300+ TOP AUTOMOBILE Interview Questions and Answers

AUTOMOBILE Engineering Interview Questions for freshers experienced :-

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1. Explain the reason that why big tyres are used in rear of vehicles.

Large tyres provide larger surface area touching the ground, thus providing the more pulling power. Basically tractors have larger rear tyres because tractors don’t have to operate at higher speeds, thus getting the same ground speed with larger tyres. Moreover gear ratios don’t have to be as high as b/c of the tyres.

2. What is kingpin offset? State some of its application.

• The kingpin offset is the part, basically called as pivot used in the steering of the vehicles. This offset helps in rotating of the steering and thus it’s very useful in steering mechanism of the cars.
• Applications: This is also used to measure scrub radius with the help of geometric parameters of wheel plane above and below ground level.
• It provides directional stability to the vehicles when it i combined with the caster.

3. Explain the basic difference between BS2 and BS3 engine.

The basic difference of BS2 and BS3 engines is the presence of catalytic convertor. Catalytic convertor is present in BS3 engine which helps in reducing the formation of HC and CO. While in BS2 engine, no catalytic convertor is present which forms HC and CO. Thus in BS3 engine there is no emission of harmful CO and HC. The full form of BS is bharat stage, which is a standard of emission in India.

4. What is an injector pressure in heavy vehicles? Why it is used?

Injector pressure i s the pressure at which the fuel can be injected into the vehicle. In heavy vehicles, injector pressure is 220 kg/cm square. It is used to set up the standard fuel injection in the vehicles. With the help of injector pressure we can calculate the amount of fuel needed, through the following formula:
Est. Horsepower x B.S.F.C / No. of injectors x duty cycle = lb/hr per injector
cc = lb/hr x 10.5

5. During the drive torque, what will be the weight shift?

In case of cars the torque is applied to the rear wheels, thus limiting accelerator due to front wheel drive due to weight transfer. This drive is bolted to the chassis of the car. Modern manufacturers therefore design rear wheel drive to have similar handling to front wheel drive wherever possible via suspension tuning.6. In a tractor, how the hydrostatic propulsion systems work?

This system is based on Pascal’s law. In a tractor the pressure is same, so the force given by the liquid to the surrounding is equal to the pressure X area. Thus, obeying the Pascal’s law hydrostatic propulsion system is designed, similarly small piston feels small force and the large piston feels larger area.

7. Explain the reason that why the tyres are always black in colour. Is this phenomena related to the heat conduction?

Tyres colour is black due to the proportion of carbon mixed in it during the vulcanization of the rubber, to make the tyre shear resistant. Without vulcanization tyres won’t be able to bear the friction heat and stress of the road. Thus carbon is responsible for giving tyres the prominent black colour. Adding of carbon prevents tyres from rapidly deteriorating because when ozone combines with the ultraviolet light from the sun. It attacks the polymer of the tyre.

8. What is BHP? How can you measure BHP?

BHP is ‘Brake Horsepower’. It reflects the powerfulness of the brakes of the vehicles. BHP stands for how much power will be required to make the engine stop working i.e. to stop the rotation of the engine.
BHP = 2 times pi times torque times revolutions; all this divided by 550.
Pi is 3.1416 and torque is in pounds-feet, and revolutions are revs per second

9. What will happen if someone adds oil to the fuel of four stroke bike engine?

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.

10. How will you differentiate between two stroke engine and four stroke engine?

In case of two stroke engine, rotation of crank shaft will be power stroke for every two rotations. During compression stroke, fuel will flow towards the crank case(suction) and during power stroke, exhaust will emit the burnt fuel through the transfer ports.
While in case of four stroke engine, rotation of crank shaft will be power stroke for every four rotation. Moreover, suction compression power and exhaust strokes are separate as there will be inlet and exhaust valves.

11. What is the size of the recommended compressor CFM? Where it can be used?

It is generally used in spray painting of very small areas. It can be used where painting with brush is very difficult. thus to improve the rate of painting the spray painting is used as this method is very fast and efficient. Usually reciprocating compressors are used but size depends on requirements.

12. What is the range of engine efficiency in case of two stroke engine?

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.

13. What do you understand by CC of engine?

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.

14. What is back compressor in engines?

Back compression means the compression capability of the engine. An diesel engine can compress at the ratio of 14:1 to as high as 25:1. Thus the higher compression leads to better efficiency of the engine. Thick black smoke is emitted when the engine’s compression is reduced which leads to the deformed ead-gasket lead into crankcase.

15. How air conditioners work in cars?

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.

16. What are three methods of heat transfer?

Three methods of heat transfer are conduction, convection and radiation.

1. Conduction: The transfer of energy by collisions between the atoms and molecules in a material.
2. Convection: Transfers heat when particles move between objects or areas that differ in temperature.
3. Radiation: The transfer of energy by waves.

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17. Why the plastic materials used in the screwdriver’s handles?

Due to non-conducting nature of plastic, it is widely used for the electricity purposes. Moreover, plastic is cheap and strong so it is less prone to damage. Furthermore, plastic does not bend and does not slips from the users hands.

18. Does diesel engine powered automobile use unit pump and unit injector?

In the case of the engines powered by diesel fuel supply systems, unit pump & unit injector are operated by camshaft & thus pressure of injected fuel depends on engine speed. Whereas,in common rail systems it is independent of engine speed.

19. If we use gasoline in diesel engine, what will happen?

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.

20. What is octane number and cetane number?

• Octane number can be 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.
• While cetane number can be 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.

21. Explain the significance of governor in automobiles?

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.

