IC Engine Basic | Interview Question and Answers
IC Engine Basic | Interview viva, oral Question and Answers
1. What is the fuel injector?
Fuel injector is used in diesel engine to inject and atomize the diesel at the end of the compression stroke.
2. What is meant by SI engine? Why it is called so?
SI engine means spark ignition engine. In SI engine air fuel mixture is ignited by spark plug hence it is called spark ignition engine. It is also called as petrol engine.
3. Give four major differences between two stroke and four stroke IC engine.
Two stroke cycle engine Vs Four Stroke cycle engine
1 .One cycle is completed in two stroke of the piston or one revolution of the crank shaft. One cycle is completed in four stroke of the piston or two revolution of the crank shaft.
2. For the same speed, twice the number of power strokes is produced than 4 stroke engine. For the same speed, half of the number of power strokes is produced than 2 stroke engine.
3. Turning moment is more uniform and hence lighter flywheel is used. Turning moment is not uniform and hence bigger flywheel is used.
4. It contains ports which are operated by the piston movement. It contains valves which are operated by valve mechanism.
4. What is meant by CI Engine? Why it is called so?
CI engine means compression ignition engine. In CI engine the fuel is injected by a fuel injector in atomized form because of high compressed air it gets ignited automatically. Hence it is called as compression ignition engine.
5. What is a two stroke engine?
A two stroke engine is an engine in which one cycle of operation is completed in two stroke of the piston or one revolution of the crank shaft.
6. What is a four stroke engine?
A four stroke engine is an engine in which one cycle of operation is completed in four stroke of the piston or two revolution of the crank shaft.
7. Name the four strokes of an IC engine?
Suction, compression, power and exhaust stroke
8. What is the purpose of heat balance sheet in IC engine?
It is the accounts of heat supplied and heat utilized in various ways in the system. The heat balance is generally done by minute basis or percentage basis.
9. Differentiate petrol and Diesel engines.
10. Define compression ratio.
It is defined as the ratio of the volume of cylinder to the clearance volume.
11. Define mean effective pressure.
It is defined as the average pressure acting on the piston during the entire power stroke that would produce the same amount of net work output during the actual cycle. It is also defined as the ratio of work-done per cycle to swept volume.
12. Define Clearance Volume.
It is the minimum volume occupied by the fluid in the cylinder when the piston reaches the top dead centre position.
13. Define work ratio of gas turbine.
It is the ratio of network to turbine work.
14. What is the function of push rod and rocker arm in IC engine?
The function of push rod and rocker arm in IC engine is to transmit motion of the cam tothe valve.
15. What is scavenging in IC engine?
The process of pushing out of exhaust gases from the cylinder by admitting the freshcharge into the cylinder is known as scavenging.
16. What is the function of idling jet in a carburetor?
The function of idling jet in a carburetor is to supply a mixture at an air fuel ratio of 10:1for low speed operation.
17. What are the requirements of a fuel injection system of a diesel engine?
- To inject the fuel at correct moment, and quantity at various load conditions
- To inject the fuel in a finely atomized condition.
- To distribute the fuel uniformly in the combustion chamber.
- To control the rate of fuel injection.
18. What is the purpose of a thermostat in an engine cooling system?
The purpose of thermostat in cooling system is to control the water flow. It allows thewater circulation only, when the temperature of the radiator is about 750°C.
19. List the advantages of electronic ignition system over the conventional system.
- Less weight.
- Spark timing can be accurately controlled.
- Wiring is simple
20.What is meant by ignition lag?
It is the time interval between the instant of spark and the instant when there is anoticeable rise in pressure due to combustion.
21. Differentiate between brake power and indicated power of an IC engine.
Brake Power: It is defined as the power developed at output crank shaft of an engine for doing external work.
Indicated Power: It is the power developed by the engine inside the cylinder due to the fuel combustion in the combustion chamber.
22. What is Morse test?
Morse test is a performance test conducted on multi cylinder engines to measure the indicated power without the use of indicator diagram.
23. Which engine will have more cooling requirement two-stroke engine or four-stroke engine? Why?
Two stroke-engines will have more cooling requirements since power is developed for each revolution of crank. So, for each crank revolution, Combustion occurs and more heat will be generated inside the cylinder.
