Question 1

Benson boiler: average operating pressure range and representative value.  Select the most commonly cited average operating pressure for a Benson boiler used in exam practice (options in bar).

Accepted Answer

Concept Benson boilers are designed for very high pressure operation (often at or above the water critical pressure of ≈221 bar). In many standard MCQs, the representative average operating pressure is taken as about 200 bar among the discrete options provided. Clarification Actual installations may operate around or above the critical pressure; however, within the choices given, 200 bar is the conventional key. Final Answer 200 bar

Question 2

Natural draught definition: verify the correctness of the statement.  Statement: A draught produced by a chimney due to the density difference between hot gases inside the chimney and the colder outside air is called natural draught.  Choose the cor…

Accepted Answer

Concept Natural draught arises from the density difference between hot flue gases in the chimney and cooler ambient air. This buoyancy effect creates a pressure difference that draws combustion air through the furnace and expels gases through the stack—without fans. Contrast Induced draught: fan draws gases out. Forced draught: fan pushes air in. Final Answer True

Question 3

Aim of compounding in steam engines: identify the principal objective(s).  Compounding splits the total expansion across multiple cylinders (HP→IP→LP) to improve performance.  Choose the best statement describing the aim.

Accepted Answer

Concept The primary aim of compounding is to reduce the temperature range within any single cylinder by spreading expansion across stages. This limits cylinder condensation and improves efficiency. About the other statements Sharing the overall expansion does lessen the per-cylinder expansion ratio (Option A), but the core aim is thermal (condensation control). Reduction in stroke length (Option B) is not a fundamental aim; it is design-dependent and not guaranteed. Final Answer To reduce the temperature range in each cylinder and thus reduce condensation

Question 4

Loeffler boiler classification: verify the circulation method.  Statement: The Loeffler boiler is a water-tube boiler that uses forced circulation of water/steam to avoid salt deposition in evaporator tubes.  Choose the correct option (True/False).

Accepted Answer

Concept The Loeffler boiler is a high-pressure water-tube boiler employing forced circulation. It superheats steam and uses a portion of that superheated steam to evaporate/feed the water externally, thereby preventing salt deposition in the main evaporator tubes. Final Answer True

Question 5

Crosshead function in a reciprocating steam engine: fill in the missing part correctly.  The function of a crosshead is to guide the motion of the __________ and prevent it from bending, while transmitting force to the connecting rod.  Choose the co…

Accepted Answer

Concept The crosshead maintains straight-line guidance of the piston rod and prevents it from bending under side thrust, while providing the joint to the connecting rod for rotary conversion at the crank. Final Answer piston rod

Question 6

Piston rod function: identify the correct role in a reciprocating steam engine.  Select the statement that correctly describes the function of a piston rod.

Accepted Answer

Concept The piston rod connects the piston to the crosshead, transmitting reciprocating motion. Guidance and bending control are duties of the crosshead (Option A), energy conversion occurs in the cylinder by piston expansion work (Option C), and exhaust timing is controlled by the valve gear (Option D). Final Answer To transfer motion from the piston to the crosshead

Question 7

Locomotive boiler dimensions: select the typical length of the boiler shell (approximate).  Choose the most commonly cited shell length among the options provided.

Accepted Answer

Concept Standard references for classic locomotive boilers cite a typical shell length ≈ 2 m (order of a couple of metres) with multi-pass fire-tubes and a large grate area for high, fluctuating steam demand in traction service. Final Answer 2 m

Question 8

Boilers classification: identify the correct combined statement about common boiler types  Check each named boiler against its family (fire-tube or water-tube) and firing arrangement.  Choose the correct option.

Accepted Answer

Given facts • Lancashire is a classic fire-tube boiler with two large furnace/flue tubes. • Typical fire-tube units (Cornish, Lancashire, locomotive, Scotch marine) are internally fired (furnace within the shell). • Babcock & Wilcox is a water-tube boiler (water/steam in tubes, hot gases outside). Concept/Approach Identify each boiler type by where the water/steam flows and where the furnace is placed. Result All three statements (a), (b), and (c) are correct, so the best choice is all of the above.

