Table of Contents
Main engine knocking is caused mainly by abnormal combustion — such as early ignition or a long ignition delay — and by excessive clearances in the running gear. This page lists the reasons, the single-unit causes, and the actions to prevent knocking.
Reasons for Main engine Knocking
- Early ignition causes an abnormally high peak pressure in the cylinder at about the top of the piston stroke. A heavy shock load will be transmitted to the running gear and bearings with a corresponding knocking sound. It may cause due to Incorrect fuel pump timing, broken or wrongly set injector springs, incorrect fuel condition, and overheating of parts inside the cylinder.
- Overload or unbalanced engine
- If fuel oil has a lesser cetane number the fuel will have a very long ignition delay period. When the ignition delay period is high the fuel-injected will not have undergone combustion and by this time the fuel-air mixture starts to accumulate and it will undergo combustion after a long delay and there will be a huge shock wave as all the fuel droplets will undergo combustion at the same time.
- Cold start of the engine. Because low working temperature does not allow vaporization of fuel in time and promotes a long delay period.
- Piston cooling oil temp. high or insufficient cooling
- Excessive bearing clearance of running gear
- Clearance between piston and liner increased
Action to prevent Engine Knocking
- Correct fuel timing
- Correct fuel rack position
- Injector overhauling or renewed
- Use good quality fuel
- Maintain the correct working temperature of the engine. Before starting warm up the engine.
Single unit
- Excessive bearing clearance of running gear
- Clearance between piston and liner increased
- The piston may be striking cylinder head at TDC
- Piston ring may be striking against the worn ridge at cylinder liner top
- Early ignition: This will cause an abnormally high peak pressure in the cylinder at about the top of the piston stroke. A heavy shock load will be transmitted to the running gear and bearings with a corresponding knocking sound.
- Incorrect fuel pump timing, broken or wrongly set injector springs, incorrect fuel condition, and overheating of parts inside the cylinder.