24. What is the function of the carburetor?
- To atomize the fuel and mix it homogeneously with the air
- To run the engine smoothly without hunting of fuel wastage.
- To provide rich mixture during starting and idling and also for quick acceleration.
- To provide a constant air fuel ratio at various loads.
- To start the engine even in cold weather conditions.
25. List the requirements of ignition system.
- Ignition should takes place at the end of compression stroke.
- There should be no missing cycle due to the spark failure.
- Ignition must add sufficient energy for starting and sub staining the charge burning
- Ignition system should supply the minimum required energy within a small volume in a very short time.
26. What are the different types of ignition system in S.I. engines?
Battery Ignition system and Magneto ignition system.
27. What are the advantages of Battery ignition system?
- The initial cost is low (except battery).
- It provides better spark at low speed of engine during starting and idling.
- Maintenance cost is negligible. (expect for battery)
- The spark efficiency remains unaffected by advance and retard positions.
- The simplicity of the distributor drive.
28. What are the disadvantages of Battery ignition system?
- The engine cannot be started if the battery is weak
- The weight of the battery is greater than the magneto.
- The wiring involved in the coil ignition is more complicated than magneto.
- The sparking voltage drops with increasing speed of the engine.
29. What is the necessity of cooling in IC engine?
- To avoid uneven expansion of the piston in the cylinder.
- To reduce the temperature of piston and cylinder.
- To avoid the overheating of the cylinder.
- To avoid the physical and chemical changes in the lubricating oil this may cause sticking of piston rings.
30. What is flash point?
Flash point is the lowest temperature at which the given oil gives sufficient vapour togive a moment of flash, when a flame is passed across the surface.
31. What are the different types of cooling in IC engines?
- Air cooling
- Water cooling system
- Thermosyphon cooling
- Forced circulation cooling
- Thermostatic regulator cooling and Evaporative cooling
32. What is the purpose of lubrication in IC engines?
- To reduce the friction and wear between the parts having the relative motion.
- To cool the surfaces by carrying away heat generated due to friction.
- To seal between two moving parts.
- To clean the surface by carrying away the carbon particles caused by wear.
- To absorb the shock between bearings and other parts and consequently reduce noise.
33. What is petrol system of lubrication?
A special type of lubrication system used in two stroke engines in which lubricant (up to60%) is thoroughly mixed with fuel and supplied to the engine. It is also known as mist lubrication.
34. What is auto ignition?
A mixture of fuel and air can react spontaneously and produce heat by chemical reaction without the uses of flame to initiate the combustion, because the temperature is high
35. What is meant by pre-ignition?
At very high temperature carbon deposits formed inside the combustion chamber ignites the air fuel mixture much before normal ignition occurred by spark plug. This is called pre-ignition.
36. What are the factors affecting ignition lag?
Compression ratio, speed of the engine, Chemical nature of fuel and air fuel ration, and Initial pressure and temperature.
37. What is meant by knocking? How it occurs in diesel engines?
If the delay period of C.I. engines is long, more fuel is injected and accumulated in the chamber. When ignition begins, pulsating pressure rise can be noticed and creates heavy noise. This is known as knocking.
38. What are the effects of knocking?
- The engine parts get overheated which may cause damage to the piston.
- It creates heavy vibration of engine and hence louder noise and roughness.
- Decrease in power output and efficiency.
- More heat is lost to the coolant as the dissipation rate is rapid.
- The auto-ignition may over heat the spark plug and hence pre-ignition occurs Carbon deposits.
39. Define specific fuel consumption?
It is the ratio of fuel consumption per unit time of power developed.
40. Explain an experimental method to determine the frictional power of an IC engine.
Retardation test can be carried out to determine the frictional power of an diesel engine. In this method, the engine is started and made to run at full load conditions at rated speed. After sometimes, the fuel supply is cutoff and the necessary readings are noted. Repeat the above procedure for 50% load and calculated the frictional power of an engine using formulas.
41. What is the use of helical groove in a fuel injection pump used for CI engine?
- To control the delivery stroke effectively.
- To control the amount of fuel supplied to the engine.
42. Define the term brake power.
It is defined as the power developed at output crank shaft of an engine for doing external work
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