SAMPLE SHEET: GATE 2015; STRENGTH OF MATERIALS (MECHANICAL ENGINEERING)

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PRACTICE WORKSHEET GATE-2015

MECHANICAL ENGINEERING

TOPIC: STRENGTH OF MATERIALS

Difficulty Level: 1

SET ONE: Each question has several entries, choose the most appropriate one

01)  The intensity of stress which causes unit strain is called

            a) unit stress                                                     b) bulk modulus

            c) modulus of elasticity                                               d) principal stress

02)  Which of the following materials has poisson’s ratio more than unity

            a) steel                                                                         b) copper

            c) cast iron                                                       d) none of these

03) The change in the unit volume of a material under tension with increase in its Poisson’s ratio will

            a) increase                                                       b) decrease

            c) increase initially and then decrease              d) remain same

04) In a tensile test, near the elastic zone, the tensile strain

            a) increases more quickly                                b) decreases more quickly

            c) increases in proportion to the stress                         d) increases more slowly

05) The stress necessary to initiate yielding is

            a) considerably greater than that necessary to continue it

            b) considerably lesser than that necessary to continue it

            c) remain same to continue it

            d) can’t be predicted

06) Flow stress corresponds to

            a) fluids in motion                                           b) breaking point

            c) plastic deformation of solids                                   d) rupture stress

07) The maximum strain energy that can be stored in a body is known as

            a) impact energy                                              b) resilience

            c) proof resilience                                            d) modulus of resilience

08) Thermal stress is always

            a) tensile                                                          b) compressive

            c) tensile or compressive                                 d) none of these

09) The loss of strength in compression due to overloading is known as

            a) hysteresis                                                     b) relaxation

            c) creep                                                            d) Bouschinger effect

10) If a material expands freely due to heating, it will develop

            a) thermal stress                                               b) lateral stress

            c) creep stress                                                  d) no stress

SAMPLE SHEET: GATE 2015; FLUID MECHANICS (MECHANICAL ENGINEERING)

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PRACTICE WORKSHEET GATE-2015

MECHANICAL ENGINEERING

TOPIC: FLUID MECHANICS

Difficulty Level: 1

SET ONE: Each question has several entries, choose the most appropriate one

01) If no resistance is encountered due to displacement then such a substance is called

            a) fluid               b) real gas                 c) ideal fluid          d) visco-elastic fluid

02) The volumetric change of a fluid due to a resistance is called as

            a) volumetric strain,                             b) volumetric index

            c) compressibility                                d) cohesion

03) Mercury does not wet glass due to a property of liquids known as

            a) adhesion                                          b) cohesion

            c) viscosity                                          d) surface tension

04) The surface tension of Mercury at normal temperature compared to that of water is

            a) more                                                          b) less

            c) depends upon the glass tube                        d) equal

05) Kinematic viscosity is dependent upon

            a) pressure       b) distance       c) density         d) flow

06) Alcohol is used in manometers because

            a) it is clearly visible                            b) it provides suitable meniscus

            c) it can provide longer column due to its low density

            d) it has low surface tension

07) The buoyancy depends upon

            a) mass of liquid displaced                  b) viscosity of the liquid

            c) pressure of the displaced liquid       d) none of the above

08) The centre of gravity of the volume of the liquid displaced by an immersed body is called

            a) meta-centre                                      b) centre of gravity

            c) centre of pressure                            d) centre of buoyancy

09) Surface energy per unit area of a surface is numerically equal to

            a) atmospheric pressure                                   b) surface tension

            c) force of cohesion                                         d)  viscosity

10) Flow occurring in a pipeline when a valve is being opened is

            a) steady flow                                                 b) unsteady flow

            c) laminar flow                                                d) vortex flow

For answers contact at 09555921800

SAMPLE SHEET: GATE 2015; THERMODYNAMICS (MECHANICAL ENGINEERING)

CRACKGATE EDUCATION

House No: 237; Sector – 5; Chiranjeev Vihar, Ghaziabad

                     Contact No : #9555921800

PRACTICE WORKSHEET GATE-2015

MECHANICAL ENGINEERING

TOPIC: BASIC THERMODYNAMICS

Difficulty Level: 1

SET ONE: Each question has several entries, choose the most appropriate one

01) Gas laws are applicable to

            a) Gases as well as vapours     b) Gases alone and not applicable to vapours

            c) Gases and Steam                  d) Gases and Superheated vapours

02) An ideal gas compared to a real gas at very high pressures occupies

            a) more volume           b) less volume            

c) same volume           d) can’t be predicted

03) Temperature of a gas is produced due to

            a) its heating value                   b) kinetic energy of the molecules

            c) molecular vibration              d) inter-molecular attractions

04)  According to kinetic theory of gases, the absolute zero temperature is attained when

            a) volume of the gas is zero                             b) pressure of the gas is zero

            c) kinetic energy of the molecule is zero                     d)  specific heat is zero 

05)  The quantity δQ – δW; where δQ is elemental heat transfer and δW is the elemental work    

transfer is

            a) path function                       b) point function

            c) cyclic function                     d) in-exact differential

06)  The workdone in an adiabatic process between a given pair of end states depends on

            a) the values of the endstates only,      b) the end states and specific heat ratio  γ

            c) the end states and polytropic index n,          d) none of the above.

07)  If the value of polytropic index n is high, then the compressor work between given pressure limits will be

            a) less                                      b) more

            c) no effect                              d) zero

08)  A perfect gas at 27^oC is heated at constant pressure till its volume becomes double. The final temperature will be

            a) 54^oC                                    b) 327^oC

            c) 108^oC                                  d) 600^oC

09)  Mixing of ice and water at 0^oC at atmospheric pressure is an example of

            a) reversible process                b) irreversible process

            c) quasi-static process              d) isentropic process

10)  Change in enthalpy in a closed system is equal to heat transferred if the reversible process takes place at constant

            a) pressure                               b) temperature

            c) volume                                d) entropy

GATE 2015: MECHANICAL ENGINEERING COACHING IN CHIRANJEEV VIHAR AND GOVINDPURAM GHAZIABAD

GATE 2015

MECHANICAL ENGINEERING COACHING IN

CHIRANJEEV VIHAR AND GOVINDPURAM

THE SALIENT POINTS OF THE COURSE:

• THE COURSE HAS BEEN DESIGNED TO HELP THOSE STUDENTS WHO HAVE DIFFICULTIES IN THE BASIC CONCEPTS.
• AT FIRST THE BASIC CONCEPTS WOULD BE TAUGHT AND THEN ADVANCED CONCEPTS WILL BE INTRODUCED.
• WHILE TEACHING A CONCEPT, SIMULTANEOUSLY MULTIPLE CHOICES QUESTIONS WILL BE SHOWN FROM THAT CONCEPT.
• MORE THAN 2500 MULTIPLE CHOICES QUESTIONS WILL BE DISCUSSED WITH SOLUTIONS.
• PROBLEM SOLVING TECHNIQUES WOULD BE TAUGHT WITH THE HELP OF MASTER CHARTS.
• TWO HOURS PER DAY SIX DAYS PER WEEK CLASSES.
• CLASSES ON IMPROVING LEARNING ABILITIES, INCREASING CONCENTRATION AND THE SCIENTIFIC STUDYING TECHNIQUES WILL BE TAKEN.
• CONCEPTS WOULD BE TAUGHT USING ANIMATIONS, GRAPHS, PICTOGRAMS, MNEMONICS AND OTHER LEARNING ENHANCEMENT TOOLS.
• ONLY 20 STUDENTS PER BATCH TO FOCUS MORE ON THE INDIVIDUAL NEEDS OF THE STUDENTS.
• ASSISTANCES FOR INDIVIDUAL PSU (LIKE ONGC, IOC etc.)
• TRIAL CLASSES ARE THERE TO BE AWARE OF THE PERFORMANCES OF THE CLASSES.
• HIGH TECH STUDY MATERIALS AT AFFORDABLE PRICE.
• COURSE DURATION IS SIX MONTHS.
• INTRODUCTORY PRICES ARE AS LOW AS @₨ 2500 PER MONTH
• CLASSES WILL BE STARTED FROM 25^th JULY; 2014
• CALL AT # +91-9458042791; +91-9555921800; +91-9678534833

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ME-301: THERMODYNAMICS FOR THIRD SEMESTER; UPTU

SECTION A: Each question carry 2 marks

01) What is point function and path function?

02) Define Enthalpy.

03) What is SFEE?

04) What is internal energy of a system

05) What is vapour dome and dryness factor?

06) What is saturated liquid line and saturated vapour line?

07) What is triple point of water?

08) Define specific heats of ideal gases.

09) Write the reduced form of Vander Waals equation for real gases.

10) Define a thermodynamic system.

11) State with reasoning whether the following systems are closed, open or isolated
i) Refrigerator; ii) Pressure Cooker

12) Distinguish between isolated system and adiabatic system.

13) Explain the concept of flow work

14) What is control volume and control surface?

15) When does a real gas behave like an ideal gas?

16) What are extensive and intensive properties?

17) What is enthalpy of evaporation of steam?

18) Define degree of under-cooling and degree of superheat.

19) What is COP of a heat pump?

20) Define throttling process.

21) Define entropy.

22) Two moles of an ideal gas occupy a volume of 4.24 m³ at 400 K temperature. Find the pressure exerted by the gas.

23) Distinguish between refrigerator and heat pump.

24) What is Free Expansion?

25) Explain Zeroth law of thermodynamics.

26) Explain the concept of compressibility factor?

27) What is PMM-1.

28) What is a superheated steam?

29) Distinguish between universal gas constant and characteristic gas constant.

30) What is Exergy?

31) Distinguish between quasi-static process and reversible process.

32) What is a diathermal system boundary?

33) What is a steady flow open system?

34) What is the difference between latent heat and sensible heat?

35) What is a thermodynamic cycle?

36) Distinguish between restraint and unrestraint process.

37) What is a thermodynamic definition of work?

38) What is work of evaporation?

39) What is a pure substance?

40) What is the concept of continuum?

41) Define thermodynamic state, process and path.

42) Distinguish between thermal equilibrium and thermodynamic equilibrium.

43) What are the conditions for reversible process?

44) Distinguish between heat and work.

45) What are the differences between gas and vapour?

SECTION B: Attempt any three of the following questions. Each question contains two parts of 5 marks each. Total marks In this section is 3x10 = 30

01) a) State Zeroth law of thermodynamics and explain how it leads to the concept of temperature.

b) Explain different types of temperature scale and the relations among them.

02) a) Explain the corollaries of first law of thermodynamics.

b) 2 kg of air is confined in a rigid container of 0.42 m³ at 4 bar pressure. When heat energy of 164 kJ is added, its temperature becomes 127°C.
Find :

i) Work done by the system.
ii) Change in internal energy.
iii) Specific heat at constant volume.

03) a) Derive an expression for heat transfer and work done in a polytropic process.

b) 1.5 kg of oxygen contained in a cylinder at 4 bar pressure and 300 K expands three times its original volume in a constant pressure process. Determine
i) Initial volume, ii) Final temperature, iii) Work done by the gas, iv) Heat added and v) Change in internal energy.
; Assume C_p = 1.005 kJ/kg-K and R = 260 J/kg-K

04) a) Make steady flow energy analysis on a turbine.

b) Find the velocity and diameter at exit of a nozzle if 5 kg/s air at 9 bar and 200°C expands through the nozzle up to pressure at 1.1 bar. Approach velocity is 50 m/s.

05) a) Differentiate between absolute pressure and gauge pressure. What is a manometer?

b) An ideal gas of molecular weight 42.4 has a pressure of 10 bar and occupies a volume of 0.3 m³ at 27°C. Determine the characteristic gas constant for the ideal gas, its mass and number of moles.

06) a) Write the first law of thermodynamics for a flow process. Derive an expression for flow work.

b) Find the total work done and efficiency for a reversible Carnot cycle.

07) a) What is continuity equation in flow process?

b) 3 kg air at 2 bar pressure and 27℃ temperature has been compressed isothermally till the pressure reaches 6 bar. Next it has been heated at constant pressure and thereafter reaches the initial state by expanding adiabatically. Find the maximum Temperature reached in the cycle and total work done by the system.

08) a) Explain the Joule's experiment.

b) Prove that internal energy is a point function.

09) a) What is thermodynamic temperature scale?

b) i) A heat engine running between 300 K and 800 K generates 2000 kJ of energy. Find the total heat extracted from the source.
ii) Determine the power required to run a refrigerator that transfers 2000 kJ/min of heat from a cooled space at 0°C to the surroundings atmosphere at 27°C.

