Unit-1
APPLIED THERMODYNAMICS
Q1) Explain Blast Furnace Gas and its Characteristics?
A1) It is a by-product flue gas obtained during the reduction of iron ore by coke in the
Blast furnace. Its calorific value is about 1,000 kcal/m3. It contains about 20-25% carbon monoxide along with CO2, N2, etc. About 1/3 of this gas is used for preheating air used in blast furnace itself; while the remaining 2/3rd is available for use in boilers or after cleaning in gas engines. It is also used for burning in a special type of stoves (called Cowper’s stove) where the furnace is preheated. This gas contains much dust and is usually cleaned before use by dust settlers, cyclones or electrolytic precipitators.
Q2) Explain Water Gas and its Characteristics?
A2) Water gas is essentially a mixture of combustible gases CO and H2 with a little fraction of non-combustible gases. It is made by passing alternatively steam and little air through a bed of red hot coal or coke maintained at about 900 to 1000Oc in a rector, which consists of a steel vessel about 3 m wide and 4 m in height. It is lined inside with fire-bricks. It has a cup and cone feeder at the top and an opening at the top for the exit of water gas. At the base, it is provided with inlet pipes for passing air and steam.
Reactions
Supplied steam reacts with red hot coke (or coal) at 900-1000oC to form CO and H2.
C + H2O =CO + H2 – 29 kcal
C + O2= CO2 + 97 kcal
Composition
The average composition of water gas is: H2 = 51%; CO = 41%; N2 = 4%; CO2 = 4%. Its calorific value is about 2800 kcal/m3.
Uses
It is used as (a) a source of hydrogen gas, (b) an illuminating gas, and (c) a fuel gas.
Q3) Explain Oil Gas and its Characteristics?
A3) Oil gas is obtained by cracking kerosene oil. Oil in a thin steam is allowed to fall on a stout red hot cast iron retort, which is heated in coal fired furnace. The resulting gaseous mixture passes out through a bonet cover to a hydraulic main, a
tank containing water. Here tar gets condensed. Then at the testing cap, the proper cracking of oil is estimated from the colour of the gas produced. A good oil gas should have a golden colour. By proper adjusting the supply of air, gas of required colour can be obtained. The gas is finally stored over water in gas holders.
Composition
The average composition of oil gas is: CH4 = 25.30%; H2 = 50-55%;
CO = 10.12%; CO2 = 3%. Its calorific value is about 6600 kcal/m3.
Uses
It is used as laboratory gas.
Q 4) Explain the difference between 2 stroke and four stroke engine?
A4)
Difference Between Two Stroke and Four Strokes | |
Two Strokes | Four Stroke |
It has one revolution of the crankshaft during one power stroke | It has two revolutions of the crankshaft during one power stroke |
It generates high torque | It generates less torque |
Its uses port for fuel’s outlet and inlet | It uses valves for outlet and inlet of a fuel |
Its engines result in lesser thermal efficiency | Its engines result in higher thermal efficiency |
It has a larger ratio in terms of power to weight | It has a lesser ratio in terms of power to weight |
It generates more smoke and shows less efficiency | It generates less smoke and shows more efficiency |
Requires more lubricating oil as some oil burns with the fuel | Requires less lubricating oil |
Due to poor lubrication, more wear and tear occurs | Less wear and tear occurs |
Engines are cheaper and are simple for manufacturing | Engines are expensive due to lubrication and valves and are tough to manufacture |
Engines are basically lighter and are noisy | Engines are basically heavier because its flywheel is heavy and are less noisy |
Q5) Explain the difference between compressed ignition engine or Diesel engine and spark ignition engine or Petrol engine?
