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The Working Principles of a Turbocharger

In an internal combustion engine where there is a need to increase the power, a turbocharger comes in application. In order to accomplish this, the turbocharger increases the mass flow rate of air entering the engine by the turbine action driven by it’s exhaust. It is widely applied in aircrafts, automobiles and motorcycles.

Turbocharger design and function:-

The turbocharger is like a miniature gas turbine, it is a small radial fan driven by the forward motion of the engine exhaust. Comprising the turbocharger are the turbine and the compressor sharing a single shaft. When the exhaust gasses enter, the fan rotates which drives a compressor. Air is then squeezed by the compressor before being delivered to the engine air intake manifold. Because air is compressed, the engine could then take in greater amounts of air to the cylinders. Usually the engine takes in air through a vacuum created by the downward stroke of the cylinder. The normal air pressure is at 14.7 psi and there is a limit to the pressure difference across the intake valves resulting in a limited air mass flow rate. In order to increase the intake, pressure must then be increased. In this way additional oxygen to the engine makes it possible to burn more fuel which increases the power of the engine. Increase air pressure is possible with the turbocharger application.

Turbochargers, although applies the same as superchargers except for small variations. Superchargers, particularly Centrifugal superchargers were spun by the rotation of the engine’s crankshaft. This made turbochargers more efficient in terms of recycling energy loss through the exhaust.

Although the turbocharger consists of a turbine and a compressor, several working components actually comprise it. The turbine and the impeller are contained in their own housing. The housings fitted around the compressor impeller and turbine directs the flow of gasses through the wheels. The motion of the gasses causes the impeller to spin. In this case the size of the impeller wheel dictates the amount of gas it could take. The single shaft connecting the turbine to the compressor is housed in the center hub rotating assembly (CHRA). The CHRA also contains bearing to minimized friction, lubrication and in some cases the turbocharger cooling system; water cooled models have entry and exit points for the engine coolants to cycle. Devices such as waste gates then control the spin of the turbine.

MECHANICAL ENGINEERING JOB INTERVIEW QUESTIONS

1.)What is the difference between alpha iron, delta iron and gamma iron ?

Ans: The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C. The lower temperature form is known as "alpha"-iron and the higher temperature form as "delta"-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as "gamma-iron".

2.)Explain the difference between the points of inflexion and contraflexure.

Ans: At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing.

3.)What do you understand by eutectic ?

Ans: It is mechanical mixture of two or more phases which solidify simultaneously from the liquid alloy.

4.)Under what condition a convergent divergent nozzle required ?

Ans: When pressure ratio is greater than critical pressure ratio

MECHANICAL ENGINEERING JOB INTERVIEW QUESTIONS

1.)What is the difference between isotropic material and homogeneous material ?

Ans: In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions.

2.)What do you understand by catenary cable ?

Ans: A cable attached to the supports and carrying its own weight.

3.)What is the difference between basic hole and basic shaft ?

Ans: A basic hole is one whose lower deviation is zero and in case of basic shaft the upper deviation is zero.

4.)In which process internal energy remains constant ?

Ans: Isothermal process.

MECHANICAL ENGINEERING JOB INTERVIEW QUESTIONS

1.)Explain what you understand by the term hydrostatic paradox ?

Ans: Hydrostatic paradox is the phenomenon that the floor load of water in vessels of different shapes carrying water at same level depends only on the area of the bottom surface and not on the shape of the vessel.

2.)What do you understand by inversions and how many inversions are possible in a kinematic chain having 'n' links ?

Ans: Inversions are different mechanisms obtained by fixing different links in a kinematic chain but keeping relative motions of links unchanged with respect to one another. A kinematic chain

with 'n' links can have 'n' inversions.

3.)What is the difference between a machine and a mechanism ?

Ans: A mechanism consists of links forming a constrained kinematic chain. Its function is basically to transmit or modify motion. A machine is a mechanism but here we are concerned with forces to be transmitted and it is used to modify mechanical work.

4.)Why excess air is required to burn a fuel completely ?

Ans: Excess air is required to ensure adequate mixing of fuel and air, avoid smoke, minimize slagging in coal burning, and to ensure maximum steam output.