Question 1

Steam engine indicator: compute expansion ratio from cut-off  A double-acting steam engine has cylinder diameter 190 mm, stroke 300 mm, and cut-off at 0.35 of the stroke. Assuming negligible clearance, determine the expansion ratio. Choose the neare…

Accepted Answer

Given Cut-off fraction of the stroke, c = 0.35. Clearance volume is neglected (standard classroom assumption unless stated). Concept Expansion ratio r is the ratio of the volume at the end of the expansion to the volume at cut-off. With negligible clearance, r ≈ 1 / c. Step-by-step calculation r = 1 / c= 1 / 0.35≈ 2.857 ≈ 2.86 Note The cylinder diameter and stroke details are not needed once cut-off fraction is given and clearance is neglected.

Question 2

Design bases for sizing cylinders in a compound steam engine  Identify valid design bases commonly used for selecting cylinder sizes in compound engines. Choose the most comprehensive answer.

Accepted Answer

Concept Compound engines can be proportioned using different (but valid) criteria, depending on the performance objective. Common bases Equal power per cylinder → smoother torque. Equal initial piston loads → standardisation of mechanical parts. Equal temperature drops → better thermal efficiency and reduced condensation losses. Final Answer All of the above.

Question 3

Natural circulation in steam boilers: driving mechanism  State how water circulation is produced in natural-circulation boilers during operation. Choose the correct statement.

Accepted Answer

Concept In natural-circulation boilers, heating in the riser tubes reduces water density, producing convection currents between risers and downcomers that circulate water without any pump. Why others are incorrect No pump or draft fan circulates water in a natural system. Injectors are for feeding water into the boiler, not for internal circulation. Final Answer Circulation is by convection currents due to density differences.

Question 4

Boiler heat-recovery devices: location of the air preheater  Identify where an air preheater is typically installed in the boiler flue-gas path relative to the economiser and chimney. Choose the correct location.

Accepted Answer

Typical arrangement Superheater → Economiser → Air preheater → Chimney (gas progressively cools). Reason Air preheaters recover the lowest grade of heat (lowest gas temperatures) to preheat combustion air before it enters the furnace, so they are usually placed just before the chimney, downstream of the economiser. Final Answer Between the economiser and the chimney.

Question 5

Boiler water-level indication: connections of the glass tube gauge  In a glass-tube type boiler water indicator, one end is connected to the water space. Identify where the other end is connected. Choose the correct connection.

Accepted Answer

Concept A boiler level gauge (glass tube) reads level by equalising pressures between water space (bottom connection) and steam space (top connection). The visible interface in the tube represents the actual drum level. Final Answer Steam space.

Question 6

Boiler component: device that raises the temperature of saturated steam at constant pressure  Name the component used to heat saturated steam further without increasing its pressure. Choose the correct component.

Accepted Answer

Concept A superheater adds sensible heat to saturated steam at (approximately) constant pressure to produce superheated steam. Why others are incorrect Blow-off cock: used to remove sludge and lower water level. Fusible plug: safety against low-water overheating. Stop valve: isolates/controls steam flow. Final Answer Superheater.

Question 7

Draught classification: steam jet below the grate in the ashpit  A steam jet issues from a nozzle placed in the ashpit under the fire grate to move air through the fuel bed. Identify the type of steam-jet draught. Choose the correct term.

Accepted Answer

Concept Forced steam-jet draught: Steam jets are applied below the grate (ashpit) to force air through the fuel bed into the furnace. Induced steam-jet draught: Steam jets are applied in the uptake or chimney to induce flow by entrainment of flue gases. Identification Placement under the grate clearly indicates a forced steam-jet system. Final Answer Forced steam jet draught.

Question 8

Boilers: identify the type when water circulation is driven by a centrifugal pump  Circulation of water in the boiler is provided by a mechanical pump rather than by density difference or natural convection.  Choose the correct boiler classification.

Accepted Answer

Concept When circulation is produced by a pump, the unit is termed a forced circulation boiler. Natural circulation relies on density difference between hot and cold water; forced systems use a centrifugal (circulating) pump to move water through the evaporator, risers, and downcomers. Why the others are wrong Internally/externally fired classify furnace position, not circulation method. Natural circulation is explicitly without a pump. Final Answer Forced circulation boiler

Question 9

Cornish boiler: typical shell diameter range  Recall the common dimensions used in a single-flue Cornish fire-tube boiler.  Choose the correct diameter range for the boiler shell.

Accepted Answer

Concept Cornish boilers are horizontal, fire-tube, single large-flue units. Typical shells have diameters around 1–2 m and lengths around 4–7 m. Lancashire boilers are larger (often 2–3 m diameter) with two flues. Elimination 0.5–1 m is too small for a practical Cornish shell; 2–3 m is typical of Lancashire, not Cornish. 1.25–2.5 m overlaps but the standard textbook range is 1–2 m. Final Answer 1 to 2 m

Question 10

Boiler draught: source of natural draught  Identify the device that produces natural draught for combustion air and flue gas movement in steam boilers.  Choose the correct option.

Accepted Answer

Concept Natural draught is created by the density (temperature) difference of hot flue gases and outside air, using the static head of a chimney. Mechanical draught uses fans or steam jets. Final Answer Chimney

Question 11

Cochran vertical boiler: orientation of the fire tubes  Cochran boiler is a vertical, multi-tubular fire-tube boiler. State the orientation of its fire tubes between the combustion chamber and the smoke box.  Choose the correct option.

