Diploma Thermal and Automobile Engineering Board Exam Answer Key – Unit 2

Diploma Thermal and Automobile Engineering Board Exam Answer Key – Unit 2

Subject : Thermal and Automobile Engineering         Scheme : M

Board exam question and answers key

2/3 marks

Unit – 2, I.C. Engines & Its performance

  1. State the functions of piston rings
  • Piston rings ( compression rings) prevent the leakage of high pressure gases from the combustion chamber into the crank case.
  • Oil rings wipe off the excess oil from the cylinder wall. It also returns the excess oil to the oil sump.
  1. What is the function of cam shaft?
  • Cam shaft is used to convert rotary motion into linear or straight line motion.
  • The opening & closing of the engine valves are controlled by the cams provided on the cam shaft.
  1. State the function of a flywheel.
  • A flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.
  • A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply.
  1. Compare wet liners with dry liners
Sr No. Dry liner Wet liner
1 Dry liner is not in direct contact with of cooling water Wet liner is in direct contact with of cooling water cooling water
2 It is difficult to replace It is easy to replace
3 No leak proof joint is Provided A leak proof joint between cylinder casting and liner has to be provided
4 The casting of cylinder block is complicated The casting of cylinder block is simplified
5 Block is more robust Block is less robust
6 Very accurate machining of block and outer liner surface is required Very accurate machining of block and outer liner surface is not required



  1. Define specific fuel consumption.

The amount of fuel consumed per brake power hour of work.

SFC = Fuel consumption per hour/ brake brake

  1. Sketch the valve of an I.C. Engine and name its features.


  1. In a diesel engine, the s.f.c was obtained as 260 gm/kwhr. The calorific value of the fuel is 42,000 kj/kg. determine brake thermal efficiency.

Answer = 32.96%

  1. What is the purpose of using cylinder liners?
  • The cylinder liner prevents the compressed gas and combustion gas from escaping outside.
  • It is necessary that a cylinder liner which is hard to transform by high pressure and high temperature in the cylinder
  1. How are the engines classified based on valves?
  • L – head Engine
  • T – head engine
  • I – head engine
  • F – head engine
  1. Difference between petrol engine and diesel engine.
Difference Between Petrol and Diesel Engine
Diesel Engine Petrol Engine
These engines work on the Diesel cycle Works on the Otto cycle
The fuel is mixed with air inside the cylinder Air and the fuel are mixed in a carburettor
Ignition is achieved with the help of the hot, compressed air. Fuel is ignited with an electric spark
High compression ratio Relatively low compression ratio
High power production Relatively low amounts of power are produced in a Petrol engine
These engines work with fuels that have low volatilities Highly volatile fuels are used in these internal combustion engines
Generally used in heavy vehicles such as trucks and buses Used in light vehicles such as motorcycles and cars.
Relatively low fuel consumption High fuel consumption.
High initial and maintenance costs Comparatively low initial cost and maintenance cost


  1. Mention the material used for cylinder block and connecting rod.
  • Material used for cylinder block: Grey cast iron or aluminium and its alloys
  • Material used for cylinder block: carbon steels, aluminium alloys & nickel alloy steels 
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