Question 1

Differential action during cornering State whether the differential allows the left and right drive wheels to rotate at different speeds while turning.

Accepted Answer

Introduction / Context: When a vehicle turns, the outer wheel travels a longer path than the inner wheel. The differential accommodates this by allowing different wheel speeds while transmitting torque. Given Data / Assumptions: Open differential with bevel gears (or limited-slip variants) in a typical axle or transaxle. Tire radii approximately equal; no wheel hop. Concept / Approach: An open differential splits input torque and permits differential motion via spider and side gears. The average speed of the two axle shafts equals the input speed ratio, but each side can rotate faster or slower than the other as needed in a turn. Step-by-Step Solution: Entering a corner: outer wheel path length increases.Differential gears allow outer wheel to rotate faster, inner slower.Traction remains adequate if road friction supports the torque. Verification / Alternative check: Jack up one wheel of a vehicle in neutral: rotating one wheel causes the other to turn in the opposite direction, demonstrating relative motion between sides. Why Other Options Are Wrong: The action is independent of ABS and drivetrain layout; both FWD and RWD (and AWD with differentials) need speed differentiation; it operates at all speeds, not only low speeds. Common Pitfalls: Assuming a differential “sends power to both wheels equally” regardless of traction—an open differential biases torque to the path of least resistance without additional devices (LSD, lockers, brake-based torque vectoring). Final Answer: True

Question 2

Brake system design — tandem master cylinder What is the chief advantage of using a tandem (dual-circuit) master cylinder in modern automobiles?

Accepted Answer

Introduction / Context: Brake system redundancy is a key safety requirement. The tandem master cylinder contains two separate hydraulic circuits within one housing to preserve braking if one circuit fails. Given Data / Assumptions: Front/rear split or diagonal split hydraulic circuits. Pedal input moves primary and secondary pistons in series or tandem. No ABS or booster assumptions are necessary for the basic function. Concept / Approach: A tandem master cylinder has two pistons and isolated fluid chambers. A leak or failure in one circuit still leaves the other available, providing partial braking so the vehicle can be controlled to a stop. This redundancy satisfies regulations and greatly improves safety over single-circuit designs. Step-by-Step Solution: Driver presses pedal → both pistons generate pressure in separate lines.If one circuit loses pressure, the remaining circuit still applies brakes to two wheels (depending on split scheme).Result: reduced but functional braking, enabling safe stopping. Verification / Alternative check: Service tests simulate one-line failure; pedal travel increases but braking remains via the intact circuit. Why Other Options Are Wrong: Vacuum boost is the job of the servo/booster, not the master cylinder. Equal pressure at each wheel is not guaranteed or even desirable—proportioning is handled separately. Pressure boosting is not a master’s function; it converts pedal force to hydraulic pressure. It does not replace ABS or proportioning valves. Common Pitfalls: Air in one circuit affects pedal feel; incorrect pushrod adjustment can block compensation ports, causing drag or poor recovery. Final Answer: enhances safety by serving two independent lines in a divided-line brake circuit

Question 3

Automotive suspension terminology — identifying the damper In vehicle suspension systems, a ‘‘damper’’ is also commonly referred to as:

Accepted Answer

Introduction / Context: The suspension of a passenger car or light commercial vehicle relies on multiple components that each play a distinct role. Learners often confuse the terms spring, damper, torsion bar, and radius rod. This question checks whether you can correctly associate the term ‘‘damper’’ with the commonly used workshop term ‘‘shock absorber’’ and understand its function in ride and handling. Given Data / Assumptions: A conventional suspension assembly with a spring (coil, leaf, air, or torsion bar) and a damper. Normal road vehicle usage, not specialized racing-only hardware. Terminology used in standard automotive service manuals. Concept / Approach: Springs store and release energy due to road inputs and body motion, while dampers dissipate that energy as heat through hydraulic resistance to control oscillations. In most markets, the damper is colloquially called a shock absorber. Other components—torsion bars (a type of spring) and radius rods (location links)—do not perform the energy-dissipation role. Step-by-Step Solution: Identify the function of a damper: dissipate energy and control oscillations.Match the function to the common name used in workshops: shock absorber.Eliminate other components that are springs or locating links. Verification / Alternative check: Exploded diagrams and parts catalogs list ‘‘damper/shock absorber’’ interchangeably; service procedures specify damper leak checks and bump/rebound damping tests, confirming the equivalence of terms. Why Other Options Are Wrong: Torsion bar: a spring element that twists to provide wheel rate. Spring: stores energy but does not damp motion. Radius rod: locates the axle or control arm longitudinally; it does not dissipate oscillatory energy. Common Pitfalls: Assuming the spring alone controls body motion; overlooking that worn dampers increase stopping distance and tyre wear due to poor contact with the road. Final Answer: shock absorber

