Question 1

Engine temperature indication in vehicles The standard temperature gauge on a car dashboard typically measures the temperature of the:

Accepted Answer

Introduction / Context: Drivers rely on the temperature gauge to monitor engine thermal state. Understanding what is actually being measured helps interpret readings and diagnose overheating or thermostat issues. Given Data / Assumptions: Typical production car with a coolant temperature sensor (CTS). Closed-loop liquid cooling system with thermostat and radiator. Gauge may be analog or digital, driven by ECU or direct sender. Concept / Approach: The sensor is located in a coolant passage (cylinder head, thermostat housing, or block water jacket). It measures coolant (jacket water) temperature, which correlates with engine metal temperatures but is not identical to piston or cylinder wall surface temperatures. Some vehicles also provide oil temperature gauges, but the default gauge is for coolant. Step-by-Step Solution: Identify standard sender location: coolant jacket.Recognize gauge label often marked 'C' to 'H' or degrees Celsius.Select 'jacket cooling water' as the parameter measured. Verification / Alternative check: Service manuals show the ECT (engine coolant temperature) sensor schematic feeding the ECU and/or the cluster gauge, confirming the measured medium is coolant. Why Other Options Are Wrong: Piston or cylinder temperatures are not directly monitored on standard dashboards; oil temperature is a separate gauge on performance models, not the default. Common Pitfalls: Assuming a centered needle always equals 90°C; many clusters damp the display. Ignoring that a failed thermostat or low coolant can mislead readings. Final Answer: jacket cooling water

Question 2

Purpose of the exhaust muffler in automotive systems The principal function of an exhaust muffler (silencer) is the:

Accepted Answer

Introduction / Context: The exhaust system handles hot, high-velocity gases and significant acoustic energy from engine firing pulses. The muffler is a key component for meeting noise regulations and customer comfort expectations. Given Data / Assumptions: Conventional road vehicle with catalytic converter and mufflers. Engine firing pulses generate pressure waves across a wide frequency band. Muffler volume, chambers, and perforated tubes are acoustically tuned. Concept / Approach: A muffler reduces sound by destructive interference, expansion chambers, absorption materials, and tuned resonators (e.g., Helmholtz). It is not the device for NOx reduction (that is the catalytic converter with appropriate chemistry) and does not significantly change gas volume; temperature drop reduces volume somewhat naturally downstream, but that is not the design goal. Exhaust efficiency (backpressure) is balanced against noise reduction but optimisation of flow is a secondary constraint, not the primary function. Step-by-Step Solution: Identify the primary design objective: lower emitted noise.Recognize methods: reflection, absorption, and resonance cancellation.Choose the option explicitly stating noise reduction. Verification / Alternative check: Regulatory tests (pass-by noise) focus on sound levels; manufacturers often employ multiple mufflers and resonators to meet targets while managing backpressure. Why Other Options Are Wrong: Optimising exhaust efficiency relates to pipe sizing and catalyst/DPF layout; NOx reduction is catalytic; reducing gas volume is not a purposeful function of the muffler. Common Pitfalls: Equating loudness solely with power; removing mufflers increases noise and may reduce torque due to loss of tuned scavenging. Final Answer: reduction of exhaust noise

Question 3

Fuel Properties in Spark-Ignition Engines In automotive fuels for petrol (gasoline) engines, the ease with which the liquid fuel changes into vapour under normal conditions is termed what?

