COOLING TOWER

COOLING tower-: In power plants, cooling towers are employed for cooling the warm water from the condensers so that the same water after cooling can be reused for condensing the steam. 

                             In other words, a cooling tower is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water's temperature . As this occurs, a small volume of water is evaporated,  reducing the temperature of the water being circulated through the tower.

              The use of cooling towers becomes essential where plenty of cooling water is not available from river or sea for direct cooling. A cooling tower can be considered as an enclosed device used for the evaporation cooling of water by contact with the air. In cooling towers,  the cooling takes place partly by an exchange of latent heat resulting from the evaporation of some of the circulating water, and partly by the transfer of sensible heat. Although the cooling effect can be produced by cooling pond , spray pond, atmospheric tower , spray filled tower. 

The types of cooling towers used in thermal power stations are : 

( 1 ) Atmospheric ( Natural draught chimney ) type cooling tower .                                            ( 2 )Mechanical draught type cooling towers. 

The cooling towers can also be classified as wet cooling towers or dry cooling towers.

Wet cooling tower -: In wet cooling towers the cooling takes place by evaporation but huge quantity of water goes along with hot air into atmosphere. 

Dry cooling tower -: In this type of cooling towers,  the cooling takes place by surface heat exchange, there being no drift losses ; of course, the initial cost is very high. 

REFRIGERATION AND AIR CONDITIONING MCQ -: 05

Q.1 On high side of ammonia absorption system allowable pressure is of the order of ______ .

A. 1 - 2 bars

B. 5 - 6 bars

C. ATM pressure 

D. 10 bars

And -: B

Q.2 The ______ temperature is the temperature above which a gas will never liquefy .

A. Atmospheric temperature 

B. Dew point temperature 

C. Wet bulb temperature 

D. Critical temperature 

And-: D

Q.3 The refrigerant for a refrigerator should have _____ .

A. High latent heat 

B. High sensible heat 

C. Low latent heat

D. Low sensible heat

And-: A

Q.4 At which pressure above which a liquid will remain liquid 

A. Absolute pressure 

B. Critical pressure 

C. Atmospheric pressure 

D. Low pressure 

And -: B

Q.5  In a flooded evaporator refrigerator  , an accumulator at suction of compressor is used to ____.

A. Collect vapour 

B. Increase refrigeration effect 

C. Collect liquid refrigerant and prevent it from going to compressor. 

D. None of the above 

Ans -: C

Q.6 In vapour compression cycle the higher temperature occurs at _____ .

A. Evaporator 

B. Condenser discharge 

C. Compressor discharge 

D. Expansion system

Ans -: C

Q.7 In which type of refrigeration system aqua ammonia is used as a refrigerant?

A. Compression 

B. Absorption 

C. Indirect 

D. None of the above 

Ans -: B

Q.8 The flow of refrigerant is controlled by which device?

A. Evaporator 

B. Compressor 

C. Condenser 

D. Expansion valve 

And -: D

Q.9 what is the effect of supercharging in a refrigeration cycle?

A. Decrease COP

B. Increase COP

C. Higher efficiency 

D. More refrigeration effect 

Ans -: A

Q.10  which temperature indicate the amount of moisture in air ?

A. Dew point temperature 

B. Critical temperature 

C. Dry bulb temperature 

D. Wet bulb temperature 

And -: D

Q.11 Generally cooling towers are installed where __.

A. For very big plant

B. Water is scarce

C. Water is available in plenty 

D. All of the above 

Ans -: B

Q.12 The percentage loss of drift in cooling towers is ____ .

A. 1 to 5 %

B. 10 to 15 %

C. 10 to 20 %

D. 25 to 50 %

Ans -: C

Q.13 Water is cooled by _____ in cooling towers system.

A. Condensation 

B. Evaporation 

C. Fusion

D. Sublimation 

And-: B

Q.14 Pure humidification can be achieved by passing air through the spray water maintained at _________ .

A. Dry bulb temperature 

B. Wet bulb temperature 

C. Dew point temperature 

D. Atmospheric temperature 

And -: A

Q.15 As warm air cools , it's relative humidity ________.

A. Increase and then decrease 

B. Decrease 

C. Increase 

D. Decrease and then increase 

And -: C

Wet bulb and Dew point temperature

Wet bulb temperature -: The wet bulb temperature is the temperature read by a thermometer covered in water-soaked cloth ( wet bulb thermometer ) over which air is passed. If the bulb of an ordinary thermometer is surrounded by a wick wetter with water and air passed around it ; water at surface will being to evaporate. The vaporisation takes heat -leatent heat of vaporisation and the wick is cooled . The temperature finally reached when cooling stops is known as wet bulb temperature. At wet bulb temperature,  the heat from the air to water surface equals the haet taken from the surface to vaporise water.

                  At 100 % relative humidity , the wet bulb temperature is equal to the air temperature ( dry bulb temperature) and it is lower at lower humidity. A wet bulb temperature indicates a temperature close to the true ( thermodynamic ) temperature. The wet bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.

