Thermal Engineering Questions and Answers – Reciprocating Steam Engine – Parts, Working and Terminology – 2

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This set of Thermal Engineering Assessment Questions and Answers focuses on “Reciprocating Steam Engine – Parts, Working and Terminology – 2”.

1. In a reciprocating steam engine, the connecting rod is connected to the crank by means of a pin called _____
a) Crank pin
b) Gudgeon pin
c) Wrist pin
d) U-pin
View Answer

Answer: a
Explanation: The connecting rod is joined to the crank by a crank pin. The end of the connecting rod connected to the crank is also called big end, and the end connected to the cross-head is called small end.
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2. One of the ends of the connecting rod is connected to the cross-head by means of a pin known as crank pin.
a) True
b) False
View Answer

Answer: b
Explanation: The end of the connecting rod connected to the cross-head is called small end. The connection at the small end is done by means of a pin known as gudgeon pin or wrist pin. The connection of the other end to the crank is done by crank pin.

3. Which of the following statements about connecting rod is FALSE?
a) It converts the reciprocating motion of the piston rod into circular motion of the crankshaft
b) The length of the connecting rod is half the length of the piston stroke
c) It is connected to the cross-head by means of a gudgeon pin or a wrist pin
d) It is connected to the crank by means of a crank pin
View Answer

Answer: b
Explanation: The length of the connecting rod isn’t half of the piston stroke, but varies from about 2 to 6 times the length of the piston stroke. The length of the connecting rod is measured from the center of the cross-head pin to the center of the crank pin.
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4. What is the function of a crank shaft?
a) It converts the reciprocating motion of the piston into rotary motion of the crankshaft
b) It converts the rotary motion of the crankshaft into reciprocating motion of the piston
c) It converts the rotary motion of the piton into reciprocating motion of the crankshaft
d) It converts the reciprocating motion of the crank shaft into rotary motion of the piston
View Answer

Answer: a
Explanation: Crank converts the reciprocating motion of the piston into rotary motion of the crankshaft. Radius of the crankshaft is defined as the distance between the axis of the crankshaft and crank pin.

5. Which of the following statements regarding the radius of a crank (of a reciprocating steam engine) is true?
a) Thrice the radius of the crank is equal to the stroke of the piston
b) One-third the radius of the crank is equal to the stroke of the piston
c) Twice the radius of the crank is equal to the stroke of the piston
d) half the radius of the crank is equal to the stroke of the piston
View Answer

Answer: c
Explanation: The distance measured between the axis of the crankshaft and the crank pin is called radius of the crank. Twice the radius of the crank is equal to the stroke of the piston. Once the crank starts rotating it can be used to drive a variety of systems like generators, pulleys etc.
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6. Which of the following statements about bearings (used to support crankshaft) is FALSE?
a) Split-type bearings are used
b) Bearings need lubrication
c) The portion of the crankshaft in the bearing is called journal
d) Bearings are used to stop the rotation of the crankshaft
View Answer

Answer: d
Explanation: Bearings are used to support and facilitate the rotation of shaft. Split-type bearings are used, as they are easy to replace. Bearings require lubrication for proper functioning. The bearings may be lubricated by ring oiling, needle lubrication, wick lubrication, drop lubrication or forced lubrication.

7. In a reciprocating steam engine, what is the function of an eccentric?
a) It converts the rotary motion of the D-slide valve into the reciprocating motion of the crankshaft
b) It converts the reciprocating motion of the D-slide valve into the rotary motion of the crankshaft
c) It converts the reciprocating motion of the crankshaft into the rotary motion of the D-slide valve
d) It converts the rotary motion of the crankshaft into the reciprocating motion of the D-slide valve
View Answer

Answer: d
Explanation: The function of the eccentric, in a reciprocating steam engine, is to convert the rotary motion of the crankshaft into the reciprocating motion of the D-slide valve. The eccentric is fixed on the crankshaft.
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8. The cylindrical grooved pulley of the eccentric, which is fixed on the crankshaft is called _____
a) Strap
b) Sheaf
c) Sheave
d) Eccentric pulley
View Answer

Answer: c
Explanation: The cylindrical grooved pulley of the eccentric is called sheave. It is fixed on the crankshaft by means of a key. It is hollowed at two places to save material and reduce weight.

9. Flywheel is used in a reciprocating steam engine to maintain constant angular motion.
a) True
b) False
View Answer

Answer: a
Explanation: A flywheel produces avoids the jerks and maintains a steady rotation of the crankshaft. Flywheel stores a part of energy, when the engine develops power, and returns this energy to the crankshaft during idle period of the cycle to maintain constant angular motion.
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10. Which of the following component of a reciprocating steam engine keeps the speed of the crankshaft constant over a period, when there is variation of load on the engine?
a) Flywheel
b) Governor
c) Eccentric
d) Piston
View Answer

Answer: b
Explanation: The correct answer is governor. It increases or decreases the supply of steam in the engine cylinder with the corresponding increase or decrease in load, in order to maintain a constant speed of the crankshaft.

11. Which of the following is the correct formula for calculating swept volume (of a reciprocating steam engine)? (L – Piston Stroke, D – Diameter of the piston)
a) \(\frac{π}{4} \) L2 D
b) \(\frac{π}{4} \) D2 L
c) \(\frac{π}{4} \) L3
d) \(\frac{π}{4} \) D3
View Answer

Answer: b
Explanation: Swept volume is defined as the total volume swept by a piston, when it moves from one dead center to another dead center. It is given by the following expression –
Swept Volume = \(\frac{π}{4} \) D2 L
Where, D – Diameter of the piston
L – Piston Stroke.

12. The steam pressure that acts on the exhaust side of the piston is known as _____
a) Cylinder Pressure
b) Base Pressure
c) Piston Pressure
d) Back Pressure
View Answer

Answer: d
Explanation: The correct answer is back pressure. It acts on the piston from the exhaust side. The net work done on a piston during a cycle is reduced due to presence of back pressure. Ideally it should be zero.

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