Questions

 Answers

(1) State difference between gas and vapour. Explain  pure substance.
Difference between Gas and Vapour :
Gas:
1)A gas is a single well-defined thermodynamic phase.
2) gas is a gaseous form of element.
3)No physical change has been undergone.
4) substance in the Gaseous state when the Temperature is above the Critical Temperature.
5) gas do not contain moisture.
6) we cannot see a gas but can only smell it.
7)are gases at room temperature.
8)present everywhere in the atmosphere.
9)A gas need not be a vapour always.
10)A gas cannot turn back and forth into liquid and solid states.
11)No solvent present
12)Examples are carbon dioxide,sulphur dioxide etc.


Vapour:
1)vapour is a mixture of the two i.e, the gas and the liquid.
2)The gaseous state of a substance that is normally a solid or liquid.
3)Vapour has experienced some sort of physical change like boiling and evaporation.
4)Vapour is used when the Temperature is below the Critical Temperature.
5) vapors contain some amount of moisture.
6) can be seen or smelled and settles down on the ground.
7)are gases only after undergoing physical changes.
8)Form only after boiling or evaporation.
9)A vapour is a type of gas.
10)Vapor can turn back and forth into liquid and solid states.
11) distribution of small particles of solvent
12)Examples are steam,(responsible for)humidity etc

Pure substances are substances that are made of only one type of atom or molecule, and the purity of a substance is the measure of the extent to which a given substance is pure. The physical properties of a pure substance include well-defined melting and boiling points.


(2) Explain formation of steam using temperature-enthalpy diagram.


-As water is heated from 0°C to its saturation temperature, its condition follows the saturated water line until it has received all of its liquid enthalpy,           hf, (A-B).

-If further heat continues to be added, the water changes phase to a water/vapor mixture and continues to increase in enthalpy while remaining at saturation temperature , hfg, (B - C).

-As the water/vapor mixture increases in dryness, its condition moves from the saturated liquid line to the saturated vapor line. Therefore at a point exactly halfway between these two states, the dryness fraction (Χ) is 0.5. Similarly, on the saturated steam line the steam is 100% dry.

-Once it has received all of its enthalpy of evaporation, it reaches the saturated steam line. If it continues to be heated after this point, the pressure remains constant but the temperature of the steam will begin to rise as superheat is imparted (C - D).

-The saturated water and saturated steam lines enclose a region in which a water/vapor mixture exists - wet steam. In the region to the left of the saturated water line only water exists, and in the region to the right of the saturated steam line only superheated steam exists.


3) Explain following terminology.
        (a) Latent heat: Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.

    (b) Sensible heat : Sensible heat is heat exchanged by a body or thermodynamic system that changes the temperature, and some macroscopic variables of the body, but leaves unchanged certain other macroscopic variables, such as volume or pressure.

    (c) Enthalpy of saturated liquid (hf) : It is defined as the quantity of heat absorbed by 1 kg of water when it is heated from 0°C (freezing point) to boiling point. It is also called total heat (or enthalpy) of water or liquid heat invariably.

    (d) Enthalpy of vapourisation (hfg) : It is the amount of heat required to convert water at a given temperature and pressure into steam at the same temperature and pressure.

    (e) Enthalpy of dry saturated steam (hg) : It is defined as the amount of heat required to raise the temperature of 1 Kg of water from 0 degree celsius to the temperature of evaporation and then convert it into dry saturated steam at the same temperature and pressure.

    (f) Enthalpy of superheated steam (hsup) : It is the amount of heat required to convert 1Kg of water from its freezing point(0 deg. celsius) into superheated steam.

    (g) Heat of superheat : The additional amount of heat supplied to the steam during superheating is called as ‘Heat of superheat’

    (h) Dryness fraction :  It is defined as the ratio of the mass of water vapour in steam to the mass of steam containing it.



