What is the Difference Between Spark Ignition and Compression Ignition?

The main difference between spark ignition and compression ignition engines lies in the method used to ignite the fuel-air mixture. Here are the key differences:

• Ignition Process: Spark ignition engines use a spark across a spark plug to ignite a compressed fuel-air mixture, typically using gasoline or natural gas as fuel. In contrast, compression ignition engines compress air to a high pressure, heating the air to the ignition temperature of the fuel, which is then injected.
• Fuel Type: Spark ignition engines use petrol as their working fuel, which is highly volatile and has a high self-ignition temperature. Compression ignition engines use diesel as their working fuel, which is less volatile and has a lower self-ignition temperature.
• Compression Ratio: Spark ignition engines have a compression ratio ranging from 6 to 10, while compression ignition engines have a compression ratio ranging from 16 to 20.
• Speed: Spark ignition engines are generally high-speed engines due to their lightweight construction and homogeneous combustion. Compression ignition engines are more efficient than spark ignition engines but produce more noise during operation.
• Method of Fuel Injection: In spark ignition engines, a mixture of air and fuel is introduced during the suction stroke, and the fuel is injected directly into the combustion chamber at high pressure in compression ignition engines.

Comparative Table: Spark Ignition vs Compression Ignition

Here is a table comparing the differences between Spark Ignition (SI) and Compression Ignition (CI) engines:

Spark Ignition engines use petrol as their working fuel and require a spark plug to ignite the fuel-air mixture. They have a compression ratio of 6 to 10 and are generally high-speed engines. These engines are used in applications that require high power output, such as sports cars and motorcycles, as well as light-duty applications like passenger cars and small trucks.

Compression Ignition engines, also known as diesel engines, use diesel as their working fuel and do not require a spark plug. Instead, self-ignition occurs due to the high temperature of highly compressed air. These engines have a compression ratio of 16 to 20 and are generally moderate-speed engines. CI engines are used in applications that require high torque output, such as heavy-duty trucks, buses, and construction equipment, as well as stationary applications like generators and industrial equipment.