Question 1

Hit-and-miss governing in I.C. engines: evaluate the truth of the statement.  Statement: “In hit-and-miss governing, the fuel supply is cut off completely during one or more cycles.” Choose whether this is correct.

Accepted Answer

Concept/Approach Hit-and-miss governing maintains average speed by completely skipping fuel delivery on selected cycles (miss), allowing the engine to coast, then resuming fuel on others (hit). Outcome Therefore, the statement is correct: fuel is indeed shut off for one or more cycles. Final Answer Agree.

Question 2

Definition of volumetric efficiency for reciprocating engines: choose the correct ratio.  Identify the ratio defined as “volume of charge admitted at NTP divided by the swept volume of the piston.”

Accepted Answer

Given Ratio: (Volume of charge at NTP) / (Swept volume). Concept That ratio quantifies how effectively the cylinder is filled compared to its displacement and is called volumetric efficiency. Final Answer Volumetric efficiency.

Question 3

Typical pressure at the end of compression in diesel (CI) engines: choose the nearest value.  Select the approximate end-of-compression pressure in a conventional automotive diesel engine.

Accepted Answer

Concept/Approach Diesel engines have high compression ratios (≈ 14–22). With intake pressure near 1 bar and polytropic compression (n ≈ 1.35–1.4), the end-of-compression pressure typically lies around 30–45 bar. Back-of-envelope check P₂ ≈ P₁ × rⁿ. Taking r = 16 and n = 1.35 → P₂ ≈ 1 × 161.35 ≈ 40 bar (order of magnitude), consistent with 30–45 bar. Final Answer 35 bar (closest option).

Question 4

Energy released per fission of a U-235 nucleus: select the approximate value in MeV.  Choose the closest standard textbook value for fission of one atom of Uranium-235.

Accepted Answer

Concept The fission of one U-235 nucleus typically releases about 200 MeV of energy (≈ 3.2 × 10−11 J). Final Answer 200 MeV.

Question 5

Spark timing in a four-stroke petrol (SI) engine: identify the usual ignition timing.  Choose the standard practice for when the charge is ignited relative to top/bottom dead centre (TDC/BDC).

Accepted Answer

Concept/Approach To allow flame development and complete combustion near TDC, spark timing is advanced. Typical advance is of the order of 10°–30° before TDC depending on speed/load. Final Answer 30° before top dead centre (representative textbook value).

Question 6

Predominant naturally occurring isotope of uranium: choose the correct nuclide.  Select the isotope that is most abundant in natural uranium.

Accepted Answer

Given Natural uranium composition by atom fraction is approximately 99.3% U-238 and 0.7% U-235 (U-234 trace). Final Answer U-238.

Question 7

Four-stroke cycle temperature profile: identify when the minimum cylinder temperature occurs.  Choose the stroke position at which the in-cylinder temperature is at its minimum during a cycle.

Accepted Answer

Concept/Approach During the suction stroke, relatively cool fresh charge is inducted. The mixture has the longest time to exchange heat before compression begins. Reasoning By the end of suction, the cylinder contains the coolest charge of the cycle (before compression raises its temperature), hence the minimum in-cylinder temperature typically occurs at this point. Final Answer End of suction stroke.

Question 8

High-speed compression engines: identify the thermodynamic cycle of operation  In internal-combustion engine theory, high-speed compression-ignition (diesel) engines are modeled to operate on which idealized cycle for analysis and design understandi…

Accepted Answer

Concept High-speed compression-ignition engines are better represented by the dual (mixed) cycle, which has part constant-volume heat addition (to capture rapid initial combustion) and part constant-pressure heat addition (to capture continued burn during piston travel). Low-speed CI engines are closer to the ideal Diesel cycle; SI engines are modeled by the Otto cycle. Why the other options are not best Otto cycle assumes fully constant-volume heat addition (typical for SI). Diesel cycle assumes fully constant-pressure heat addition. The dual cycle combines both, matching high-speed CI combustion phasing more closely. Final Answer Dual-combustion (mixed) cycle

Question 9

Nuclear fission basics: average neutrons from U-235 fission  On average, how many fast neutrons are produced per fission of U-235 in a thermal reactor context? Choose the correct option.

Accepted Answer

Given data Nuclide: U-235 undergoing fission by thermal neutron absorption. Concept A single U-235 fission typically releases ~2–3 fast neutrons. Standard reference value ≈ 2.43–2.47; a commonly used nominal figure is 2.46. Check Order of magnitude must be ~2–3, not tens or hundreds. Final Answer 2.46

Question 10

Moderator used in nuclear power plants: identify a common choice  Which of the following is commonly used as a neutron moderator in power reactors? Choose the correct option.

Accepted Answer

Concept A moderator slows down fast neutrons to thermal energies to sustain fission efficiently. Common moderators used in power reactors include heavy water (D2O) and graphite. Concrete is primarily a shielding material, not a moderator. Why choose heavy water here Among the listed choices, both graphite (A) and heavy water (B) are valid moderators; with a single answer MCQ and typical power-plant emphasis (e.g., PHWRs), heavy water is the most fitting selection. Options involving concrete are incorrect as moderators. Final Answer Heavy water

Question 11

Engine testing: Morse test applicability  For which engines can the Morse test (cylinder cut-out method for indicated power estimation) be conducted? Choose the correct option.

