REFRIGERATION MCQ -: 01

Q.1 From which device the moisture in a refrigerant is removed ?

A. Evaporator 

B. Driers

C. Expansion valve

D. Dehumidifier 

Ans-: B

Q.2 One tone of refrigeration is equal to ___.( In SI unit )

A. 100 kJ / min

B. 840 kJ / min

C. 240 kJ / min

D. 420 kJ / min

Ans -: C

Q.3 The coefficient of performance of a domestic refrigerator is ___ .

A. Less than 1

B. Equal to 1

C. Zero

D. More than 1

Ans -: D

Q.4 Air refrigeration cycle is used in ____ .

A. Commercial refrigerator 

B. Air-conditioning 

C. Gas liquefaction 

D. Air handling unit 

Ans -: C

Q.5 Freezing temperature of ammonia is __.

A. 77.8 °C

B. - 32.5 ° C

C. 89.2 ° C

D. - 77.8 °C

Ans -: D

Q.6 Which of the following is properties of Freon?

A. Colourless

B. Odourless

C. Nontoxic 

D. All of these 

Ans -: D

Q.7 Freon-22 also known as _____ .

A. CH2ClF2

B. CHClF2

C.  Cl2CHF2

D. CFC

Ans -: B

Q.8 Boiling temperature of Freon-22 is __ .

A. - 40 ° C

B. - 50 ° C

C. - 92 ° C

D. - 273.15 ° C

Ans -: A

Q.9 Capillary tube refrigeration system also known as ____ .

A. Automatic expansion system 

B. Restrictor system 

C. Dry type system 

D. Low side float system 

Ans -: B

Q.10 Where does the lowest temperature occur in a vapour compression cycle?

A. Receiver 

B. Expansion valve 

C. Evaporator 

D. Condenser 

Ans -: C

Q.11 Which is the most suitable refrigerant for a commercial ice plant ?

A. Brine

B. Freon

C. Air

D. NH3

Ans -: D

Q.12 Presence of moisture in a refrigerant affects the working of which unit ?

A. Expansion valve 

B. Condenser 

C. Compressor

D. Heat exchanger 

Ans -: A

Q.13 In freon refrigeration plant , the condenser and evaporator tubes are made of ____ .

A. Steel

B. Brass

C. Copper 

D. Aluminium 

Ans -: C

Q.14 Air is dehumidified by which process?

A. Heating 

B. Cooling 

C. Chemical absorption 

D. B + C

Ans -: D

Q.15 Air is normally dehumidified by ____ .

A. Injecting water

B. Cooling 

C. Heating 

D. Superheating

Ans -: B

I.C. ENGINE MCQ -: 04

Q.1 The constant volume process in I.C. engines is characterstic of ______.

A. Compression -ignition 

B. Spark ignition 

C. Two stroke engine 

D. Four stroke engine 

Ans -: B

Q.2 Which machine will produce continuous work without receiving any energy from other system ?

A. Simple machine

B. Hydraulic machine 

C. Perpetual motion machine 

D. All of the above 

Ans -: C

Q.3 In which type of engine , low CO and hydrocarbon emission occurs at low and moderate loads ?

A. Diesel engine 

B. Petrol engine 

C. Gas engine 

D. S.I. engine 

Ans -: A

Q.4 Hunting occur in the engine due to ____ .

A. Faulty governor 

B. Over - control by the governor 

C. Bad engine designs

D. Improperly designed governor 

Ans-: B

Q.5  Commonly used antifreeze solution in automobiles is ?

A. Lead ethyl

B. Iso-octane 

C. Glycol 

D. Heptane 

Ans -: C

Q.6 The automobiles generally utilise batteries having voltage ____ .

A. 10 V

B. 6 V

C. 12V

D. 24 V

Ans -: C

Q.7 For compression ignition engine, compression ratio usually  varies between __.

A. 4 - 6

B. 10 - 18

C. 14 - 25

D. 6 - 12

Ans -: C

Q.8  Which device is used for atomising and vaporising the fuel and micing it with air in varying proportions?

A. Vaporizer 

B. Carburettor 

C. Compressor 

D. None of these 

Ans -: B

Q.9 Which of the following engines can work on very lean mixture?