10) a) What is PMM - 2? State Kelvin-Planck statement of second law of thermodynics.

b) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.

11) a) Explain the Vander Waal's gas equation.

b) 4 kg of steam at 16 bar occupies a volume of 0.28 m³. The steam expands at constant volume to a pressure of 8 bar. Determine the final dryness fraction, final internal energy and change in entropy.

12) a) Explain and derive Clausius Inequality.

b) 3 kg of air is heated reversibly at constant pressure of 2.5 bar from 23°C to 227°C. If the lowest available temperature is 20°C determine the increase in the available energy of air due to heating. Take C_p = 1.005 kJ/kg-K.

13) a) What is thermodynamic definitions of work? Distinguish between ∫pdV work and other types of work.

b) 3 kg of air at 1.5 bar pressure and 350 K is compressed isothermally to a pressure of 6 bar. Then heat of 350 kJ is added at constant volume. What will be the maximum temperature of air during the process? Find the total work done in the processes. Also find the change in internal energy of air.

14) a) Write the limitations of second law of thermodynamics. Prove that C_p - C_v = R

b) 10 kg of air at 300 K is stored in a totally insulated cylinder of volume 0.3 m³/kg. If 1 kg air has been taken out of the system, then what will be the value of new pressure?

15) a) Steam at 1.2 bar and a dryness fraction of 0.5 is heated at constant pressure until it becomes saturated vapour. Calculate the heat transferred per kg of steam.

b) Steam at 8 MPa and 500°C passes through a throttling process such that the pressure is suddenly dropped to 0.3 MPa. Find the expected temperature after throttling.

16) a) What are the causes of irreversibility?

b) Distinguish between a quasi-static process and reversible process.

17) a) 3 kg of air at 400 K and 4 bar pressure adiabatically mixed with 4 kg of air at 500 K and 3 bar pressure. Find the change in entropy of the universe.

b) Explain the principle of increase of entropy.

SECTION C : marks 50, 5 questions of 10 mark each. Each question contains 3 parts. Attempt any two parts out of three from each question.

01) a) Steam at 20 bar pressure and 300°C expands isentropically in a turbine to a pressure of 2 bar. Find the final condition of the steam. Also Calculate the work delivered by the turbine.

b) What is isentropic efficiency of a turbine? Calculate internal energy of steam at 6 bar pressure and 300°C.

c) Explain the steam formation process at constant pressure.

02) a) What is adiabatic mixing of two ideal gases? Derive the expressions for final temperature and pressure.

b) 5 kg of steam at 8 bar pressure and 200°C mixed with 3 kg of steam at 5 bar and dryness fraction x = 0.8 adiabatically. Find the final condition of the steam.

c) 5 kg of air at 4 bar pressure is heated at constant pressure from 300 K to 500 K. Find the change in entropy of the system.

03) a) Prove that in an adiabatic process pV^γ = Constant.

b) Polytropic compression of air from state 1 to state 2 where p₁ = 100 kPa and T₁ = 300 K, p₂ = 300 kPa and n = 1.2 where as mass of air is 3 kg. If R = 0.287 kJ/kg-K. Then find

i) heat exchange during the process
ii) change in internal energy
iii) total work done by the air
iv) change in entropy


c) A non flow reversible process occurs for which pressure and volume are correlated by the relation p = (V² + 6V), where V is the volume in m³ and pressure p is in bar. Determine work done if volume changes from 3 to 6 m³.

04) a) A gas expands according to the equation pv = 100, where " p " is the pressure in kPa and " v " is the specific volume. Initial and final pressures are 1000 kPa and 500 kPa respectively. The gas is then heated at constant volume back to it'd original pressure of 1000 kPa. Determine the net work done. Also sketch the processes in p-v coordinates.

b) What is the definition of thermodynamic work?

c) What is the efficiency of a thermodynamic cycle?

05) a) What is paddle work? Distinguish between ∫pdV work and ∫-vdp work.

b) If pV = mRT, determine whether the expression (V/T).dp + (p/T).dV is a property of a system.

c) 2 kg of air at 1 bar pressure and 300 K is compressed adiabatically to a pressure of 6 bar. Then heat of 200 kJ is added at constant pressure. What will be the maximum temperature of air during the process? Find the total work done in the processes. Also find the change in internal energy of air.

06) a) Find the expression for heat transfer in terms of work done in a polytropic process.

b) What is the specific heat C_n for a polytropic process?

c) 2 kg of air at pressure 2 bar and 300 K is compressed reversibly to 4 bar and 650 K temperature in a polytropic process. Determine the polytropic index (n) of the process.

07) a) Find an expression for mechanical work in steady flow process.

b) What is the meaning of - vdp work?

c) Air flows through a gas turbine system at a rate of 5 kg/s. It enters with a velocity of 150 m/s and an enthalpy of 1000 kJ/kg. At exit the velocity is 120 m/s and enthalpy is 600 kJ/kg. If the air passing through the turbine looses 30 kJ/kg of heat to the surroundings, determine the power developed by the system.

08) a) Write the assumptions considered in Kinetic theory of gases? Prove that C_p - C_v = R

b) Explain the law of corresponding states.

c) 10 kg of air at 300 K is stored in a cylinder of volume 0.3 m³/kg. Find the pressure exerted by air using Vander Waals gas equation. Critical properties of air are: P_c = 37.7 bar, T_c = 132.5 K, v_c = 0.093 m³/kg_mole, R = 287 J/kg-K

09) a) What are the limitations of Vander Waals gas equation? Explain reduced properties of a real gas?

b) What is a undercooled liquid and degree of undercooling? Also define enthalpy of water.

c) What are the properties of steam at critical state? Explain sublimation process and triple point line.

10) a) What are the differences between dry saturated steam and superheated steam at a same pressure? Also, explain vapourdome, saturated liquid line, saturated vapour line and critical point.

b) What are the differences between work of evaporation and enthalpy of evaporation?

c) An inventor claims to have developed a refrigeration unit which maintains −10℃ in the refrigerator which is kept at a room where the surrounding temperature is 25℃ and which has COP of 8.5. Find the claim of the inventor is possible or not.