Dew point temperature -: The dew-point temperature is the temperature at which moisture will condense out of the air for a given specific humidity and pressure, as air moisture temperature is reduced. It is important to note that dew point temperature remains constant as long as there us no change in moisture. 

                   The dew-point temperature is always lower than Or equal to the air temperature. If the air temperature cools to the dew point, or if the dew point raises to equal the air temperature, then dew , fog or coouds being to form. At this point where the dew point temperature equals the air temperature, the relative humidity us 100%.

At 100% humidity, wet bulb temperature is equal to the dry bulb temperature. Drier is the air , more will be the difference between dry bulb and wet bulb temperature.

REFRIGERATION MCQ 04

Q.1 While changing from a liquid phase to vapour phase, fluids _______ heat.

A. Convert

B. Extract 

C. Absorb

D. No changes in heat

Ans-: C

Q.2 In reversed carnot cycle working on vapour, work done during isothermal process is _____ .

A. Maximum 

B. Minimum 

C. Increase 

D. Zero

Ans -: D

Q.3 The heat , which can be added or removed from a substance without a change in state is called ?

A. Sensible heat

B. Leatent heat

C. Extra heat

D. None of the above 

Ans -: A

Q.4 At which temperature , centigrade and Fahrenheit scale have same reading ?

A. - 45 °

B. - 40 °

C. - 100 °

D. - 273 °

Ans -: B

Q.5 Usually the quantity of free air per person in air conditioning system is taken as ______ .

A. 1.2 m^3 / min

B. 1.2 m^3 / sec

C. 0.2 m^3 / he

D. 1.12 m^3 / min

And-: A

Q.6 The dry bulb temperature is ____ , in spray humidification process .

A. Raised

B. Same

C. Lowered 

D. Zero

Ans -: C

Q.7 During evaporative cooling process the wet bulb temperature is ___.

A. Remain constant

B. Increased 

C. Decreased 

D. Zero

Ans -: A

Q.8 Which of the following is commonly used liquid absorbent ?

A. Silica gel

B. Ethylene glycol 

C. Activated alumina

D. None of the above 

Ans -: B

Q.9 One of the reasons for an evaporator to not cool may be ?

A. Frozen oil

B. Leaking refrigerant 

C. Faculty thermostat 

D. Insufficient lubricant in refrigerant 

And-: A

Q.10 The refrigerator which does not require compressor in known as ____.

A. Carnot refrigerator 

B. Tubo-refrigerator

C. Electrolux refrigerator 

D. Vapour absorption refrigerator 

And-: C

HUMIDITY

Humidity-: Humidity is the amount of water vapour in the air. If there is a lot of water in the air , the humidity will be high.

                               In simple words , humidity means water vapour in the air, but not to be liquid droplets in the fog , clouds,or rain. Higher Humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. The gaseous state of water, is generally invisible to the human eye. Humidity indicate the likelihood for precipitation, dew or fog to be present.  The amount of water vapour needed to achieve saturation increase as the temperature increases.

There are three types of humility-:

1. Absolute humidity 

2. Relative humidity 

3. Specific humidity 

1. Absolute humidity -: Absolute humidity is the measure of water vapour or moisture in the air, regardless of temperature.  It is expressed as grams of moisture per cubic meter of air ( g/m^3). 

                    In other words , the total mass of water vapour present in a given volume of the mass of the air known as " absolute humidity ". It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C. It is the mass of water vapour divided by the volume of the air and water vapour mixture, which can be expressed as -

Absolute humidity = mH2O / V(net)                                                                 

The absolute humidity changes as air temperature or pressure changes , if the volume is not fixed.

2. Relative humidity -: Relative Humidity is actual amount of moisture in air at any given temperature,  divided by the greatest amount of moisture the same air could hold without condensation. Relative humidity could also be expressed by moisture, divided by the highest vapour pressure ( saturation condition ) possible under the same conditions. 

                 Highest pressure that water vapour can have without condensation,  i.e. ,100 % relative humidity at various atmospheric temperature. 

3. Specific humidity -: Specific humidity is the ratio of the mass of water vapour to the total mass of the air parcel. Specific humidity is approximately equal to the mixing ratio,which defined as the ratio of the mass of water vapour in an air parcel to the mass of dry air for the same parcel. As the temperature decreasing the amount of the water vapour needed to reach saturation also decreases. As the temperature of a parcel of air become lower it Will eventually reach the point of saturation without adding or losing water mass.

                                     

REFRIGERATION MCQ-: 03

Q.1 ______ leatent heat of vaporisation is desirable in a refrigerant.

A. Low

B. High

C. Minimum 

D. Maximum 

Ans -: B

Q.2 The maximum temperature of a refrigerant at which it can be condensed into liquid known as ____ .

A. Boiling temperature 

B. Desirable temperature 

C. Critical temperature 

D. Refrigeration temperature 

Ans -: C

Q.3 Refrigeration compressor designed to oprate with R22 refrigerant and can't be oprated with R12 , because  Condensing pressure of R22 at any given temperature is ________ than that of R12.