Question 9

Steam engines: effect of wire drawing (throttling during valve events) on the indicator diagram and work done  Assess whether throttling (wire drawing) reduces the diagram area and thus the indicated work of the engine.  State whether the statement …

Accepted Answer

Given statement Wire drawing (throttling through ports/valves) decreases the area of the indicator diagram and hence reduces work per cycle. Concept Wire drawing lowers the mean effective pressure (MEP) during admission/exhaust due to throttling losses; reduced MEP directly reduces the area enclosed by the pressure-volume (P–V) indicator diagram. Step-by-step logic • Losses at admission/exhaust → reduced pressure trace.• Reduced P–V area → lower indicated work per cycle. Final Answer True — area decreases and indicated work reduces

Question 10

Reciprocating steam engine: conversion of steam's thermal energy into mechanical work  Confirm the basic working principle — heat in steam is converted into piston reciprocation and then shaft work.  State whether the statement is true or false.

Accepted Answer

Working principle Steam expands against the piston producing a to-and-fro motion, which the mechanism converts to rotary work on the crankshaft. Thus the engine converts thermal energy of steam into mechanical energy. Final Answer True — heat energy in steam → piston to-and-fro motion → work

Question 11

Governing of steam engines — speed regulation under load changes State whether the function of a governor in a steam engine is to keep the engine speed approximately constant as the load varies.

Accepted Answer

Introduction: Governing is essential for prime movers to maintain nearly constant speed when load fluctuates. In steam engines, a governor automatically adjusts steam admission so that the mean speed remains within acceptable limits despite changing torque demand from the driven machinery. Given Data / Assumptions: Conventional centrifugal or mechanical governor linked to the throttle or cut-off mechanism. Reasonably steady boiler pressure and adequate steam supply. Normal operating regime, not emergency trips. Concept / Approach: A governor senses speed (or speed error) and modulates energy input. In a steam engine, this is commonly achieved by changing valve cut-off or throttle position. Increased load tends to slow the engine; the governor responds by admitting more steam; decreased load tends to accelerate the engine; the governor restricts steam admission. The goal is speed regulation, not exact constancy, as there is always some droop for stability. Step-by-Step Solution: Identify disturbance: load increases or decreases cause speed deviations.Governor action: adjust steam flow to oppose speed error.Outcome: engine speed is maintained approximately constant around the set point. Verification / Alternative check: Speed-time plots for governed engines show small deviations and corrections instead of runaway acceleration or stalling. The same principle underlies governors in turbines and internal combustion engines. Why Other Options Are Wrong: No / startup-only: contradicts the continuous control role. Only at constant steam pressure: a governor compensates for load changes even if steam pressure varies slightly; boiler controls handle pressure regulation. Applies only to hydraulic turbines: governing is a cross-technology concept. Common Pitfalls: Confusing governor action (speed control) with flywheel action (energy storage for cyclic speed smoothing); expecting zero droop, which can cause instability. Final Answer: Yes

Question 12

Lancashire boiler — identify all applicable classifications How is a Lancashire boiler correctly classified with respect to position, firing, and tube arrangement?

Accepted Answer

Introduction: Boiler classification helps engineers understand construction, operation, and typical applications. The Lancashire boiler is a classic shell-type boiler used historically in industries and small power plants. Recognizing its multiple classification attributes ensures correct identification on exams and in practice. Given Data / Assumptions: Conventional Lancashire construction with a large cylindrical shell and two large furnace tubes running longitudinally. Fixed installation (not mobile) and typical brickwork settings. Concept / Approach: The Lancashire boiler is a horizontal shell, fire-tube boiler: hot gases pass through large furnace tubes within the water-filled shell. It is internally fired because the furnaces are inside the shell. It is stationary in the sense that it is installed permanently on a foundation. Therefore, all of the given correct attributes apply simultaneously. Step-by-Step Solution: Identify tube arrangement: fire-tube (hot gases inside tubes, water outside).Identify firing: internal (furnace within shell).Identify position: horizontal orientation.Identify installation: stationary (fixed on site). Verification / Alternative check: Standard boiler texts depict the Lancashire with two internal furnaces, reversal chambers, and flue passes inside a horizontal cylindrical shell resting on brickwork, confirming all listed classifications. Why Other Options Are Wrong: Selecting only one attribute omits others that are equally true for the Lancashire boiler. Water tube, externally fired, vertical: the opposite of Lancashire design attributes. Common Pitfalls: Confusing Lancashire with Cornish (single furnace tube); mixing fire-tube with water-tube terminology; overlooking the internal firing feature due to the presence of brick setting outside. Final Answer: all of these