Question 4

Battery charging basics — correct method for recharging a lead–acid battery A rechargeable automotive (lead–acid) battery should be charged by:

Accepted Answer

Introduction / Context: Understanding how to properly charge a lead–acid battery is essential for safety, service life, and electrical system reliability. This question focuses on the correct principle of recharging rather than common but incorrect workshop myths like ‘‘just add acid’’ to fix a low battery. Given Data / Assumptions: Conventional 12 V automotive lead–acid battery in serviceable condition. Regulated charger or alternator available. Electrolyte level can be adjusted with distilled water, if required, but chemistry is not otherwise altered. Concept / Approach: Charging requires an external DC source of the correct polarity and a voltage slightly above the battery’s open-circuit EMF so that current flows into the battery. Modern chargers and alternators regulate voltage and current to avoid overcharge. Adding acid does not charge a battery; it only changes specific gravity and can damage plates. Reversing polarity risks severe damage and safety hazards. Step-by-Step Solution: Identify the goal: restore charge by forcing current into the battery.Ensure correct polarity: positive to positive, negative to negative.Apply a controlled voltage slightly higher than EMF (e.g., ~14.0–14.4 V for a 12 V battery in cyclic charge).Avoid chemical shortcuts like adding acid; only top up with distilled water to cover plates. Verification / Alternative check: Vehicle alternators regulate around 13.8–14.4 V while the engine runs, demonstrating the principle of charging with a voltage above the battery EMF. Why Other Options Are Wrong: Adding distilled water merely corrects level; no charging occurs. Adding sulphuric acid alters chemistry, accelerates corrosion, and is unsafe. Reversing polarity causes damage and is never used to charge a healthy battery. Common Pitfalls: Confusing specific gravity correction with state-of-charge recovery; using unregulated chargers that overheat batteries; ignoring temperature compensation. Final Answer: applying a DC voltage of correct polarity slightly higher than the battery EMF

Question 5

Engine lubrication — function of an oil control orifice In the cylinder head oil circuit, the oil control orifice primarily:

Accepted Answer

Introduction / Context: Modern engines meter oil to the top end (camshaft, lifters/followers, valve train) using calibrated restrictions. Knowing what an oil control orifice does helps technicians diagnose top-end noise, low-pressure warnings, and oil starvation issues. Given Data / Assumptions: Pressurized lubrication from a positive-displacement oil pump. Fixed orifices or restricted galleries in the cylinder head feed. Full-flow filtration occurs prior to—or in parallel with—cylinder head feeds. Concept / Approach: An orifice is a hydraulic restriction that controls flow rate for a given pressure differential. By limiting flow to the head, system pressure in the main gallery is maintained while ensuring sufficient lubrication of the valve train. Filtration is performed by the oil filter, not the orifice; misting is handled by splash and windage, not by a metering hole; and drains rely on gravity via dedicated return passages rather than being ‘‘accelerated’’ by the orifice. Step-by-Step Solution: Identify the component: a small, precise hole in the feed line or banjo/jet.Recall fluid principle: flow through an orifice depends on pressure drop and area.Relate to engine needs: maintain gallery pressure while supplying adequate top-end oil.Select the option describing pressure/flow regulation to the head. Verification / Alternative check: Service manuals specify ‘‘orifice jet’’ sizes and warn that enlarged jets lower system pressure and increase consumption, which corroborates the metering function. Why Other Options Are Wrong: High-speed return is not an orifice function; oil misting is incidental; impurity removal is the filter’s role. Common Pitfalls: Drilling orifices larger during rebuilds; misdiagnosing low pressure as pump failure when a missing jet is the cause. Final Answer: regulates the pressure and flow of engine oil supplied to the cylinder head mechanism and related passages