Accepted Answer

Introduction / Context: For spark-ignition (petrol) engines, the fuel must readily form a combustible air–fuel mixture. The property that indicates how easily the liquid turns into vapour is crucial for cold starting, throttle response, and drivability. This question asks you to identify the correct term for that property. Given Data / Assumptions: Engine type: petrol (gasoline) spark-ignition. Ambient conditions typical of vehicle operation. We are comparing standard fuel-property terms used in automotive engineering. Concept / Approach: Volatility describes a liquid’s tendency to evaporate. Petrol with appropriate volatility will vaporize adequately in the intake manifold and ports, assisting mixture preparation. Too low a volatility causes poor cold start and hesitation; too high a volatility can cause vapour lock and excessive evaporative emissions. Other listed terms (octane, cetane) measure entirely different fuel behaviors (anti-knock and ignition quality, respectively) rather than ease of vaporization. Step-by-Step Solution: Identify the needed property: ease of vaporization → volatility.Check alternatives: octane relates to knock resistance; cetane to autoignition quality in diesel; oxidation is chemical reaction with oxygen, not a volatility metric.Therefore, choose the option that directly describes evaporation tendency: volatility. Verification / Alternative check: Fuel datasheets report distillation curves (e.g., ASTM D86) and Reid vapour pressure. These are volatility indicators used by refiners to tune seasonal fuel blends. Why Other Options Are Wrong: Oxidation: relates to long-term stability and gum formation, not instant vaporization.Octane number: measures anti-knock in SI engines; unrelated to evaporation ease.Cetane number: measures diesel ignition quality; irrelevant for petrol.Vapour lock index: not a standard single-property name; vapour lock is a symptom influenced by volatility. Common Pitfalls: Confusing octane with “overall fuel quality”; it does not indicate starting or evaporation behavior.Assuming higher volatility is always better; excessively high volatility can cause vapour lock in hot conditions. Final Answer: volatility

Question 4

Autoignition (Self-Ignition) Temperature Comparison For typical automotive fuels, how does the self ignition temperature of diesel fuel compare with that of petrol (gasoline)?

Accepted Answer

Introduction / Context: Compression-ignition (diesel) engines rely on the fuel autoigniting in hot compressed air, so the self ignition temperature is critical. Spark-ignition (petrol) engines avoid uncontrolled autoignition (knock). Knowing the relative autoignition temperatures explains why diesels use much higher compression ratios than petrol engines. Given Data / Assumptions: Typical commercial diesel and petrol formulations. Self ignition temperature refers to the temperature at which fuel vapour ignites without an external spark under specified conditions. Pressure and mixture effects exist, but we compare general typical values. Concept / Approach: Diesel fuel has a lower autoignition temperature (around the low 200s °C) compared with petrol, which often requires roughly 280–450 °C depending on test method. A lower autoignition temperature facilitates ignition in diesel engines when air is heated by compression. Petrol’s relatively higher self ignition temperature helps prevent spontaneous combustion in SI engines until a spark occurs. Step-by-Step Solution: Recall typical ranges: diesel ≈ 210–260 °C; petrol ≈ 280–450 °C.Compare: diesel threshold is lower than petrol’s.Conclude: diesel has lower self ignition temperature than petrol. Verification / Alternative check: Engine design corroborates this: diesels depend on compression heating alone; petrol engines need a spark and use lower compression ratios to avoid knock. Why Other Options Are Wrong: Higher/same: contradicts well-documented property ranges.Depends on fuel quality: though formulation shifts values slightly, the general ordering (diesel lower) holds.Cannot be compared: they are routinely compared in engineering data. Common Pitfalls: Confusing octane (anti-knock) with autoignition temperature; they are related phenomena but different measures. Final Answer: lower

Question 5

Engine Reconditioning Practice What is the name of the finishing process that imparts a fine cross-hatch pattern to cylinder bore surfaces during reconditioning?

Accepted Answer

Introduction / Context: Engine rebuilds often require restoring cylinder surface texture to promote proper ring seating and controlled lubrication. The characteristic cross-hatch pattern you see on fresh cylinder walls is not accidental; it is produced intentionally by a specific finishing operation. Given Data / Assumptions: Cylinder bores need a plateaued, cross-hatched surface. Goal is to optimize oil retention, ring seating, and wear life. We are choosing among common metalworking processes. Concept / Approach: Honing uses abrasive stones moved in a combined rotary and reciprocating motion to create a shallow-angle cross-hatch. This texture holds a thin oil film, reduces scuffing, and provides initial asperity removal during break-in. Boring enlarges/true-ups the bore but leaves a different surface; honing typically follows boring to achieve final finish and geometry. Step-by-Step Solution: Identify desired pattern: cross-hatch at controlled angle (commonly 30–45 degrees).Match the process: only honing produces this patterned finish as a primary outcome.Therefore, select honing. Verification / Alternative check: Workshop manuals specify honing after boring/reaming to achieve proper Ra/Rz and cross-hatch angles for ring bedding. Why Other Options Are Wrong: Porous plating: a coating process; not a finishing texture operation.Boring: sizing operation, not the final texturing step.Shot peening: induces compressive stress on surfaces like springs/gears; not used inside cylinder bores for cross-hatching.Lapping: produces very smooth surfaces; does not create cross-hatch oil-retentive pattern. Common Pitfalls: Assuming boring alone is sufficient; without honing, ring seating and oil control suffer. Final Answer: honing

Question 6

Wheel Alignment Terminology — Positive Caster In steering geometry, caster is called positive when the top of the steering axis (kingpin or virtual kingpin line) is inclined toward which direction?

