What is the Difference Between a Petrol Engine and a Diesel Engine?
For JEE Main 2025, understanding the difference between petrol and diesel engines is essential, as it is a common topic in Mechanical Engineering concepts. Petrol and diesel engines both operate as internal combustion engines but differ significantly in their working principles, fuel usage, efficiency, and applications. A petrol engine, also known as a spark-ignition engine, uses a spark plug to ignite a fuel-air mixture, creating the power needed to drive the engine. In contrast, a diesel engine, or compression-ignition engine, relies on the compression of air to high temperatures, which ignites the diesel fuel upon injection, making it more fuel-efficient but with a slower ignition process.
Students preparing for engineering exams like JEE Main. Vedantu provides the best explanation of the topic in a very understandable way to help in cracking JEE Mains.
What are Petrol and Diesel Engines?
Cars, trucks, buses and other automobiles run on engines based on fossil fuels. The two most common types of engine are petrol engine and diesel engine. Most of the vehicles run either on petrol engines or diesel engines. The main difference between a petrol engine and a diesel engine is that in a petrol engine, fuel and air both are compressed with a spark, while in a diesel engine, only air is compressed, and fuel is injected in compressed air. Petrol engines and diesel engines work on the Otto cycle and diesel cycle, respectively.
Petrol Engine
Petrol engines are mostly used in cars, scooters, machines, etc. It is an internal combustion engine with spark ignition. It is also known as a gasoline engine. It was 1st invented in Europe, in 1876. It was a very basic model of the petrol engine. After this many improvisations have been done and the present model which people are using is the latest one. In petrol engines, air and fuel are mixed before compression and then an electric spark is used for ignition. Ignition temperature is the lowest temperature at which a fuel or combustible substance, when heated, catches fire. It works on the Otto cycle. Otto cycle explains how in gasoline engines, chemical energy is converted into thermal energy and then into motion.
Petrol Engine
How Does The Petrol Engine Work?
The working of petrol engine can be expressed by the following four steps shown in the image below.
Working of a Petrol Engine
Step 1. Fuel (petrol) and air are added to the cylinder and mixed.
Step 2. The mixture of petrol and air is compressed by the use of a crankshaft.
Step 3. Now spark is used in the mixture and the mixture forces the piston down.
Step 4. Gases go out from the exhaust valve.
Diesel Engine
Generally, trucks and other heavy vehicles run on diesel engines. It is also an internal combustion engine that works on diesel. In these engines, the air is compressed, so it becomes very hot and then fuel (diesel) is injected into it. Thus, diesel reaches its ignition temperature by the heat of compressed air. It is also known as a compression-ignition engine. It was 1st developed by Rudolf Diesel in 1893 in Germany. Diesel engines were mainly used in trains at that time.
How Does a Diesel Engine Work?
A diesel engine works on a diesel cycle. It can be explained by the following steps shown in the figures below:
Step 1. Induction Stroke – Piston of the engine goes down and air comes into the cylinder.
Step 2. Compression Stroke – Piston goes up and compresses the air. Now the air is getting hot.
Step 3. Power Stroke – Now, fuel or diesel is added to the cylinder.
Step 4. Exhaust Stroke – Fuel or diesel starts burning due to ignition temperature provided by hot air. Smoke goes out from the valve.
Petrol Engine vs Diesel Engine
Diesel and petrol both are fossil fuels, but the working of petrol engines and diesel engines differ from each other. The difference between a petrol engine and a diesel engine can be explained by the following points.
Here's the table below illustrates the difference between Petrol and Diesel Engine :
Significance of the Topic Difference Between Petrol and Diesel Engines JEE Main 2025
Understanding the difference between petrol and diesel engines is crucial for JEE Main 2025 as it lays the foundation for questions on thermodynamics, internal combustion, and energy efficiency.
This topic helps students grasp essential concepts in mechanical and automotive engineering, including fuel efficiency, power output, and environmental impact, which are often tested in JEE Main.
Mastery of these topics equips students with the knowledge required to solve questions on engine mechanics and combustion processes.
