Difference Between Otto Cycle and Diesel Cycle

Published: 18 Dec 2025

In this article, we will discuss the Difference Between Otto Cycle and Diesel Cycle in a simple and easy way. Both cycles are air-standard internal combustion cycles. They convert chemical energy into mechanical energy. These cycles are widely used in modern vehicles and machines. Understanding them helps students and beginners learn engine basics. Let’s explore the details step by step.

Dimensions	Otto Cycle	Diesel Cycle
Definition	The Otto cycle is a thermodynamic cycle used in petrol engines. It adds heat at a constant volume. A spark plug ignites the air-fuel mixture. Nikolaus Otto introduced this cycle in 1876.	The Diesel cycle is used in diesel engines. It adds heat at constant pressure. Fuel ignites due to high air temperatures. Dr. Rudolph Diesel introduced this cycle in 1897.
Method of Ignition	Uses a spark plug to start combustion. The spark ignites the compressed air-fuel mixture.	Does not use a spark plug. Fuel ignites automatically due to a high compression temperature.
Heat Addition Process	Heat is added at a constant volume. The piston remains at the top dead center during combustion.	Heat is added at constant pressure. The piston keeps moving while the fuel burns.
Fuel Used	Uses petrol or gas as fuel.	Uses diesel fuel only.
Compression Ratio	Works with a lower compression ratio. It usually ranges from 7:1 to 10:1.	Uses a higher compression ratio. It usually ranges from 15:1 to 22:1 for self-ignition.
Efficiency	Offers good efficiency at high speeds. It gives a smooth and quick response.	Provides higher thermal efficiency. It also gives better fuel economy.
Engine Weight	Engines are lighter in weight due to lower pressure.	Engines are heavier and stronger to handle high pressure.
Speed and Performance	Best for high-speed and smooth operation. It produces less vibration.	Best for high-torque and heavy-duty work. It performs well under load.
Applications	Used in cars, bikes, lawn mowers, and small petrol engines.	Commonly found in trucks, buses, generators, ships, and other heavy-duty machines.
Cost	Engines are usually cheaper. Maintenance is also easier and less costly.	Engines cost more initially. They last longer and reduce fuel costs over time.

Conclusion

In conclusion, in this article, we covered the Difference Between Otto Cycle and Diesel Cycle in detail. Both cycles have their own advantages and uses. Hope you find this helpful. Then share it with your friends and help them learn too.