Accepted Answer

Introduction / Context: Caster is one of the primary wheel alignment angles (along with camber and toe). Understanding positive versus negative caster is essential for diagnosing steering return, straight-line stability, and steering effort characteristics. Given Data / Assumptions: Front-wheel steering with a defined steering axis (kingpin or steering knuckle pivot line). Vehicle stationary reference axes: front–rear and left–right. Small angles typical of road vehicles (a few degrees). Concept / Approach: Positive caster means the steering axis tilts rearward at the top (like a shopping cart caster trailing behind its pivot). This geometry promotes self-centering and directional stability because the contact patch trails the steering axis projection on the ground, generating a restoring moment when the wheels are turned. Step-by-Step Solution: Visualize the steering axis in side view.Tilt direction check: top toward rear → positive caster.Therefore, select “rear of the vehicle”. Verification / Alternative check: Most modern cars use positive caster to enhance straight-line stability; specifications list positive degrees of caster. Why Other Options Are Wrong: Front of the vehicle: defines negative caster.Left/right: describes camber/toe asymmetry or SAI differences, not caster direction.Vertical: zero caster, offering little self-centering. Common Pitfalls: Confusing caster with camber (front view tilt of the wheel). Final Answer: rear of the vehicle

Question 7

Cooling Systems — Raising the Boiling Point in Automotive Radiators Which component of a car’s radiator system primarily allows the coolant to operate at a higher boiling point during normal service?

Accepted Answer

Introduction / Context: Engine cooling systems run under pressure to raise the boiling point of the coolant, improving heat transfer and preventing boil-over. Identifying the part responsible for pressurizing the system is a core maintenance and design concept. Given Data / Assumptions: Closed-loop liquid cooling with a radiator, hoses, and pressure cap. Coolant is water or water–glycol blend. Normal passenger car application. Concept / Approach: Boiling point increases with pressure. The radiator pressure cap includes a spring-loaded valve calibrated to maintain a specific system pressure, typically between 0.7 and 1.4 bar above ambient. By holding pressure, the cap elevates the coolant’s boiling point, allowing higher operating temperatures without phase change. It also contains a vacuum (return) valve to admit coolant back from the reservoir during cooldown. Step-by-Step Solution: Identify function needed: raise boiling point by increasing pressure.Recognize the device that sets system pressure: the pressure cap.Therefore, choose “pressure cap”. Verification / Alternative check: Service manuals specify cap ratings (e.g., 1.1 bar). Raising cap rating increases boiling point by several degrees Celsius. Why Other Options Are Wrong: Drain plug: only for draining; no pressure function.Water jacket: provides flow passages but does not set pressure.Vacuum valve: part of the cap, but the pressure function is the key for boiling point.Thermostat: regulates flow vs. temperature, not pressure. Common Pitfalls: Assuming thermostat affects boiling point; it affects warm-up and flow path, not system pressure. Final Answer: pressure cap

Question 8

Automotive Instruments — What Does a Tachometer Measure? In standard passenger cars, the tachometer displays which operating parameter?

