Combustion induced induced vibration of a fan is usually caused by the effects of combustion system dynamics and failure of operational procedures. The pressure transient of a combustion system oscillates within a certain frequency range. This pressure is then imparted to the fan and caused it to vibrate.
The pressure can fluctuate with the air flow or with changes in the combustion chambers temperature. When the pressure waves move through the combustion system, the combustion chambers wall become stressed. This built in strain can cause the fan to vibrate at certain frequencies.
The vibration can be further exacerbated by the operation of the fan itself, e.g. during high starting or stopping of the fan. When this happens, the fan shaft become unbalanced and will vibrate much more violently than normal.
The combustion induced vibration of a fan can also be caused by a number of other factors:
• Incorrect air/fuel ratio setting - when burning a mixture of air and fuel, a fuel to air ratio that is too lean or too rich can cause abnormal flame dynamics which can induce vibration at certain frequencies in the combustion chamber.
• Excessive back pressure in the system - high pressure in the exhaust can create vibrations in the fan due to air expansion and contraction.
• Improper operation or maintenance of the fan - incorrect settings or maintenance of the fan can cause unbalanced running, resulting in increased vibrations.
• Damage or wear to the fan blade - damage or excessive wear on the fan blade will affect its travel around the hub, causing imbalance and vibration.
Combustion induced fan vibration can be difficult to diagnose and rectify, but can be alleviated by careful attention to operational and maintenance procedures.
Firstly, if the combustion system or fan is suspected to be the main cause of the vibration, it is important to verify the correct air fuel mixture ratio, ensuring the best settings for stable combustion. Secondly, the fan blade should be inspected for any signs of damage or wear and tear. Finally, it is important to ensure good operational and maintenance practices are adhered to, such as running the fan at the correct speed, taking account of any back pressure, and keeping the fan properly lubricated.
These steps can help to prevent and reduce combustion induced fan vibration, and ensure the smooth running of the combustion system.