11) a) Prove that the absolute zero temperature is impossible to achieve according to second law of thermodynamics.

b) Two reversible heat engines A and B are arranged in series. A rejects heat directly to B. Engine A receives 200 kJ at a temperature of 421℃ from the hot source while engine B is in communication with a cold sink at a temperature of 5℃. If work output of A is twice that of B, find :
(i) Intermediate temperature between A and B.
(ii) Efficiency of each engine.
(iii) Heat rejected to the sink.


c) Prove that the reversible heat engines are the most efficient.

12) a) Steam at 1 bar and a dryness fraction of 0.523 is heated in a rigid vessel until it becomes saturated vapour. Calculate the heat transferred per kg of steam.

b) Steam at 9 MPa and 600°C passes through a throttling process such that the pressure is suddenly dropped to 0.4 MPa. Find the expected temperature after throttling.

c) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.

13) a) Explain the change of entropy in a perfectly isolated system during a process in the system.

b) Explain the conditions those must be satisfied by a reversible process.

c) Two kg of water at 90℃ is mixed with three kg of water at 10℃ in a perfectly isolated system. Calculate the change in entropy of the system.

14) a) Explain the second law of thermodynamics and prove that no engine can have a 100% efficiency.

b) Explain the theoretical Carnot cycle and derive its efficiency with diagrams.

c) A reversible engine working in a cycle takes 4800 kJ of heat per minute from a source at 800 K and develops 35 kW power. The engine rejects heat to two reservoirs at 300 K and 360 K. Determine the heat rejected to each sink.

15) a) What are the causes of external irreversibility?

b) Write the first and second Tds equations and derive the expression for the change of entropy during a polytropic process.

c) Prove that reversible engines are most efficient.

16) a) Explain the second law of thermodynamics.

b) Derive the Clausius inequality.

c) Steam at 160 bar and 550℃ is supplied to a steam turbine. The expansion of steam is adiabatic with increase in entropy of 0.1 kJ/kg-K. If the exhaust pressure is 0.2 bar, calculate specific work of expansion.

17) a) 5 kg of water at 400 K is isobarically and adiabatically mixed with 3 kg of water at 500 K. Find the change in entropy of the universe.

b) Explain i) Second law efficiency, ii) Effectiveness of a system and iii) Availability of a closed system.

c) Explain the principle of increase of entropy.

18) a) Explain Helmholtz and Gibbs function.

b) Explain the concept of PMM-I and PMM-II.

c) Find an expression of exit velocity C₂ in terms of pressure ratio when air passes through a nozzle from a pressure of p₁ and temperature T₁ to a pressure p₂.

19) a) Distinguish between enthalpy and internal energy.

b) What is absolute or thermodynamic temperature? Explain briefly.

c) Two Carnot engines work in series between the source at temperature 500 K and sink at temperature 300 K. If both develop equal power, determine the intermediate temperature.

20) a) Show that two adiabatic curves on p-V diagram never intersects each other.

b) Define and classify thermodynamic systems.

c) In an isentropic flow through nozzle, air flows at the rate of 600 kg/hr. At inlet to the nozzle pressure is 2 MPa and temperature is 27℃. The exit pressure is 0.5 MPa. Initial air velocity is 300 m/s, determine
i) exit velocity of air
ii) inlet and exit area of the nozzle

THE END

IC ENGINES: A CONCEPTUAL ANALYSIS

• INTRODUCTION: 

The idea of engines come from heat engines. Expanding steam was the working substance of the primitive kind of Steam Engines. But, locomotion was tough using steam engines as it needed continuous supply of water and coal as fuel. People started to think about a compact engines, light and portable and combustion will be the basis of heat generation. If heat generation could be taken place inside the cylinder, then it will be easier to design a compact engine which could be used to run a locomotive vehicle.

This semester, I am teaching IC Engines and Compressors. The text book is selected as IC Engines by Sharma and Mathur published by Dhanpat Rai Publications. The course is designed by MTU (Mahamaya Technical University, Noida and Gautam Budh Technical University) and it is taught in 5th semester. Although it is a 50 marks paper, still it is a subject which every Mechanical Engineering students must know. It is completely based on the principles of thermodynamics.

The course starts with defining IC Engines, introducing the components used in IC engines, different terms and processes related with IC engines, general working procedures of an IC engine and at last describing the classification of IC engines. Then the thermodynamic analysis of the engine operations along with Air-standard thermodynamic cycles are studied. If any one wants to know the subject deeply, then he should know very basic concepts of thermodynamics. 

• PRE-REQUISITE KNOWLEDGE:

As air-standard cycles are one of the basic models based on which engines are practically run and is a highly simplified or even oversimplified version of the original engine operation and due to this, the experimental values of the engine efficiencies are much below the value predicted by the air standard cycles. The large amount of deviations of actual cycles from the theoretical air standard cycles are due to assumptions taken during air standard cycle analysis.

• DESCRIPTION OF THE IC ENGINE:

While describing IC engines, one should start with the engine cylinder which acts as the combustion chamber which has a variable volume due to a piston which can slide inside the cylinder. 

One end of the cylinder is sealed off by cylinder head which provides the space for clearance volume and it also housed the inlet and exhaust valves. 

The other end of the cylinder is covered by the piston which can slide along the principal axis of the cylinder. 

Inside the cylinder air-fuel mixture is sucked into and then compressed it in case of SI engines, where as in CI engine only air is sucked into the cylinder. 

The piston is connected to a link known as Connecting rod by a pin named Gudgeon or Piston or Wrist pin. 

This connecting rod has unequal ends. The smaller end is connected to piston by gudgeon pin and the bigger end is connected to the eccentric on the Crank. 

It is joined to the eccentric by a pin named Crank pin. Piston, Connecting Rod and Crank constitute a "Slider-Crank Mechanism" which translates a linear "to and fro motion" of the piston into "rotational motion" of the crank. 

Here, connecting rod is the element that bears the whole load, hence it fails quite frequently. 

Crank is mounted on a crank shaft and crank shaft operates two valve mechanism through poppet valve, rocket arm and cams. 

These valve mechanisms are responsible for the opening and closing of inlet as well as exhaust valves. 

This valves are regulated by cams. Cams are mounted on a cam shaft which is geared with crankshaft by a step down gear mechanism so that for every two revolutions of crankshaft rotation the camshaft makes one rotation. So, the complete thermodynamic cycle of two crankshaft rotation crankshaft makes only one cycle. The idea behind this step down mechanism, is valves are needed to open and close once in a complete thermodynamic cycle and a cam profile can be designed easily. 

