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engineering
introduction mechanical engineering

Questions and Answers of Introduction Mechanical Engineering

What is scavenging? Explain the structure and working of two-stroke petrol engine.
Mechanical efficiency of two-stroke engine in comparison to four-stroke engine is:(a) More(b) Same(c) Less(d) None of the above
What is supercharging? Explain the structure and working of two-stroke diesel engine.
Thermal efficiency of two-stroke engine in comparison to four-stroke engine is:(a) More(b) Same(c) Less(d) None of the above
The following results refer to a test on C.I. Engine:Indicated power \(=37 \mathrm{~kW}\);Frictional power \(=6 \mathrm{~kW}\);Brake specific fuel consumption \(=0.28 \mathrm{~kg} / \mathrm{KWh}\);
During testing of single cylinder two-stroke petrol engine, following data were obtained-brake torque \(=640 \mathrm{Nm}\); cylinder diameter \(=21 \mathrm{~cm}\), speed \(=250 \mathrm{rpm} ;\)
Explain the valve timing diagram of four-stroke petrol and diesel engines.
Following readings were taken during test of single cylinder four-stroke engine:Cylinder diameter \(=250 \mathrm{~mm}\); stroke length \(=\) \(400 \mathrm{~mm}\); m.e.p. \(=6.5\) bar; Engine speed
In a petrol engine, charge is ignited with:(a) Spark plug(b) Compression(c) Both(d) None of the above
Derive an expression for the efficiency of Otto cycle.
In an ideal diesel cycle, the temperatures at the beginning and at the end of compression are \(57^{\circ} \mathrm{C}\) and \(603^{\circ} \mathrm{C}\), respectively. The temperatures at the beginning
In four-stroke petrol engine:(a) Intake valve closes after top dead center(b) Intake valve closed after bottom dead center(c) Exhaust valve closes after top dead center(d) Exhaust valve closes after
Explain the working of the dual cycle with the help of P–V and T–S diagrams. Derive an expression for air standard efficiency of the dual cycle in terms of compression ratio, pressure ratio,
In an air standard Otto cycle, the compression ratio is 10 and begins at \(37.8^{\circ} \mathrm{C}, 1\) bar and maximum temperature of the cycle is \(1060^{\circ} \mathrm{C}\). Determine: (i) heat
Compression ratio in petrol engine ranges from:(a) 6 to 10(b) 10 to 15(c) 15 to 25(d) 25 to 40
Write down working of two-stroke petrol engine with neat sketch.
In an air standard diesel cycle, the compression ratio is 15 and pressure and temperature of the air at the beginning of the compression are 1 bar and \(288 \mathrm{~K}\). The peak temperature in the
A gas engine working on four-stroke cycle has a cylinder of \(250 \mathrm{~mm}\) diameter, length of stroke \(450 \mathrm{~mm}\) and is running at \(180 \mathrm{rpm}\). Its mechanical efficiency is
How are I.C. engines classified? Draw P–V diagrams of Otto and diesel engine cycles.
If compression ratio in petrol engines kept higher than that is in diesel engines, then:(a) Pre-ignition of fuel will occur(b) Ignition of fuel will be delayed(c) Detonation will occur(d) None of the
Compression ratio in diesel engine ranges from:(a) 6 to 10(b) 10 to 15(c) 14 to 22(d) 25 to 40
Draw the diesel cycle on P–V and T–S coordinates and explain its functioning.
A four-stroke single cylinder petrol engine has a bore of \(150 \mathrm{~mm}\) and stroke of \(250 \mathrm{~mm}\). At \(500 \mathrm{rpm}\) and full load, the net load on friction brake is \(435
In C.I. Engines, the combustion is:(a) Homogeneous(b) Heterogeneous(c) Both(d) None of the above
Differentiate between C.I and S.I. engine.
Following observations were made during a trail on four-stroke diesel engine. Cylinder diameter \(=250 \mathrm{~mm}\), stroke \(=400 \mathrm{~mm}\), speed \(=250 \mathrm{rpm}\) brake load \(=70
Explain with the neat sketch, working of the two-stroke petrol engine.
Which of the following is not related to C.I. engine:(a) Fuel pump(b) Fuel injector:(c) Carburetor(d) Flywheel
Following data were collected from a four-stroke single cylinder I.C. engine at full load. Bore \(=\) \(200 \mathrm{~mm}\), stroke \(=280 \mathrm{~mm}\), speed \(=300 \mathrm{rpm}\), m.e.p. \(=5.6\)
Indicator on an engine is used to determine:(a) B.H.P(b) Speed(c) Temperature(d) I.H.P and M.E.P
Derive an equation for air standard efficiency of Otto cycle.
During testing of single cylinder two-stroke petrol engine following data were obtained. Brake torque \(=640 \mathrm{Nm}\), cylinder diameter 21 \(\mathrm{cm}\), speed \(350 \mathrm{rpm}\), stroke
Morse test is conducted on:(a) Vertical engines(b) Horizontal engines(c) Single cylinder engines(d) Multi cylinder engines
Derive the equation for air standard efficiency of Diesel cycle.
