Category: Objective Questions

Steam and Gas Turbines Multiple Choice Questions on “Efficiencies”.

1. What does thermodynamic efficiency of steam turbine mean?
a) Ratio of power developed to the power that can be developed by ideal turbine
b) Ratio of power that can be developed by ideal turbine to the power developed by the actual turbine
c) Ratio of inlet temperature to outlet temperature
d) None of the mentioned

Answer: a
Clarification: Thermodynamic efficiency is the ratio of power developed by actual turbine to the power that can be developed by ideal turbine.

2. What does aerodynamic efficiency mean?
a) Energy that can be extracted from a given volume of steam at given temperature and pressure
b) Amount of steam turbine blade can allow to flow inside
c) Amount of energy contained in steam
d) None of the mentioned

Answer: a
Clarification: Aerodynamic efficiency means energy that can be extracted from given volume of steam at given pressure and temperature.

3. If efficiency of boiler increases then efficiency of steam turbine ______
a) decreases
b) increases
c) cannot be determined
d) none of the mentioned

Answer: b
Clarification: If the efficiency of steam boiler increases temperature also increases which indirectly increases its efficiency.

4. If condenser efficiency increases then overall efficiency of steam turbine _______
a) decreases
b) increases
c) remains constant
d) none of the mentioned

Answer: b
Clarification: If condenser efficiency increases it raises the steam temperature and hereby increasing overall efficiency.

5. What does combustion efficiency mean?
a) Boiler ability to burn the fuel to fuel that is not burned and amount of air present at exit
b) Calorific value that can be obtained by burning a fuel
c) Energy that is released when fuel is burned
d) None of the mentioned

Answer: a
Clarification: Combustion efficiency is used to denote the amount of fuel burned by using the air.

6. What does fluid to fuel efficiency mean?
a) It indicates the overall efficiency of the boiler
b) Indicates fuel efficiency
c) Overall efficiency excluding boiler efficiency
d) None of the mentioned

Answer: a
Clarification: Fluid to fuel efficiency indicates overall efficiency including Boiler efficiency, conduction, convection and radiation, etc.

7. The total energy in the fuel is called as _____________
a) boiler efficiency
b) boiler energy
c) gross calorific value
d) none of the mentioned

Answer: c
Clarification: Gross calorific value indicates the total energy a fuel can release when burned.

8. Flue gases _______ efficiency.
a) decreases
b) increases
c) does not effect
d) none of the mentioned

Answer: b
Clarification: Flue gases effect combustion of the fuels and due to that it affects the overall efficiency.

9. Nozzle efficiency can be defined by __________
a) ratio of kinetic energy of the steam leaving the nozzle to the potential energy available with the steam while entering
b) pressure of the steam leaving the nozzle to pressure of the steam entering the nozzle
c) temperature of the steam leaving the nozzle to the temperature of the steam entering the nozzle
d) none of the mentioned

Answer: a
Clarification: Nozzle is used to convert the potential energy of the steam available into kinetic energy to run the turbine.

10. What is the typical efficiency of the nozzle?
a) 0.45-0.56
b) 0.9-0.99
c) 0.5-0.7
d) 0.67-0.86

Answer: b
Clarification: The typical efficiency of the nozzle is between 0.9 and 0.99.

Steam and Gas Turbines Multiple Choice Questions on “Cascade Principle”.

1. Arrangement of blades in an order to represent the blade ring in Turbo machinery is called as cascade.
a) True
b) False
Answer: a
Clarification: Cascade is an array of blades to represent the blade ring in turbo machinery.

2. Cascades __________ the efficiency.
a) decreases
b) increases
c) does not effect
d) none
Answer: b
Clarification: Cascades are introduced to improve the efficiency.

3. When steam is passed through the cascade the direction of air __________
a) reverse
b) remains the same
c) turned
d) cascade is nowhere related to direction
Answer: c
Clarification: When steam is passed through cascade its direction is reversed.

4. Across the turbine cascade static pressure _________
a) drops
b) increases
c) remains same
d) none of the mentioned
Answer: a
Clarification: Across the turbine cascade the static pressure drops.

