes adiabatic compression which results in so much heat that the fuel is ignited. In diesel engines, the compression ratio is very high. In diesel engines, the fuel is ignited by compressed air. The air-fuel mixture is compressed to 23 to 24 times its original volume. No spark plugs are used. Diesel engines have a Diesel cycle consisting of a constant pressure process, a constant volume process and two isentropic processes.
Ques: What is the difference between diesel and petrol engines on the basis of cost efficiency? (2 marks)
Ans: Diesel engines use 15-20% less fuel comparatively, hence a cheap running cost. These engines are made at higher costs. Moreover, the fixing and repairing of these engines is more expensive. Petrol engines on the other hand consume more fuel, hence quite expensive running costs. But the manufacturing and maintenance cost is comparatively lower than diesel engines.
Ques: Explain the petrol engine? (4 marks)
Ans: In a petrol engine, both the air and fuel undergo compression. The air-fuel mixture is put into the carburettor after compression. The compression ratio is comparatively lower.
- In petrol engines, the air-fuel mixture is ignited by using spark plugs.
- Petrol, being highly volatile and inflammable, immediately burns with a spark.
- Petrol engines work on the Otto cycle, mainly consisting of two isochoric and two isentropic processes.
- They have a higher rpm, which provides great pick-up speed to the vehicles; hence, they are mostly used in lighter vehicles.
- Petrol engines consume more fuel, hence quite expensive running costs.
Ques: Explain the working of diesel engine? (4 marks)
Ans:The working of the diesel engine is based on four steps:
- Induction Stroke: In this case, the piston of the engine is pulled down, and air enters the engine cylinder.
- Compression Stroke: In the compression stage, the piston of the engine is pulled up to compress the air.
- Power Stroke: In the power stroke stage, fuel is added to the air, which is compressed.
- Exhaust Stroke: In this stage, fuel starts burning because of the required ignition temperature created by the compressed air.
Ques: Explain the working of petrol engine? (4 marks)
Ans: The working of a petrol engine is as follows:
- In the first stage, petrol is added to the cylinder of the engine along with the air.
- Next, petrol and air are mixed together and compressed by the use of a crankshaft.
- In the next stage, sparks are used in the mixture of petrol and air.
- The mixture will push the piston downwards.
- Lastly, gas is released from the valve.
Ques: What are the disadvantages of diesel cars? (4 marks)
Ans: The disadvantages of diesel car are as follows:
- Diesel fuel is quite costly.
- Its insurance cost is 10-15% higher in comparison to petrol cars.
- Diesel cars produce large amounts of NO2.
- The particles in diesel fuel will cause asthma.
- It is quite noisy.
Ques: What is the difference between combustion and burning? (3 marks)
Ans: The difference between combustion and burning are as follows:
| Combustion | Burning |
|---|---|
| Combustion is a type of flameless process. | Burning produce large amount of flame. |
| It produce more amount of heat. | It produce less heat. |
| It place in presence of hydrocarbon. | It take place in presence of solid fuels. |
Read Also:
Comments