# Automotive Job Interview Questions - Part 02

Question No. 26
What is the range of the engine efficiency for two stroke engine? Why you don't see two stroke engines in car? What are problem with two stroke engine?
Answer: The range of two stroke engine is too high compare to the four stroke engine because of each revolution one power in two stroke engine. I cannot see the 2 stroke engine in car. Power loss is more.

Question No. 27
What is the formula for calculating BHP in SI units?
Answer: Boiler horse power (BHP) is a power unit used for measuring the power output of boilers, widely used in the past, but now confined to North America. The boiler horsepower conversion formula is as follows.
1 Boiler Horsepower = 9,809.5 Watts

Question No. 28
What is the meaning of CC engine?
Answer: CC stands for Cubic centimeter. CC represents the total volume of an engine cylinder. The engine which has more CC can produce more power than others.

Question No. 29
Why freezer in the fridge is placed in top level?
AnswerBecause density of cold air is higher than warm air, hence it is placed at top. Cold air comes downward & cool the bottom part.

Question No. 30
Poisons ratio is higher in (rubber/steel/wood)
AnswerWhen a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called the Poisson 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.

Question No. 31
What type of gears is used in small cars?
AnswerA gear in a car is used mainly in the transmission system, the steering system and the differential system.  In the transmission system the gears used are helical gears these provide better efficiency, better safety and durability at high speeds,  steering system uses rack and pinion type of gear system.  While differential uses bevel gears.  As the torque is to be transmitted perpendicularly.

Question No. 32
How is power generated from fuel?
AnswerFuel generates power by being burned, oxidized is the technical term. In the process of burning, heat is released.  The energy of the heat is used to do work. Exactly what kind of work depends on what kind of energy absorbing device the energy is put into.
Steam power can be generated by burning the fuel under a container with water in it and using the steam for some purpose.

Question No. 33
What are the different type’s sun gears and planet gears used in differential?
AnswerA differential is a particular type of simple planetary gear train that has the property that the angular velocity of its carrier is the average of the angular velocities of its sun and annular gears. This is accomplished by packaging the gear train so it has a fixed carrier train ratio R = -1, which means the gears corresponding to the sun and annular gears are the same size. This can be done by engaging the planet gears of two identical and coaxial epicyclic gear trains to form a spur gear differential. Another approach is to use bevel gears for the sun and annular gears and a bevel gear as the planet, which is known as a bevel gear differential

Question No. 34
What is pan hard rod or track bar?
AnswerA 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.

Question No. 35
What is DTSI? Why this technology is used in motor bikes?
AnswerDTSI 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.

Question No. 36
What is the reason for emitting the white exhaust smoke during start of the vehicle? How will you prevent this?
AnswerThe 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.

Question No. 37
What are three methods of heat transfer?
• Conduction: The transfer of energy by collisions between the atoms and molecules in a material.
• Convection: Transfers heat when particles move between objects or areas that differ in temperature.
• Radiation: The transfer of energy by waves.

Question No. 38
What is BHP? How can you measure BHP?
AnswerBHP 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.
Ï€ (Pi) is 3.1416 and torque is in pounds-feet, and revolutions are revs per second

Question No. 39
During the drive torque, what will be the weight shift?
AnswerIn 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.

Question No. 40
Explain the reason that why big tyres are used in rear of vehicles.
AnswerLarge 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.

Question No. 41
When we start a vehicle, exhaust smoke appears white. Why?
AnswerWhen you start, the mixture is rich, and the exhaust will be cold, so any unburned hydrocarbons and water vapor will condense out into a cloudy mist and appear white.
Once the engine is warmed up, the exhaust system gets hot enough that the vapor is invisible.

Question No. 42
What is an injector pressure in heavy vehicles? Why it is used?
AnswerInjector 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 × B.S.F.C / No. of injectors × duty cycle = lb/hr per injector
cc = lb/hr × 10.5

Question No. 43
What is the size of the recommended compressor CFM? Where it can be used?
AnswerIt 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.

Question No. 44
What is a pressure cap in the radiator?
AnswerIt is a seal in the radiator that maintains the selected pressure in the cooling system when the engine is hot.

Question No. 45
How to generate power from differential gear?
AnswerDifferential Gear comes under the category of Power transmitting mechanisms called Gears. Gears can't generate power; they can only transmit the power from one source to the receiver.
A Differential Gear has three jobs.
1. It directs engine power to the wheels. It's the connecting link between the drive shaft and the wheel axles.
2. It acts as the final gear reduction in the vehicle, slowing the rotational speed of the transmission before it hits the wheels.
3. The differential also transmits the power to the wheels while allowing them to rotate at different speeds.

Question No. 46
How to calculate bearing number to diameter of the inner and outer?
AnswerDivide the shaft diameter size by 5, it will give last two digit of the bearing no. and according to type of load we have to choose the type of bearing and that will give prior no. of the bearing.

Question No. 47
Define fit?
Answer: Fit is defined as the degree of tightness and looseness between two meeting parts.

Question No. 48
What is transverse weight shift due to drive torque?
Answer: It is weight of drive torque which is bolted to chassis of the car.

Question No. 49
Why tractor rear wheel is big then front wheel?