5. Due to the formation of boundary layers on blades friction losses _________
a) remains the same
b) decreases
c) increases
d) none of the mentioned
Answer: c
Clarification: Due to the formation of boundary layers frictional losses increase due to viscous forces.

6. In compressor cascade when internal pressure is lost ____________
a) axial force is gained
b) axial force is reduced
c) efficiency reduces
d) none of the mentioned
Answer: a
Clarification: In compressor cascade when internal pressure is lost axial force is developed.

7. Drag force is parallel to lift force.
a) True
b) False
Answer: b
Clarification: Drag force is always perpendicular to lift force.

8. Due to viscosity lift force is __________
a) increased
b) decreased
c) remains constant
d) none
Answer: b
Clarification: Due to viscosity lift force is decreased.

9. Due to turbine cascade the drag ________ the lift.
a) increases
b) decreases
c) does not change
d) none of the mentioned
Answer: a
Clarification: Due to turbine cascade drag contributes some useful work which increases the lift.

10. Due to compressor cascade, the static pressure is __________
a) reduced
b) does not change
c) increased
d) none of the mentioned
Answer: c
Clarification: Due to compressor cascade viscous force decreased and hence static pressure is also decreased.

Automobile Engineering Multiple Choice Questions on “Flywheel”.

1. What is the maximum fluctuation of energy?
a) It is the sum of maximum and minimum energies
b) It is the ratio of the maximum and minimum energies
c) It is the ratio of the mean resisting torque to the work done per cycle
d) It is the difference between the maximum and minimum energies
Answer: d
Clarification: The maximum fluctuation of energy is the difference between the maximum and minimum energies. The fluctuation of energy can be found out by the turning moment diagram for one complete cycle of operation.

2. What is the coefficient of fluctuation of energy?
a) The ratio of the maximum fluctuation of energy to the minimum fluctuation of energy
b) The ratio of the maximum fluctuation of energy to the work done per cycle
c) The ratio of the minimum fluctuation of energy to the maximum fluctuation of energy
d) The ratio of the work done per cycle to the maximum fluctuation of energy
Answer: b
Clarification: The coefficient of fluctuation of energy (C_E) is the ratio of the maximum fluctuation of energy to the work done per cycle. C_E =(frac{Delta E}{T_{mean} theta}) where ΔE = maximum fluctuation of energy, T_mean*θ = work done per cycle, T_mean = mean torque, and θ = angle turned in radian in one cycle.

3. Which of the following is true about the flywheel?
a) Flywheel regulates speed over a period of time
b) Flywheel takes care of the quantity of fluid
c) Flywheel controls (frac{dN}{dt})
d) Flywheel regulates the speed by regulating the quantity of charge of the prime mover
Answer: c
Clarification: Flywheel controls the rate of fluctuation of the speed during a cycle. Flywheel controls the speed in one cycle. It does not control the supply of fuel to the engine.

4. Given that maximum fluctuation of energy is 2000 N-m/s and coefficient of fluctuation of speed is 0.02. What is the mean kinetic energy of flywheel?
a) 50 kN-m/s
b) 40 kN-m/s
c) 30 kN-m/s
d) 20 kN-m/s
Answer: a
Clarification: The maximum fluctuation of energy in a flywheel = ΔE, mean kinetic energy of the flywheel = E, and coefficient of fluctuation of speed = C_s. ΔE = 2*E*C_s ⇒ 2000 = 2*E*0.02 ⇒ E = 50 kN-m/s.

5. What is the coefficient of fluctuation of speed?
a) The ratio of the maximum fluctuation of speed to the mean speed
b) The ratio of the maximum fluctuation of energy to the mean speed
c) The ratio of the minimum fluctuation of energy to the mean speed
d) The ratio of the work done per cycle to the mean speed
Answer: a
Clarification: The coefficient of fluctuation of speed is the ratio of the maximum fluctuation of speed to the mean speed. C_s = (ω₁ – ω₂)/ω =2 (ω₁ – ω₂) / (ω₁+ω₂) or C_s = 2(N₁-N₂) / (N₁+N₂).