A flywheel is mounted on the crankshaft, so that it can absorb and store energy during power stroke or expansion stroke and releases energy to power suction, compression and exhaust stroke.

In SI engine, after the end of compression stroke, the pressure and temperature of the air-fuel mixture becomes sufficiently high to sustain the ignition process after ignition takes place. After the compression pressure becomes 10 to 12 bar and temperature becomes 300^o C to 500^o C. It is still below the temperature at which spontaneous auto-ignition generally starts. If the temperature after compression is above the temperature at which auto ignition starts, then auto ignition will start during the last phases of compression stroke and it will create an explosion known as knocking and detonation.

Then theoretical basis of an IC engines are discussed. While analyzing any phenomena, the best way is to make an idealized modelling of the phenomena by considering certain assumptions which would reduce the complexity of the phenomena and make a oversimplified model and then add the complexity one by one. 

Similarly, here we oversimplified the model of IC engine operation by considering the working substance an ideal gas like air and study some reversible thermodynamic cycles those resemble with the processes those occurs inside an IC engine. 

As those cycles are considered having air as working substance and hence, they are called Air-Standard cycles. But, as Air-Standard Cycle are the idealized version of the real life working principle of an IC engines, its analysis can not be used to gauge the performances of the engine with closest accuracy.

 
Thermodynamic Air-standard cycles like Otto, Diesel, Dual, Stirling and Ericsson cycles are discussed. 

Derivation of total work done, Efficiency, Mean Effective Pressure and graphs in p-v and T-s diagrams are studied.

 
In the air standard cycles, working substance is assumed to be perfect gas like pure air, but in actual cycles the working substance is different and it is the mixture of air and fuels. In air standard cycle it is assumed that specific heats are constant where as in reality, specific heats are functions of temperature and it increases with the increase of temperature. 

Moreover, in air standard cycle, it is assumed that working substance is chemically non-reactive and there is no chemical changes inside the engine cylinder, but in reality, inside the cylinder combustion process takes place and the chemical composition of the working substance rapidly changes during the combustion process which alters the composition as well as number of moles of the working substances also got changed.

The combined effect of both the phenomena is to reduce the temperature and pressure after the end of compression stroke as well as it reduces the maximum cycle temperature and pressure after the end of combustion. 

While expanding adiabatically during the power stroke, the temperature and pressure after expansion is higher than the predicted value according to air standard cycle and as a result it increases the value of rejected heat into the thermal sink. 

Therefore, the actual cycle efficiency is much lower than the air standard cycle efficiency. Moreover, there are several other losses during the actual cycle due to various other design limitations. The major losses are 

• (i) burning time losses, 
• (ii) losses due to incomplete combustion, 
• (iii) Direct heat losses due to colder cylinder and heat carried away by coolants, 
• (iv) pumping losses, 
• (v) friction losses due to rubbing of parts, 
• (vi) blow down losses during exhaust.

So, we have first idealized the engine operations and oversimplified it to have an idealized version, but its prediction will not be accurate, but we shall get an upper limit of the efficiencies of IC engines. Now, to get more accurate analysis, we shall modified the simplistic assumptions we have considered during the air standard cycles analysis.

The most important assumption of the air standard cycle is the choosing pure air as our working substance, which is in reality a mixture of air with fuel, which has been mixed homogeneously in the carburettor and then supplied into the engine cylinder which acts as combustion chamber. Therefore, we first substitute air with the air fuel mixture in the air standard cycles and it is hence called "Fuel Air Cycles".

Due to the replacement of working substance by air fuel mixture in stead of pure air, our two key assumptions have been changed too. First of all, fuel-air mixture doesn't show a constant specific heats in stead specific heats are functions of temperature, linearly at low temperatures, non linearly at high temperatures.

C_p = aT² + bT + k

C_v = cT² + dT + k'

STRATIFIED CHARGE INTERNAL COMBUSTION ENGINE

Internal combustion engines or popularly known as IC Engines are life line of human society which mostly served as a mobile, portable energy generator and extensively used in the transportation around the world. 

There are many types of IC Engines, but among them two types known as petrol or SI engines and diesel or CI engines are well established. Most of the automotive vehicles run on either of the engines. Despite their wide popularity and extensive uses, they are not fault free. 

Both SI Engines and CI Engines have their own demerits and limitations. 


Limitations of SI Engines (Petrol Engines) 

Although petrol engines have very good full load power characteristics, but they show very poor performances when run on part load. 

Petrol engines have high degree of air utilisation and high speed and flexibility but they can not be used for high compression ratio due to knocking and detonation. 

Limitations of CI or Diesel Engines: 

On the other hand, Diesel engines show very good part load characteristics but very poor air utilisation, and produces unburnt particulate matters in their exhaust. They also show low smoke limited power and higher weight to power ratio. 

The use of very high compression ratio for better starting and good combustion a wide range of engine operation is one of the most important compulsion in diesel engines. High compression ratio creates additional problems of high maintenance cost and high losses in diesel engine operation. 

For an automotive engine both part load efficiency and power at full load are very important issues as 90% of their operating cycle, the engines work under part load conditions and maximum power output at full load controls the speed, acceleration and other vital characteristics of the vehicle performance. 

Both the Petrol and Diesel engines fail to meet the both of the requirements as petrol engines show good efficiency at full load but very poor at part load conditions, where as diesel engines show remarkable performance at part load but fail to achieve good efficiency at full load conditions. 

Therefore, there is a need to develop an engine which can combines the advantages of both petrol and diesel engines and at the same time avoids their disadvantages as far as possible. 

Working Procedures: 

Stratified charged engine is an attempt in this direction. It is an engine which is at mid way between the homogeneous charge SI engines and heterogeneous charge CI engines. 

Charge Stratification means providing different fuel-air mixture strengths at various places inside the combustion chamber. 

It provides a relatively rich mixture at and in the vicinity of spark plug, where as a leaner mixture in the rest of the combustion chamber. 

Hence, we can say that fuel-air mixture in a stratified charge engine is distributed in layers or stratas of different mixture strengths across the combustion chamber and burns overall a leaner fuel-air mixture although it provides a rich fuel-air mixture at and around spark plug. 

