Question 1

Purpose of testing an internal combustion engine: identify the most complete reason.  Context: Engine tests can validate design data, provide performance information not available by calculation, and satisfy customer acceptance criteria. Choose the …

Accepted Answer

Given Engine testing serves multiple purposes, not just one. Concept/Approach Testing provides (i) empirical data beyond analytical reach, (ii) validation of assumed/estimated parameters used in design, and (iii) evidence of performance for customers. Final Answer All of the above.

Question 2

Otto cycle efficiency for a given compression ratio: compute the thermal efficiency.  Given: Compression ratio r = 5.5 for an ideal Otto cycle with γ ≈ 1.4. Find the approximate thermal efficiency (percentage).

Accepted Answer

Given data Compression ratio r = 5.5 Specific heat ratio γ ≈ 1.4 (air-standard) Formula ηOtto = 1 − 1/r(γ−1) Step-by-step calculation r(γ−1) = 5.50.4 ≈ 1.977η = 1 − 1/1.977 ≈ 1 − 0.5056 ≈ 0.494η ≈ 49.4% ≈ 50% Final Answer 50%.

Question 3

Fast-neutron reactor moderation requirement: identify the correct moderator choice.  Context: Reactor designed to operate with fast neutrons using highly enriched fuel. Choose the correct statement about the moderator.

Accepted Answer

Concept Fast reactors rely on fast neutrons for fission and therefore deliberately avoid slowing (moderating) neutrons. Highly enriched fuel enables a self-sustaining chain reaction without a moderator. Final Answer No moderator is needed.

Question 4

Carburettor compensating jet: why is its petrol flow nearly constant across speed?  Context: A compensating (air-bleed/emulsion) jet is used to correct mixture at higher speeds/suctions. Choose the best explanation.

Accepted Answer

Concept A compensating jet uses an emulsion/air-bleed arrangement (and a separate well vent) that causes the effective head and/or discharge pathway to change with suction. As air velocity and venturi depression rise, more air is bled into the emulsion, reducing the net fuel head and thus limiting the increase of fuel flow. The result is an approximately constant fuel delivery per unit of suction increase, correcting mixture strength. Why other options are incorrect Main-jet diversion: Not a simple diversion mechanism; it is a calibrated secondary circuit. Constant diameter/Cd: True facts, but they do not explain constancy with speed. Static head only: Would make flow rise strongly with venturi suction; it does not ensure constancy. Final Answer The effective jet area varies automatically with suction, keeping fuel flow nearly constant.

Question 5

Causes of pre-ignition in a spark-ignition (petrol) engine: identify the correct cause(s).  Pre-ignition is spontaneous ignition before normal spark timing at the end of the compression stroke. Choose the best option.

Accepted Answer

Concept Pre-ignition is triggered by local hot spots that ignite the mixture prematurely. Common hot spots include overheated plug electrodes, glowing carbon deposits, or excessively hot combustion-chamber surfaces. Final Answer Any one of these (all are possible causes).

Question 6

Valve timing (four-stroke petrol engine): when does the inlet valve open and close?  State the most accurate generic timing description (qualitative) for the inlet valve events. Choose the correct option.

Accepted Answer

Concept Typical valve timing uses valve lead and valve lag for better volumetric efficiency: the inlet valve usually opens a little before TDC (overlap with exhaust) and closes a little after BDC to take advantage of intake inertia. Why other options are incorrect Exact TDC/BDC opening/closing (Option B) is not used in practice; Options C and D misrepresent the standard timing sequence. Final Answer Opens slightly before TDC and closes slightly after BDC.

Question 7

Carburettor function in SI engines: identify what mixture it supplies to the engine.  Select the correct combination that a carburettor prepares and delivers to the intake.

Accepted Answer

Concept A carburettor (in spark-ignition engines) meters liquid fuel (petrol/gasoline) and mixes it with air to form an air–fuel mixture for induction. Lubricating oil is supplied separately in four-stroke engines. Final Answer Petrol and air.

Question 8

Nuclear power engineering: Reactor type used at Tarapur Atomic Power Station (TAPS)  Tarapur nuclear power station at Boisar, Maharashtra (India) — identify the type of reactor installed in the original units. Choose the correct option.

Accepted Answer

Concept Tarapur Atomic Power Station Units 1 & 2 (the original units) are classic GE Boiling Water Reactors (BWRs). In BWRs, water boils directly in the reactor vessel to produce steam that drives the turbine. Why other options are incorrect Pressurized water reactors keep water under pressure so it does not boil in the core.Gas-cooled and liquid-metal cooled are different designs not used in the original TAPS units. Final Answer Boiling water

Question 9

Basic engine hardware: number of valves in a typical diesel engine cylinder  For a conventional four-stroke diesel engine cylinder, how many valves are commonly provided? Choose the correct option.

Accepted Answer

Concept A conventional four-stroke cylinder (diesel or petrol) typically has two valves: one intake and one exhaust. Although many modern designs use 3 or 4 valves per cylinder to improve breathing, the basic textbook configuration is two. Common pitfall Confusing modern multi-valve performance designs with the standard instructional baseline. Final Answer Two valves

Question 10

Exhaust stroke thermodynamics: cylinder pressure compared to atmosphere  During the exhaust stroke of a four-stroke engine (exhaust valve open, piston moving up), how does the in-cylinder pressure compare to atmospheric pressure? Choose the correct …

Accepted Answer

Given data Exhaust valve open; piston travels toward TDC expelling burnt gases. Concept/Approach A slight positive pressure above atmospheric is needed to drive gases out through the exhaust port and manifold. Pressure waves and valve timing may cause small fluctuations, but the mean pressure is slightly above atmospheric during most of the stroke. Step-by-Step reasoning Exhaust blow-down begins near BDC with high cylinder pressure; as the piston rises, pressure reduces yet stays a little above ambient to maintain mass flow. Final Answer More than atmospheric

Question 11

Diesel engines: open combustion chamber air motion statement  Statement: In open combustion chambers of diesel engines, the piston-crown shape and the inlet port/valve layout are designed to generate strong swirl/turbulence of the air–fuel mixture f…

Accepted Answer

Concept Open (undivided) chambers rely on air motion (swirl, squish, and tumble) created by piston-crown geometry and port/valve layout to atomize and mix the injected fuel rapidly, promoting fast, efficient combustion. Final Answer True

Question 12

Applications of nuclear reactors  Identify the full range of common nuclear-reactor applications listed. Choose the correct option.

