Mechanical Engineering Interview Questions

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  • What is the function of EGR valve

EGR means Exhaust Gas Recirculation. The main function of EGR is to control NOx emission from the engine. At elevated temperature (during long run & full condition)if due to some reasons engine gets heated up beyond certain level… it produces NOx emission. In order to avoid this pollution , we have to control the temperature rise inside the cylinder. This can be achieved by mixing some amount of exhaust gas with intake air. By doing this the temperature inside the combustion chamber is reduced. And NOx is controlled.

  • What is the difference between Critical speed & Whirling speed?

In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation.

Whirling Speed is due to the unbalanced forces acting on a rotating shaft.

  • What is the significance of Torque(in N-m) given in the engine specification ?
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It give the moment about any point or simple rotation.

  • What is the abbreviation of Welding rod 7018?

7018=

70=tensile strength 70000psi

1= welding position

8=current flux

  • In ultrasonic machining the tool is made of
    1. High speed steel
    2. Diamond
    3. Plain carbon
    4. Brass & Copper

Answer:

Plain carbon

  • What are the uses of Graphite electrode in various field.

Graphite electrode is used in EDM and in Battery cells. It is also used in electric arc furnaces to melt the steel .

  • When a 40 watt lamp is connected in series with a 100 Watts lamp across a 220 V supply which one glows brighter
    1. 100 watt lamp
    2. 40 watt lamp
    3. Both will glow with equal brightness
    4. It cannot be predicted

Answer:

40 watt lamp

Reason:

When connected in series, the current through each lamp is same. But resistance of 40 W lamp is more. Therefore greater heat is produced in the 40W lamp.

  • Difference between TIG & MIG welding
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Tungsten inert gas welding-non consumable electrode

MIG-Metal inert gas welding-uses consumable electrode

  • Specific speed of turbine?

The specific speed is defined as the the speed of the geometric turbine which can produce unit power at unit head

  • Material of Aircraft turbine blade?

Ni, Cr, Al, Traces of C

  • Do you know epicyclic gear box? What are the practical application of epicyclic gear box?

Epicyclic gear box consists of sun gear planetary gears and an annular called ring gear. Different speed ratios are obtained by locking any one gear. If you lock any two gear, direct gear will be obtained mostly used in overdrives. Wrist watch is a practical application of epicyclic gear box

  • What do you mean by super critical above 500MW in Thermal power plant?

In super critical boiler means all the steam to converted in to superheated steam at outlet of boiler no need to sent
to super heater once again.

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