A. Higher

B. Lower

C. Equal

D. None of these 

Ans-: A

Q.4 What is the name of combined process of cooling and humidifying ?

A. Vaporisation 

B. Condensation 

C. Evaporative cooling

D. None of these 

Ans -:C

Q.5 What is the value of sensible heat factor for humidification or dehumidification process ?

A. 1.5

B. 2

C. 1.5

D. Zero

Ans -: D

Q.6 In gas refrigeration cycle, ______ cycle is used .

A. Compression cycle 

B. Bell-coleman / Brayton cycle 

C. Expansion cycle 

D. Evaporation cycle 

Ans -: B

Q.7 Which refrigeration cycle is used in aircraft?

A. Water refrigeration cycle 

B. Air refrigeration cycle 

C. A + B

D. None of these 

Ans -: B

Q.8 How can we detect leakage of Freon in a refrigeration system?

A. Using freon detector 

B. Using a halide torch

C. Using Freon meter

D. All of the above 

Ans -: B

Q.9 One tone of refrigeration is equal to ___ .

A. 3.5 kW

B. 4.5 kW

C. 1.15 kW

D. 5.2 kW

Ans -: A

Q.10 In a refrigerant moisture is removed by which device?

A. Dehumidifier 

B. Evaporator 

C. Heat exchanger 

D. Driers 

Ans -: D

Q.11 In domestic refrigerator back side tubes are used , are known as _____ .

A. Capillary tube 

B. Evaporating tube

C. Condenser tube

D. None of these 

Ans -: C

Q.12 The coefficient of performance of a domestic refrigerator is ____.

A. More than 1

B. Less than 1

C. 100 %

D. Zero

Ans-: A

Q.13 In which type of refrigeration system only have droplets of liquid in the evaporator?

A. Flooded type 

B. Dry type

C. Low side float system 

D. Capillary tube type 

Ans -: B

Q.14 The rate at which refrigeration is produced and is expressed in tons of refrigeration known as _____ .

A. Power of refrigerator 

B. Capacity of refrigerator 

C. C.O.P. of refrigerator 

D. None of these 

Ans -: B

Q.15 At -15° C carbon dioxide ( CO2 ) has low specific volume in order of _____ .

A. 0.52 m^2/ kg

B. 0.016 m^3/ kg

C. 0.025 m^3 / kg

D. 1.57 m^2 / kg

Ans -: B

Q.16 As compared to ammonia,  freon-12 has _____ specific volume.

A. Large

B. Same

C. Small

D. Very high 

Ans -: C

Q.17 Absorption system normally uses which refrigerant?

A. CO2

B. SO2

C. Ammonia 

D. CFC

Ans -: C

Q.18 In ammonia absorption plant,  cooling water is required for which equipment?

A. Absorber

B. Condenser 

C. Separator 

D. All of the above 

Ans -: D

Q.19 Generally oil separator is installed between _____ in refrigeration system. 

A. Compressor and condenser 

B. Evaporator and flow control device 

C. Compressor and Evaporator 

D. None of these 

Ans -: A

Q.20 What is the use of brine agitator in ice plant ?

A. Increase COP

B. Increasing refrigeration effect

C. Obtain uniform temperature of brine

D. All of the above 

Ans -: C

REFRIGERATION MCQ-: 02

Q.1 Air refrigerator cycle works on ____ cycle.

A. Bell-coleman

B. Air cooling cycle 

C. Carnot cycle 

D. Raynold cycle 

Ans -: A

Q.2. Fluid ____ heat while changing from a liquid phase to vapour phase .

A. Remove

B. Convert

C. Absorb 

D. Increase

Ans -: C

Q.3 What is the boiling temperature  of carbon dioxide?

A. 31° C

B. 78.5 ° C

C. - 78.5 ° C

D. -48.5  ° C

Ans -: C

Q.4 What is the boiling temperature of ammonia?

A. - 33° C

B. - 45° C

C. 75 ° C

D. 22.5 ° C

Ans-: A

Q.5 Operating pressure of Freon- 12 is ____ .

A. 5 kgf/cm^2

B. 8 kgf/cm^2

C. 10 kgf/cm^2

D. 22 kgf/cm^2

Ans -: B

Q.6 Sulphur dioxide ( SO2 ) has low working pressure _____ .

A. 5.5 kgf/cm^2

B. 7.5 kgf/cm^2

C. 4.5 kgf/cm^2

D. 1.8 kgf/cm^2

Ans -: C

Q.7 As compared to Freon-12 , freon-22 has _____.

A. High specific volume 

B. Low specific volume 

C. Equal specific volume 

D. None of these 

Ans -: B

Q.8 Freon-12 is mostly used in which type of plants?

A. Commercial 

B. Domestic 

C. Never used

D. A + B

Ans-: B

Q.9 Sulphur dioxide has a critical temperature of ______ .

A. 157.2 ° C

B.  225.5 ° C

C. 100 ° C

D.  127.5 ° C

Ans-: A

Q.10 What happed , when SO2 contact with moisture?