Accepted Answer

Introduction / Context: The instrument cluster provides the driver with essential information. While the speedometer shows road speed, the tachometer serves a different purpose that helps with shifting, diagnosing engine behavior, and avoiding over-revving. Given Data / Assumptions: Conventional dashboard with speedometer, tachometer, and other gauges. Engine is spark- or compression-ignition with a rotating crankshaft. Concept / Approach: A tachometer measures rotational speed, typically the crankshaft’s revolutions per minute (r.p.m.). It informs the driver about engine load relative to speed and gearing. On manual transmissions, it guides shift points; on automatics, it aids diagnostics. Modern electronic tachometers read signals from ignition systems or crank sensors. Step-by-Step Solution: Identify variable displayed: rotational speed of engine crankshaft.Unit: revolutions per minute.Match to option: “engine r.p.m.” Verification / Alternative check: Owner’s manuals and instrument legends label tachometers with ×1000 r/min scales. Why Other Options Are Wrong: Speed: shown by speedometer (km/h or mph).Distance: shown by odometer/trip meter.Fuel consumption: requires separate computer/gauge.Oil pressure: separate gauge or warning lamp. Common Pitfalls: Misinterpreting tachometer redline; sustained operation above redline risks engine damage. Final Answer: engine r.p.m.

Question 9

Cylinder Finish and Tribology Honing leaves a cross-hatch on cylinder sleeves. Which performance characteristic is most directly enhanced by this surface texture?

Accepted Answer

Introduction / Context: The micro-texture of cylinder walls strongly influences ring sealing, friction, and wear. The cross-hatch left by honing provides controlled valleys and plateaus that interact with engine oil and piston rings during operation and break-in. Given Data / Assumptions: Cylinder wall is properly honed with a prescribed cross-hatch angle. Correct ring materials and tension are used. Normal lubrication and oil quality are assumed. Concept / Approach: The cross-hatch increases oil retention by creating microscopic valleys that act as reservoirs, ensuring continuous lubrication between the ring face and liner. This mitigates scuffing and controls friction. While improved lubrication reduces wear over time, the most direct and immediate benefit of the texture is enhanced lubrication performance and oil control, which then indirectly supports wear resistance and ring seating. Step-by-Step Solution: Identify function of cross-hatch: retain oil in valleys while providing plateaus for load support.Primary effect: stable oil film → better lubrication.Secondary outcome: reduced wear and controlled friction after proper break-in.Therefore, choose “lubrication performance”. Verification / Alternative check: Surface metrology (Ra, Rz, Rpk/Rvk) targets for plateau honing are specified to balance oil retention and load-bearing plateaus, confirming lubrication as the main goal. Why Other Options Are Wrong: Cooling efficiency: governed by coolant flow and material conductivity, not wall microtexture.Resistance to wear: improves indirectly, but it is a consequence of better lubrication rather than the direct purpose.Combustion efficiency: has minimal direct relation to cylinder surface finish. Common Pitfalls: Assuming rougher is better; excessive roughness increases oil consumption and wear. Final Answer: lubrication performance

Question 10

Emissions and Crankcase Ventilation What is the primary function of the positive crankcase ventilation (PCV) system on a road vehicle?

Accepted Answer

Introduction / Context: Blow-by gases are combustion products that leak past piston rings into the crankcase. If not managed, they contaminate oil, increase pressure, and pollute the atmosphere. The positive crankcase ventilation (PCV) system is a core emissions and engine health feature in modern vehicles. Given Data / Assumptions: Spark-ignition engine with a closed PCV system. Intake manifold vacuum available at idle and part load. PCV valve or metering orifice controls flow. Concept / Approach: The PCV system routes crankcase vapours (unburned hydrocarbons, moisture, blow-by gases) back to the intake stream to be re-burned in the cylinders. This reduces emissions, prevents sludge formation, and maintains crankcase pressure near ambient or slightly negative, improving seal life. A PCV valve meters flow and prevents backfire from igniting vapours in the crankcase. Step-by-Step Solution: Identify problem: blow-by accumulates in crankcase.Required action: remove and reburn these gases safely.Mechanism: PCV routes gases to intake under vacuum control.Conclusion: option describing return to intake is correct. Verification / Alternative check: Emission regulations require closed crankcase ventilation; service manuals show PCV plumbing from rocker cover to intake. Why Other Options Are Wrong: Mixing fuel with air or inducing swirl is the carburetor/throttle-body/port design’s role, not PCV.Routing to exhaust manifold is unsafe and nonstandard.Pressurizing the crankcase is harmful; slight vacuum is preferred. Common Pitfalls: Blocked PCV valves cause oil leaks, sludge, and increased emissions. Final Answer: returns blow-by gases from the crankcase to the intake system

Question 11

Exhaust Emissions Testing — Idle CO Measurement Conditions Under which test condition should the idle carbon monoxide (CO) percentage be measured for a vehicle?