Question 6

Automotive coatings — role of pigments in paint In vehicle paint formulations, adding pigment primarily:

Accepted Answer

Introduction / Context: Automotive coatings combine resins, solvents (or water), pigments, and additives to achieve durability and aesthetics. This question checks whether you recognize the primary function of pigments within that system. Given Data / Assumptions: Conventional primer, basecoat, and topcoat layers. Pigments include colour pigments and extenders/fillers. Application by spray with appropriate reducers and hardeners. Concept / Approach: Pigments provide colour (hue), opacity (hiding power), and contribute to film build and surface coverage by filling microscopic surface irregularities. Viscosity is tuned by solvents/reducers and rheology agents. Film hardness primarily depends on resin chemistry and curing (e.g., isocyanate crosslinkers in 2K urethanes), not pigment addition per se. Step-by-Step Solution: Identify the function sought: visual appearance and coverage.Map to pigment roles: colour and opacity, plus filling/hiding.Eliminate process control and curing functions assigned to other ingredients. Verification / Alternative check: Technical data sheets specify pigment volume concentration (PVC) targets for coverage and durability; changing pigment content shifts hiding power and shade without directly setting hardness. Why Other Options Are Wrong: Viscosity control comes from solvents and thinners; hardness from crosslink density and cure—not pigment. Common Pitfalls: Over-thinning to chase hiding; ignoring primer-surfacer’s role in filling deep scratches. Final Answer: provides colour, opacity, and filling (hiding) power to the paint

Question 7

Diesel cycle idealization — mode of heat addition In the idealized Diesel (compression-ignition) engine cycle, the primary heat addition occurs at:

Accepted Answer

Introduction / Context: Ideal cycles help engineers approximate real engine behavior. For Diesel engines, ignition occurs after high compression, and fuel is injected over a finite crank angle. Recognizing the textbook heat-addition model distinguishes Diesel from Otto cycle analysis. Given Data / Assumptions: Air-standard analysis (working fluid is air with constant properties). Compression-ignition with high compression ratio. Heat addition idealized either at constant volume (Otto) or constant pressure (Diesel). Concept / Approach: In the Diesel cycle, heat addition is modeled at constant pressure while the piston continues to move, reflecting continued fuel injection and combustion as the volume expands. In contrast, the Otto cycle assumes instantaneous heat addition at top dead center (constant volume). While real engines exhibit mixed behavior, the Diesel ideal uses the constant-pressure assumption to derive efficiency and performance relations. Step-by-Step Solution: Recall ideal cycle definitions: Otto (constant volume), Diesel (constant pressure).Match Diesel to constant-pressure heat addition segment.Select the correct mode: constant pressure. Verification / Alternative check: Pressure–volume diagrams show the Diesel heat-addition line nearly horizontal compared to the vertical Otto line at TDC, confirming the modeling assumption. Why Other Options Are Wrong: Constant volume corresponds to Otto. Constant temperature resembles idealized external combustion (not applicable here). Adiabatic describes compression and expansion strokes, not heat addition. Common Pitfalls: Equating real DI combustion phasing directly to the ideal model; forgetting that actual pressure can rise—‘‘constant’’ is an approximation for analysis. Final Answer: constant pressure

Question 8

Tyre maintenance — recommended rotation interval For most passenger vehicles under normal service, tyre rotation is generally performed at approximately:

Accepted Answer

Introduction / Context: Tyre rotation equalizes wear among all wheel positions, improving tread life, traction, and noise characteristics. Service intervals vary by vehicle and tyre type, but recognizing a typical interval is valuable for maintenance planning. Given Data / Assumptions: Passenger car on paved roads with normal load. Non-directional radial tyres (or rotation pattern permitted by manufacturer). No staggered fitment or asymmetric tread constraints. Concept / Approach: Many manufacturers recommend rotation around every 5000–8000 km. This interval balances practical service visits (e.g., oil change schedule) with benefits in even wear. Choosing 6000 km falls squarely within this common band and aligns with typical owner’s manual guidance. Step-by-Step Solution: Identify standard maintenance ranges: 5000–8000 km.Select the option nearest the middle of that range: 6000 km.Note that severe service (towing, aggressive alignment) may require shorter intervals. Verification / Alternative check: Inspection-based rotation can also be triggered by tread depth differentials between front and rear; many shops pair rotations with every second engine oil service in kilometer-based markets. Why Other Options Are Wrong: 1000 km is too frequent and impractical. 4000 km may be acceptable but is earlier than common recommendations. 10000 km is sometimes used, but 6000 km better reflects typical median guidance. Common Pitfalls: Ignoring directional tyres (must stay on same side), and staggered sizes (front/rear swap not possible); forgetting to re-torque wheel nuts after rotation. Final Answer: 6000 km

Question 9

Engine lubrication safeguards — oil filter bypass valve An engine's oil filter bypass valve is designed to open when:

Accepted Answer

Introduction / Context: Continuous lubrication is critical to engine survival. To prevent oil starvation, many full-flow filtration systems include a bypass valve that maintains oil flow if the filter media is blocked or the oil is too viscous (e.g., during cold starts). Given Data / Assumptions: Full-flow oil filter located in the main gallery path. Spring-loaded bypass valve set to a differential pressure threshold. Healthy pump and galleries aside from the filter restriction. Concept / Approach: The bypass valve monitors pressure differential across the filter. When delta-P exceeds a preset limit (due to clogging or very viscous oil), the valve opens to route unfiltered oil to the engine, prioritizing flow over filtration to avoid bearing damage. Step-by-Step Solution: Recognize the triggering condition: excessive pressure drop across the filter.Relate scenarios: clogged media or very cold oil.Choose the option describing clogging/over-restriction. Verification / Alternative check: Service bulletins often warn that extended oil-change intervals increase bypass events, which can be inferred from used-oil analysis showing higher particulate levels. Why Other Options Are Wrong: Cold engines may or may not open the bypass; temperature alone is not the control—pressure drop is. Overheating and high RPM are not direct triggers. Common Pitfalls: Assuming bypass means failure; it is protective. Reusing collapsed filters can block flow entirely. Final Answer: the oil filter becomes clogged or the pressure drop across it is excessive

Question 10

Wheel alignment — identifying camber When the top of a road wheel is tilted outward (away from the vehicle), the condition is called:

Accepted Answer

Introduction / Context: Wheel alignment geometry—camber, caster, and toe—affects tyre wear, steering feel, and straight-line stability. Camber specifically refers to inward or outward tilt of the wheel relative to vertical when viewed from the front or rear of the vehicle. Given Data / Assumptions: Front suspension of a passenger car with adjustable camber. Observation is made from ahead or behind the vehicle. Small angles measured in degrees or minutes. Concept / Approach: Positive camber means the top of the wheel leans outward. Negative camber means it leans inward at the top. Caster, by contrast, is the fore–aft tilt of the steering axis (kingpin/strut) seen from the side, and is not described by inward/outward top tilt when viewed from the front. Step-by-Step Solution: Identify the described tilt: top of wheel outward.Match to definition: positive camber.Discard caster options as they refer to longitudinal tilt of steering axis. Verification / Alternative check: Alignment specifications commonly label camber with positive values when tops lean outward; negative values when tops lean inward. Visual inspection and camber gauge readings confirm this nomenclature. Why Other Options Are Wrong: Negative camber is the opposite direction. Positive/negative caster concerns steering axis angle in the side view, not wheel tilt in the front view. Common Pitfalls: Confusing camber with toe; overlooking that some performance setups intentionally run slight negative camber to improve cornering grip. Final Answer: positive camber

Question 11

Wheel alignment — definition of caster angle Caster refers to the:

Accepted Answer

Introduction / Context: Caster is one of the three fundamental wheel alignment parameters (the others are camber and toe). While camber concerns inward/outward wheel tilt, caster is about the tilt of the steering axis when viewed from the side of the vehicle. Given Data / Assumptions: Steering axis may be a kingpin on SLA suspensions or a MacPherson strut axis. Angle is measured relative to vertical in the longitudinal plane. Sign convention: top of axis rearward = positive caster; forward = negative caster. Concept / Approach: By definition, caster is the fore–aft inclination of the steering axis. It can be either forward (negative) or backward (positive). Positive caster enhances straight-line stability and self-centering, while negative caster reduces those effects. Therefore, a correct definition must allow for both directions rather than only one. Step-by-Step Solution: Identify parameter: steering axis tilt in side view.Recognize two possible senses: backward (positive) and forward (negative).Choose the option acknowledging both possibilities. Verification / Alternative check: Alignment specifications will list caster as a positive or negative value; vehicles are commonly set with small positive caster for stability. Why Other Options Are Wrong: Options a and b give only one direction, not the general definition. ‘‘None of these’’ is incorrect because option c fully captures the concept. Common Pitfalls: Confusing caster with camber (front-view tilt) or toe (plan-view convergence). Misinterpreting sign conventions between manufacturers. Final Answer: either ‘‘a’’ or ‘‘b’’ (the steering axis tilt can be forward or backward, corresponding to negative or positive caster)

Question 12

Automotive glazing — behavior of laminated glass on impact When laminated safety glass cracks in service, it typically:

Accepted Answer

Introduction / Context: Vehicle glazing uses different glass types for safety: tempered (toughened) glass and laminated glass. Understanding how laminated glass fails is important for occupant protection and for first responders who must manage broken glass safely. Given Data / Assumptions: Laminated glass comprises two glass sheets bonded by a polyvinyl butyral (PVB) or similar interlayer. Used commonly for windshields; side and rear windows may be tempered. Impact or crack growth is considered, not explosive shattering from extreme conditions. Concept / Approach: Laminated glass is designed so that when either ply fractures, the interlayer holds fragments together. This prevents ejection of shards, maintains a barrier against ejection of occupants, and reduces laceration risk. Tempered glass, by contrast, fractures into many small granular pieces that usually fall away from the opening. Step-by-Step Solution: Identify the construction: glass–interlayer–glass sandwich.Recognize the failure mode: cracking with fragments adherent to interlayer.Select the option describing fragment retention by the sandwiched layer. Verification / Alternative check: Crash tests and manufacturer literature show windshield ‘‘spider web’’ cracking patterns while remaining largely intact due to the PVB interlayer adhesion. Why Other Options Are Wrong: Sharp-edged fragments typically describe annealed glass. Granular pieces describe tempered glass. Crystal-like shards are not the intended failure mode of laminated safety glass. Common Pitfalls: Assuming all vehicle glass behaves the same; in many regions only the windshield must be laminated, while other windows are tempered. Final Answer: has its sandwiched interlayer trap and retain the glass fragments

Question 13

Engine Intake Systems — Purpose of the Resonator In modern spark-ignition engines, what is the primary function of the intake resonator installed in the air-intake ducting?

Accepted Answer

Introduction / Context: An intake resonator is a common plastic chamber connected to the air cleaner or intake ducting on passenger cars. Students often confuse it with performance devices like tuned runners. This question tests understanding of what the resonator mainly does in a production vehicle’s intake system. Given Data / Assumptions: Road car with a conventional air filter box and ducting. No active valves or variable-geometry runners are part of the resonator itself. Goal is to identify the principal role under normal driving conditions. Concept / Approach: Air rushing past throttle plates and intake valves creates pressure pulsations. These pressure waves radiate as sound through the intake tract. A resonator is a side branch cavity (often Helmholtz-type) tuned to the dominant noise frequencies. By destructive interference, it attenuates objectionable intake roar, boom, and whistle without adding much restriction to airflow. Step-by-Step Solution: Recognize that a resonator is a passive acoustic device, not a flow controller.Its geometry (cavity volume and neck size) is chosen to target specific frequency bands produced by the engine.Therefore the best description of its job is to reduce intake air noise for NVH improvement. Verification / Alternative check: Vehicle NVH development routinely swaps resonator volumes and necks during testing to meet interior noise targets while maintaining pressure drop within limits. That confirms the acoustic, not metering, role. Why Other Options Are Wrong: Regulates intake flow rate: flow is set by throttle and engine demand, not the resonator.Enhances intake efficiency: any volumetric-efficiency gains are incidental; tuning runners do that, not the resonator.Regulates intake air temperature: that is a job for air path routing or active shutters, not the resonator.Dust separation: the air filter handles particulates. Common Pitfalls: Assuming “resonator” implies power increase; in production cars it is primarily an NVH component. Final Answer: reduces the intake air noise