A. Highly toxic 

B. Corrosive 

C. Non- corrosive 

D. A + B

Ans-: D

Q.11 Carbon dioxide has critical temperature in the order of _____ .

A. 52 ° C

B. 25 ° C

C. 31 ° C

D. 125 ° C

Ans -: C

Q.12 Ammonia is mostly used in ____ .

A. Domestic purpose 

B. Large commercial installation 

C. A + B

D. None of the above 

Ans-: B

Q.13 The ratio of the refrigeration obtained to the net work done on the system in the cycle known as _____ .

A. Refrigeration ratio

B. Work done

C. Coefficient of performance of refrigerant 

D. Refrgerant quality 

Ans-: C

Q.14 Compression refrigeration system also known as _____ .

A. Flood refrigeration system 

B. Mechanical refrigeration system 

C. Dry refrigeration system 

D. None of these 

Ans -: B

Q. 15 The ratio of actual and theoretical coefficient of performance is known as ____ .

A. Relative Coefficient of performance 

B. Refrigeration C.O.P.

C. Total work done

D. None of these 

Ans -: A

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. 

Scavenging and auto ignition

Scavenging -: In an I.C. engine , scavenging is the process of replacing the exhaust gases in the cylinder with the fresh air or fuel mixture for the next cycle. 

                   In other words,  scavenging is the process of removing the brunt gases from the engine cylinder.  Efficient scavenging is necessary for good combustion of fuel in the engine cylinder. The passage of scavenge air will also assist cooling of the cylinder,  pistpn and the valves. 

There are three types of scavenging process-:

1. Loop scavenging 

2. Uniflow scavenging 

3. Cross scavenging 

1.Loop scavenging -: In loop scavenging process , the incoming air passes over the piston crown then rises toward the cylinder head.  The exhaust gases are forced before the air passing down and out of exhaust ports located above the inlet port .

                      Fig -: loop scavenging 

2.Cross scavenging -: In this type of scavenging process,  the incoming air is directed upwards and pushing the exhaust gases before it from the engine cylinder. The exhaust gases then travel down and out of the exhaust ports. 

                   Fig -: cross scavenging 

3.  Uniflow scavenging -: In the uniflow scavenging process, the incoming air enters at the lower end of the cylinder and leave at the top of the cylinder. During this travel incoming air push the brunt gases outside of the cylinder.  The outlet at the top of the cylinder may be ports or a large valve. 

Auto ignition -: It is the phenomenon of fuel catching fire without external source of ignition energy . As the name suggests, the fuel particles auto-ignite. So when the spark is introduced ,the flame front propagates,  this flame boundary further increases the temperature of fuel molecules which is already at a high temperature. 

                  Auto ignition occurs the mixture of the gases or vapour ignites spontaneously with no external ignition source and after reaching a certain temperature , the Auto ignition temperature.  The auto ignition temperature is not an intrinsic property of gases or vapours but is the lowest temperature in the system whene the rate of heat evolved from the gases or vapour increases beyond the rate of heat loss to the surrounding , resulting in ignition .

                 Auto-ignition is accelerated by the normal heptane and resisted by iso-octane. 

SUPERCHARGING

Supercharging -: Supercharging is the process of increasing the mass of air or density of air fuel mixture to the engine cylinder by compressing intake air initially with a view to obtain high power. This is usually done with the help of a compressor or blower.

                          Supercharging is used in I.C. engine to increase the volumetric efficiency. It is most common used in petrol engine. During supercharging the pressure of inlet air is increased above the atmospheric pressure by the supercharger. It can push high volume of air than the volume of air intaked by naturally aspirated engine of same capacity. 

                      Naturally aspirated engine have volumetric efficiency below the 90% but the supercharged engine the volumetric efficiency is above the 100 %.

                           Due to availability of higher oxygen during the combustion of fuel which ensure the better combustion of fuel . The advantage of supercharging is better combustion of fuel into the camber of cylinder. Due to this total power produced by the engine is also increased. There are two units used for increasing volumetric efficiency of engine , supercharger and turbocharger. The main difference in supercharger and turbocharger is that , supercharger is commonly used in petrol engine and turbocharger is commonly used in diesel engine. Turbocharger get the power from the exhaust gases of the engine to run the compressor through the turbine. In petrol engine combustion pressure is low so the energy of exhaust gas is also low as compare to diesel engine. For this reason turbocharger is not used in the petrol engine. 

        Supercharging is used generally at high altitude,  where density of atmospheric air is low . 

Concept of supercharging -: 

  

DETONATION

Detonation -: Detonation is generally caused by fuel with low octane rating - is the tendency for the fuel to pre - ignite or auto ignite in a engine's combustion chamber. The auto-ignition propagates a high pressure wave through fuel air mixture, giving a voilent blow to the walls of cylinder. A fuel having higher self ignition temperature detonates less.

                         The effect of detonation may be anywhere from arbitrary to serve. prolonged and intense knocking can break the piston or the engine , through it is can also endure this slight issue for thousand miles. 