THE IMPORTANCE OF MANUFACTURING ENGINEERING

If we carefully think about human civilization, one shall notice an wonderful fact about human beings. The thing that made us different from other hominids is the skill to manufacture tools. We just triumphed due to our ability to make primitive tools out of stone and metals during the dawn of the civilizations. Since then much time has passed and we have entered into a Machine Era and man has been still continuously engaged in converting the natural resources into useful products by adding value to them through machining and other engineering activities applying on the raw materials. Manufacturing is the sub branch of Engineering which involves the conversion of raw materials into finished products.

The conversion of natural resources into raw materials is normally taken care of by two sub branches of engineering viz. Mining and Metallurgy Engineering. The value addition to the raw materials by shaping and transforming it to final products generally involves several distinct processes like castings, forming, forging, machining, joining, assembling and finishing to obtain a completely finished product.

Understanding Manufacturing Engineering largely based upon three engineering activities and they are Designing,  Production and Development of new more efficient techniques.

At the Design stage, engineering design mainly concentrates on the optimization of engineering activities to achieve most economical way to manufacture a goods from raw materials. It also chooses the raw materials and impart the requisite engineering properties of materials like hardness, strength, elasticity, toughness by applying various heat treatment to them.

During the production stages, the selection of the important process parameters to minimize the idle time and cost, and maximizing the production and its quality is very important.

The New Technologies must be implemented to adapt to the changing scenarios of the markets and demands to make the sales competitive and sustainable.

FUEL USED IN IC ENGINES AND REFINERY PROCCESSES; EME-505

FUEL USED IN IC ENGINES

An article on fossil fuels

Internal Combustion Engines are the generators of the energy mainly used for transportation. Almost more than 90% of the total IC Engines run on fossil fuels or different derivatives of petroleum.

IC Engines are a kind of open cycle heat engine where heat is supplied to the engine by the combustion of working fluids thus releasing huge amount of energy due to the combustion processes of the working fluids. Combustible working fluids are called fuels.

The natural petroleum oil is the largest single source of internal combustion engine fuels. Petrol and Diesel are the most used among them. The boiling point of petrol is 30°C to 200°C and that of diesel oil is from 200°C to 375°C.

Fuels of most of the IC Engines are the derivatives of Petroleum like gasoline, diesel oil, kerosene, jet fuel etc. All of these fuels are produced during the fractional distillation of Petroleum Oil obtained from crude from oil wells.

The fuels used in the IC Engines are designed to satisfy the performance requirements of the engine system in which they are used. As a result the fuels must have certain

• (i) physical,
• (ii) chemical and
• (iii) combustion properties.

Following are the some characteristics a fuel must have in order to produce the desirable output to the engine performance.

1. A fuel must have a large energy density to be capable to release huge amount of energy during its combustion in side the combustion chamber.
2. A fuel must posses a good combustion quality to produce large amount of energy in smooth way.
3. A fuel must have high thermal stability or pre-ignition may occur.
4. A fuel must show a low deposit forming tendency else gum formation and other deposit forming processes will hamper the combustion process.
5. A fuel must be non-toxic, easy to handle and storage.

CRUDE PETROLEUM OIL:

Petroleum or often referred as "Crude Oil" is a naturally occurring inflammable mixtures of liquid and mud and it contains a complex mixture of different hydrocarbons of various molecular weights. It is mainly recovered through a process called "Oil Drilling".

Oil Wells and Gas Wells:

An oil well produces mainly crude oil with some natural gas dissolved in it. In contrast a gas well produces natural gases although it may contain heavier hydrocarbons like pentane, hexane or hepthane in gaseous state due to the extreme pressure and temperature inside the well, but at surface conditions condensation starts and forms "Natural Gas Condensate" or simply known as Condensate.



COMPOSITIONS OF CRUDE WELL:

Basically, crude well is the muddy mixtures of different hydrocarbons of different molecular weights. Alkanes, Cyclo-alkanes or napthenes, aromatics. It contains nitrogen, oxygen, sulfur and phosphorous. It may also contains metallic compounds too.

Four different types of hydrocarbon molecules appear in crude oil. The relative percentages are widely varied from oil to oil. They are:

• i) Paraffins (alkanes,  C_nH_{2n + 2} )
• ii) Olefins (alkenes, C_nH_2n),
• iii) Napthenes (cyclo-alkanes, C_nH_2n ),
• iv) Aromatics (having benzene ring, C_nH_{2n - 6}).

It is then refined by fractional distillation in oil refinery to obtain a large number of consumer products, from petrol or gasoline, diesel to kerosene, heavy oil, fuel oil, asphalt, chemical reagents, plastics etc.

Most of the derivatives of the petroleum have been used as fuel or heating purpose. The major products of a petroleum refinery are:

• (i) Gasoline,
• (ii) Kerosene,
• (iii) Diesel Oil,
• (iv) Fuel oil,
• (v) Heavy Oil,
• (vi) Lubricating Oil,
• (vii) Asphalts

INTRODUCTION: 

As the demands for gasoline, kerosene/ jet fuel and diesel oil are maximum, refineries around the world have started to convert heavy fuels and other higher hydrocarbons into gasoline, kerosene and diesel oil. To perform this, refineries have adopted several thermo-chemical processes those can convert high molecular weight hydrocarbons into lighter ones by breaking them.

GENERAL REFINERY PROCESSES:

Petroleum refining has evolved continuously in response to changing consumer demand for better and different products. The original requirement was to produce kerosene as a cheaper and better source of light than whale oil. The development of the internal combustion engine led to the production of gasoline and diesel fuels. The evolution of the airplane created an initial need for high-octane aviation gasoline and then for jet fuel, a sophisticated form of the original product, kerosene. Present-day refineries produce a variety of products including many required as feedstock for the petrochemical industry.

a) Distillation Processes:

The first refinery, opened in 1861, produced kerosene by simple atmospheric distillation. Its by-products included tar and naphtha. It was soon discovered that distilling petroleum under vacuum could produce high-quality lubricating oils. However, for the next 30 years kerosene was the product consumer wanted. Two significant events changed this situation. The invention of the electric light decreased the demand for kerosene and the invention of the internal combustion engine created a demand for diesel fuel and gasoline (naphtha). 

b) Thermal Cracking Processes:

With the advent of mass production and World War I, the number of gasoline-powered vehicles increased dramatically and the demand for gasoline grew accordingly. However, distillation processes produced only a certain amount of gasoline from crude oil. In 1913, the thermal cracking process was developed, which subjected heavy fuels to both pressure and intense heat, physically breaking the large molecules into smaller ones to produce additional gasoline and distillate fuels. Visbreaking, another form of thermal cracking, was developed in the late 1930's to produce more desirable and valuable products. 

c) Catalytic Processes:

Higher-compression gasoline engines required higher-octane gasoline with better antiknock characteristics. The introduction of catalytic cracking and polymerization processes in the mid- to late 1930's met the demand by providing improved gasoline yields and higher octane numbers.   Alkylation, another catalytic process developed in the early 1940's, produced more high-octane aviation gasoline and petrochemical feedstock for explosives and synthetic rubber. Subsequently, catalytic isomerization was developed to convert hydrocarbons to produce increased quantities of alkylation feedstock. Improved catalysts and process methods such as hydrocracking and reforming were developed throughout the 1960's to increase gasoline yields and improve antiknock characteristics. These catalytic processes also produced hydrocarbon molecules with a double bond (alkenes) and formed the basis of the modern petrochemical industry. 

d) Treatment Processes:

Throughout the history of refining, various treatment methods have been used to remove non-hydrocarbons, impurities, and other constituents that adversely affect the properties of finished products or reduce the efficiency of the conversion processes. Treating can involve chemical reaction and/or physical separation. Typical examples of treating are chemical sweetening, acid treating, clay contacting, caustic washing, hydrotreating, drying, solvent extraction, and solvent dewaxing. Sweetening compounds and acids desulfurize crude oil before processing and treat products during and after processing. 

Following the Second World War, various reforming processes improved gasoline quality and yield and produced higher-quality products. Some of these involved the use of catalysts and/or hydrogen to change molecules and remove sulfur. 

 Basics of Hydrocarbon Chemistry:

Crude oil is a mixture of hydrocarbon molecules, which are organic compounds of carbon and hydrogen atoms that may include from one to 60 carbon atoms. The properties of hydrocarbons depend on the number and arrangement of the carbon and hydrogen atoms in the molecules. The simplest hydrocarbon molecule is one carbon atom linked with four hydrogen atoms: methane. All other variations of petroleum hydrocarbons evolve from this molecule. 

 

Hydrocarbons containing up to four carbon atoms are usually gases, those with 5 to 19 carbon atoms are usually liquids and those with 20 or more are solids. The refining process uses chemicals, catalysts, heat, and pressure to separate and combine the basic types of hydrocarbon molecules naturally found in crude oil into groups of similar molecules. The refining process also rearranges their structures and bonding patterns into different hydrocarbon molecules and compounds. Therefore it is the type of hydrocarbon (paraffinic, naphthenic, or aromatic) rather than its specific chemical compounds that is significant in the refining process. 

Principal Groups of Hydrocarbon

• Paraffins - The paraffinic series of hydrocarbon compounds found in crude oil have the general formula C_nH_2n+2 and can be either straight chains (normal) or branched chains (isomers) of carbon atoms. The lighter, straight chain paraffin molecules are found in gases and paraffin waxes. Examples of straight-chain molecules are methane, ethane, propane, and butane (gases containing from one to four carbon atoms), and pentane and hexane (liquids with five to six carbon atoms). The branched-chain (isomer) paraffins are usually found in heavier fractions of crude oil and have higher octane numbers than normal paraffins. These compounds are saturated hydrocarbons, with all carbon bonds satisfied, that is, the hydrocarbon chain carries the full complement of hydrogen atoms.
  • Example of simplest hydrocarbon molecule: Methane (CH₄), Examples of straight chain paraffin molecule (Butane) and branched paraffin molecule (Isobutane) with same chemical formula (C₄H₁₀)
    
    
    
    
• Aromatics - Aromatics are unsaturated ring-type (cyclic) compounds which react readily because they have carbon atoms that are deficient in hydrogen. All aromatics have at least one benzene ring (a single-ring compound characterized by three double bonds alternating with three single bonds between six carbon atoms) as part of their molecular structure. Naphthalenes are fused double-ring aromatic compounds. The most complex aromatics, polynuclears (three or more fused aromatic rings), are found in heavier fractions of crude oil.
  • Example of simple aromatic compound: Benzene (C₆H₆), Examples of simple double-ring aromatic compound: Naphthalene (C₁₀H₈)
    
    
    
    
• Naphthenes - Naphthenes are saturated hydrocarbon groupings with the general formula C_nH_2n, arranged in the form of closed rings (cyclic) and found in all fractions of crude oil except the very lightest. Single-ring naphthenes (monocycloparaffins) with five and six carbon atoms predominate, with two-ring naphthenes (dicycloparaffins) found in the heavier ends of naphtha.
  • Example of typical single-ring naphthene: Cyclohexane (C₆H₁₂), Examples of naphthene with same chemical formula (C₆H₁₂) but different molecular structure: Methyl cyclopentane (C₆H₁₂)

Other Hydrocarbons

• Alkenes - Alkenes are mono-olefins with the general formula C_nH_2n and contain only one carbon-carbon double bond in the chain. The simplest alkene is ethylene, with two carbon atoms joined by a double bond and four hydrogen atoms. Olefins are usually formed by thermal and catalytic cracking and rarely occur naturally in unprocessed crude oil.
  • Example of simples Alkene: Ethylene (C₂H₄), Typical Alkenes with the same chemical formula (C₄H₈) but different molecular structures: 1-Butene and Isobutene
    
    
    
    
• Dienes and Alkynes - Dienes, also known as diolefins, have two carbon-carbon double bonds. The alkynes, another class of unsaturated hydrocarbons, have a carbon-carbon triple bond within the molecule. Both these series of hydrocarbons have the general formula CnH2n-2. Diolefins such as 1,2-butadiene and 1,3-butadiene, and alkynes such as acetylene,occur in C5 and lighter fractions from cracking. The olefins, diolefins, and alkynes are said to be unsaturated because they contain less than the amount of hydrogen necessary to saturate all the valences of the carbon atoms. These compounds are more reactive than paraffins or naphthenes and readily combine with other elements such as hydrogen, chlorine, and bromine.
  • Example of simplest Alkyne: Acetylene (C₂H₂), Typical Diolefins with the same chemical formula (C₄H₆) but different molecular structures: 1,2-Butadiene and 1,3-Butadiene