Question 14

Brake Systems — Function of the Proportioning Control Valve (PCV) In a hydraulic service-brake system, what does the proportioning control valve do when line pressure exceeds a calibrated threshold?

Accepted Answer

Introduction / Context: Under heavy braking, weight shifts forward, greatly increasing the front axle’s normal load while unloading the rear axle. Brake system designers use proportioning to prevent premature rear-wheel lock, which can cause instability. This question focuses on the specific action of the proportioning control valve (PCV). Given Data / Assumptions: Typical passenger car with front-disc/rear-drum or rear-disc brakes. Hydraulic split with a mechanical or pressure-sensitive PCV. High pedal effort where line pressure rises above a set “knee” point. Concept / Approach: A PCV is a pressure-sensitive device that reduces the rate of pressure rise to the rear circuit after a threshold. Below the knee, front and rear pressures rise nearly 1:1. Above it, the rear circuit sees a reduced slope so that rear brakes develop less torque than a simple 1:1 system would, matching available tire–road friction at the rear. Step-by-Step Solution: Identify vehicle dynamics: forward load transfer makes rear tires easier to lock.Control objective: limit rear pressure at high deceleration.Device action: above threshold, the PCV “proportions” so rear pressure < front pressure.Therefore select the option describing reduced rear pressure at higher line pressures. Verification / Alternative check: Brake balance charts show a kinked rear line beyond the knee pressure; lab tests confirm delayed rear lock compared to an un-proportioned system. Why Other Options Are Wrong: Equal pressure at all times: contradicts proportioning function.Generic “reduce pressure near lockup”: that is the job of ABS modulators, not a fixed PCV.Less pressure to front: opposite of safe biasing under weight transfer.Bypass to reservoir: not a PCV function. Common Pitfalls: Confusing the PCV with ABS; PCV is passive and pressure-sensitive, ABS is active and wheel-speed-based. Final Answer: cause less fluid pressure to act on the rear brakes than the front brakes when the fluid pressure exceeds a predetermined level

Question 15

Spark-Ignition vs. Diesel Engines — Core Differences Which statement best summarizes a fundamental difference of the Diesel (compression-ignition) engine compared with the spark-ignition engine?

Accepted Answer

Introduction / Context: Internal-combustion engines are broadly divided into spark-ignition (SI) and compression-ignition (CI or Diesel). Understanding the thermodynamic and hardware differences is foundational for automotive engineering and service diagnostics. Given Data / Assumptions: Conventional four-stroke SI and DI Diesel architectures. Modern fuels used (petrol for SI; diesel for CI). Generalized description without brand-specific exceptions. Concept / Approach: Diesels operate by compressing air to a high pressure and temperature. Near the end of compression, fuel is injected; atomized droplets mix with the hot air and ignite spontaneously. SI engines instead pre-mix air and fuel upstream and ignite the mixture via a timed electric spark. Therefore, several interrelated statements about air-only compression, autoignition due to temperature, and late fuel injection are simultaneously true for Diesels. Step-by-Step Solution: Check statement 1: Diesels compress air only → Correct.Check statement 2: Ignition source is hot compressed air → Correct.Check statement 3: Fuel is injected near T.D.C. on the compression stroke → Correct for typical DI Diesels.Thus all statements are valid → choose “all of the above”. Verification / Alternative check: Review of CI cycle shows high compression ratio (often 15–25) raising temperature above fuel autoignition threshold, with injection timing in degrees BTDC to ATDC around T.D.C. Why Other Options Are Wrong: Any single statement alone is incomplete; together they define the Diesel principle.“None of the above” contradicts established engine operation. Common Pitfalls: Assuming Diesels always use pre-chambers; many modern units are direct-injection. Final Answer: all of the above

Question 16

Engine Power Accounting If the indicated power (I.P.) and the frictional power (F.P.) of an engine are known, which quantity can be directly computed?