6. Which of the following is the expression of the maximum fluctuation of energy in a flywheel where I = mass moment of inertia of the flywheel, C_s = coefficient of fluctuation of speed, ω = mean angular speed of ω₁ and ω₂, and E = mean kinetic energy of the flywheel?
a) I*ω*(ω₁+ω₂)
b) I*ω*C_s
c) 2*E²*C_s
d) I*ω²*C_s
Answer: d
Clarification: The maximum fluctuation of energy in a flywheel = I*ω*(ω₁-ω₂) = I*ω²*C_s = 2*E*C_s = I*ω²*C_s. The maximum fluctuation of energy can be calculated by using the turning moment diagram.

7. In the single-cylinder, single acting, four-stroke gas engine, the total fluctuation of speed is not to exceed ±3 percent of the mean speed. What is the coefficient of fluctuation of speed?
a) 0.04
b) 0.03
c) 0.09
d) 0.06
Answer: d
Clarification: Since the total fluctuation of speed is not to exceed ±3 percent of the mean speed, therefore ω₁ – ω₂ = 6% ω and coefficient of fluctuation of speed = C_s = (ω₁ – ω₂)/ω = 0.06.

8. The steam engine has a flywheel which is having a radius of gyration of 1.1 m and mass of 2200 kg. The starting torque is 1550 Nm and assumed constant. What is the angular acceleration of the flywheel?
a) 0.54 rad/s²
b) 0.58 rad/s²
c) 0.62 rad/s²
d) 0.52 rad/s²
Answer: b
Clarification: I = mass moment of inertia of the flywheel, m = mass of the flywheel, k = radius of gyration, T = stating torque, and α = angular acceleration of the flywheel. I = m*k² = 2200*1.1² = 2662 kg-m². T = I*α ⇒ 1550 = 2662 * α ⇒ α = 0.58 rad/s².

9. The engine has the flywheel of mass 7 tons and the radius of gyration is 1.7 m. The fluctuation of energy is 55 kN-m. The mean speed of the engine is 150 rpm. What is the coefficient of fluctuation of speed?
a) 0.021
b) 0.011
c) 0.031
d) 0.041
Answer: b
Clarification: The fluctuation of energy = ΔE, the mass of the flywheel = m, the radius of gyration = k, the mean speed of the flywheel = N. ΔE = (frac{π^2}{900})*m*k²*N*(N₁-N₂) = (frac{π^2}{900})*7000*1.7²*150*(N₁-N₂) = 33277*(N₁-N₂) ⇒ 55000 = 33277*(N₁-N₂) ⇒ (N₁-N₂)= (frac{55000}{33277}) = 1.652 rpm. Coefficient of fluctuation of speed = C_s = (frac{N_1-N_2}{N}) = (frac{1.652}{150}) = 0.011.

10. The flywheel stores the potential energy.
a) True
b) False
Answer: b
Clarification: The flywheel stores the rotational energy. The amount of energy that flywheel can store is proportional to the square of the mass and its rotational velocity. The lighter flywheels are used in a sports car for easy and quick recovery of the RPM.

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Automobile Engineering Questions and Answers for Aptitude test on “Performance Parameters and Characteristics”.

1. Which of the following is correct?
a) Thermal efficiency varies directly as specific fuel consumption
b) Thermal efficiency varies inversely as specific fuel consumption
c) Thermal efficiency varies as root as specific fuel consumption
d) Thermal efficiency varies as square as specific fuel consumption
Answer: b
Clarification: Specific fuel consumption is the ratio of fuel consumption rate to the power produced. Thermal efficiency is the ratio of the power produced to the fuel consumption rate. Hence both are inversely proportional to each other.

2. What is mechanical efficiency?
a) The ratio of friction power to brake power
b) The ratio of the brake power to indicated power
c) The ratio of indicated power to friction power
d) The ratio of friction power to indicated power
Answer: d
Clarification: Mechanical efficiency is the ratio of friction power to indicated power. Mechanical efficiency takes into account the mechanical losses. The mechanical losses are divided into friction losses; power absorbed, ventilating action, and work of charging the cylinder.