In an engine working on Otto cycle, air has a pressure of 1.0 bar and temperature \(30^{\circ} \mathrm{C}\) at the entry. Air is compressed with a compression ratio of 6 . The heat is added at
The m.e.p. of a diesel engine with fixed compression ration can be improved by:(a) Increasing cut-off ratio(b) Increasing back pressure(c) Increasing operating pressure(d) Reducing charge density
Differentiate between Petrol engine and diesel engine.
In an Otto cycle, the compression ratio is 10 . The temperature at the beginning of compression and at the end of heat supply is 300 and \(1600 \mathrm{~K}\), respectively. Assume, \(\gamma=1.4\) and
An engine is said to be square if cylinder bores equal to _______ .
Explain the working of four-stroke petrol engine with neat sketch.
The following data refers to a single cylinder 4 strokes petrol engine. Cylinder diameter \(=30\) \(\mathrm{cm}\), piston stroke \(=40 \mathrm{~cm}\), engine speed \(=1,400\) rpm, indicated mean
The period during both inlet and exhaust valve remain open is known as _____.
Explain the working of four-stroke petrol engine with neat sketch and P–V diagram.
In ideal constant volume cycle, the pressure and temperature at the beginning of compression are \(97 \mathrm{kPa}\) and \(50^{\circ} \mathrm{C}\), respectively. The volume ratio is 8. The heat is
A two-stroke engine employs ______ cut in the wall of cylinder instead of ______.
With the neat sketch, explain the principle of MPFI?
A four cylinder two-stroke petrol engine with stroke to bore ratio 1.2 develops \(35 \mathrm{~kW}\) brake power at 2,200 rpm. The mean effective pressure in each cylinder is 9 bar and mechanical
In four-stroke petrol engine, size of intake valve is ______ than that of exhaust valve.
With the neat sketch, explain the principle of CRDI?
An engine operates on the air standard diesel cycle. The conditions at the start of the compression stroke are \(353 \mathrm{~K}\) and \(100 \mathrm{kPa}\), while at the end of compression stroke the
Carburetion is the process of ____ and ____.
Give advantages of two-stroke engine over four stroke engine.
An air at \(15^{\circ} \mathrm{C}\) and 1 bar is compressed adiabatically to 15 bar by an engine working on Otto cycle. The maximum pressure of the cycle is 40 bar. Calculate air standard efficiency,
Draw a schematic diagram of I.C. engines and name the parts.
A four-stroke diesel engine has a piston diameter \(250 \mathrm{~mm}\) and stroke \(400 \mathrm{~mm}\). The mean effective pressure is 4 bar and speed is \(500 \mathrm{rpm}\) the diameter of the
Define—Thermal efficiency and mechanical efficiency of I.C. engine.
The inner surface of a plain brick wall is at 80°C and the outer surface is at 30°C. Calculate the rate of heat transfer per m2 of the surface area of the wall, which is 280 mm thick. The thermal
A gas engine working on 4-stroke cycle has a cylinder diameter \(300 \mathrm{~mm}\) and stroke length of 500 \(\mathrm{mm}\) is running at \(220 \mathrm{rpm}\). Its mechanical efficiency is \(80 \%\)
What do you mean by heat transfer? Explain its applications in engineering.
Heat transfer takes place as per:(a) Zeroth law of thermodynamics(b) First law of thermodynamics(c) Second law of thermodynamics(d) All the three
Explain the different modes of heat transfer.
A steel tank of wall thickness \(10 \mathrm{~mm}\) contains water at \(90^{\circ} \mathrm{C}\). Calculate the rate of heat loss per \(\mathrm{m}^{2}\) of tank surface area when the atmospheric
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred at as heat transfer by:(a) Conduction(b) Convection(c) Radiation(d) None of
Derive the expression for heat flow in steady state conduction without heat generation using Fourier Law.
A furnace wall consists of \(100 \mathrm{~mm}\) thick refractory brick and \(800 \mathrm{~mm}\) thick insulating firebrick separated by an air gap. The outside wall is covered with a \(20
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred to as heat transfer by:(a) Conduction(b) Convection(c) Radiation(d)
Explain Newton’s law of cooling and derive the heat flow in convection.
A steel pipe of \(100 \mathrm{~mm}\) bore and \(10 \mathrm{~mm}\) wall thickness, carrying steam at \(250^{\circ} \mathrm{C}\), is insulated with \(30 \mathrm{~mm}\) of a molded high-temperature
Heat transfer in liquids and gases takes place by:(a) Conduction(b) Convection(c) Radiation(d) None of these
Explain Stefan and Boltzmann’s law of and derive the heat flow in convection.
