The Best Latest Tutorial On | Vibration In Marine Diesel Engine

Vibration in marine diesel engine

Introduction

In this Post on Vibration in marine diesel engine, we will discuss essential guidelines for the vibrations, type of vibrations, and measurement of vibrations on diesel engines.

We will also explain the acceptable levels of vibrations on the marine Diesel engines and associated electrical and mechanical components of the engines.

This post on Vibration in marine diesel engine will use the vibration norms and theoretical aspects of Vibrations. The preliminary knowledge of the established techniques will also form the base of the post.

There could be confusion due to the several vibration acceptable standards. The available standards don’t provide any guidelines for the engine-mounted components. I will also consider the past knowledge of my colleagues and my understanding of 45 years working on marine and industrial engines.

This post aims to produce a standard that will be useful in Diesel Engines regarding vibration.

These guidelines will suggest the location of points for the placement of sensors for measuring vibration readings and the interpretation of results.

The guidelines produced in this post on Vibration in marine diesel engine will also be helpful to non-technical background individuals.

What is Vibration in marine diesel engine?

A periodic motion of the particles of an elastic body in alternately opposite directions from the equilibrium position when there is a disturbance in equilibrium is the definition of vibration.

Types of Vibration

1. Free Vibration
2. Forced Vibration
3. Damped Vibration

During the operation of an engine, there is the creation of many types of excitations.

It is impossible to achieve complete control of vibration in diesel engines due to the engine’s rotating parts and firing and gas pressure.

The design considerations are too precious to control the Vibration in marine diesel engine from getting closer to the natural frequency,

Higher forces and catastrophic failures will occur if the Natural Vibration comes close to the natural frequency in a running engine.

Different parts of the engine will have different levels of vibration. Carry out the vibration checks at various points and directions in the longitudinal, transversal, and vertical axis.

Obtained readings should be normal in each direction. The reading s exceeding the prescribed normal limits need through investigations and checks, and corrections.

Free /Vibration in marine diesel engine

Free Vibration in marine diesel engine is the result of a body’s disturbance from its equilibrium position. The natural frequency of a body will influence the free vibration.

Forced Vibration in marine diesel engine

An external periodic force produces the forced vibration. The frequency of forced vibration is directly proportional to the external periodic force.

Damped Vibration in marine diesel engine

When there is reduction in amplitude over every cycle of vibration the motion is known as damped vibration.

Basic Theory of Vibration in marine diesel engine

The following three parts constitute the Vibration in marine diesel engine arrangement.

1. Spring for the storage of potential energy

2. A mass (Inertia) for the storage of Kinetic Energy.

3. A damper for the gradual loss the energy.

In a Vibration in marine diesel engine system, energy alternates between kinetic and potential forms. During each cycle, a damping system loses energy.

Amplitude Displacement

Amplitude

Amplitude is the maximum duration of the repeating event. Amplitude is the function of the magnitude of the difference between the variable’s extreme values.

The RMS value is the most common in measuring the speed values for the rotating machines, and the unit of part measurement is Revolution per minute (RPM).

The physical quantities of amplitude measurement are listed below.

1. Displacement;- Displacement means the maximum movement of an object from its stable position to exceed position. The unit of displacement measurement is mils.

2. Velocity;- Velocity is the rate of change of distance concerning time. It indicates the speed of the measured part’s movement. The unit of velocity is mm/s or ips ( inch per second)

3. Acceleration;- Acceleration is the rate of change of a velocity concerning time. Acceleration indicates the speed of change of velocity of a measured point.

Frequency

Frequency is the reiteration of vibration. The no. of times a system reiterates one cycle in one second is equal to the frequency. The measurement unit of frequency is HZ.

Frequency Formula

Damping

Damping is a consequence in an oscillatory system having the effect of minimizing or restricting its oscillation.

Formula of Damping

Natural Frequency

The frequency at which a system continues to vibrate under excitation is known as natural frequency.

Resonance

If the frequency of the vibrating object is similar to the other thing, then a resonance will take place and will force the other non-vibrating object to vibrate. The high amplitude of the resonance can damage the structure of the equipment.

Vibration Measuring Specifications

Following vibration parameters for the measurement of vibration is in practice by the Engine manufacturers.

1. Displacement measurement;- This type of measurement is applicable for measuring frequency below 30 Hz and below.
2. Velocity measurement;- This type of measurement is appropriate for measuring the frequency between 10 -300 HZ.

International Standards

Following international standards for the measurement of vibrations are available.

1. ISO 8528–9;- For the evaluation of mechanical Vibrations
2. ISO 10816–6;- for the reciprocating machines above 100 KW rating
3. ISO 8528–9;- for the basic knowledge of measuring the vibration and measuring points on an engine. Measure the x, y, and z-axis of the engine, a measurement point at the top, front, back, and bottom front and back of the engine and at the base of the generator. Measure the bearings also.

As per the standard, measure the 0 Temperature and the rated power temperature.

The specified Vibration level for the reciprocating internal combustion engines is between 2 HZ to 300 HZ. For the whole generator with the system, measurement should be 2HZ to 1000 HZ.