Accepted Answer

Introduction / Context: Engine performance analysis separates the power produced inside the cylinder from what is actually delivered at the crankshaft. Understanding the simple relationship among indicated power, brake power, and frictional power is vital for test-cell calculations and coursework problems. Given Data / Assumptions: I.P. = power developed by gas pressure on the piston. F.P. = mechanical losses due to friction, pumping, and auxiliaries. All values at the same operating point (speed and load). Concept / Approach: The power balance is linear: brake power is what remains after mechanical losses are subtracted from the gross indicated power. This is often written as B.P. = I.P. − F.P. The relationship underpins definitions of mechanical efficiency and is used when deriving other performance metrics. Step-by-Step Solution: Start with the power balance: B.P. + F.P. = I.P.Rearrange: B.P. = I.P. − F.P.Since I.P. and F.P. are known, compute B.P. directly by subtraction. Verification / Alternative check: Mechanical efficiency can be checked as eta_m = B.P. / I.P. If eta_m is within a plausible range (say 0.75–0.9 for many engines), the calculation is consistent. Why Other Options Are Wrong: Compression ratio: depends on geometry, not power figures.Specific air consumption and mean effective pressure: require mass-flow or pressure–volume data, not just I.P. and F.P.Volumetric efficiency: needs airflow and displacement information. Common Pitfalls: Mixing units or using kilowatts and horsepower inconsistently. Final Answer: brake power

Question 17

Engine Lubrication — Typical Oil Flow Path Identify the correct order of components in the lubrication circuit of a conventional automobile engine.

Accepted Answer

Introduction / Context: Pressure lubrication keeps bearings, pistons, and valve gear supplied with filtered oil. Knowing the order of elements in the oil circuit is essential for troubleshooting low pressure, contaminated oil, or relief-valve issues. Given Data / Assumptions: Wet-sump engine using a gear/rotor pump. Full-flow oil filter in the main gallery. Pressure relief valve integrated with or near the pump. Concept / Approach: The pickup (strainer) in the sump prevents large debris from entering the pump. The pump raises pressure and, if pressure is excessive (cold oil/high rpm), the relief valve bypasses flow to protect the system. Pressurized oil is then filtered and distributed through galleries first to the crankshaft and block, then up to the head for valvetrain lubrication, finally draining back by gravity to the pan. Step-by-Step Solution: Sump → Strainer: pre-screening.Pump: creates pressure.Relief valve: limits maximum pressure.Filter: removes fine contaminants.Galleries in block then head: supply bearings and valvetrain.Oil drains back to the pan. Verification / Alternative check: Service schematics of most engines show this flow; some designs combine the relief valve with the filter head, but the functional order remains. Why Other Options Are Wrong: Starting with the pump before the strainer risks pump damage.Routing to head before block inverts typical gallery priority.Random insertions (e.g., oil pan mid-pressure path) are incorrect. Common Pitfalls: Confusing bypass filter paths (partial-flow) with full-flow systems used in most modern engines. Final Answer: oil strainer → oil pump → relief valve → oil filter → cylinder block → cylinder head → oil pan

Question 18

Engine Efficiencies — Mechanical Efficiency of an I.C. Engine Given indicated power (I.P.), brake power (B.P.) and frictional power (F.P.), which expression defines mechanical efficiency ηm?