A. S.I. engine

B. C.I. engine 

C. Two stroke engine 

D. Four stroke engine 

Ans-: B

Q.10 The four stroke cycle is complete in ___ revolution of crankshaft.

A. 1

B. 1/2

C. 4

D. 2 

Ans -: D

Q.11 Which device takes care of the fluctuations or the cyclic variations in speed ?

A. Piston rings

B. Fly wheel

C. Crank shaft

D. Connecting rod 

Ans -: B

Q.12  The air fuel ratio in a petrol engine fitted with suction carburettor, operating with dirty air filter as compared to clean filter will be ___ .

A. Lower 

B. Unpredictable 

C. Higher 

D. None of the above 

Ans -: C

Q.13 Minimum temperature to which oil is heated in order to give off inflammable vapours in sufficient quality to ignite momentarily when brought in contact with a flame known as __ .

A. Cloud point

B. Flash point

C. Pour point 

D. None of the above 

Ans -: B

Q.14 Optimum spark advance is the timing which develops maximum ___ .

A. Torque 

B. Power

C. Efficiency 

D. None of these 

Ans -: A

Q.15 The ratio of actual fuel air ratio and chemical  correct fuel air ratio known as____.

A. Relative fuel air ratio 

B. Actual fuel air ratio

C. Compression ratio

D. None of these 

Ans -: A

REFRIGERATION SYSTEM

Refrigeration system may be classified as -:

1. Flooded type

2. Dry type

Flooded type -: In flooded type refrigeration system , there is a pool of refrigerant in the evaporator. In this system,  the refrigerant level in the evaporator is maintained through the action of refrigerant flow control device. This system oprates at higher average suction pressure and operating cost is low with high efficiency. It also provides closer control of temperature. More liquid on low pressure side of tge system provides a greater area of wetted surface,  and allows a higher rate of heat transfer through the evaporator walls and tubing. 

Flooded type system are classified depending on the type of flow control device used -:

1. Low side float system 

2. High side float system 

3. Capillary tube or restrictor systems. 

1. Low side float system -: In low type float system,  the working of which is self- explanatory. Here the refrigerant charge used in system is not critical as any exess or over-charge will remain in the liquid receiver. 

2. High side float system -: In this type of system , the flow of liquid refrigerant in this system is controlled by both the high side float in the liquid receiver and the pressure reducing valves at the evaporator to maintain differential pressure between the refrigerant in the liquid lines and the refrigerant in the evaporator, the refrigerant charge in the high side float system is very critical. 

            Excess charge will result in flood back and liquid refrigerant in that case will flow into suction line of compressor causing frost to appear and may damage compressor.

3. Capillary tube or restrictor systems -: This system is widely used because of low cost, trouble free opration, simplicity and achieving of hermetically sealed system. In this system,  the amount of refrigerant allowed to flow is dependent upon the length and inside diameter of capillary tube provided between the filter and evaporator . Overcharge may result in floodback.

Dry type refrigeration system -: Dry type refrigeration system have only droplets of liquid refrigerant in the evaporator.                                            In dry type system, the refrigerant passing through the valve is partially evaporated immediately after passing the orifice. The fine suspended droplets of liquid refrigerant are completely evaporated as they flow through the balance of the evaporator. Evaporator is generally made from one continuous length of tubing which ensure better control of liquid refrigerant when the flow control device is properly adjusted. 

Dry type refrigeration system are classified in two types -: 

1. Automatic expansion system 

2. Thermostatic expansion valve system.

Automatic expansion valve system -:

This system uses a pressure operated refrigerant flow control device which when properly adjusted, keep the evaporator fully refrigerated .

Thermostatic expansion valve system -:

In thermostatic expansion valve system,  thermostatic control is used to maintain evaporator outlet temperature in combination flow of with evaporator pressure by automatic expansion valve. It provides more accurate control of refrigerant in the evaporator. 

I.C. ENGINE MCQ -: 04

Q.1 The finished part of a shaft which rotates in or against a bearing is called ----- .

A. Journal 

B. Propeller 

C. Impeller 

D. Crank 

Ans -: A

Q.2 What is the effect of early or late injection of fuel in the diesel engine?