Question 13

Name the heat-recovery device in boiler practice Which device recovers part of the waste heat of flue gases to preheat the air supplied to the furnace for combustion?

Accepted Answer

Introduction: Thermal efficiency of steam plants improves when waste heat is recovered from flue gases. Two common heat exchangers are the economiser and the air preheater. Differentiating their roles is vital for boiler operation and energy audits. Given Data / Assumptions: Conventional coal or oil-fired boiler with flue gas path. Air supply system with forced or induced draught fans. Concept / Approach: An air preheater transfers heat from hot flue gases to the incoming combustion air, raising its temperature before it enters the furnace. This enhances flame stability, improves fuel-air mixing, increases furnace temperature for a given fuel input, and reduces unburnt losses. An economiser, by contrast, heats feedwater using flue gas waste heat. A superheater raises the temperature of steam beyond saturation; an injector uses steam to force feedwater into the boiler and is not a heat-recovery exchanger. Step-by-Step Solution: Identify target medium: combustion air → requires air preheater.Map other devices: economiser → feedwater; superheater → steam; injector → feed system component, not a heat-recovery air heater.Select air preheater as the correct device. Verification / Alternative check: Flue gas temperature profiles across air preheater sections show significant air temperature rise, leading to reduced fuel consumption and improved boiler efficiency. Why Other Options Are Wrong: Superheater: acts on steam, not air. Economiser: acts on feedwater, not air. Injector/de-aerator: not flue gas heat-recovery devices for air preheating. Common Pitfalls: Mixing up economiser and air preheater roles; assuming both heat the same medium; overlooking fouling and corrosion control that impact their performance. Final Answer: air preheater

Question 14

Effect of mechanical draught on plant efficiency Consider a steam-plant firing system. As mechanical draught (fan-assisted air and flue-gas movement) is implemented and properly controlled, the overall plant efficiency generally ________.

Accepted Answer

Introduction: Draught provides the pressure difference necessary to move air into the furnace and carry flue gases through the boiler passes and chimney. Natural draught relies on chimney buoyancy, while mechanical draught uses fans. This question probes understanding of how mechanical draught influences energy efficiency. Given Data / Assumptions: Appropriate fan selection (forced/induced draught) with correct control. Adequate combustion tuning (excess air control, air–fuel ratio). Reasonable maintenance of leakage and fouling. Concept / Approach: Mechanical draught provides better control of air supply and gas flow than natural draught, enabling optimal excess air, higher furnace temperatures, and improved heat transfer. It reduces stack losses via precise air control and supports air preheaters and economisers at design conditions. Although fans consume auxiliary power, the net effect is typically an increase in overall plant efficiency due to improved combustion and heat recovery. Step-by-Step Solution: Introduce fans to control air and flue-gas flow precisely.Tune excess air to minimize unburnt fuel and stack losses.Recover more heat in economisers/air preheaters due to controlled flow, raising boiler efficiency. Verification / Alternative check: Energy balance: auxiliary fan power is small compared to fuel energy saved by better combustion and lower flue-gas exit temperatures, producing a higher net plant efficiency. Why Other Options Are Wrong: Decreases: contradicts typical outcomes when properly designed. Remains constant: ignores the tangible benefits of control and recovery. Oscillates or drops to zero: unrealistic and not aligned with engineering practice. Common Pitfalls: Running with excessive excess air due to poor control (which can negate gains); neglecting leakage in ducts; ignoring fan power in net efficiency calculations. Final Answer: increases

Question 15

Definition check — evaporative capacity of a boiler Is the statement correct? “The evaporative capacity of a boiler is defined as the evaporation of 15.653 kg of water per hour from and at 100°C.”