Non-hydrocarbons

• Sulfur Compounds -  Sulfur may be present in crude oil as hydrogen sulfide (H₂S), as sulfur compounds such as mercaptans, sulfides, disulfides, thiophenes, etc. or as elemental sulfur. Each crude oil has different amounts and types of sulfur compounds, but as a rule the proportion, stability, and complexity of the compounds are greater in heavier crude-oil fractions. Hydrogen sulfide is a primary contributor to corrosion in refinery processing units. Other corrosive substances are elemental sulfur and mercaptans. Moreover, the corrosive sulfur compounds have an obnoxious odor.  Pyrophoric iron sulfide results from the corrosive action of sulfur compounds on the iron and steel used in refinery process equipment, piping, and tanks. The combustion of petroleum products containing sulfur compounds produces undesirables such as sulfuric acid and sulfur dioxide. Catalytic hydrotreating processes such as hydrodesulfurization remove sulfur compounds from refinery product streams. Sweetening processes either remove the obnoxious sulfur compounds or convert them to odorless disulfides, as in the case of mercaptans.
  
  
• Oxygen Compounds -  Oxygen compounds such as phenols, ketones, and carboxylic acids occur in crude oils in varying amounts. 
  
  
• Nitrogen Compounds -  Nitrogen is found in lighter fractions of crude oil as basic compounds, and more often in heavier fractions of crude oil as nonbasic compounds that may also include trace metals such as copper, vanadium, and/or nickel. Nitrogen oxides can form in process furnaces. The decomposition of nitrogen compounds in catalytic cracking and hydrocracking processes forms ammonia and cyanides that can cause corrosion. 
  
  
• Trace Metals -  Metals, including nickel, iron, and vanadium are often found in crude oils in small quantities and are removed during the refining process. Burning heavy fuel oils in refinery furnaces and boilers can leave deposits of vanadium oxide and nickel oxide in furnace boxes, ducts, and tubes. It is also desirable to remove trace amounts of arsenic, vanadium, and nickel prior to processing as they can poison certain catalysts. 
  
  
• Salts -  Crude oils often contain inorganic salts such as sodium chloride, magnesium chloride, and calcium chloride in suspension or dissolved in entrained water (brine). These salts must be removed or neutralized before processing to prevent catalyst poisoning, equipment corrosion, and fouling. Salt corrosion is caused by the hydrolysis of some metal chlorides to hydrogen chloride (HCl) and the subsequent formation of hydrochloric acid when crude is heated. Hydrogen chloride may also combine with ammonia to form ammonium chloride (NH₄Cl), which causes fouling and corrosion. 
  
  
• Carbon Dioxide -  Carbon dioxide may result from the decomposition of bicarbonates present in or added to crude, or from steam used in the distillation process. 
• Naphthenic Acids -  Some crude oils contain naphthenic (organic) acids, which may become corrosive at temperatures above 450° F when the acid value of the crude is above a certain level.

 Major Refinery Products

• Gasoline. The most important refinery product is motor gasoline, a blend of hydrocarbons with boiling ranges from ambient temperatures to about 400 °F. The important qualities for gasoline are octane number (antiknock), volatility (starting and vapor lock), and vapor pressure (environmental control). Additives are often used to enhance performance and provide protection against oxidation and rust formation.
• Kerosene. Kerosene is a refined middle-distillate petroleum product that finds considerable use as a jet fuel and around the world in cooking and space heating. When used as a jet fuel, some of the critical qualities are freeze point, flash point, and smoke point. Commercial jet fuel has a boiling range of about 375°-525° F, and military jet fuel 130°-550° F. Kerosene, with less-critical specifications, is used for lighting, heating, solvents, and blending into diesel fuel.
• Liquified Petroleum Gas (LPG). LPG, which consists principally of propane and butane, is produced for use as fuel and is an intermediate material in the manufacture of petrochemicals. The important specifications for proper performance include vapor pressure and control of contaminants.
• Distillate Fuels. Diesel fuels and domestic heating oils have boiling ranges of about 400°-700° F. The desirable qualities required for distillate fuels include controlled flash and pour points, clean burning, no deposit formation in storage tanks, and a proper diesel fuel cetane rating for good starting and combustion.
• Residual Fuels. Many marine vessels, power plants, commercial buildings and industrial facilities use residual fuels or combinations of residual and distillate fuels for heating and processing. The two most critical specifications of residual fuels are viscosity and low sulfur content for environmental control.
• Coke and Asphalt. Coke is almost pure carbon with a variety of uses from electrodes to charcoal briquets. Asphalt, used for roads and roofing materials, must be inert to most chemicals and weather conditions.
• Solvents. A variety of products, whose boiling points and hydrocarbon composition are closely controlled, are produced for use as solvents. These include benzene, toluene, and xylene.
• Petrochemicals. Many products derived from crude oil refining, such as ethylene, propylene, butylene, and isobutylene, are primarily intended for use as petrochemical feedstock in the production of plastics, synthetic fibers, synthetic rubbers, and other products.
• Lubricants. Special refining processes produce lubricating oil base stocks. Additives such as demulsifiers, antioxidants, and viscosity improvers are blended into the base stocks to provide the characteristics required for motor oils, industrial greases, lubricants, and cutting oils. The most critical quality for lubricating-oil base stock is a high viscosity index, which provides for greater consistency under varying temperatures.

Common Refinery Chemicals

• Leaded Gasoline Additives: Tetraethyl lead (TEL) and tetramethyl lead (TML) are additives formerly used to improve gasoline octane ratings but are no longer in common use except in aviation gasoline.
• Oxygenates: Ethyl tertiary butyl ether (ETBE), methyl tertiary butyl ether (MTBE), tertiary amyl methyl ether (TAME), and other oxygenates improve gasoline octane ratings and reduce carbon monoxide emissions.
• Caustics: Caustics are added to desalting water to neutralize acids and reduce corrosion. They are also added to desalted crude in order to reduce the amount of corrosive chlorides in the tower overheads. They are used in some refinery treating processes to remove contaminants from hydrocarbon streams.
• Sulfuric Acid and Hydrofluoric Acid: Sulfuric acid and hydrofluoric acid are used primarily as catalysts in alkylation processes. Sulfuric acid is also used in some treatment processes.
  
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