           Detonation is mostly caused by the use of low- grade engine fuel and it is resulting deterioration of your engine's parts. The shape, size and spark location and geometry of the design all help determine where these detonation are likely to occur. An over-heated spark plug tip can also cause pre-ignition 

Detonation in petrol engines can be reduced by the addition of a small amount of lead ethide or ethyl fluid to the fuel. This is the known as doping. 

                           The knocking tendency in a petrol engines can be prevented by ensuring that the charge away from the spark plug has low density , low temperature,  long ignition delay, and rich mixture. It is also decreased by reducing compression ratio, and increasing the engine speed with fixed octane rating fuel. However knocking in the petrol engines is increased by increase in cooling water temperature and supercharging .

                The knocking tendency in diesel engines can be prevented by reducing the delay period, increasing the compression ratio , inlet pressure og air and injection pressure. 

I.C. ENGINE MCQ 02

Q.1 which fuels are taken as a reference for the cetane rating ?

A. Cetane and n- heptane

B. Cetane and α- methyl naphthalene

C. Cetane and isocetane

D. Tetraethyl lead and cetane

Ans-: B

Q.2 In diesel engine, pistons are usually cooled by __ .

A. Water 

B. Fuel oil 

C. Lubricating oil 

D. Air 

Ans-: C

Q.3 Which device is used to reduce exhaust noise ?

A. Exhaust manifold 

B. Filter

C. Tail pipe 

D. Muffler

Ans-: D

Q.4 Cetane number is the measure of _____ .

A. Ignition quality 

B. Viscosity of fuel

C. Additions in fuel

D. Density of fuel

Ans -: A

Q.5 What is the freezing temperature of the petrol engine?

A. - 20 to - 10 ° C

B. 50 to - 30 ° C

C. - 10 to - 4 ° C

D. 40 to 100 ° C

Ans -: B

Q.6 Which test is done to determine the mechanical efficiency of multi-cylinder engines ?

A. Air flow test 

B. Fuel consumption test

C. Morse test

D. Power test 

Ans -: C

Q.7 The percentage of CO (carbon monoxide) in exhaust gases in the compression ignition engine is ?

A. 10 to 20 %

B. 5 to 10 %

C. Zero

D. 10 to 12 %

Ans -: C

Q.8 High speed diesel engines need a cetane number of ____ .

A. 100

B. 50 

C. 75

D. 25

Ans -: B

Q.9  If diesel is fed by mistake in the oil tank of petrol engine , then engine will __ .

A. Knock

B. Detonate

C. Not run

D. Give lot of smoke 

Ans -: C

Q.10 Which type of carburettor is preferred .

A. Vertical type 

B. Horizontal type

C. Eccentric type 

D. Concentric type 

Ans -: D

Q.11 The compression ratio of motor car is ____.

A. 7

B. 5

C. 10

D. 15

Ans-: A

Q.12 The knocking tendency in a S.I. engine can be reduced by increasing _______ .

A. Compression ratio of fuel

B. Speed

C. Lubricating oil quality 

D. None of these

Ans -: B

Q.13 What is HUCR ?

A. Highest useful compression ratio

B. Highest useful compression radiation 

C. A lubricating device 

D. None of these 

Ans -: A

Q.14 Most high speed compression engines oprate on _____ .

A. Otto cycle 

B. Dual cycle 

C. Carnot cycle 

D. Four stroke cycle 

Ans -: B

Q.15 Piston rings are usually made of which material ?

A. Carbon steel

B. Aluminium 

C. Cast iron 

D. High speed steel

Ans -: C

I.C. ENGINE MCQ :- 01

Q.1 Under which condition otto cycle is more efficient than diesel cycle?

A. At lower compression ratio

B. For same compression ratio

C. For same maximum pressure 

D. For same maximum temperature 

Ans-: B

Q.2 How many working cycle two stroke engine have ?

A. 1

B. 2

C. 1/2

D. 4

Ans -: A

Q.3 In diesel engine, the fuel is injected by ____.

A. Combustion chamber 

B. Spark plug

C. Injected fuel

D. Heat resulting from compressing air that is supplied for combustion 

Ans -: D

Q.4 At what pressure the fuel is normally injected in diesel engine ?

A. 20 - 50 kg/cm^2

B. 50 - 60 kg/cm^2

C. 90 - 130 kg/cm^2

D. 5 - 10 kg/cm^2

Ans -: C

Q.5 The inlet value of a four stroke cycle I.C. engine remain open for _____.

A. 180°

B. 235°

C. 275 °

D. 360°

Ans -: B

Q.6 which of the following is compressed in a diesel engine cylinder?

A. Air 

B. Fuel

C. Air + fuel

D. Air+fuel+lub oil 

Ans -: A

Q.7 For idling speed of a petrol engine,  air fuel ratio is ______ .

A. 10 : 1

B. 1 : 1

C. 5 : 1

D. 20 : 1

Ans -: A

Q.8 How many valves  diesel engine has ?