Accepted Answer

Introduction / Context: Mechanical efficiency expresses how effectively an engine converts indicated (in-cylinder) power to useful crankshaft power. It quantifies the fraction of power that survives mechanical and pumping losses. Given Data / Assumptions: B.P. is measured at the dynamometer shaft. I.P. is deduced from indicator diagrams or cylinder pressure analysis. F.P. represents all internal mechanical losses. Concept / Approach: The power balance is I.P. = B.P. + F.P. Mechanical efficiency is defined as useful output (B.P.) divided by the power developed inside the cylinder (I.P.). Hence, eta_m = B.P. / I.P. This ratio is always less than 1 and typically ranges from about 0.75 to 0.9 for many automotive engines depending on speed, load, and design. Step-by-Step Solution: Start with I.P. = B.P. + F.P.Define eta_m = B.P. / I.P.Therefore, select B.P/I.P. as the correct expression. Verification / Alternative check: Check dimensional consistency: both numerator and denominator are powers → dimensionless ratio 0–1, as expected. Why Other Options Are Wrong: I.P./B.P. is the inverse; it would exceed 1.B.P./F.P. or F.P./B.P. do not define efficiency; they are loss ratios.I.P./(B.P.+F.P.) reduces to 1, which is meaningless. Common Pitfalls: Confusing mechanical efficiency with overall efficiency, which also includes thermal efficiency and fuel energy content. Final Answer: B.P/I.P.

Question 19

Typical Compression Ratio of a Petrol (SI) Engine Select the compression ratio that most closely represents a conventional petrol engine.

Accepted Answer

Introduction / Context: Compression ratio strongly influences thermal efficiency, knock tendency, and combustion quality. While modern engines may vary, a baseline value is helpful for quick estimates and comparative questions. Given Data / Assumptions: Conventional, naturally aspirated petrol engines without extreme high-efficiency or forced-induction tuning. Historical textbook ranges (older designs 7:1 to 9:1; many modern engines 9:1 to 12:1 with knock mitigation). Concept / Approach: Petrol engines are limited by knock; thus their geometric compression ratios are moderate compared with Diesels. A representative book value used in many basic problems is about 8:1. Diesels, by contrast, commonly use 15:1 to 25:1 to ensure autoignition of injected fuel. Step-by-Step Solution: Identify engine type: spark-ignition petrol.Recall typical range: approximately 7:1 to 10:1 in many classical references.Choose the nearest listed value: 8:1. Verification / Alternative check: Contemporary direct-injection engines may use 10–12:1; the question asks for a “nearly” value, for which 8:1 is the standard textbook approximation. Why Other Options Are Wrong: 4:1 is too low; would yield very poor efficiency.15:1 and 20:1 are Diesel territory.30:1 is unrealistic for light-duty reciprocating engines. Common Pitfalls: Assuming turbocharged or Atkinson-cycle numbers; the question targets a basic, conventional SI engine. Final Answer: 8:1

Question 20

Front Suspension Layouts — Key Feature of MacPherson Strut What is considered the main feature/advantage of the MacPherson strut suspension used widely in passenger cars?

Accepted Answer

Introduction / Context: MacPherson struts are ubiquitous on the front axle of compact and midsize cars. The arrangement uses a shock absorber that doubles as the upper suspension link, with a single lower arm for lateral location. This question probes recognition of the layout’s primary advantage in typical automotive design trade-offs. Given Data / Assumptions: Front-engine, front-wheel-drive packaging is common. Comparisons are against double-wishbone or multi-link systems. Road car priorities include cost, mass, packaging, and adequate handling. Concept / Approach: By eliminating the upper control arm and using the strut as a load-bearing member, MacPherson layouts reduce part count and mass at the wheel. Lower unsprung mass improves ride over small inputs and helps tire contact. The layout is also compact laterally, freeing engine bay space, though it does require vertical tower height. Simplicity and lower mass are central reasons for its widespread adoption. Step-by-Step Solution: List known benefits: fewer links, simpler knuckle, reduced cost and mass.Pick the option that best captures a core advantage: lighter unsprung mass vs. double-wishbone.Therefore, choose the statement about reduced unsprung mass. Verification / Alternative check: OEM platform comparisons commonly cite lower component count and mass as benefits, with adequate kinematics for most applications. Why Other Options Are Wrong: Vertical size more compact: MacPherson typically needs more vertical height (strut towers).Forces supported only by arms: lateral/longitudinal loads are shared; the strut itself carries side loads through the top mount.More complicated design: it is simpler, not more complex.Eliminates springs: the spring is integral on the strut; it is not eliminated. Common Pitfalls: Confusing lateral packaging compactness with vertical packaging (it is tall but narrow). Final Answer: the unsprung mass is lighter than many double-wishbone layouts

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