Accepted Answer

Introduction / Context: Idle CO measurement is a basic emissions diagnostic for spark-ignition engines. To obtain repeatable and comparable results, standardized test conditions are used to minimize load variations on the engine during the measurement. Given Data / Assumptions: Engine at normal operating temperature. Vehicle idling at specified rpm (often 600–900 rpm as per manufacturer). No additional vehicle loads unless specified by the test protocol. Concept / Approach: Turning on electrical consumers (headlights, blower, rear defogger) raises alternator load, which can alter idle rpm and mixture control, skewing CO readings. Therefore, the usual requirement is to perform the idle CO test with accessories off to reflect baseline engine-out emissions rather than accessory load response. Step-by-Step Solution: Stabilize engine at operating temperature.Ensure no auxiliary loads: lights and accessories off.Insert probe into tailpipe; measure CO at specified idle speed.Record value as idle CO percentage. Verification / Alternative check: Inspection procedures in many regions stipulate accessories off during idle emissions checks, sometimes with the radiator fan cycling allowed if automatic. Why Other Options Are Wrong: Switching on loads increases alternator drag and can change mixture control, compromising standardization.Headlights-only or blower-only options still represent added load and are not the default baseline condition. Common Pitfalls: Measuring immediately after cold start; a warmed-up engine is needed for consistent readings. Final Answer: Headlights and all other electrical devices switched off

Question 12

Suspension Choice — When Is a Rigid (Solid Axle) Suspension Beneficial? Identify the situation in which using a rigid suspension (solid axle) is most advantageous for a vehicle chassis.

Accepted Answer

Introduction / Context: Suspension architectures trade off comfort, handling, load capacity, durability, and cost. Rigid (solid) axles connect left and right wheels with a solid beam, common in trucks and off-road vehicles. Understanding when this layout is preferred helps in vehicle design choices. Given Data / Assumptions: Comparison is between rigid axles and independent suspensions. Vehicle may experience large payload variation and operate on rough terrain. Priorities include robustness, articulation, and axle location under heavy loads. Concept / Approach: Rigid axles excel in durability, load-carrying capacity, and maintaining axle geometry under heavy loads. Leaf springs or multi-link setups can provide long suspension travel and strong lateral/longitudinal location. Although unsprung mass is higher and high-speed ride/handling can be inferior to independent setups, solid axles are advantageous where load changes are large and ruggedness is paramount (e.g., commercial trucks, some 4x4s). Step-by-Step Solution: Define need: large load variation and need for robust stroke.Match solution: rigid axle with heavy-duty springs/dampers tolerates high loads and articulation.Conclude: choose the option describing large-load, large-stroke robustness. Verification / Alternative check: Look at heavy-duty pickups and trucks: solid axles remain common due to durability and payload needs. Why Other Options Are Wrong: Reducing unsprung mass: rigid axles increase it.More flexibility/independent control: that is the domain of independent suspensions.Improved tyre contact on uneven surfaces at high speed: independent systems generally perform better.Axle tramp minimization alone does not dictate rigid vs. independent; tuning can address it. Common Pitfalls: Assuming rigid axles are always inferior; they are optimal for heavy loads and harsh duty cycles. Final Answer: when large changes in load make it necessary to have a large, durable suspension stroke and robust axle location

Question 13

Automotive tyres — diagnosing tread wear from inflation level For a passenger vehicle on standard road tyres, an under-inflated tyre typically shows its most pronounced tread wear in which region of the tread?