A. 1 valve

B. 3 valve

C. 2 valve 

D. No valve 

Ans -: B

Q. 9 For increasing power output _______ is usually done .

A. Detonation 

B. Knocking 

C. Scavenging 

D. Supercharging

Ans -: C

Q.10  Iso-octane has octane number of ___.

A. 100 

B. 200

C. 150

D. 250

Ans -: A

Q.11 The specific gravity of diesel oil is __.

A. 0.7

B. 0.5

C. 0.75

D. 0.85

Ans -: D

Q.12 The efficiency of I.C. engine is of the order of ___ % .

A. 25

B. 95

C. 85

D. 35

Ans -: D

Q.13 The magneto system of ignition is used in ____.

A. Motor cycles 

B. Aeroplanes 

C. Racing cars

D. High speed engines 

E. All of the above 

Ans -: E

Q.14  In which type of engine NOx emission is more ?

A. Petrol engine 

B. Diesel engine 

C. Steam engine 

D. Electric  engine 

Ans -: B

Q.15 The difference of research octane number and motor octane number is konwn as _____.

A. Fuel octane number 

B. Fuel density

C. Fuel sensitivity 

D. Cetane number 

Ans -: C

IGNITION SYSTEM IN PETROL ENGINE

In a petrol-engine , electric spark produced between the points of a spark plug due to this spark the combustible mixture is ignited. 

There are two systems of electric ignition:-

1. Battery ignition ( or coil ignition )

2. Magneto ignition 

1.Battery or coil ignition system -:

It relates to four cylinder petrol engine it has two circuits, the primary circuit and the secondary circuit. The function of ignition coil is to set-up 6 or 2 volts from the battery to the high tension voltage of about 24,000 volts . Closing the switch,  the current from the battery passes through the ammeter , the primary of the induction coil and contact breaker point , the contact pint being closed. The secondary of the induction coil is connected to the distributor arm. The primary winding has a small number of turns of coarse-wire ( between 100 to 200 )whereas a secondary winding has a large number of turns of very fine wire ( of the order of 10,000).

                       When spark is required in a cylinder,  the contact breaker points are opened by the cam and this induces high voltage( the order of 2400 volts ) in secondary. At the same time the distributor arm comes opposite to the point from from where the wire leads to the saprk plug of these cylinder. The high voltage induced in secondary give spark at the spark-plug .

        

         Fig. Battery ignition system 

2. Magnet Ignition System-: 

 In magnet type ignition system , is not required a battery for voltage . It generates its own voltage for the primary. Here an armature having wound upon it in the primary coil of a few hundred turn of enamelled copper wire and secondary coil of several thousand turns of fine insulated wire, rotates in a permanent magnetic field. 

                  In the mordern trend , the armature is to keep stationary and magnets is to keep rotating. By this action,  the primary voltage is generated in accordance with the law of electric generator , which is then transformed into a very high secondary voltage exactly on the lines described in the battery ignition system. Generally magneto system is used in high speed engines like scooter,  racing cars aeroplanes etc .

Valve timing Diagrams

Valve timing Diagram -: The opening and closing of intake and exhaust valves of the engine is graphically represented by a diagram , is known as " valve timing Diagram ". The opening and closing of the valves of the engine depend upon the movement of the piston from TDC to BDC , this relation between piston and valves is controlled by setting a graphical representation between these two , which is known as valve timing Diagram .

                  Theoretically the valve should open and close at the end or start of the stroke. But in actual practice it is not desirable to do so in order to obtain better results. The valves are generally opened earlier and closed later . 

                     Valve timing Diagram comprises of a 360 degrees figure which represent the movement of the piston from Top dead centre to bottom dead centre . In all the stroke of the engine cycle , which is measured in degrees and the opening and closing of the valves is controlled according to these degrees. 

Starting from the suction stroke , the intake valve is opened about 10 ° to 30 ° begore the TDC . Exhaust valve is also open at this movement . By opening the intake valve earlier,  more chances to fresh charge coming in are made . As fresh chagre move in , it helps in expelling the exhaust gases also from the chamber. 

                                                                                   Fig. (a) Inlet valve open, inlet valve close       

  

The inlet valve does not close at B.D.C. , but is closed at after it . It generally closes 30° to 40 ° after B.D.C. by doing so , a large amount of fresh chagre is ensured,  as the charge during suction stroke was get going in and compression by piston has not yet been able to push out the charge. 

During compression , the spark is ignited before the T.D.C. in case of otto . This is about 10 ° before T.D.C. or tge fuel is injected about  5 to 10 ° before T.D.C. . This is done so , because the whole of the fuel can't burn instantaneously.  Fuel also has some delay  period , ( i.e. period between spark and actual ignition ). Also time is required for the spark to travel and spread throughout the cylinder. 

        

        In expansion stroke , the exhaust valve opens about 30 to 40 ° before B.D.C. and closes about 10 ° after T.D.C. . Thus the period of exhaust is increased and complete  and effective scavenging is ensured. If this is not done , then residual  combustible mixture results in the dilution of fresh chagre. 