22. What is the reason for emitting the white exhaust smoke during start of the vehicle? How will you prevent this?

The main cause of white smoke is water or anti-freeze entering the cylinder, so the engine starts to burn it with the fuel. That white smoke is nothing but steam.
Prevention measures: There are special gaskets i.e. head gaskets and primary gaskets that prevent the anti-freeze from entering into the cylinder area. This anti-freeze will produce a white steam which will accumulate at the tailpipe area.

23. What are MPFI and TPFC systems?

• MPFI stands for Multi Point Fuel Injection. In this system fuel is injected into the intake ports which is situated just upstream of each cylinder’s intake valve. These systems are sequential systems, in which injection is timed to coincide with intake stroke of each cylinder.
• TPFC stands for transient power fuel control system. In this type of systems constant choke carburetor is used. The salient feature of this carburetor is that it provides jerk less engine raise. In these systems, throttle valve creates vacuum which opens the slide which controls the air fuel ratio through a tapered jet.

24. What is SAE? Mention the importance of SAE to the automobile domain.

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.

25. What is DTSI? Why this technology is used in motor bikes?

DTSI stands for Digital Twin Spark Ignition. This is used to get better combustion in the combustion chamber. In this technique double spark plugs are used to obtain better combustion of fuel in cylinder head. Through this technique fuel is ignited properly. Moreover it provides better efficiency and it is economical in fuel consumption.

26. How does the thermostat work?

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.

27. What is a pressure cap in the radiator?

It is a seal in the radiator that maintains the selected pressure in the cooling system when the engine is hot.

28. Why does a compression engine use high –octane fuel?

The property of a fuel, which describes how fuel will or will not self-ignite, is called the octane number or just octane. Engines with low compression ratios can use fuels with lower octane number, but high compression engines must use high-octane fuels to avoid self-ignition and knock.

29. What is the use of hydrogen in automobile?

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.

30. 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

31. What is pitching in the suspension system?

Pitching is a rocking action about a transverse axis through the vehicle, parallel to the ground. The front suspension moves out of phase with the rear, experiencing the rocking effect due to pitching.

32. What do you mean by Independent suspension?

Independent suspension refers to the mounting of the wheel on a separate axle, so that road shocks affect only the particular wheel.

33. What is pan hard rod or track bar?

A pan hard rod is a bar or tube running from one side of the axle to the frame on the other side of the vehicle. It helps the leaf spring in keeping the axle centered under the body during turning a corner.

34. What is clutch drag?

When the clutch is not disengaging fully and provides some difficulty in changing the gears then this defect is called clutch drag.

1. What is the significance of BS 3 or 4 engines?
2. Explain the consequences of using BS3 engine fuel with BS4 engines.
3. What will happen if wrong fuel is burnt in engine?
4. Why oil is mixed with coolant and what are causes of this?
5. What is an injector pressure in heavy vehicle?
6. What is engine efficiency?
7. What is the engine efficiency range in two stroke engine?
8. Why two stroke engine can’t be used in cars?
9. What is the function of commutator in starting system?
10. Explain the crankshafts used in two piston system.
11. What is a stage time?
12. How power can be generated in engine?
13. Why front wheel is bigger than rear wheel in tractor?
14. How efficiency can be calculated in 500 k.v.a diesel generator?
15. Due to drive torque,What is transverse weight shift?
16. Why black colour are used for tyres?Is there anything related with heat conduction?
17. Explain the working principle of hydrostatic propeltion system in a tractor?
18. Can servomotor be used for applying torque or load to the gear box drive shaft at various speeds for gear box testing purpose.
19. Why rear wheels are bigger in vehicles?
20. What is king pin offset?
21. How BHP can be calculated in SI units?
22. Differentiate between two stroke engines four stroke engines.
23. What size of a compressor (CFM) is recommended for the purpose of inflating car tyres, spray painting, etc.?
24. Do the design & fittings depend on the type of the vehicle engine? Why is petrol used for engines only & vice versa.
25. Will engine performance be damaged by mixing oil in fuel of four stroke bike ?
26. How to calculate the Speedometer ratio in the vehicle?
27. What is BHP?
28. How BHP is measured?
29. What is the difference between BS2 & BS3 engine?
30. Explain the concept of CC of engines?
31. What is back compressor in engine?
32. Explain Terminal Engine Meltdown?
33. What is meant by1.8 TSI 4V 1798cc turbocharged?
34. What is CPK value?
35. Why wheel type steerig is used in cars instead of hand steering used in auto-rickshaw?
36. Where is fan located in car?
37. Why oil with petrol can be used in two stroke engines but not in four stroke engines (two wheelers)?
38. What stands for AC in AC mechanical fuel pump?
39. Which engines have the high mechanical efficiency either 2 stroke engines or 4 stroke engines?
40. What happens if you use petrol in diesel engine?
41. How the engine does start working when we start our two wheeler?
42. Why are I/P transducer connected with 24V DC not to 220V AC?
43. What is the engine rating required for 1000 KVA generator set?
44. How much diesel does 1000 KVA rating DG set at full load consume?
45. How can you test the Speedo meter?
46. What is the allowable -ve crankcase pressure (vacuum) in the gas engine of 1.5 MW,
47. What is the fundamental equation for correct steering?
48. Is filter Generated (Diesel filter & Air Filter) from Diesel Generators are Hazardous waste?
49. What is meaning of 1640 write on the trailor?
50. What is the composition of Cast Iron Grade: GG P70?
51. What are the troubles in inaccurate gauge reading?
52. How air condition work in the car?
53. What is the three method of heat transfer?