(4) Explain following calorimeter
    (a) Barrel or Bucket Calorimeter : PENDING

    (b) Separating Calorimeter : It consists of two concentric chambers, the inner chamber and the outer chamber, which communicates with each other through an opening at the top.  As the steam discharges through the metal basket, which has a large number of holes, the water particles due to their heavier momentum get separated from the steam and collect in the chamber.  The comparatively dry steam in the inner chamber moves up and then down aging through the annular space between the two chambers and enters the Throttling Calorimeter.
It is a vessel used initially to separate some of the moisture from the steam, to ensure superheat conditions after throttling. The steam is made to change direction suddenly; the moisture droplets, being heavier than the vapor, drop out of suspension and are collected at the bottom of the vessel.

    (c) Throttling Calorimeter : It consists a narrow throat (Orifice).  Pressure and temperature are measured by pressure gauge and thermometer.  The steam after throttling process passes through the heat exchanger and condensate is collected.  Steam Generator is also provided to supply the saturated steam (Max) at 2kg/cm2 pressure.   There is no need of boiler.
It is a vessel with a needle valve fitted on the inlet side. The steam is throttled through the needle valve and exhausted to the condenser.   

    (d) Combined separating and Throttling Calorimeter: Separating calorimeter does not give an accurate result and the throttling calorimeter fails if the steam is not superheated after throttling. A combination of separating and throttling calorimeter is therefore found most suitable for accurate measurement of dryness of steam


(5) Derive efficiency equation for following cycle.
    (a) Rankine cycle: PENDING
    (b) otto cycle: PENDING
    (c) Diesel cycle: PENDING
    (d) Carnot cycle: PENDING

(6) Give classification of internal combustion engine.
Classification of Internal Combustion (IC) engines is listed below:
1. Application

    Automobile Engine
    Aircraft Engine
    Locomotive Engine
    Marine Engine
    Stationary Engine

2. Basic Engine design

    Reciprocating: Single cylinder, Multi-cylinder In-line, V, radial, opposed cylinder, Opposed Piston.
    Rotatory: Single motor, Multi motor

3. Operating cycle

    Atkinson (For complete expansion SI Engine)
    Diesel (For the Ideal Diesel Engine)
    Dual (For the Actual Diesel Engine)
    Miller (For Early/Late Inlet valve closing type SI Engine)
    Otto (For the Convectional SI Engine)

4. Working cycle

    Four stroke cycle
    Two stroke cycle
        Scavenging ; direct/crankcase/cross flow; back flow/loop; Uni flow
        Naturally Aspirated or Turbocharged

5. Valve/port Design and location

    Design of valve/port
        Poppet valve
        Rotatory valve
    Location of valve/port
        T-head
        L-head
        F-head
        L-head

6.Fuel

    Convectional
        Crude oil derivatives; Petrol, diesel
        Other sources; coal, Bio-mass, Tar stands, shale
    Alternative
        Petroleum derived: CNG, LPG
        Bio-mass Derived: alcohols, Vegetable oils, producer gas,   Biogas and Hydrogen
    Blending
    Bi-fuel and Dual fuel

7. Mixture preparation

    Carburetion
    Fuel injection

8. Ignition

    Spark ignition
    Compression Ignition

9. Stratification of charge

    Homogeneous Charge
    Stratified charge
        With carburetion
        With fuel injection

10. Combustion chamber Design
    Open chamber: Disc, wedge, hemispherical, Bowl-in-piston, Bath tub.
    Divided chamber:
        (For CI) 1. Swirl chamber, 2. Pre-chamber
        (for SI) 1. CVCC, 2. Other designs

11. Cooling

    Direct air-cooling
    Indirect air-cooling
    Low heat rejection engine


(7) Differentiate between (i) Four stroke and two stroke engine (ii) S.I.Engine and C.I.Engine