1. ISO 10816–6;- This standard is applicable for engines above 100 KW. As per this standard, the vibration level should be 2 HZ to 1000HZ. Measure x,y, and z-axis on various other points on both sides of the engine.

The 1st point should be on the base level of the engine block, 2ns at the crankshaft level, and the one at the top of the engine block.

Vibration Measurement Locations (Points)

1. Coupling end of the engine,
2. Middle of the engine,
3. Free end of the engine.

Carry out all the measures at the operating temperature of the engine.

Measure the severity of the vibrations as the overall RMS value of displacement, velocity, and acceleration

Measurements

Measure the vibration on different points on the Engine as per the above picture.

There are specific measuring locations on the Engine block, the generator, and the common base frame. Measure the Engine Pumps and filters. During the measurement of vibration at the Engine, the crankshaft will be in the longitudinal direction, but during the measurement at Turbocharger, the Turbocharger will be in the longitudinal direction

Important Vibration measuring Instruments

Accelerometer

An accelerometer is an electromechanical instrument that measures the acceleration forces on a vibrating body.

Accelerometers are available both as an analog and digital devices.

The accelerometer works on the principle of conversion of mechanical motion into an electrical signal.

The basic principle of an accelerometer is as compared to mass dumping on a spring. When this device experiences acceleration, mass displacement continues until the spring can move the mass quickly, with the same rate equal to the sensing of acceleration. The instrument uses the displacement value to measure the acceleration

Vibration Damper

A vibration Damper is a device fitted on the free end of the crankshaft to minimize or overcome the stresses resulting from the torsional vibration from the crankshaft.

Installing the Vibration damper will alter the vibration frequency of the crankshaft.

The fitting of the vibration damper is on the free end of the crankshaft of a medium-speed Diesel engine to reduce the torsional vibration from the peak amplitude.

Torsional Vibration Damper (spring and oil dashpot type viscous Damper)

The damper has sufficient mass to act as a flywheel also. The damper has two round masses with a pack of sleeve springs at the joining surfaces.

Spring space is packed with oil through connected grooves. The driving part rigidly mounts with the shaft ad is an integral part of the vibrating shaft. The design of driven mass will tend to oppose the vibration of the driver. The movement of the upper concentric mass is normal and even with the engine rotating mass. In the event of vibration, the resiliently fitted upper mass will follow the fixed mass with phase displacement. This phenomenon will compress the spring pack for the oil to flow from one space to another space through grooves.

The upper mass’s inertial lag will restrict the entrance of amplitude vibration to the critical range.

There is a disadvantage of using oil in this type of damper. The absorption of vibration energy during the damping process will heat the oil. Hot oil will lose viscosity resulting in dropping in damper efficiency

Silicone Damper

This design of damper uses silicone in a hermetically self-contained unit instead of oil.

The damper consists of a lightweight flywheel casing ‘A,’ which rigidly fits at the free end of the crankshaft. Within the Flywheel rim casing, there is A loose floating mass ‘B.’ The space between the floating mass and the case has the filling of silicone fluid. Due to the higher viscosity of silicone fluid, there is very little change in viscosity.

The inertia of Mass ‘B’ with silicone viscous drag effect will oppose the casing vibration.

The viscous shear force will absorb mass A, and mass B will absorb the maximum vibration energy.

Mass B will maintain the uniform motion by its inertia.

Causes of Vibration

Listed below causes are the most critical causes of the- linear or torsional vibrations in Diesel Engines and generating sets.

1. Misalignment of Prime Mover and the Alternator.

2. If there is unbalance in the Engine, coupling, Vibration damper, Alternator rotor components. Unbalance due to the causes of conventional unbalance, not the attribute of Engine combustion forces.

3. Structural mass and rigidity combinations are creating resonance.

4. Engine Firing Cylinders attempt to create a twist in the rotor.

5. Misfiring in cylinders.

6. Heavy forces developed during the combustion process.

7. Unbalance in reciprocating parts.

8. Electromagnetic forces.

Harms of Vibration

Vibration in an engine is most unwanted for the following reasons.

1. Increases stress

2. Addition in wear of parts

3. Increases sound levels

4. Excessive material fatigue

5. Loss in energy

6. Increase in bearing loading.

All the above factors will result in failure and breakdown in an Engine

Remedial action for reducing the Vibrations

Listed below is remedial action to reduce the vibration in Diesel Engines.

1. Correct the misalignment of the Engine with the driven unit like generator or propeller.

2. Check the Anti-vibration mountings for the proper height and correct the same if found irregular.

3. Periodical checks of Engine performance test and correct the abnormal observations from the EPD readings.

4. Check the flexible connections between engine and system pipes and fittings.

5. Never allow the machine to run at a critical speed.

6. Carry out the periodical checks of tightness of foundation bolts.

7. Analyse the condition of the alternator bearing and replace the bearing if there are symptoms of bearing getting overheat and abnormal sound during the operation.

Conclusion

I sincerely hope that the post on Vibration in marine diesel engine has been useful to the readres.