A5)
S.no | Parameter | SI Engine | CI Engine | ||||
1. | Definition | It is an engine in which the spark is used to burn the fuel. | It is an engine in which heat of compressed air is used to burn the fuel. | ||||
2. | Fuel used | Petrol is used as fuel. | Diesel is used as fuel. | ||||
3. | Operating cycle | It operates on Otto cycle. | It operates on Diesel cycle. | ||||
4. | Compression ratio | Low compression ratio.(6 to 10) | High compression ratio.(15 to 25) | ||||
5. | Thermal efficiency | Low thermal efficiency because of low compression ratio .Up to 26 %. | High thermal efficiency because of high compression ratio up to 40%. | ||||
6. | Method of ignition | Spark plug is used to produce spark for the ignition. | Heat of compressed air is used for the ignition. | ||||
7. | Engine Speed | High speed engines. | Low speed engines. | ||||
8. | Pressure generated | Low pressure is generated after combustion. About 10 bar | High pressure is generated | ||||
9. | Constant parameter during cycle | Constant volume cycle. | Constant pressure cycle. | ||||
10. | Intake | Air + fuel. | Only air. | ||||
| Weight of engine | Si engine has less weight. | CI engine are heavier. | ||||
12. | Noise production | It produces less noise. | It produces more noise. | ||||
13. | Production of hydrocarbon | Less Hydrocarbon is produced. | More hydrocarbons is produced. | ||||
14. | Starting | The starting of SI engine is easy. | The starting of CI engine is difficult. | ||||
15. | Maintenance cost | Low | High | ||||
16. | Vibration problem | Less | Very High | ||||
17. | Cost of engine | Less cost | High cost | ||||
18. | Volume to power ratio | Less | High | ||||
19. | Fuel supply | carburettor | Injector | ||||
20. | application | It is used in light commercial vehicles like motorcycle, cars. | It is used in heavy duty vehicles likes bus, trucks, ships etc. | ||||
Q6) The following data was recorded during testing of a TWO STROKE gas engine:
Diameter of the piston d= 150 mm
Stroke length L= 180 mm
Clearance volume Vc = 0.89 litre
RPM of the engine N = 300
Indicated mean effective pressure pm= 6.1 bars
Gas consumption m. = 6.1 m3/h
Calorific value of the gas (fuel) CF = 17000 kJ/m3
Determine the followings:
Air Standard Efficiency
Indicated power (IHP)developed by the engine
Indicated thermal efficiency of the engine
A6)
Swept volume Vs = πd2L/4 = π(0.150)2 x 180/4 = 0.00318 m3
Clearance volume Vc= 0.00089 m3
Total volume = Swept volume + clearance volume
= 0.00318 + 0.00089 = 0.00407 m3
Compression ratio γ = Total volume/Clearance volume
= 0.00407/0.00089 = 4.573
Air standard Efficiency
η = 1 –1/(r)γ—1 = 1—1/(4.573)1.4—1
= 0.456 = 45.6 %
Indicated power IHP = 100 pLAN/60
When p is in bars
= 100 x 6.1x 0.180 x [π (0.150)2 /4] x 300 / 60
= 9700 W
(c ) Indicated Thermal Efficiency
ηit= Indicated power in (kJ/s)/Heat supplied in (kJ/s)
= (9700/1000)/ (6.1 x 17000/3600)
= 0.3367 = 33.67 %
Q7) Explain bituminous coal?
A7) Bituminous Coal:-It is a superior and naturally available coal containing very less moisture content but high carbon content. Its average calorific value is 33500 kJ/kg. It is further of two types: Caking Bituminous coal and Non-Caking Bituminous coal. Caking bituminous is a soft coal but swells and form pasty mass on burning. So burning is difficult to take place. It is useful for producing coal gas. Non-Caking variety is superior in burning and produces less smoke. It is mostly used in boilers for making steam and so is called Steam Coke.
Q8) Explain how coke produces?
A8) Coke:-It is produced by heating of naturally available coal continuously for two days in the absence of air. This process is known as carbonization of coal as the carbon content increases by removing of moisture and other gases. Due to high carbon content, it has a high calorific value. If coal is prepared on heating at a temperature of 500-700oC, it remains soft and called as Soft Cake. It is used in domestic applications. If coke is prepared at a higher temperature i.e. 900oC to 1100oC, it is called as hard coke. It is used in Cupola furnace for producing Cast Iron.
Q9) Explain Classification of Petroleum?
A9) The chemical nature of crude petroleum varies with the part of the world in which
it is found. They appear, however, to be three principal verities.
Paraffinic Base Type Crude Petroleum
This type of petroleum is mainly composed of the saturated hydrocarbons from CH4 to C35 H72 and a little of the napthenes and aromatics. The hydrocarbons from C18 H38 to C35 H72 are sometimes called waxes.
Asphaltic Base Type Crude Petroleum
It contains mainly cycloparaffins or napthenes with smaller amount of paraffin’s and aromatic hydrocarbons.
Mixed Base Type Crude Petroleum
It contains both paraffinic and asphaltic hydrocarbons and are generally rich in semi-solid waxes.
Q10) Write the advantages and disadvantages of liquid fuels?
A10) The advantages and disadvantages of liquid fuels can be summarized as follows:
Advantages
(a) They possess higher calorific value per unit mass than solid fuels.
(b) They burn without dust, ash, clinkers, etc.
(c) Their firing is easier and also fire can be extinguished easily by stopping liquid fuel supply.
(d) They are easy to transport through pipes.
(e) They can be stored indefinitely without any loss.
(f) They are clean in use and economic to handle.
(g) Loss of heat in chimney is very low due to greater cleanliness.
(h) They require less excess air for complete combustion.
(i) They require less furnace space for combustion.
Disadvantages
(a) The cost of liquid fuel is relatively much higher as compared to solid fuel.
(b) Costly special storage tanks are required for storing liquid fuels.
(c) There is a greater risk of five hazards, particularly, in case of highly inflammable and volatile liquid fuels.
(d) They give bad odour.
(e) For efficient burning of liquid fuels, specially constructed burners and spraying apparatus are required.