A small hemispherical oven is built of an inner layer of insulating firebrick \(110 \mathrm{~mm}\) thick, and an outer covering \(80 \%\) magnesia \(45 \mathrm{~mm}\) thick. The inner surface of the
When heat is transferred by molecular collision, it is referred to as heat transfer by:(a) Conduction(b) Convection(c) Radiation(d) None of these
Heat flows from one body to other when they have:(a) Different heat contents(b) Different specific heat(c) Different atomic structure(d) Different temperature
The amount of heat flow through a body by conduction is:(a) Directly proportional to the surface area of the body(b) Dependent upon material of the body(c) Directly proportional to the temperature
Thermal conductivity of a material may be defined as the:(a) Quantity of heat flowing in one second through one cubic meter of material when opposite faces are maintained at a temperature difference
Heat transfer by radiation mainly depends upon:(a) Its temperature(b) Nature of the body(c) Kind and extent of its surface(d) All of the above
If two surfaces of area \(A\) distance \(L\) apart, of a material having thermal conductivity \(\mathrm{k}\), are at temperatures \(t_{1}\) and \(t_{2}\) then heat flow rate through it will be:(a)
According to Stefan's Law, the total radiation from a black body per second per unit area is proportional to:(a) \(\mathrm{T}\)(b) \(\mathrm{T}^{2}\)(c) \(\mathrm{T}^{3}\)(d) \(\mathrm{T}^{4}\)
If the inner and outer surfaces of a hollow cylinder (having radii \(r_{1}\) and \(r_{2}\) and length \(\mathrm{L}\) ) are at temperature \(t_{1}\) and \(t_{2}\), then rate of radial heat flow will
If the inner and outer walls of a hollow sphere having surface areas of \(A_{1}\) and \(A_{2}\), and inner and outer radii \(r_{1}\) and \(r_{2}\), are maintained at temperatures \(t_{1}\) and
LMTD for a heat exchanger is given by:(a) \(\frac{\Delta t_{2}-\Delta t_{1}}{\log _{e} \frac{\Delta t_{2}}{\Delta t_{1}}}\)(b) \(\frac{\Delta t_{2}-\Delta t_{1}}{\log _{e} \frac{\Delta t_{1}}{\Delta
The heat flow equation through a sphere of inner radius \(r_{1}\) and outer radius \(r_{2}\) is to be written in the same form as that for heat flow through a plane wall. For wall thickness
The cooling effect in refrigeration is obtained by:(i) Mechanical refrigeration technique(ii) Passing a direct current through the junction of two dissimilar metals(iii) Sublimation of carbon
Differentiate the working of refrigeration and heat pump, thermodynamically.
Carnot refrigeration cycle absorbs heat at \(280 \mathrm{~K}\) and rejects heat at \(310 \mathrm{~K}\).(a) Calculate the coefficient of performance of this refrigeration cycle.(b) If the cycle is
The cooling effect produced by refrigeration finds application in:(i) Construction of cold storages(ii) Cooling of concrete in dams(iii) Comfort air conditioning of hospitals(iv) Liquification of
Enumerate the various components used in a refrigerator and explain their working.
The capacity of a refrigerator is \(200 \mathrm{TR}\) when working between \(-4^{\circ} \mathrm{C}\) and \(22^{\circ} \mathrm{C}\). Determine the mass of ice produced per day from water at
A refrigeration system:(a) Removes heat from a system at low temperature and transfers the same to a system at high-temperature(b) Delivers less heat to the system at high temperature than it
Write advantages and disadvantages of air refrigeration cycle.
A glass of water is mixed with ice. The moisture from the air begins to condense on the surface of glass when the temperature of water comes \(12^{\circ} \mathrm{C}\). If the room temperature and
The COP of a Carnot refrigeration cycle decreases on:(a) Decreasing the difference in operating temperatures(b) Keeping the upper-temperature constant and increasing the lower-temperature(c)
The pressure and temperature of the mixture of air and water vapor at 1 bar and \(22^{\circ} \mathrm{C}\). The dew point temperature of the mixture is \(12^{\circ} \mathrm{C}\). Find partial pressure
Find the expression for COP using Reversed Carnot cycle and Bell Coleman cycle.
A Carnot refrigerating cycle used in house air conditioning delivers heat to the surroundings at the rate of \(10 \mathrm{kw}\) of power. The coefficient of performance of this refrigerator would
Find the derivation for COP in Vapor Compression cycle.
If a Carnot cycle is to have a coefficient of performance of 5 , the ratio of maximum temperature to minimum temperature in the cycle should be:(a) 1.2(b) 1.5(c) 2.0(d) 2.5
Explain the effect of subcooling and superheating on COP of Vapor Compression Cycle.
The DBT and \(\mathrm{RH}\) of air are \(38^{\circ} \mathrm{C}\) and \(60 \%\) respectively. The atmospheric pressure is 1 bar. Determine the specific humidity and vapor pressure of moisture in the
A Carnot refrigerator rejects \(3000 \mathrm{kj}\) of heat at \(400 \mathrm{k}\) while using \(1000 \mathrm{kj}\) of work. The lowest operating temperature in the cycle should be:(a) \(15^{\circ}

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