                                                                                               Fig . ( c ) expansion stroke 

FOUR STROKE ENGINE

The engine is classified as four stroke depending upon the number of stroke it requires to complete the basic four events of opration. The otto ,diesel and dual cycle are completed in four strokes , therefore engines based on these are called "four stroke engine " .

             

  It is the most common type of the internal combustion engine and used in various automobiles like cars , trucks ,some motorcycles etc . It deliver one power stroke for every two cycles of the piston or four piston stroke. Four stroke engine has valves    (inlet or exhaust) which is operated by the push rod ,cam , roker arms etc.

Four stroke engine complete two cycles in four strokes -: 

1. Suction or intake stroke 

2. Compression stroke 

3. Power or expansion stroke 

4. Exhaust stroke 

1.Suction/ Intake stroke -: In this stroke piston move downward to the bottom,  this increase the volume , inlet valve open and  allow a air -fue mixture to enter into the chamber. In this process inlet valve open and exhaust valve close. Now half cycle is complete. 

2.Compression stroke -: In compression stroke inlet valve close and the piston move upward or top dead centre. Due to movement of piston upward intake fuel mixture compress . And at the the end of this strokea spark plug is present to ignition. At this stage one cycle is complete .

3.Power stroke -: In the power stroke the compressed air-fuel mixture is ignited by the spark plug and combustion is start. Due to burning of fuel very high pressure gases produced which oppose the piston at the top face and now piston move downward and create the power output. Now one and half cycle is completed. In this stroke both valves are closed .

4. Exhaust stroke -: At the end of compression stroke the brunt gases is remain into the chember and which pushes the piston top side . At this time of syroke exhaust valve open and due to upward motion of piston waste gases is expelled outsude from the chamber through the exhaust valve. At the end of this stroke two complete cycles of four stroke engine is complete. 

               Again piston move downward and allow to enter fuel into the chember process will again start and cycle begins again. 

TWO STROKE ENGINE

Two stroke engine-: As the name implies, the two stroke engine only requires two piston movement or one cycle. In two stroke engines , the two ideal cycle i.e. suction and exhaust stroke are eliminated ( in other words both are not have separate stroke ). So we have one power stroke per revolution of crank in two stroke engine.

                      In two stroke engine ports are used instead of the inlet and exhaust valves oprated by complicated mechanism. The engine is able to produce power after one cycle because intake and exhaust of the gas occur simultaneously. 

Two - stroke engine 

Two stroke engine contain two processes:-

1. Compression stroke -: In this stroke first the inlet port open, air-fuel mixture enters in the chamber and piston move upward. Movement of the piston from downward to upward compress the fuel mixture at high pressure ratio. due to compression temperature and pressure of fuel increase and now spark plug ignite and burn the mixture at this point compression stroke end.

2. Power stroke-: In the power stroke the brunt fuel gases exerted very high pressure on the piston ,due to this pressure piston move downward ( expansion) and waste or exhaust gases is out from the exhaust port due to piston movement. Now one cycle is complete. 

As compare to four-stroke engine , two stroke engines are lighter , more efficient and also have tha ability to use lower- grade fuel. Therefore the lighter engines results in a higher power to weight ratio.

Two stroke engine can proceed with intaking the fuel mixture as seen in processes --:

Process 1-2-: During process 1-2 inlet port open and piston at the bottom dead centre to come upward top dead centre . Now fuel-air mixture intake and piston move upward, compresse the fuel. Due to compression cause the mixture to increase temperature and pressure and no heat exchange in this process. This is a adiabatic process. At the end of the process fuel is met by the spark plug to be ignited. 

Process 2-3-: In this process, fuel is burn by the sapkr plug ignition and combustion of fuel occurs. Due to combustion high pressure heat is generated at this point this process is end. 

 P -V diagram of two stroke engine 

Process 3-4-: The thermal energy in the chamber as a result of combustion is used to do work on the piston which pushes the piston downward and increasing the volume of the chamber. This process also known as power stroke.

Process 4-1-: In this process 4-1 , all the waste gases is expelled from the engine chamber.  As the heat leave the gas , molecules lose kinetic energy causing the decreasing in pressure. There is no exhaust phase in a two stroke engine, so the cycle begins again by allowing the air-fuel mixture in the combustion chamber. 

Two stroke engines ideal for ships , motorcycles and lawnmower etc.

Components of engine

There are various components are used in the structure of the engine.Every component have specific quality by which an engine work with desired efficiency .

1. Cylinder -: Internal combustion engine cylinder is designed to withstand the high pressure and temperature conditions. It should be able to transfer unused heat efficiently so that metal temperature does not approach at danger.In this type of engine cylinder liners or sleeves are use because these are more economical because of ease of replacement after wear and tear.also instead of making of the whole of the cylinder of best grade material ,only liner can be made of better grade. 

             In the cylinder of the I.C. engine all the process take place ( fuel intake , compression, expansion etc.) .

2. Cylinder head -: cylinder head close one end of the cylinder.  Air and fuel valves are also accommodate in it. A copper gasket is placed between the cylinder and cylinder head to make gas tight joint .

