11 April 2014

Interview Questions with answers on IC Engine for Freshers/ Experienced -13

Q.: what are the advantages of lubrication in IC Engine?
Ans.:  following are the advantages of lubrication in IC Engine:
►it reduces the wear and tear of the moving parts.
►it damps down the vibration of the engine.
►it cleans the moving parts.
►it makes the piston gas tight.



Q: Why have eight cylinders in an engine? Why not have one big cylinder of the same displacement of the eight cylinders instead?
Ans.: There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big 4-liter cylinder. The main reason is smoothness. A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.

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Q: What causes white smoke in two stroke locomotive engines?
Ans.: That is because of engine running too lean mixture (lack of fuel). This condition will lead to overheating and failure of the engine.



Q: Why efficiency of gas turbines is lower compared to I.C. Engines?
Ans.:  In gas turbines, 70% of the output of gas turbine is consumed by compressor. I.C. engines have much lower auxiliary consumption. Further combustion temperature of I.C. engines is much higher compared to gas turbine.



Q: What do you understand by timed cylinder lubrication?
Ans.:  For effective lubrication, lubrication oil needs to be injected between two piston rings when piston is at bottom of stroke so that piston rides in oil during upward movement. This way lot of lubrication oil can be saved and used properly.



Q: In some engines glycerin is used in place of water for cooling of engine. Why?
Ans.:  Glycerin has boiling point of 90°C which increases its heat carrying capacity. Thus weight of coolant gets reduced and smaller radiator can be used.



Q: Why we do not use same technology to start both SI /CI engine
Ans.: The S.I. or spark ignition engine uses petrol as a fuel and the C.I. or compression ignition engine uses diesel as a fuel. Both the fuels has different compression ratio.
In SI engine the compression ratio is 8-12:1.
In CI engine the compression ratio is 16-22:1.
So in case of SI engine, the compression ratio is not sufficient for fuel to burn so a spark plug is used, whereas in ci engine, the compression ratio is so high that due to its internal heat the fuel is combusted so there is no need for a spark plug. So the technology used in SI engine is different from CI engine.



Q: Which has more efficiency: Diesel engine or Petrol engines?
Ans.: Diesel engine has the better efficiency out of two.



Q: What is the position of Piston Ring?
Ans.:     In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.

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