A. Knocking 

B. Detonation 

C. Loss of power 

D. More exhaust gases 

Ans -: C

Q.3 The stroke-bore ratio in case of aircraft engines in normally ____ .

A. Above 1.5

B. Below 1.0

C. 1.2 to 1.4

D.  None of these 

Ans -: B

Q.4 The ratio of brake power output to the fuel energy input per unit time is called __.

A. Mechanical efficiency 

B. Power produced 

C. Thermal efficiency 

D. Engine efficiency 

Ans -: C

Q.5 Which components are used to produce gas-tight seal between the piston and the cylinder liners ?

A. Piston crown 

B. Lube oil 

C. Piston pin 

D. Piston rings

Ans-: D

Q.6 For 6 cylinder petrol engine, standard firing order is _____ .

A. 1-4-2-3-5-6

B. 1-2-3-4-5-6

C. 1-4-2-6-3-5

D. 1-3-5-2-4-6

Ans -: C

Q.7 The thermal efficiency of petrol engine in comparison to diesel engine is ____ .

A. Higher 

B. Lower

C. Same

D. None of these 

Ans -: B

Q.8 In the spark ignition engine,  normal heptane in the fuel ______ .

A. Increase power output 

B. Decrease auto ignition 

C. Accelerates auto ignition 

D. None of these 

Ans -: C

Q.9 If fuel air ratio is greater than one then the mean effective pressure is ______ .

A. Minimum 

B. Maximum 

C. Higher

D. Lower 

Ans -: B

Q.10 Brake power of  diesel engine can be increased by increasing pressure of ____ .

A. Intake air 

B. Injecting fuel 

C. Lubricating oil 

D. All of the above 

Ans -: A

Q.11 What is the principal source of exhaust carnon monoxide ?

A. Poor mixture combustion 

B. Rich mixture combustion 

C. Lower grade fuel combustion 

D. None of these 

Ans -: B

Q.12 Which of these emissions cause photochemical smog ?

A. NOx

B. HC

C. CO

D. A+B

Ans -: D

Q.13 Which acid is used in automobiles battery?

A. HCL

B. H2SO4

C. HNO3

D. Hydrogen 

Ans -: B

Q.14 When an engine is idling , it requires ___.

A. High compression ratio 

B. Lower compression ratio 

C. Rich fuel air mixture 

D. Less fuel 

Ans -: C

Q.15 which medium is used for cooling of piston in diesel engines?

A. Water 

B. Air 

C. Synthetic oil 

D. Lubricating oil

Ans -: D

I.C. ENGINE MCQ 0-3

Q.1 The gap between two electrodes of spark plug is the order of ______ .

A. 0.5 to 0.7 mm

B. 0.3 to 0.5 mm

C. 0.3 to 0.7 mm

D. 1.5 to 1.8 mm

Ans-: C

Q.2 Ignition quality of the diesel oil is expressed by which number?

A.  Octane number 

B. Cetane number 

C. Oil number 

D. None of these 

Ans-: B

Q.3 Removing the brunt gases from the engine cylinder is known as ______.

A. Exhaust process

B. Compression process 

C. Scavenging process

D. Detonation 

Ans-: C

Q.4 The density of atmospheric air is _____ at high altitude. 

A. High

B. Minimum 

C. Maximum 

D. Low

Ans-: D

Q.5 The power available at the shaft known as ____.

A. Brake HP

B. Indicated HP

C. Total power 

D. Shaft power 

Ans -: A

Q.6 In which type of scavenging process,  the incoming air is directed upward,  pushing the exhaust gases before it ?

A. Cross scavenging 

B. Loop scavenging 

C. Uniflow scavenging 

D. None of these 

Ans -: A

Q.7 The incoming air enters at the lower end of the cylinder and leave at the top in ______ scavenging process .

A. Loop scavenging 

B. Uniflow scavenging 

C. Cross scavenging 

D. None of these 

Ans -: B

Q.8 Gaseous-fuel guarantees are based on ____.

A. Mean heat value of oil

B. Low heat value of oil

C. Calorific value of oil 

D. All of the above 

Ans -: B

Q.9  A 75 CC engine has following parameter as 75 CC .