Accepted Answer

Concept The Morse test estimates indicated power by cutting out one cylinder at a time and measuring changes in brake power. This requires more than one cylinder; it can be applied to either SI or CI engines provided they are multi-cylinder. Final Answer Multi-cylinder engines

Question 12

Typical thermal efficiency of diesel engines (textbook value)  Select the closest approximate overall thermal efficiency commonly quoted for conventional diesel engines. Choose the correct option.

Accepted Answer

Concept Conventional, naturally aspirated diesel engines typically show overall brake thermal efficiency around 25–35%, with practical textbook figures commonly cited near 30%. Large, slow-speed diesels can be higher, but 30% is the standard MCQ benchmark. Final Answer 30%

Question 13

Neutron economy: effect of a reflector in a nuclear power plant  Statement: In nuclear power plants, adding a reflector reduces the fuel requirement because more neutrons are returned to the core to sustain the chain reaction. Decide whether the sta…

Accepted Answer

Concept A reflector surrounding the core scatters and returns leakage neutrons back into the fuel region, improving neutron economy. This allows achieving criticality with less fissile inventory or enhances margin for a given loading. Final Answer True

Question 14

Thorium fuel cycle: production pathway of U-233  How is fissile U-233 obtained in reactor systems? Choose the correct option.

Accepted Answer

Concept Thorium-232 absorbs a neutron → Th-233 → β-decay → Pa-233 → β-decay → U-233 (fissile). Thus, U-233 is bred from thorium under neutron irradiation. Why others are incorrect U-233 is not a naturally abundant basic raw material; U-238 fission does not produce U-233 (U-238 primarily captures to Pu-239 via Np-239). Final Answer Produced when thorium is irradiated by neutrons

Question 15

Improving brake power of a diesel engine (other parameters constant)  Which change will increase brake power output for a given engine configuration? Choose the correct option.

Accepted Answer

Concept Brake power rises with higher trapped air mass (more oxygen) enabling more fuel to burn. Supercharging or turbocharging raises intake pressure, increasing air density and mass flow per cycle. Why others decrease power Lower density or lower pressure reduce air mass. Higher intake temperature lowers density at a given pressure, also reducing mass. Final Answer Increase the pressure of intake air

Question 16

Primary fuel used in nuclear power plants (common fissile)  Identify the principal fissile fuel widely used to sustain the chain reaction in thermal power reactors. Choose the correct option.

Accepted Answer

Concept U-235 is the naturally occurring fissile isotope (≈0.7% in natural uranium) and is the primary fuel in many light-water reactors (enriched). U-238 is fertile (captures to Pu-239), while Pu-239 is fissile but generally bred and used in MOX; Pu-233 is uncommon. Final Answer U-235

Question 17

Effect of coolant temperature on knocking tendency in a petrol (SI) engine  How does increasing the cooling-water temperature influence the knocking tendency in a spark-ignition petrol engine? Choose the correct option.

Accepted Answer

Increases knocking tendency

Question 18

Terminology in SI engines: identify whether “detonation” is also called knocking or pinking.  Statement to evaluate: “The detonation phenomenon is also referred to as engine knocking or pinking.” Choose whether the statement is correct.

Accepted Answer

Concept/Approach In spark-ignition (petrol) engines, detonation refers to the auto-ignition of the end-gas after normal spark-initiated flame starts. The rapid pressure waves produce the metallic pinging sound known as knock or pinking. These terms are widely treated as synonyms in SI engine context. Clarification Pre-ignition is a distinct phenomenon (ignition before the spark due to hot spots). Detonation/knock occurs after the spark when the end-gas auto-ignites. Final Answer Agree.

Question 19

Knock rating reference fuels for spark-ignition engines: choose the correct pair used to define the octane scale.  Context: Knock intensity in SI engines is calibrated using blends of two standard reference fuels. Select the correct pair that forms …

Accepted Answer

Given Octane number quantifies resistance to knock by comparing a fuel to blends of two references. Concept/Approach Iso-octane (2,2,4-trimethylpentane) is assigned 100 octane (high knock resistance). n-Heptane is assigned 0 octane (low knock resistance). Real fuel octane equals the % iso-octane in an iso-octane/n-heptane blend giving the same knock tendency. Why others are wrong Alpha-methyl naphthalene and aniline are not the modern octane references; normal hexane is not used for the octane number scale. Final Answer Normal heptane and iso-octane.

Question 20

Valve positions during compression in a four-stroke petrol engine: evaluate the statement.  Statement: “During the compression stroke the charge is compressed when both the inlet and exhaust valves are closed.” Choose whether the statement is correc…

Accepted Answer

Concept/Approach In the ideal four-stroke SI cycle, once the intake stroke ends, both valves close and the piston compresses the trapped charge. Although real engines may have a small valve overlap near TDC for breathing, the compression phase occurs with valves effectively closed. Final Answer Agree.

IC Engines and Nuclear Power Plants Questions