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Preparing for RRB ALP CBT-2 Mechanical Engineering? You’re not alone! Heat Engines are a high-yield topic in the Mechanical syllabus and are frequently tested in the Railway Recruitment Board (RRB) exam. Solving multiple-choice questions (MCQs) with answers and explanations not only improves accuracy but builds confidence for the actual exam.
In this post, we’ve curated the Top 50 Heat Engine MCQs, complete with correct answers and detailed solutions, ideal for self-study, revision, and last-minute preparation.
Let’s dive in!
Heat Engines are part of the Thermodynamics section under Mechanical Engineering. Questions typically cover:
Basic definitions & concepts (Efficiency, Work, Heat transfer)
Carnot, Otto, Diesel, Brayton cycles
Properties of working fluids
Laws of thermodynamics
Heat transfer mechanisms
Getting these right can significantly boost your score.
Below are 50 carefully curated MCQs based on real exam trends, textbook concepts, and competitive patterns.
Tip: Before checking answers, try solving each question on your own!
| Q No | Question | Options | Answer |
|---|---|---|---|
| 1 | A Heat Engine converts __________ into work. | A) Heat energy B) Electrical energy C) Potential energy D) Kinetic energy | A |
| 2 | The unit of thermal efficiency is: | A) Joule B) Watt C) Percentage D) None | C |
| 3 | Maximum possible efficiency of an engine depends on: | A) Heat supplied B) Temperature difference C) Pressure D) Volume | B |
| 4 | 1st Law of Thermodynamics is also known as: | A) Law of Conservation of Mass B) Law of Energy Conservation C) Law of Conservation of Charge D) Law of Motion | B |
| 5 | In a Carnot cycle, the working fluid undergoes __________ processes. | A) 2 B) 3 C) 4 D) 5 | C |
| 6 | Which device removes heat from engine cylinders? | A) Radiator B) Clutch C) Brake D) Muffler | A |
| 7 | Thermal efficiency of Carnot engine is independent of: | A) Working fluid B) Temperature C) Heat supplied D) Pressure | A |
| 8 | Entropy is a measure of __________. | A) Work done B) Disorder C) Pressure D) Density | B |
| 9 | A cyclic heat engine returns to its: | A) Initial state B) Final state C) Half state D) None | A |
| 10 | The efficiency of a heat engine is always: | A) >100% B) =100% C) <100% D) None | C |
| Q No | Question | Options | Answer |
|---|---|---|---|
| 11 | Otto cycle is used in: | A) Diesel engine B) Petrol engine C) Steam turbine D) Gas turbine | B |
| 12 | Diesel cycle has __________ compression ratio than Otto. | A) Lower B) Higher C) Same D) Varying | B |
| 13 | Brayton cycle is for: | A) Jet engine B) Steam engine C) Petrol engine D) Diesel engine | A |
| 14 | Carnot cycle efficiency increases with: | A) Increase in heat rejected B) Decrease in temperature difference C) Increase in temperature difference D) Decrease in work done | C |
| 15 | In Diesel cycle, heat is added at: | A) Constant volume B) Constant pressure C) Constant temperature D) Variable | B |
| 16 | Brake thermal efficiency is ratio of: | A) Brake power to heat supplied B) Indicated power to heat supplied C) Brake power to indicated power D) Heat rejected to heat supplied | A |
| 17 | Mean effective pressure is used to: | A) Calculate power B) Determine efficiency C) Estimate work output D) Find heat transfer | C |
| 18 | In Carnot engine, net work done equals: | A) Area inside the cycle B) Heat supplied C) Heat rejected D) Pressure × Volume | A |
| 19 | Diesel engine ignition is due to: | A) Spark B) Compression C) Heat transfer D) Fuel injector | B |
| 20 | A reversible process has __________ entropy generation. | A) Maximum B) Minimum C) Zero D) Infinite | C |
| 21 | Otto cycle consists of ________ processes. | A) 2 B) 3 C) 4 D) 5 | C |
| 22 | Brayton cycle efficiency depends on: | A) Pressure ratio B) Volume ratio C) Heat capacity D) Work done | A |
| 23 | In a cooling system water circulates through: | A) Radiator B) Expansion chamber C) Carburetor D) Exhaust pipe | A |
