Automobile Engineering Interview Questions and Answers - ObjectiveBooks

Automobile Engineering Interview Questions and Answers

Automobile Engineering Job Interview Questions and Answers for fresher and Experienced Automobile and Mechanical Engineers:

Question No. 01
What is Automobile Engineering? 
Answer: Automobile Engineering is a branch of engineering which deals with designing, manufacturing and operating automobiles. It is a segment of vehicle engineering which deals with motorcycles, buses, trucks, etc. It includes mechanical, electrical, electronic, software and safety elements.

Question No. 02
How will you differentiate between two stroke engine and four stroke engines?
Answer: 2-stroke piston engine has an intake and an exhaust stroke. All air, fuel, and combustion products must be moved in those 2 strokes. A 4-stroke engine has a separate stroke for moving burned (or burning) and unburned mixtures - intake, compression, expansion, and exhaust. Using 4-stroke results in cleaner emissions at the expense of specific power.

Two stroke: For each explosion in cylinder piston moves downwards and upwards (one complete cycle) (Power stroke and Exhaust stroke).

Four stroke: for each explosion in cylinder piston moves down and upwards twice (two complete cycle) (Intake , compression, power, exhaust stroke.)

Four stroke is highly efficient than two stroke.
But two stroke is powerful than four stroke.

Question No. 03
What is the range of engine efficiency in case of two stroke engine?
Answer: The two stroke engines have very high range to be compared to the four stroke engines. Because power stroke is generated every two revolution while in four stroke, power stroke is generated every four revolutions.

Question No. 04
Definition of Octane number & Cetane number
  • Octane Number - 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 Number - 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.

Question No. 05
What do you understand by CC of engine?
Answer: The meaning of CC is cubic centimeters. It represents the total volume of the engine cylinder. This reflects that the engines with more CC can generate more powers than the other engines. CC can also be related as inversely proportional to the fuel consumption.

Question No. 06
If we use gasoline in diesel engine, what will happen?
Answer: Adding gasoline to the diesel engine may blast off the engine. Compression ratio of the petrol engine is 6 to 10 and diesel engine is 15 to 22. Thus gasoline will get very highly compressed and might result in blast off engine.

Question No. 07
Explain the significance of governor in automobiles?
Answer: Governor is an important component of automobile engine. It is used to regulate the main speed of engine during the variations in loads. With the variations in the load, fuel supply has to be maintained. This task is performed by the governor. In the case of high load on the engine, speed decreases, hence fuel supply has to be increased and similarly when load decreases then the fuel supply has to be decreased.

Question No. 08
What is the use of hydrogen in automobile?
Answer: Low emissions. Essentially no CO or HC in the exhaust as there is no carbon in the fuel. Most exhaust would be H₂O and N₂ Fuel availability. There are a number of different ways of making hydrogen, including electrolysis of water.

Question No. 09
What is the use of Natural gas in automobiles?
  • High octane number makes it very good S.I engine fuel
  • Low engine emissions. Less aldehydes than with methanol

Question No. 10
What is an automotive differential and how does it work?
Answer: The automotive differential is designed to drive a pair of wheels while allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism.

Question No. 11
What is the working principle of hydrostatic propulsion system in a tractor?
Answer: It depends on Pascal law. As the pressure in the system is the same, the force that the fluid gives to the surroundings is therefore equal to ‘pressure × area’. In such a way, a small piston feels a small force and a large piston feels a large force

Question No. 12
What is oil grade SAE stands for?

Question No. 13
By mixing oil in fuel of four stroke bike will it damage engine, performance? If not than what happen?
Answer: Yes, absolutely. It leads to higher wear and tear in cylinder liners, piston and damage of the piston. It even leads to knocking and detonation where abnormal combustion appears and dark smoke and harsh sound will be produced by the engine.

Question No. 14
Why are car steering wheels round?
  1. A steering wheel is round so that your hands locate in the same place regardless of the steering wheel's orientation. 
  2. While turning / steering the car it is ergonomically the best design. 
  3. Also as design is circle, there are no edges to hit while turning / steering is moving as the circle position remains the same.
  4. From Design view, it should be able to give uniform force i.e. torque, by varying the distance from center will vary the torque provided.

Question No. 15
How Trains take turns, though there is no any differential?
Answer: 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.

Question No. 16
What is the difference between BS2 & BS3 engine?
Answer: IN BS2 there is No catalytic converter to reduce formation of co and HC whereas in BS3 catalytic converter is available to reduce the formation of HC and CO. So less emission of HC and co will take place in BS3

Question No. 17
Why big tyre used in rear of Tractors?
Answer: Tractors have big rear tires because, the larger the surface area of the tractor's wheels touching the ground, the more pulling power you have. Like how tractor pullers have large tires.
Another reason is that the tractor doesn't have to operate at a higher speed to get the same ground speed with larger tires. Gear ratios don't have to be as high b/c of the larger tires.

Question No. 18
What will happen if someone adds oil to the fuel of four stroke bike engine?
Answer: This will result in damaging of the engine faster. Adding oil will lead to the higher wear and tear of the cylinder liner, piston and damage to the piston. It will lead to abnormal combustion and knocking and detonation. Dark smoke and abnormal sounds will be generated by the engine. One should not mix oil with the fuel of four stroke engine.

Question No. 19
How air conditioners work in cars?
Answer: Air conditioners are based on the principles of evaporation and condensation and then compression and expansion. The hot air of the car is removed by the process of evaporation and then the condensation of the evaporated air takes places which is then further compressed by the compressor and then finally expanded to us in the form of cold breeze. Somehow, Air conditioning reduces the average of the car, as the energy is required to remove the hot air and then compression and expansion.

Question No. 20
Why entropy decreases with the increase in temperature?
Answer: The relation is ds = dQ/T
Entropy is inversely proportional to the temperature so as temperature increases, entropy decreases.

Question No. 21
What is SAE? Mention the importance of SAE to the automobile domain.
Answer: SAE stands for society of automotive engineers. This society is responsible for developing the standards for the engineering of powered vehicles of all kind. The vehicles may include car, boat, truck and even aircraft. SAE has developed standards for ground vehicles and aerospace vehicles. SAE also encourages students of engineering, technology, science and math’s disciplines. This society has been publishing technical information since 1906.

Question No. 22
How does the thermostat work?
Answer: When the engine is too cold the thermostat closes the main valve, thus stopping the flow to the radiator. When the engine is too hot, it opens the main valve for normal circulation through the radiator.

Question No. 23
Why involute curve used in gear?
  • It’s smooth to drive the gear.
  • In gears contact is only point, this type is curve take the more load than normal one

Question No. 24
What does it mean when your car emits white smoke?
Answer: White smoke is a sign of a coolant leak as is milky brownish oil. This could be due to bad head gasket or cracked block. Burning oil smoke is usually more bluish in color. White smoke is usually associated with a coolant leak, but burning oil can also look like white smoke

Question No. 25
What happens if gasoline is used in a Diesel engine? Diesel engine will work?
Answer: 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.