Accepted Answer

Introduction / Context: Tread-wear patterns are a quick diagnostic for tyre health and vehicle setup. Recognizing the characteristic wear caused by incorrect inflation pressure helps improve safety, tyre life, and fuel economy. Given Data / Assumptions: Pneumatic radial tyre on a passenger car. Vehicle alignment and suspension components are otherwise serviceable. Tyre operated significantly below recommended cold inflation pressure. Concept / Approach: Tyre contact patch shape changes with inflation pressure. Under-inflation increases sidewall deflection, letting the shoulders carry a higher share of vertical load and shear stress. This accelerates wear on the outer tread bands (both edges) while the centre carries less load and wears comparatively less. Step-by-Step Solution: Identify inflation condition: pressure lower than the manufacturer’s specification.Understand load distribution: larger, flatter contact patch with higher shoulder loading.Predict wear pattern: shoulders (tread edges) scrub more, wearing faster than the centre.Correlate observation: visual inspection reveals feathering and depth loss mainly at edges. Verification / Alternative check: Measure tread depth at three positions across the tyre (inner edge, centre, outer edge). Under-inflated tyres show lower depth at both edges relative to centre. Restoring proper pressure and rotating tyres slows further edge wear. Why Other Options Are Wrong: Near the centre: typical of over-inflation, not under-inflation. Lateral/cross-direction patterns: describe cupping or scalloping from imbalance/shock issues, not primarily pressure-related. Uniform wear: indicates correct inflation and alignment over time. Common Pitfalls: Confusing under-inflation edge wear with negative camber wear (usually one edge only); ignoring seasonal temperature changes that reduce cold inflation pressure. Final Answer: near the edges

Question 14

Lead–acid batteries — chemistry at full discharge In a fully discharged automotive lead–acid battery, which compound predominantly forms on both the positive and negative plates?

Accepted Answer

Introduction / Context: Understanding the chemical state of a lead–acid battery at various charge levels is essential for diagnostics and maintenance. Plate chemistry directly influences terminal voltage, internal resistance, and recoverability on recharge. Given Data / Assumptions: Conventional flooded lead–acid starting battery. Battery is at or near full discharge (no catastrophic damage assumed). Electrolyte is aqueous sulphuric acid solution. Concept / Approach: In a charged state, the positive plate is primarily lead dioxide (PbO2) and the negative plate is spongy lead (Pb). During discharge, both plates react with sulphate ions, forming lead sulphate (PbSO4) while the electrolyte becomes more water-rich (specific gravity drops). Thus, at full discharge both plates are covered largely with PbSO4. Step-by-Step Solution: At positive plate during discharge: PbO2 + 4H+ + SO4^2− + 2e− → PbSO4 + 2H2O.At negative plate during discharge: Pb + SO4^2− → PbSO4 + 2e−.Net effect: both plates convert toward PbSO4; acid concentration decreases.Measured symptom: lower specific gravity and lower open-circuit voltage. Verification / Alternative check: Hydrometer readings show reduced specific gravity; visual inspection after teardown reveals sulphation on both plates in a deeply discharged battery. Why Other Options Are Wrong: PbO2 and Pb are the charged-state materials, not discharged. H2SO4 is the electrolyte, not a solid plate deposit. PbO alone is not the dominant discharge product. Common Pitfalls: Allowing prolonged deep discharge causes hard sulphation that resists normal charging, permanently reducing capacity. Final Answer: lead sulphate (PbSO4)

Question 15

SI engine emissions — most effective in-use control method For a spark-ignition (petrol) vehicle, which method is the most effective at reducing harmful exhaust emissions during normal operation?

Accepted Answer

Introduction / Context: Modern SI engines meet stringent emission limits using closed-loop control and aftertreatment. Knowing the most impactful technology in real-world use is fundamental for automotive engineering. Given Data / Assumptions: Three-way catalytic converter (TWC) with stoichiometric fueling and oxygen sensor feedback. Normal operating temperature (converter light-off achieved). Standard unleaded gasoline without exotic additives. Concept / Approach: The TWC simultaneously oxidizes carbon monoxide and unburned hydrocarbons to carbon dioxide and water, and reduces nitrogen oxides to nitrogen, when the air–fuel ratio is controlled near stoichiometry. This achieves large percentage reductions compared to engine-out emissions. Step-by-Step Solution: Engine management holds lambda ≈ 1 using an upstream O2 sensor.Converter stores and releases oxygen (via washcoat), enabling oxidation of CO/HC and reduction of NOx.Net tailpipe emissions drop dramatically once the catalyst is at operating temperature. Verification / Alternative check: Regulatory certification and inspection data show order-of-magnitude reductions in CO, HC, and NOx with a healthy TWC compared to no aftertreatment. Why Other Options Are Wrong: EGR (recirculating exhaust) reduces NOx but not CO/HC comprehensively in SI engines. Additives offer marginal benefits and cannot replace aftertreatment. Retarded timing lowers NOx but raises CO/HC and decreases efficiency. Common Pitfalls: Ignoring catalyst warm-up; a cold catalyst is ineffective, which is why fast light-off strategies exist. Final Answer: using catalytic converter

Question 16

Steering geometry — definition of the included angle In front suspension/steering geometry, the “included angle” is defined as the sum of which two alignment angles?