Conclusion
Understanding petrol and diesel engines is vital for tackling questions on combustion and mechanical efficiency in JEE Main 2025. Understanding this topic not only helps in solving direct questions on engines but also strengthens students’ grasp of broader concepts of thermodynamics and energy.
JEE Main 2025 Subject-Wise Important Chapters
The JEE Main 2025 subject-wise important chapters provide a focused strategy for Chemistry, Physics, and Maths. These chapters help students prioritise their preparation, ensuring they cover high-weightage topics for better performance in the exam.
Important Study Materials Links for JEE Exams 2025
JEE Exams 2025, having the right study materials is crucial for success. The JEE Main and Advanced exams require a strong grasp of Physics, Chemistry, and Mathematics, as well as thorough practice with exam-style questions.
Access to quality resources, including sample papers, practice tests, and detailed notes, helps students review key topics and practice effectively.
FAQs on Difference Between Petrol and Diesel Engine for JEE Main 2025
1. What is the primary difference between petrol and diesel engines?
The major difference between diesel and gasoline engines is that gasoline engines utilise spark plugs to ignite the air-fuel mixture, whereas diesel engines rely entirely on compressed air. Rudolf Diesel discovered that by significantly compressing air, the temperature could be raised to a sufficient level. The temperature would climb to the point where it could cause diesel fuel to ignite.
2. Give the other name of the diesel engine.
Diesel engines are sometimes known as compression-ignition engines. They're also self-igniting engines. It's because, at the end of the compression stroke, the air compresses and gasoline injects into extremely hot air. As a result, the engine uses the heat of compression to start the ignition.
3. What are gasoline engines?
Petrol engines, as the name suggests, run on petrol, which we also refer to as gasoline. As a result, we also call them gasoline engines.
4. What is the difference between petrol and diesel engines?
The main difference between a petrol engine and a diesel engine lies in their ignition methods. Petrol engines use spark plugs for ignition, while diesel engines rely on high compression to ignite the fuel.
5. Can you explain the difference between the petrol engine and diesel engine for JEE Main?
In petrol engines, fuel and air are mixed before compression, while in diesel engines, only air is compressed, and fuel is injected later. This difference affects efficiency and application.
6. What is the compression ratio of petrol engines and diesel engines?
The compression ratio of a petrol engine is generally lower, around 8:1 to 12:1, compared to a diesel engine, which ranges from 14:1 to 25:1. Diesel engines achieve higher efficiency due to this higher compression ratio.
7. What are some major differences between petrol engines and diesel engines?
Key differences include ignition methods, efficiency, fuel type, torque output, and environmental impact, with diesel engines typically being more fuel-efficient and producing more torque.
8. List five differences between petrol and diesel engines important for JEE Main 2025.
Five differences are ignition type (spark vs. compression), fuel efficiency, torque, maintenance needs, and application (lightweight vehicles for petrol vs. heavy-duty for diesel).
9. How does the difference between petrol engines and diesel engines affect vehicle applications?
Petrol engines are commonly used in cars and motorcycles for smooth acceleration, while diesel engines, with higher torque and fuel efficiency, are preferred for trucks and industrial machinery.
10. What is the significance of the compression ratio of petrol engines and diesel engines for performance?
The higher compression ratio of diesel engines leads to greater fuel efficiency and power output, making them ideal for heavy-duty applications, while petrol engines offer smoother and quieter operation.
11. How does the difference between petrol and diesel engines impact fuel efficiency?
Diesel engines are generally more fuel-efficient than petrol engines due to their higher compression ratio and energy-dense diesel fuel, which is beneficial for long-distance and heavy-duty use.
12. Does Vedantu offer a detailed explanation of the petrol engine and diesel engine differences for JEE Main 2025?
Yes, Vedantu provides a comprehensive breakdown of petrol and diesel engine differences, covering key concepts like the combustion process, efficiency, and practical applications relevant to JEE Main 2025.
13. Why is it important to know the difference between petrol engines and diesel engines for JEE Main Chemistry?
Understanding these differences is essential in JEE Main Chemistry as it connects to concepts in thermodynamics, combustion, and efficiency, all of which are key topics in engineering applications.