Accepted Answer

Introduction: Boiler performance is characterized by several related terms: evaporative capacity, equivalent evaporation, and boiler horsepower. Confusing these leads to wrong sizing and comparisons. This question asks you to validate a specific numeric definition attributed to evaporative capacity. Given Data / Assumptions: Standard engineering definitions used in steam engineering texts. Reference condition “from and at 100°C” for equivalence calculations. Concept / Approach: Evaporative capacity is the mass of water the boiler can evaporate per unit time (e.g., kg/h) under stated conditions. It has no fixed universal value. The number 15.653 kg/h corresponds to the historical definition of one boiler horsepower (BHP): 34.5 lb/h ≈ 15.653 kg/h of steam evaporated from and at 100°C per boiler horsepower. Thus, 15.653 kg/h is a unit conversion constant for BHP, not the definition of evaporative capacity itself. Step-by-Step Solution: Recognize the claim: evaporative capacity equals 15.653 kg/h “from and at” temperature.Recall correct concept: evaporative capacity is a variable rating (kg/h) dependent on boiler size and duty.Identify the 15.653 kg/h value as the mass flow represented by 1 boiler horsepower, not the definition of evaporative capacity. Verification / Alternative check: Equivalent evaporation and boiler horsepower relations: 1 BHP = 34.5 lb/h ≈ 15.653 kg/h from and at 100°C. Large boilers have capacities many orders higher, confirming that evaporative capacity is not tied to this fixed number. Why Other Options Are Wrong: Yes / qualified “correct” options: conflate a unit definition (BHP) with the general parameter. Economiser or SI caveats: irrelevant to the definition. Common Pitfalls: Mixing up evaporative capacity with equivalent evaporation; believing 15.653 kg/h is a universal constant rather than a per-horsepower yardstick. Final Answer: No

Question 16

Chimney draught — factors affecting natural draught magnitude Select all influential factors. The available chimney draught varies with which of the following?

Accepted Answer

Introduction: Natural draught arises from density differences between hot flue gases in a chimney and cooler outside air. The pressure head it produces is small and sensitive to several environmental and design factors. Recognizing these dependencies is vital for sizing chimneys and assessing seasonal performance. Given Data / Assumptions: Chimney operating with hot gases hotter than ambient air. Steady conditions but subject to weather changes. Concept / Approach: The draught pressure is proportional to the height of the chimney and the difference between outside air density and flue gas density, which depends on temperature (and composition). Climate affects ambient temperature, wind, and barometric pressure, all of which alter density and, hence, draught. Therefore, chimney height, gas temperature, and climatic conditions all influence natural draught magnitude. Step-by-Step Solution: Relate draught head to height: larger height → greater pressure difference.Relate density difference to temperature: higher gas temperature → lower density → stronger buoyancy.Include climate: ambient temperature and weather shift outside air density and stack effect; wind affects effective draught and dispersion. Verification / Alternative check: Stack effect formulas include chimney height and temperatures; climatic variability appears through ambient temperature and pressure terms, confirming all listed factors matter. Why Other Options Are Wrong: Any single factor alone omits other equally important influences. None of these: contradicts both theory and practice. Common Pitfalls: Ignoring seasonal derating of natural-draught systems; assuming height alone guarantees adequate draught regardless of temperature or weather. Final Answer: all of these

Question 17

Define the expansion ratio in steam/IC engines The expansion ratio is defined as the ratio of which two cylinder volumes with respect to the cut-off point during the power stroke?