Accepted Answer

Introduction / Context: Accurate interpretation of alignment angles is essential for diagnosing tyre wear and handling issues. The “included angle” is a derived angle used by alignment machines and service manuals. Given Data / Assumptions: Front-steer vehicle with measurable camber and steering axis inclination (SAI, also called KPI). Static alignment readings with vehicle at curb load. Concept / Approach: The included angle equals camber (wheel tilt relative to vertical) plus the steering axis inclination (the inward tilt of the steering axis when viewed from the front). It does not involve castor (a side-view angle) or toe (plan-view settings). Step-by-Step Solution: Measure camber: angle between wheel plane and vertical in the front view.Measure SAI: angle between steering axis and vertical in the front view.Compute included angle: included = camber + SAI (sign conventions per OEM). Verification / Alternative check: Alignment equipment prints included angle directly after entering camber and SAI; OEM specifications list acceptable ranges. Why Other Options Are Wrong: Castor is a side-view angle; toe is a plan-view setting; neither forms the included angle with camber. Common Pitfalls: Confusing SAI with castor; misinterpreting sign conventions causing apparent discrepancy with specs. Final Answer: camber and S.A.I.

Question 17

Shock absorbers (dampers) — typical location where fluid leakage is observed During visual inspection of a hydraulic twin-tube damper on a passenger car, from where is fluid leakage typically noticed first?

Accepted Answer

Introduction / Context: Dampers contain hydraulic oil and seals. Recognizing where leakage appears helps decide replacement and ensures suspension safety, braking stability, and tyre wear control. Given Data / Assumptions: Twin-tube hydraulic or gas-charged damper oriented vertically. Vehicle used on public roads; no racing coilovers assumed. Leak origin is commonly the rod seal at the top of the damper body, but oil travels downward by gravity. Concept / Approach: Although the initial failure is typically at the upper rod seal, leaked oil runs down the damper body and often accumulates and drips from the lower end, where it is most easily observed during inspection. Hence technicians frequently report leakage “from the bottom of the damper.” Step-by-Step Solution: Identify damp patches near the rod seal and along the body.Trace the gravity path of oil to the lowest point of the unit.Observe dust contamination stuck to oil film and drips near the bottom eye/bushing.Conclude damper is leaking and requires replacement in axle pairs. Verification / Alternative check: Clean the damper, road test briefly, then re-inspect: fresh oil streaks reappear and collect at the lower region, confirming visible leakage at the bottom. Why Other Options Are Wrong: Upper mounting or spring seat: may get oily secondarily but are not reported as the typical visible drip point. Mid-body tube clearance: not a designed leak path; persistent oil there still runs to the bottom. “Top rod seal never leaks”: false; it is the usual origin. Common Pitfalls: Confusing external road grime with oil; overlooking that misting on gas-charged shocks can be normal if minimal and dry. Final Answer: bottom of damper

Question 18

Combustion in SI engines — meaning of auto-ignition In a spark-ignition petrol engine, auto-ignition refers to which phenomenon within the combustion chamber?