S.No.	Four stroke engine	Two stroke engine
1.	It has one power stroke for every two revolutions of the crankshaft.	It has one power stroke for each revolution of the crankshaft.
2.	Heavy flywheel is required and engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft.	Lighter flywheel is required and engine runs balanced because turning moment is more even due to one power stroke for each revolution of the crankshaft.
3.	Engine is heavy	Engine is light
4.	Engine design is complicated due to valve mechanism.	Engine design is simple due to absence of valve mechanism.
5.	More cost.	Less cost than 4 stroke.
6.	Less mechanical efficiency due to more friction on many parts.	More mechanical efficiency due to less friction on a few parts.
7.	More output due to full fresh charge intake and full burnt gases exhaust.	Less output due to mixing of fresh charge with the hot burnt gases.
8.	Engine runs cooler.	Engine runs hotter.
9.	Engine is water cooled.	Engine is air cooled.
10.	Less fuel consumption and complete burning of fuel.	More fuel consumption and fresh charge is mixed with exhaust gases.
11.	Engine requires more space.	Engine requires less space.
12.	Complicated lubricating system.	Simple lubricating system.
13.	Less noise is created by engine.	More noise is created by engine.
14.	Engine consists of inlet and exhaust valve.	Engine consists of inlet and exhaust ports.
15.	More thermal efficiency.	Less thermal efficiency.
16.	It consumes less lubricating oil.	It consumes more lubricating oil.
17.	Less wear and tear of moving parts.	More wear and tear of moving parts.
18.	Used in cars, buses, trucks etc.	Used in mopeds, scooters, motorcycles etc.

S.no	Aspect	Spark Ignition Engine	Compression Ignition Engine
1	Engine speed	SI engines are high speed engines.	CI engines are low speed engines.
2	Cycle efficiency	SI engines have low thermal efficiency	CI engines have high thermal efficiency.
3	Fuel used	Petrol is used as fuel, which has high self ignition temperature.	Diesel is used as fuel, it has low self ignition temperature.
4	Time of knocking	Knocking takes place at the end of combustion.	Knocking takes place at the beginning of combustion.
5	Cycle operation	SI engine works on otto cycle.	CI engine works on diesel cycle.
6	Pressure generated	Homogeneous mixture of fuel, hence high pressure is generated.	Heterogeneous mixture of fuel, hence low pressure is generated.
7	Constant parameter during cycle	Constant volume cycle.	Constant pressure cycle.

(8) Draw neat sketch of I.C.Engine and explain each part in detail.
1. Cylinder block
-main body of IC engine.
-Cylinder is a part in which the intake of fuel, compression of fuel and burning of fuel take place.
-Main function of cylinder is to guide the piston.
-it is made by high grade cast iron.

2. Cylinder head
-The top end of cylinder is closed by means of removable cylinder head.
-The main function of cylinder head is to seal the cylinder block and not to permit entry and exit of gases on cover head valve engine.

3. Piston
-A piston is fitted to each cylinder as a face to receive gas pressure and transmit the thrust to the connecting rod.
-It is the prime mover in the engine.
-The main function of piston is to give tight seal to the cylinder through bore and slide freely inside of cylinder.

4.Connecting rod
 -Connecting rod connects the piston to crankshaft and transmits the motion and thrust of piston to crankshaft.
-It converts the reciprocating motion of the piston into rotary motion of crankshaft.

5.Crankshaft
- Receives the efforts or thrust supplied by piston to the connecting rod and converts the reciprocating motion of piston into rotary motion of crankshaft.

6.Crankcase
- The main body of the engine to which the cylinder are attached and which contains the crankshaft and crankshaft bearing is called crankcase.
-It serves as the lubricating system too and sometime it is called oil sump. All the oil for lubrication is placed in it.

7.Valves
-To control the inlet and exhaust of internal combustion engine
-The valves are fitted in the port at the cylinder head by use of strong spring. This spring keep them closed.

8. Spark plug
-It is used in spark ignition engine.
-The main function of a spark plug is to conduct the high potential from the ignition system into the combustion chamber to ignite the compressed air fuel mixture.
-It is fitted on cylinder head.

9. Injector
-It sprays the fuel into combustion chamber at the end of compression stroke. It is fitted on cylinder head.
-used in compression ignition engine.