Accepted Answer

Introduction: In reciprocating steam engines (and by analogy in some IC engine analyses), the expansion ratio quantifies how much the working fluid expands after steam admission is cut off. It is a key parameter affecting efficiency and indicated work because it determines how fully pressure energy is utilized during expansion. Given Data / Assumptions: Cut-off occurs during the forward power stroke. Volumes are measured in-cylinder, typically referenced from inner dead centre. Clearance volume is present at all times, but the definition involves total cylinder volumes at specific crank positions. Concept / Approach: Let V_c be clearance volume, V_cut be the cylinder volume at the cut-off crank position, and V_e be the total cylinder volume at the end of the stroke. The expansion ratio r_exp expresses the extent of volumetric expansion after cut-off and is defined by r_exp = V_e / V_cut. This definition captures the thermodynamic leverage obtained by allowing the working fluid to expand over a larger volume before exhaust or release. Step-by-Step Solution: Identify the two reference states: at cut-off and at end of stroke.Write definition: r_exp = V_end_of_stroke / V_cutoff.Interpretation: larger r_exp implies longer expansion for the same admission, improving efficiency up to limits imposed by condensation, leakage, and mechanical constraints. Verification / Alternative check: Indicator diagrams show steam admission up to cut-off followed by expansion; the horizontal (volume) spread from V_cut to V_e corresponds to the expansion process, confirming the ratio definition. Why Other Options Are Wrong: Clearance-to-cut-off or swept-to-clearance: not the standard definition; these ratios have other uses. Cut-off to end-of-stroke: inverse of the correct expansion ratio. Swept-to-cut-off: ignores the unavoidable clearance volume component contained in both volumes. Common Pitfalls: Forgetting to include clearance volume in total cylinder volumes; confusing expansion ratio with compression ratio in IC engines; using stroke length directly instead of actual volumes defined by geometry. Final Answer: volume at end of stroke to volume at cut-off

Question 18

Water-tube boiler principle — flow paths of water and hot gases State whether the following is correct: “In water-tube boilers, water passes through the tubes while the surrounding space carries flames and hot gases.”

Accepted Answer

Introduction: Boilers are broadly categorized into fire-tube and water-tube types. Understanding which medium (water or hot gases) flows inside the tubes is fundamental to identifying performance characteristics such as operating pressure, steam-raising rate, and response to load changes. Given Data / Assumptions: Conventional water-tube designs (e.g., Babcock & Wilcox, Stirling, modern high-pressure units). Combustion occurs in a furnace volume external to the tubes. Concept / Approach: In water-tube boilers, the tubes carry water/steam mixture, and combustion gases flow around the outside of these tubes and headers. This configuration enables higher allowable pressures, faster steam generation, and better heat transfer control compared with fire-tube boilers, where hot gases pass inside the tubes and water surrounds them in the shell. Water-tube arrangements also facilitate superheaters, reheaters, and economisers in the gas path. Step-by-Step Solution: Identify flow carriers: water/steam inside tubes; flames and hot gases outside.Relate to advantages: high pressure capability, fast response, safer large-capacity operation.Conclude the statement is correct. Verification / Alternative check: Typical layouts show membrane walls and banks of generating tubes bathed in furnace radiation and convection gas passes, confirming the stated flow directions. Why Other Options Are Wrong: No / fire-tube claim: reverses the roles and describes fire-tube boilers instead. Restrictions to vertical or economiser sections: inaccurate; the definition applies broadly across water-tube types and orientations. Common Pitfalls: Confusing “water-tube” with “water-wall” terminology; assuming small package fire-tube boilers are water-tube because water surrounds the tubes in the shell. Final Answer: Yes

Question 19

Boiler Efficiency — Identifying the Largest Source of Heat Loss In a typical steam boiler operating with proper combustion and reasonable excess air, which of the following accounts for the maximum heat loss from the boiler system?