Accepted Answer

Concept Reactors provide thermal energy for power generation, can breed/produce fissile materials in special configurations, and have long been used for naval propulsion (ships/submarines). Experimental aircraft reactors also existed historically. Final Answer All of these

Question 13

Engine classification terminology: diesel engines are also known as what type?  Fill the blank with the standard engine classification term. Choose the correct option.

Accepted Answer

Concept Diesel engines are compression-ignition (CI) engines: fuel auto-ignites due to high temperature produced by compressing air. Spark-ignition (SI) uses an electric spark, while EC engines (e.g., steam) burn fuel outside the working cylinder. Final Answer Compression-ignition engines

Question 14

Fuels: auto-ignition (self-ignition) temperature comparison  The self-ignition temperature of petrol (gasoline) compared with diesel oil is: Choose the correct option.

Accepted Answer

Concept Auto-ignition temperature (AIT) is the minimum temperature required for a fuel–air mixture to ignite without an external spark. Typical AIT: diesel ≈ 210°C (lower), petrol ≈ 280–450°C (higher, depending on blend). Implication Because petrol has a higher AIT, it is used in SI engines; diesel's lower AIT enables compression ignition. Final Answer Higher

Question 15

Valve timing for a four-stroke petrol engine: exhaust valve events  Select the correct typical timing for the exhaust valve opening and closing in a four-stroke petrol engine. Choose the correct option.

Accepted Answer

Concept Typical valve timing uses early exhaust opening (≈ 40–60° before BDC) for blow-down, and exhaust closing slightly after TDC (≈ 10–20°) to aid scavenging and benefit from exhaust inertia. Why A is right The given pair (≈ 50° before BDC / 15° after TDC) lies within common textbook values. Final Answer Opens at 50° before BDC and closes at 15° after TDC

Question 16

Power (expansion) stroke timing in a four-stroke diesel engine  Identify the typical angular span for the expansion stroke (combustion/expansion period) in a four-stroke diesel engine. Choose the correct option.

Accepted Answer

Concept In a diesel engine, fuel injection begins near TDC and continues slightly after; peak pressure follows soon after TDC. The useful expansion then proceeds until exhaust opens typically some degrees before BDC (≈ 30–50°), ending the effective expansion early. Reasoning Thus, a representative textbook span is: start ≈ few degrees after TDC, end ≈ some degrees before BDC — matching option C. Final Answer Starts at 15° after TDC and ends at 30° before BDC

Question 17

Fuel additives: inhibitor of pre-ignition/knock in spark-ignition engines  Identify the effective inhibitor historically used to suppress pre-ignition/knock. Choose the correct option.

Accepted Answer

Concept Tetraethyl lead (TEL) was historically used to raise octane number and reduce knock/pre-ignition in petrol engines by slowing end-gas reactions. (Modern fuels use unleaded additives due to environmental regulations.) Notes Alcohol/water injection can reduce charge temperature and suppress knock in specific setups but TEL was the classic chemical inhibitor. Final Answer Lead

Question 18

Pre-ignition vs. detonation in SI engines: evaluate the truth of the statement.  Statement: “Pre-ignition occurs before the spark is produced, whereas detonation (knock) develops after the introduction of the spark.” Choose whether this statement is…

Accepted Answer

Concept/Approach Pre-ignition is spontaneous ignition of the mixture before the intended spark event due to hot spots (e.g., glowing deposits, overheated plug). Detonation (knock) is the auto-ignition of the end-gas that occurs after the normal flame is initiated by the spark. Why the statement is correct The timing of the phenomena is the key: pre-ignition precedes the spark; knock follows spark initiation. Final Answer Agree.

Question 19

Role of a moderator in nuclear power plants: identify the primary function.  Context: A moderator is mixed with the fuel mass in thermal reactors. Choose the correct purpose it serves.

Accepted Answer

Given data Component: Moderator in a nuclear reactor Concept/Approach A moderator (e.g., light/heavy water, graphite) reduces the kinetic energy of fast neutrons via elastic scattering, increasing the probability of thermal fission in fuels like U-235. Why other options are incorrect Control the reaction: That is primarily the job of control rods (absorbers), not the moderator. Reduce temperature / Extract heat: Heat removal is by the coolant circuit, not by the moderator per se (though some moderators are also coolants). Final Answer Slow down the speed of fast moving neutrons.

Question 20

Effect of supercharging on knocking tendency in a petrol (SI) engine with fixed fuel octane and fixed compression ratio.  Fill the blank: Supercharging will ______ the knocking tendency under these constraints. Choose the correct effect.

Accepted Answer

Concept/Approach Supercharging raises the inlet density and pressure, leading to higher end-gas temperature and pressure during compression. For a fixed octane rating and fixed geometric compression ratio, this promotes auto-ignition. Mechanism Higher charge density → higher charge temperature after compression → reduced knock margin → increased knocking tendency. Final Answer Increase.

IC Engines and Nuclear Power Plants Questions