Accepted Answer

Introduction / Context: Auto-ignition is central to knock (detonation) in spark-ignition engines. Recognizing its definition distinguishes normal flame propagation from abnormal combustion. Given Data / Assumptions: SI engine with spark-initiated flame kernel. Homogeneous mixture in the combustion chamber. End-gas region subject to pressure and temperature rise during combustion. Concept / Approach: Normal combustion begins at the spark plug and a flame front travels across the chamber. Auto-ignition occurs when unburned end-gas spontaneously ignites due to high temperature/pressure and reaction kinetics before the flame front reaches it, often producing pressure waves perceived as knock. Step-by-Step Solution: Spark initiates flame kernel near top dead center.Flame propagates; end-gas is compressed and heated.If end-gas reaches its auto-ignition conditions, spontaneous ignition occurs ahead of the flame.Rapid energy release generates pressure oscillations (knock). Verification / Alternative check: Knock sensors detect characteristic frequency vibrations; higher octane fuels resist auto-ignition by elevating knock resistance. Why Other Options Are Wrong: “Automatic ignition at end of compression” is vague and not specific to end-gas auto-ignition. Spark-induced ignition is normal, not auto-ignition. Supplemental ignition event is not a standard engine process. ECU spark control is unrelated to spontaneous chemical ignition. Common Pitfalls: Confusing pre-ignition (hot spot triggered before scheduled spark) with knock (auto-ignition of end-gas after spark). Final Answer: ignition of part of the charge ahead of the flame front (end-gas) before the flame reaches it

Question 19

Intake stroke fundamentals — cylinder pressure relative to atmosphere During the suction (intake) stroke of a four-stroke engine, how does the instantaneous in-cylinder pressure compare to atmospheric pressure?

Accepted Answer

Introduction / Context: The intake (suction) stroke draws fresh charge into the cylinder. Pressure differential across the intake system drives this flow and is key to volumetric efficiency. Given Data / Assumptions: Throttle-controlled SI engine or unthrottled CI engine operating at typical speeds. Ambient atmospheric pressure acts at the intake entry. Valves and ports provide finite flow resistance. Concept / Approach: As the piston moves down from top dead center with the intake valve open, the cylinder volume increases. Because air cannot fill the expanding volume instantaneously through restrictive passages, in-cylinder pressure falls slightly below atmospheric. This pressure drop drives air into the cylinder. Step-by-Step Solution: Piston descends during intake, increasing cylinder volume.Flow inertia and restriction cause a small pressure drop in-cylinder.Atmospheric pressure at the intake pushes air into the cylinder.Near bottom dead center, pressure approaches ambient as flow stabilizes. Verification / Alternative check: Manifold absolute pressure (MAP) sensors show values below atmospheric during intake, especially on throttled SI engines at part load (e.g., 30–60 kPa absolute vs. ~101 kPa ambient). Why Other Options Are Wrong: More than atmospheric: occurs in boosted engines, not typical unboosted intake. Equal to atmospheric: only approximately true at specific moments. Half atmospheric or undefined: not representative of real operation. Common Pitfalls: Confusing boosted intake (above atmospheric) with naturally aspirated part-load conditions. Final Answer: less than the atmospheric pressure

Question 20

Maintenance-free (MF) batteries — key characteristic for servicing Which statement best describes the main service characteristic of a maintenance-free (MF) automotive lead–acid battery?

Accepted Answer

Introduction / Context: MF batteries are widely used in modern vehicles to reduce user maintenance. Understanding what “maintenance-free” actually implies prevents improper servicing. Given Data / Assumptions: Sealed, valve-regulated or low-water-loss lead–acid battery design. Correct charging voltages and temperatures maintained by vehicle regulator. No visible filler caps for routine topping up. Concept / Approach: MF batteries minimize water loss by using improved grid alloys, recombination of gases, and sealed designs. Under normal charging, water consumption is extremely low, so periodic topping up is not necessary. They still require correct charging and can be recharged using appropriate chargers. Step-by-Step Solution: Identify sealed construction that limits electrolyte evaporation.Recognize that recombination reduces need for adding water.Conclude routine topping is unnecessary; proper charging practice remains essential. Verification / Alternative check: Manufacturer datasheets specify “no topping up required under normal service” and provide charging profiles instead of electrolyte maintenance procedures. Why Other Options Are Wrong: Adding plain water routinely: not required; also electrolyte concentration must remain correct. Shorter shelf life: typically equal or better if stored properly. Recharging impossible: false; MF batteries are rechargeable lead–acid cells. Monthly acid top-ups: incorrect and dangerous. Common Pitfalls: Overcharging which vents gas and shortens life; using unregulated chargers; opening sealed plugs voiding warranty. Final Answer: Since it is sealed, water loss from evaporation is minimized; routine topping up is not required

Automobile Engineering Questions