Accepted Answer

Introduction: Understanding where most of the energy escapes in a boiler helps engineers focus improvement efforts. In routine operations with correct firing and adequate air supply, the dominant loss pathway is usually sensible heat carried away by hot, dry flue gases exiting the chimney. Recognizing this is essential for optimizing economisers, air preheaters, and excess-air settings. Given Data / Assumptions: Combustion is stable with moderate excess air (not grossly high or low). Fuel is conventional (coal, oil, gas) without extreme moisture content. Boiler surfaces are in good condition; blowdown is normal. Concept / Approach: The heat balance of a boiler distributes input chemical energy into useful steam generation and several losses. The sensible heat in stack gases rises with exit temperature and increases with the amount of excess air because higher mass of gas carries more energy. Losses due to moisture-in-fuel and hydrogen (latent plus sensible in water vapour) can be significant, but, for most plants, the single largest line-item remains the dry flue gas sensible heat. Step-by-Step Solution: Identify main losses: (1) dry flue gas sensible heat, (2) moisture/steam (latent and sensible), (3) unburnt carbon, (4) radiation and unaccounted.Relate to operating variables: stack temperature and excess air strongly influence dry flue gas loss.Compare magnitudes: in balanced-draft boilers, dry gas loss commonly exceeds other single categories unless fuel moisture is extreme.Conclude the maximum heat loss is via hot, dry flue gases leaving the stack. Verification / Alternative check: Typical heat-balance worksheets show dry flue gas losses in the range of 5–12% or more of fuel input depending on stack temperature and excess air, often surpassing other individual losses in well-tuned plants. Why Other Options Are Wrong: Moisture in fuel: Important for very wet fuels, but usually smaller than dry gas sensible loss for standard fuels. Steam formation: Latent loss from hydrogen-in-fuel can be large for natural gas but still often not the single largest in many coal/oil units with high stack temperatures. Unburnt carbon: Indicates poor combustion; in a well-run boiler it is kept minimal. Common Pitfalls: Confusing latent losses (water vapour) with sensible dry gas losses, and ignoring the strong effect of excess air on mass flow and stack temperature. Final Answer: dry flue gases leaving the stack

Question 20

Compound Steam Engines — Flywheel Requirement for Tandem Arrangement Evaluate the statement: “A tandem-type compound steam engine requires a larger flywheel.” Consider how torque fluctuations differ from cross-compound arrangements.

Accepted Answer

Introduction: Compound engines split expansion across high-pressure (HP) and low-pressure (LP) cylinders to improve efficiency. The mechanical arrangement (tandem vs. cross-compound) affects turning-moment uniformity and thus the size of flywheel needed to smooth speed fluctuations through the cycle. Given Data / Assumptions: Tandem compound: HP and LP in line on the same piston rod acting on the same crank (cranks effectively 0° apart). Cross-compound: Cylinders on separate cranks typically at 90°, yielding phase-shifted torque contributions. Objective: reduce cyclic speed variation by energy storage in the flywheel. Concept / Approach: Flywheels mitigate fluctuations by storing/releasing kinetic energy as torque deviates from mean. When multiple cylinders deliver their peaks out of phase (e.g., 90°), the combined torque is more uniform, so a smaller flywheel suffices. In a tandem arrangement, both cylinders act in phase on the same crank, so torque peaks and troughs align, increasing fluctuation and requiring a larger flywheel to keep speed within limits. Step-by-Step Solution: Model torque T(θ) as sum of cylinder contributions.For tandem: T_total(θ) ≈ T_HP(θ) + T_LP(θ) with same phase ⇒ higher amplitude of fluctuation.For cross-compound: phase shift near 90° reduces resultant fluctuation factor.Flywheel energy coefficient depends on fluctuation of energy per cycle, which is larger for the tandem case ⇒ larger flywheel moment of inertia needed. Verification / Alternative check: Design texts show lower coefficient of fluctuation of speed for multi-cylinder engines with cranks evenly spaced, validating the argument for larger flywheels when torque sources are in phase. Why Other Options Are Wrong: False: ignores phasing effects that increase fluctuation for tandem. Speed-specific or single-acting qualifiers: the need arises from torque phasing, not merely speed or acting mode. Common Pitfalls: Assuming “more cylinders” always means smoother torque; phasing and crank geometry matter as much as cylinder count. Final Answer: True

Steam Boilers and Engines Questions