Combustion Chamber Designs and Knocking in SI Engine

Knocking is a phenomenon in the SI engine where the air-fuel mixture ignites before the spark plug fires, resulting in a rapid pressure rise and an audible knocking sound. Knocking can cause engine damage and decrease efficiency. Different combustion chamber designs have different tendencies to knock.

Order of Combustion Chamber Designs and Knocking

The order of combustion chamber designs in decreasing tendency to knock is as follows:

I head, T head, F head.

Explanation:

- I head: In an I head (also known as overhead valve or OHV) engine, the valves are located in the cylinder block, and the combustion chamber is located in the cylinder head. This design has a high tendency to knock because the flame front has to travel a longer distance to reach the spark plug, which increases the likelihood of pre-ignition.
- T head: In a T head engine, the intake and exhaust valves are located in the cylinder block, and the combustion chamber is located in a separate chamber in the cylinder head. This design has a lower tendency to knock than an I head because the spark plug is closer to the center of the combustion chamber, reducing the distance the flame front has to travel.
- F head: In an F head (also known as overhead valve-in-block) engine, the intake valve is located in the cylinder block, and the exhaust valve and spark plug are located in the cylinder head. This design has the lowest tendency to knock because the spark plug is located close to the center of the combustion chamber, and the intake charge has a more direct path to the combustion chamber, reducing the likelihood of pre-ignition.

Therefore, the order of combustion chamber designs in decreasing tendency to knock is I head, T head, and F head.