Latest Mechanical Interview Questions & Answers | Thermal Interview Q & A | Automobile Interview Q & A

• What happens if gasoline is used in a Diesel engine?Diesel engine will work ?

No, It will not work,as the Compression ratio of Petrol engine is 6 to 10 & that of Diesel engine is 15 to 22. Thus on such high compression, gasoline gets highly compressed & it may blast.

• Which Mechanism is used in Automobile gearing system

Differential mechanism

• Why different types of sound are produced in different bikes though they say run on SI engine

Engine specifications are different in different manufactures like as Bore Diameter(CC), Ignition timing.Also the exhaust passage take more responsible for sound.

• Why entropy decreases with the increase in temperature?

ds=dQ/TEntropy is inversely proportional to the temperature so.as temp. increases,entropy decreases.

746.2Watt

• How to calculate bearing number to diameter of the inner and outer

Divide the shaft diameter size by 5, it will give last two digitof the bearing no. and according to type of load we have tochose the type of bearing and that will give prior no. ofthe bearing.

• Explain Bicycle rear wheel Sprocket working?

Rear wheel sprocket works under the principle of ratchet and pawl.

• In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the
1. Expansion valve to the evaporator
2. Evaporator to the thermostat
3. Condenser to the expansion valve
4. Condenser to the evoparator

Exapansion valve to the evaporator

Reason:

A capillary tube is the replacement of thermostatic valve and connects expansion valve to the evaporator

• Definition of Octane number & Cetane number

Octane No.- Octane number is defined as the percentage, by volume, of iso octane in the mixture of iso octane and h-heptane. It is the measure of rating of SI engine.

Cetane No.- Cetane number is defined as the percentage, by volume, of n-cetane in the mixture of n-cetane and alpha methyl naphthalene. It is the measure of rating of CI engine.

• Poisons ratio is higher in (rubber/steel/wood)

When a material is compressed in one direction, it usuallytends to expand in the other two directions perpendicular tothe direction of compression. This phenomenon is called thePoisson effect. Poisson’s ratio is a measure of the Poisson effect.

For rubber = 0.5

For steel = 0.288

For wood < 0.2

Thus Poisson’s ratio is higher in RUBBER.

• The Fatigue life of a part can be improved by ?

Improving the surface finish by Polishing & providing residual stress by Shot peening.

• The commonly used material for insulator of spark plug is
1. Bekelite
2. Asbestos
3. Alumina
4. Copper

1. Alumina
• When crude oil heated Which Hydro carbon comes first?

Natural gas(Gasoline)… at 20 Celsius

• 1hp=how much rpm

We need Torque to find out.

Apply this formula:

T = HP x 5252
rpm

T = torque (in lb-ft)
HP = horsepower
5252 = constant
rpm = revolutions per minute

• which mechanism is used in automobile gearing system

Differential mechanism

• why different types of sound are produced in different bikes though they say run on SI engine

Engine specifications are different in different manufactures like as bore diameter(cc),ignition timing.Also the exhaust passage take more responsible for sound.

• why entropy decreases with the increase in temperature?

ds=dQ/T

Entropy is inversely proportional to the temperature so.as temp. increases,entropy decreases

• What type of metal is used in a propeller

Aluminium,stainless steel,magnesium bronze,NIBRAL(nickel,brass,aluminium)

• why involute curve used in gear

1) it’s smooth to drive the gear.
2) in gears contact is only point, this type is curve take the more load than normal one

• How Trains take turns, though there is no any differential

Purpose of the differential is to enable vehicles to take turn, by allowing both the wheel to rotate with different speed. This is required when wheels, like in car, are connected with same axle. Interestingly, wheel in trains are not connected with the axle, they are independent and hence can take turns without ant differential. This is same as how the bullock cart takes turns, without any differential.

• In condensation of steam power plant, steam sent in shell side and cooling water on the tube side because
1. To increase overall heat transfer coefficient of water side velocity can be increases if water is on the tube side
2. Condenser can act as a storage unit for condensed steam
3. Rate of condensation of steam is invariably smaller than the mass flow rate of cooling water
4. It is easier to maintain vacuum on the shell side than on the tube side

1. To increase overall heat transfer coefficient of water side velocity can be increases if water is on the tube side

Reason:

Specific volume of steam is larger so more volume is required in condenser

• Why freezer in the fridge is placed in top level?

Because density of cold air is higher than warm air,hence itis placed at top.Cold air comes downward & cool the bottom part.

• what is more dangerous longitudinal stress or Hoop stress and why?

Hoop stress is more dangerous thanlongitudinal stress, because the dangerous area coming underthe hoop stress is circumferential,while in longitudinal,theaxial area will come under dangerous area will will be lessthan circumferential area.So the hoop stress is more dangerous than longitudinal stress

• In a spray washing system, if the water temperature is higher than the dry bulb temperature of entering air then the air is
1. Heated and dehumidified
2. Heated and humidified
3. Cooled and humidified
4. Cooled and dehumidified