3. What is volumetric efficiency?
a) A measure of the power of the engine
b) A measure of the speed of the engine
c) A measure of pressure rise in the cylinder
d) A measure of breathing capacity of the engine
Answer: d
Clarification: Volumetric efficiency is the ratio of the displaced volume of the fluid by the piston to the swept volume. It is the ratio of actual mass of air drawn by the engine to the theoretical mass which should be drawn by the engine.

4. What does the Sankey diagram represent?
a) Torque vs speed
b) Heat balance of the engine
c) Air consumption vs speed
d) ηbth vs brake power
Answer: b
Clarification: Sankey diagram represents the heat balance sheet of the engine. In this diagram, the width of the stream represents the heat quantity being considered.

5. The Otto engine consumes 9 liters of petrol per hour and develops 30 kW. The specific gravity of petrol is 0.8 and its calorific value is 45000 kJ/kg. What is the indicated thermal efficiency of the engine?
a) 33.33%
b) 25%
c) 30%
d) 32%
Answer: d
Clarification: η_ith = heat equivalent of indicated power / heat input = (30 * 60 * 60 * 100) / (9*10^-3*800)*45000 = 33.33%.

6. Which of the following relation between indicated mean effective pressure (imep), brake mean effective pressure (bmep) and friction mean effective power (fmep) is correct?
a) imep = fmep + bmep
b) imep = fmep * bmep
c) imep = fmep – bmep
d) imep = fmep / bmep
Answer: a
Clarification: Indicated mean effective pressure (imep) considered to be consists of the brake mean effective pressure (bmep) and the friction mean effective pressure (fmep).

7. The indicated power of the single-cylinder engine is 1.9 kW. It develops torque of 10 Nm at 1600 rpm. What is the friction power as the percentage of brake power?
a) 12.43%
b) 13.43%
c) 14.43%
d) 15.43%
Answer: b
Clarification: Brake power = bp, Indicated power = ip = 1.9kW, friction power = fp, speed = N = 1600 rpm, and torque = T = 10 Nm. Brake power = bp = 2πNT / 60000 = 2π * 1600 * 10 / 60000 = 1.675 kW. Friction power = fp = ip – bp = 1.9 – 1.675 = 0.225 kW. Percentage loss = (fp / bp)*100 = (0.225 / 1.675)*100 = 13.43%.

8. The bore and stroke of the single-cylinder four-stroke engine are 90 mm and 120 mm respectively. The torque is 24 Nm. What is the brake mean effective pressure of the engine?
a) 3.9 bar
b) 4.9 bar
c) 5.9 bar
d) 6.9 bar
Answer: a
Clarification: Brake mean effective pressure = p_bm, torque = T = 24 Nm, stroke = L = 120 mm, bore = D = 90 mm. p_bm = 16T / D²L = (16*24) / (0.09*0.09*0.12) = 3.9 * 10⁵ Pa = 3.9 bar.

9. What is brake specific fuel consumption of engine whose fuel consumption if 6 grams per second and power output is 90 kW?
a) 0.24 kg/kWh
b) 0.0667 kg/kWh
c) 0.54 kg/kWh
d) 0.44 kg/kWh
Answer: a
Clarification: Brake specific fuel consumption = ṁ_f / bp where bp = brake power and ṁ_f = brake specific fuel consumption. Brake specific fuel consumption = 6 / 90 = 0.0667 g/kW-s = (0.0667 * 3600) / 1000 = 0.24 kg/kWh.

10. If the ip =2.62 kW and bp = 2.4 kW than fp = 5.04 kW
a) True
b) False
Answer: b
Clarification: Friction power = fp, brake power = bp = 2.4 kW, and indicated power = ip = 2.62 kW. ip = bp + fp ⇒ fp = ip – bp = 2.62 – 2.4 = 0.22 kW.

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