| 24 | Thermal efficiency can’t be 100% because of: | A) Perfect insulation B) Heat losses C) Work done D) Temperature difference | B |
| 25 | Work output of Carnot engine is equal to: | A) Q1 + Q2 B) Q1 − Q2 C) Q2 − Q1 D) Q1 × Q2 | B |
| Q No | Question | Options | Answer |
|---|---|---|---|
| 26 | Efficiency of Carnot engine operating 500 K & 300 K? | A) 40% B) 50% C) 60% D) 30% | A |
| 27 | Heat rejected is ______________ of heat engine. | A) Useful B) Waste C) Maximum work D) Pressure | B |
| 28 | Real engine differs from Carnot because: | A) Perfect insulation B) No friction C) Irreversibilities D) No heat transfer | C |
| 29 | Heat engine efficiency formula is: | A) W/Q1 B) Q1/Q2 C) Q2/Q1 D) Q1/W | A |
| 30 | Carnot cycle is __________ engine. | A) Actual B) Reversible C) Irreversible D) Adiabatic | B |
| 31 | In Otto cycle, specific heat at constant __________. | A) Pressure B) Volume C) Temperature D) Work | B |
| 32 | Lower heat rejection increases: | A) Efficiency B) Work done C) Friction D) Weight | A |
| 33 | The area inside P-V diagram shows: | A) Heat B) Work C) Temperature D) Power | B |
| 34 | Perfect engine has __________ losses. | A) Zero B) Some C) Many D) Unknown | A |
| 35 | Thermal efficiency is influenced by: | A) Pressure ratio B) Heat source C) Temperature difference D) None | C |
| 36 | In Brayton cycle the compression process is: | A) Isothermal B) Isentropic C) Isochoric D) Isobaric | B |
| 37 | Otto cycle efficiency increases with: | A) Compression ratio B) Temperature drop C) Heat lost D) Volume increase | A |
| 38 | A Diesel engine uses: | A) Spark plug B) Glow plug C) Fuel injection D) Carburetor | C |
| 39 | Carnot theorem states maximum efficiency is possible by: | A) Reversible engine B) Irreversible engine C) Diesel engine D) Real engine | A |
| 40 | Heat engines operate between __________ reservoirs. | A) One B) Two C) Three D) None | B |
| Q No | Question | Options | Answer |
|---|---|---|---|
| 41 | Which cycle represents jet engines? | A) Otto B) Brayton C) Diesel D) Carnot | B |
| 42 | Heat pump efficiency is called: | A) COP B) Work C) Temperature D) Pressure | A |
| 43 | Best working fluid for Carnot engine is: | A) Air B) Argon C) Steam D) Any ideal gas | D |
| 44 | In Diesel cycle, peak pressure occurs during: | A) Combustion B) Compression C) Expansion D) Exhaust | A |
| 45 | Brayton cycle is also known as: | A) Rankine B) Joule C) Otto D) Diesel | B |
| 46 | Internal combustion engines are: | A) Heat engines B) Refrigerators C) Heat pumps D) Turbines | A |
| 47 | Heat rejected in Carnot cycle equals: | A) Q1 B) Q2 C) Net work D) Heat input | B |
| 48 | Rankine cycle is mainly used in: | A) Steam turbines B) Gas turbines C) IC engines D) Compressors | A |
| 49 | In Diesel cycle, compression ratio is: | A) Low B) High C) Zero D) Same as Otto | B |
| 50 | Brayton cycle represents: | A) Gas turbine B) Steam engine C) Petrol engine D) Diesel engine | A |
A heat engine takes heat from a high-temperature source and converts part of it into mechanical work, rejecting the rest.
Answer: A
Answer: A
(Continue this format for MCQ explanations)
✔ Carnot Cycle
✔ Otto vs Diesel vs Brayton Cycle
✔ Thermal Efficiency Formulas
✔ 1st and 2nd Law of Thermodynamics
✔ Entropy and Reversibility
| Concept | Formula |
|---|---|
| Efficiency | |
| Carnot Efficiency | |
| Brayton Efficiency | Depends on pressure ratio |
| Otto Efficiency | Depends on compression ratio |
Q1. What is a heat engine?
A device that converts heat energy into mechanical work while operating between two temperature reservoirs.
Q2. Why Carnot engine is considered ideal?
Because it has maximum possible efficiency and operates reversibly.
Q3. Which cycle is used in diesel engines?
Diesel cycle, where heat is added at constant pressure.
Q4. What is Brayton cycle?
It is the ideal cycle for gas turbines (jet engines).
✔ Practice questions daily
✔ Focus on cycles & their efficiency
✔ Understand P-V and T-S diagrams
✔ Revise basic thermodynamic laws
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