Accepted Answer

Concept The Cochran boiler has a vertical shell and horizontal fire tubes. Hot gases from the hemispherical furnace/combustion chamber pass through many small-diameter horizontal tubes to the smoke box, transferring heat to the surrounding water. Final Answer Horizontal tubes

Question 12

Connecting rod: functional role in a reciprocating engine  Evaluate the statement: 'The function of a connecting rod is not to convert the piston's reciprocating motion into rotary motion.'  Choose the correct truth value.

Accepted Answer

Concept The crank converts reciprocating motion to rotary motion. The connecting rod primarily transmits force and motion between piston and crank, acting as a link under combined axial and bending loads. Conclusion The statement is correct. Final Answer True

Question 13

Flywheel: principal function in engines  Identify the primary purpose of a flywheel in a reciprocating engine with cyclic torque fluctuations.  Choose the correct option.

Accepted Answer

Concept A flywheel stores kinetic energy during power strokes and releases it during non-power strokes, thereby reducing speed fluctuation. It cannot keep speed perfectly uniform under varying load (governors address average speed). Why others are wrong (a) is the crank mechanism's job, (b) is done by cams/eccentrics/valve gear, (d) is idealized and not achievable solely by a flywheel. Final Answer Prevent fluctuation of speed (store/release kinetic energy)

Question 14

Cornish boiler geometry: flue tube diameter relative to shell  In a single-flue Cornish boiler, state the typical ratio of flue tube diameter to shell diameter.  Choose the correct proportion.

Accepted Answer

Concept A Cornish boiler has a single large furnace/flue. Typical practice makes the flue relatively large—about 0.6 of the shell diameter—to provide adequate grate and gas flow area while maintaining water volume for heat transfer. Elimination 1/4 or 1/3 is more characteristic of multi-flue (e.g., each flue in a Lancashire boiler). 2/5 is small for the single-flue Cornish; 3/5 is the usual textbook value. Final Answer Three-fifths of shell diameter

Question 15

Willan's line (steam engine): straight-line relation  Willan's line for a steam engine is an approximately straight-line plot between steam consumption per hour and which output measure?  Choose the correct option.

Accepted Answer

Concept For steam engines, Willan's line plots steam consumption rate vs. indicated power; its intercept estimates the no-load steam consumption (friction/standby losses) and the slope gives steam rate per kW indicated. (For IC engines, an analogous Willan's line is often shown for fuel vs. brake power.) Final Answer Indicated power

Question 16

Steam engine valve losses: initial cylinder pressure vs. boiler pressure  At the beginning of the piston stroke, how does the cylinder steam pressure compare with the boiler pressure (considering throttling and valve losses)?  Choose the correct rel…

Accepted Answer

Concept Due to throttling across ports/valves and pressure drops in the steam pipe, the initial admission pressure in the cylinder is lower than the boiler pressure in practical engines. Final Answer Less than the boiler pressure

Question 17

Locomotive/marine boiler safety valve: commonly used type  Select the safety valve type predominantly used on locomotive and marine boilers, where orientation and vibration demand a non-gravity mechanism.  Choose the correct option.

Accepted Answer

Concept Locomotive and marine boilers experience motion, vibration, and attitude changes, making gravity-based valves unsuitable. Spring-loaded safety valves maintain set pressure independent of orientation and are compact and responsive. Why others are wrong Lever and dead-weight types rely on gravity and are more suited to stationary land boilers. A high-steam/low-water valve is a different protective device, not the standard main safety valve. Final Answer Spring loaded safety valve

Question 18

Boiler power (boiler horsepower): choose the correct standard definition used in steam engineering.  According to classic practice, boiler ‘‘power’’ is referenced to a fixed rate of evaporation ‘‘from and at 100°C’’ (dry saturated steam).  Select th…

Accepted Answer

Concept 'Boiler power' in traditional boiler-room practice is referenced to boiler horsepower (BHP). One BHP is defined as the evaporation of 34.5 lb/h (≈ 15.653 kg/h) of water from and at 100°C into dry saturated steam. Why the other options are not correct Option A is the definition of boiler efficiency (useful heat to furnace heat input). Option B is the evaporation ratio (kg steam per kg fuel). Option C describes equivalent evaporation in general terms, but boiler power requires a rate basis (per hour). Key takeaway Boiler power is tied to a fixed reference rate of equivalent evaporation: 15.653 kg/h from and at 100°C.

Question 19

Uniflow (uniflow-scavenged) steam engine: identify the correct flow path of steam through the cylinder.  Definition focus: where admission occurs and where exhaust leaves in a unidirectional flow pattern for better thermal efficiency.  Choose the co…

Accepted Answer

Concept In a uniflow engine, steam flows in one direction. Admission occurs at the cylinder head (end), while exhaust takes place through ports located near the middle of the cylinder, uncovered by the piston near the end of the power stroke. Why this improves performance Reduces thermal cycling of the cylinder ends (lower condensation losses). Improves scavenging because the flow is predominantly one-way. Answer note Option B captures the essential feature: admission at the end and exhaust near the centre.

Question 20

Cut-off governing of steam engines: what parameter is varied to control output?  Context: In cut-off governing, the point of admission is altered while speed/load change, without throttling the inlet pressure.  Choose what is actually controlled und…

Accepted Answer

Concept In cut-off governing, the governor varies the admission period (cut-off) so that the quantity/volume of steam admitted each cycle changes. The supply pressure is not deliberately throttled (unlike throttle governing). Why others are incorrect Pressure variation is characteristic of throttle governing, not cut-off governing. Temperature is not the control variable; it is a function of boiler/superheater operation. Key takeaway Cut-off governing controls engine power by metering steam quantity (admission duration), not by throttling pressure.

Steam Boilers and Engines Questions