10. Flywheel
-Stores energy required to rotate the shaft during preparatory strokes.
-Makes crankshaft rotation more uniform.
-Facilitates the starting of the engine and overcoming the short time overloads

11.Piston ring:
-It forms a gas tight combustion chamber for all positions of piston.
-It reduces contact area between cylinder wall and piston wall preventing friction losses and excessive wear.
-It controls the cylinder lubrication.
-It transmits the heat away from the piston to the cylinder walls. 

12. Governor:
-A device for regulating automatically output of a machine by regulating the supply of working fluid.


(9) Explain working of  two stroke and four stroke petrol  and diesel engine with neat sketch and p-v diagram.
(Only working of 2 stroke diesel and 4 stroke petrol engine is given below.)
- The two-stroke diesel engine  cycle goes like this:
1. When the piston is at the top of its travel, the cylinder contains a charge of highly compressed air. Diesel fuel is sprayed into the cylinder by the injector and immediately ignites because of the heat and pressure inside the cylinder.

2. The pressure created by the combustion of the fuel drives the piston downward. This is the power stroke.

3. As the piston nears the bottom of its stroke, all of the exhaust valves open. Exhaust gases rush out of the cylinder, relieving the pressure.

4. As the piston bottoms out, it uncovers the air intake ports. Pressurized air fills the cylinder, forcing out the remainder of the exhaust gases.

5. The exhaust valves close and the piston starts traveling back upward, re-covering the intake ports and compressing the fresh charge of air. This is the compression stroke.

6. As the piston nears the top of the cylinder, the cycle repeats with step 1.


- The 4-stroke petrol engine cycle goes like this:
1.Induction stroke:  The inlet valve is opened and the exhaust valve is closed. The piston descends, moving away from the cylinder head. This depression induces (sucks in) a fresh charge of air and atomized petrol

2.Compression stroke: Both the inlet and the exhaust valves are closed. The piston begins to ascend towards the cylinder head. The induced air-and-petrol charge is progressively compressed which squeezes the air and atomized-petrol molecules closer together and raises the temperature and pressure.

3. Power stroke: Both the inlet and the exhaust valves are closed and, just before the piston approaches the top of its stroke during compression, a spark-plug ignites the dense combustible charge.  By the time the piston reaches the innermost point of its stroke, the charge mixture begins to burn, generates heat, and rapidly raises the pressure in the cylinder until the gas forces exceed the resisting load. The burning gases then expand and so change the piston's direction of motion and push it to its outermost position. The cylinder pressure then drops from a peak value near the outermost movement of the piston. 

4.Exhaust stroke: At the end of the power stroke the inlet valve remains closed but the exhaust valve is opened. The piston changes its direction of motion and now moves from the outermost to the innermost position. Most of the burnt gases will be expelled by the existing pressure energy of the gas, but the returning piston will push the last of the spent gases out of the cylinder through the exhaust-valve port and to the atmosphere.  The gas pressure in the cylinder will fall from the exhaust-valve opening pressure to atmospheric pressure or even less as the piston nears the innermost position towards the cylinder head.



(10 ) Explain following terminology associated with I.C.Engine
(a) indicated power(I.P): indicated power is the power produced in the cylinder.

(b) brake power(B.P): is the useful power at the output shaft. Brake power is always less than indicative, due to losses by mechanical friction and parasitic loads (oil pump, air conditioner compressor, etc...)

(c) friction power(F.P): is defined as the horsepower being used toovercome internal friction. Anytime two objects touch each other whilemoving, friction is produced. Friction has a tendency to slow down theengine. f.p = i.p – b.p 

(d) mechanical efficiency:  is the percentage of energy that the engine puts out after subtracting mechanical losses such as friction, compared to what the engine would put out with no power loss.

(e) Thermal efficiency:   It is the ratio of power produced to the energy in the fuel burned to produce this power.

(f) compression ratio:  the ratio of the maximum cylinder volume when the piston is at its outermost position (BDC) to the minimum cylinder volume (the clearance volume) with the piston at its innermost position (TDC)

(g) swept volume : the volume through which a piston or plunger moves as it makes a stroke.

(h) clearance volume:  is  the volume remaining in the cylinder when the piston is  at TDC.