A. Fuel tank capacity 

B. Swept volume 

C. Cylindrical volume

D. Carbon consumption 

Ans -: B

Q.10 In an engine, size of inlet valve is ____ than exhaust valve. 

A. More 

B. Same 

C. Less

D. Depends on capacity of engine 

Ans-: C

Q.11 In a cycle the spark lasts roughly for ___ second .

A. 0.001 

B. 0.0001

C. 0.02 

D. 0.002

Ans -: A

Q.12 which is the most volatile and lightest liquid fuel ?

A. Kerosene 

B. Petrol

C. Diesel 

D. Gasoline 

Ans -: D

Q.13 Which device is used to diminish noise of the intake or exhaust?

A. Muffler 

B. Noise reducer

C. Converter

D. None of these

Ans -: A

Q.14 what is the standard firing order for 4 cylinder petrol engine?

A. 1-3-4-2

B. 1-2-3-4

C. 1-4-3-2

D. 1-4-2-3

Ans -: A

Q.15 What device is used for obtaining required firing order in S.I. engine ?

A. Carburettor 

B. Distributor 

C. Fly wheel

D. Valves 

Ans -: B

REFRIGERATION PROCESS

Refrigeration -: Refrigeration is artificial cooling process. The term refrigeration mean cooling a space , substance or system to lower or also maintain it's temperature below the ambient one. In other words , refrigeration is the process of moving heat from one location to other in the control conditions. In this energy in the form of heat is removed from a lower temperature reservoir and transferred to a high temperature reservoir. 

                       Refrigeration has many applications,  including,  but not limited to : industrial freezers,  household refrigerator , air conditioning and cryogenics .

                      A refrigeration system is an combination of mechanical equipment in which a refrigerant is circulated for cooling , or extracting heat from bodies or space. A refrigerant having its boiling temperature less than atmospheric temperature will start boiling immediately if subjected to atmospheric conditions, absorbing heat from its surroundings, thereby producing cooling effect . 

Refrigeration system could be of two types-:

1. Compression 

2. Absorption 

                 Compression system, also sometimes known as mechanical system is the more popular of the two .                                                      

In this figure the compression refrigeration system is shown. This cycle is followed by the compression refrigeration system.

* In this process first , the refrigerant gas is compressed by the compressor and this compressed refrigerant then discharged into the condenser.

* In condenser it is cooled by the atmospheric air or water which is being used for abstracting heat from condenser. Condenser now condensed to liquid. 

* Condensed , and warm high pressure refrigerant then travel through the strainer or drier which prevents plugging of the flow control device by tapping scale,  dirt and moisture. 

* Flow control device controls the flow of refrigerant and refrigerant is trottled.

*  Now in the evaporator , refrigerant is subjected to a much lower pressure due to the combined suction of the compressor and the pressure drop across the flow control device.

             As a result,  refrigerant tends to expand and evaporate thereby cooling the air passing over evaporator. Refrigeration takes place from the absorption of heat during vaporization in the cooling coils. The gas is drawn again into compressor and the cycle is repeated .

Pre-ignition , octane number and cetane number

Pre-ignition -: pre-ignition is caused by the spontaneous combustion of the mixture before the end of the compression stroke in spark ignition engine, i.e. , even before the spark occurs in the spark plug . It may occur generally due to the red hot carbon deposited , or the cylinder walls being too hot , or overheated spark plug , or the pressure wave due to detonation. It may also due to the faulty timings .

                 In S.I. engine the fuel air mixture is drawn into the chamber during the suction stroke and is compressed until the spark plug ignite it. When the engine is running on high loads , there might be a hot carbon deposite or overheated spark plug's tip that might lead to pre ignition. 

                    The low flash point temperature,  of the petrol also adds to this problem . This is completely eliminated by the intervention of fuel injection into petrol 

Octane number -: It is defined as the percentage by the volume of iso-octane in a mixture of iso-octane and n-heptane which show the same tendency to knock as the fuel in question under same conditions . Ignition quality of petrol is expressed by octane number. 

Cetane number-: Cetane number is defined as the percentage by the volume of cetane in a mixture of cetane and α-methyl-napthalane which has the same ignition delay as the fuel in question under same conditions. Ignition quality of diesel oil is expressed by cetane number.