3.piston-:Piston is an important part of an I.C. engine which receive impulse from the expanding gases in side the cylinder and transmits the energy to the crankshaft through the connecting rod.It also disperses large amount of heat from the combustion chamber to the cylinder walls .

               Its construction should be rigid enough to withstand mechanical and thermal distortion. I.C. engine have trunk type piston which consists of head or crown to carry the cylinder pressure. To maintain the piston temperature within limits , the heat from the crown of piston must be dissipated quickly. It should have least friction and noiseless opration. Material of the piston must possess good wearing qualities ,so that the piston is able to maintain surface hardness upto the operating temperature and there should be little or not tendency towards corrosion. The most common used material for the piston of I.C. engine are: cast iron , cast aluminium, cast steel ,forged aluminium and forged steel.

4. Piston rings-: Piston rings are designed on the piston which impart the necessary radial pressure to maintain the seal between the piston and the cyliderbore .The piston rings inserted at the top function as compression rings or pressure rings and may be in number of 3,4,5,6 and 7.It absorb part of piston fluctuation due to side thrust and also transfer heat from piston to cylinder liner.

             In the oil ring , either bottom outer edge is stepped or bevelled,or slot cut at the centre of the ring all round the periphery and lower edge of the grove of the piston is bevelled and small holes drilled toward the instead of the piston so that excess oil scrapped by the ring flows through these holes and fall in the sump.

         Compression rings are made usually of rectangular cross- section and diameter is larger than cylinder bore .

Piston rings are usually made of cast iron and alloy cast iron .

5.connecting rod-: It is used to transmit the motion from the reciprocating piston to the rotating crank. It also convey the lubricating oil from the crank pin to the piston pin and provide splash or jet cooling of the piston crown. It consists an eye at the small end or piston pin bearing , a long shank usually I-section, and a big end opening which is usually split to take the crankpin bearing shells. The connecting rod of I.C. engine are mostly manufactured by drop forging with outer surfaces left unfinished. 

6.Crank shaft-: It is used to convert reciprocating motion of piston to rotary motion. Crank shaft consist of the shaft parts which revolve in the main bearing ,the crankpin to which the big end of the connecting rod are connected,  the crank webs connect the crank pin and the shaft parts.

7. Fuel nozzle-: The fuel in diesel engines is fed by an injection system consisting of a pump , fuel line and the injector/fuel nozzle. Fuel is fed by this nozzle ina fine spray under pressure. 

8. Intake and Exhaust valves-: these both valves are spring loaded and oprated by the cam. The valves are mounted either in the cylinder block or the cylinder head . Usually conical valves having angle of 30° or 45 °are used. As the head of the valves are subjected to high temperature of the burning gases ,these should not wrap under the influence of heat and there seats should not scale or corrode,otherwise they would start leaking. 

9.Cam shaft -: It is driven from the crank-shaft by a timing gear on a chain . It operates the intake and exhaust valves through the cam, cam followers ,push rods and rocker arms.

INTERNAL COMBUSTION ( I. C. )ENGINE

In internal combustion ( I.C. ) engine, the combustion of fuel takes place inside the engine. In this type of engine energy loss in the form of geat is less than steam or outside combustion engine. Because in steam engine combustion of fuel is takes place outside of the engine . 

* Theefficiency of I.C. engine is of the order of 35 % and the steam engine is about 15%. this is becauseof the fact that very high tem- perature can be achieved in I.C. engines.

* I.C. engine are mostly single acting, thereby avoiding the necessity of leak proof stuffing box, piston rod,D-slide valve etc.

* I.C. engine is more compact unit Because it does not involve several cumbersome auxi-liaries .

* Combustion of fuel takes place inside the cylinder, therefore overall size is reduced and these become portable. 

Flurial hydraulics and basic fluid mechanics

Flurial hydraulics -: The study of flow of the water in mobile boundary channels is dealt in flurial hyraulics. The channel may be classified as mobile boundary or rigid boundary channels . Mobile boundary channels include rivers and unlined alluvial chanls , the boundaries of which are made of loose soil which can be esaly eroded and transported by flowing water .

Pressure gradient -: The pressure gradient in a fluid is equal to the body force per unit volume and acts in the same direction.      The term pressure gradient ( grad p ) = ρ K = ρ ( ix + jy + kz ) , where i,j and k are the unit vectors in the direction of the axes of the coordinate system .

The one - seventh power law-: In this law of turbulent, velocity variation corresponds to a much favoured velocity profile and the mean velocity increases as the one- seventh power of the distance from the boundary wall.

Geometric similarity -:Geometric similarity imples similarity of form. The model is a geometric reduction of the prototype and is accomplished by maintaining a fixed ratio for all homologous lengths between the model and the prototype. 

Kinematic similarity -: Kinematic similarity involves the scale of time as well as length.It implies similarity in motion. Kinematic simi-larity between a model and the prototype is attained if the homologous moving particles have the same velocity ratio along geo-metrically similar path.