Question 1

Engine Cycles — Where Are Ports Used Instead of Poppet Valves? Identify the engine type that typically uses inlet and exhaust ports rather than mechanically actuated valves.

Accepted Answer

Introduction / Context: Gas exchange in engines can be managed by cam-operated poppet valves or by timing the piston’s uncovering of ports in the cylinder wall. Recognizing which cycle relies on ports is a basic engine design concept. Given Data / Assumptions: Conventional piston engines considered. Focus on typical automotive and small engine practices. Special exceptions (e.g., sleeve valves) are out of scope. Concept / Approach: Two-stroke engines commonly employ scavenging and exhaust via ports cut in the cylinder wall. As the piston moves, it sequentially uncovers and covers transfer and exhaust ports, controlling flow without a valve train. Four-stroke engines almost universally use poppet valves operated by a camshaft to control intake and exhaust events every other revolution. Step-by-Step Solution: Identify engine cycle: two-stroke completes a power cycle every crank revolution.Note gas exchange: piston-controlled ports instead of valve gear.Therefore, the correct choice is the two-stroke engine. Verification / Alternative check: Common two-stroke small engines (mopeds, chainsaws) use ported cylinders with crankcase compression or external blowers. Why Other Options Are Wrong: Four-stroke engines rely on valves and a camshaft.“V-6” describes configuration, not cycle; many V-6 engines are four-stroke with valves.“None of these” is incorrect given the two-stroke option. Common Pitfalls: Assuming all engines use poppet valves; port-timed two-strokes are prevalent in small power applications. Final Answer: Two-stroke internal-combustion engines

Question 2

Lead–Acid Battery Behavior — Effect of Temperature on Electrolyte Specific Gravity As the temperature of a lead–acid starter battery increases, how does the specific gravity (SG) of its sulphuric acid electrolyte change (for the same state of charge…

Accepted Answer

Introduction / Context: Battery testing and maintenance often involve hydrometers to read electrolyte specific gravity, a proxy for state of charge. However, SG is temperature-dependent, so correct interpretation requires understanding how temperature skews readings. Given Data / Assumptions: Chemistry: lead–acid with sulphuric acid electrolyte. State of charge is fixed; only temperature changes. Hydrometer reading is not temperature-compensated unless corrected. Concept / Approach: Density of liquids generally decreases as temperature rises due to thermal expansion. Sulphuric acid solutions follow this trend: at higher temperatures, the same amount of acid occupies a larger volume, reducing density and therefore measured SG. This is why hydrometers include temperature correction charts. Step-by-Step Solution: Hold state of charge constant; vary only temperature.Increased temperature → decreased density → lower SG reading.Therefore, the SG decreases with increasing temperature. Verification / Alternative check: Service manuals provide correction factors (e.g., add or subtract points per 10 °C) to normalize readings to a reference temperature. Why Other Options Are Wrong: “Increases” contradicts the known thermal expansion behavior.“Remains the same” ignores temperature dependence of density.“None/oscillates” have no physical basis here. Common Pitfalls: Failing to temperature-correct hydrometer readings leads to misjudging state of charge, especially in hot or cold climates. Final Answer: decreases

Question 3

Four-wheel drive (4WD) — core purpose and benefit on low-traction surfaces In light vehicles equipped with a selectable or full-time four-wheel drive (4WD) system, what is the primary purpose of 4WD in everyday engineering terms, especially when the…

Accepted Answer

Introduction / Context: A four-wheel drive (4WD) driveline distributes engine torque to both the front and rear axles. This question probes the fundamental reason manufacturers equip vehicles with 4WD: to improve traction and mobility when the available tyre–road friction is low. Given Data / Assumptions: Vehicle has a functional 4WD transfer case or coupling. Road surface offers reduced friction (ice, snow, mud, loose gravel, wet grass). Tyre type and inflation are appropriate and the braking system is standard. Concept / Approach: Traction is limited by the normal load on a tyre multiplied by the friction coefficient. When only one axle is driven, wheel slip on that axle can limit launch or hill-climb performance. By sending torque to four contact patches instead of two, 4WD increases the probability that at least some tyres have usable grip, thereby allowing higher tractive effort before slip occurs. Step-by-Step Solution: Identify the primary limitation on slippery surfaces: low friction leads to easy wheelspin.Recognize that driving four wheels shares the torque among more tyres.With torque spread, each tyre operates at a lower slip ratio for the same vehicle tractive force.Therefore, the system ensures more effective torque transmission to the ground and better vehicle mobility. Verification / Alternative check: Comparative testing shows shorter launch times and improved gradeability for 4WD over 2WD on low-μ surfaces, all else being equal. Why Other Options Are Wrong: Improved cornering on dry roads: chassis tuning and tyres dominate; 4WD alone is not for dry-road cornering gains. Eliminates snow tyres/chains: false; tyres remain critical for safety. Ensures effective braking: braking is primarily limited by tyre friction and ABS, not 4WD torque delivery. Guarantees better fuel economy: 4WD often increases mass and losses, slightly reducing economy. Common Pitfalls: Assuming 4WD defeats physics; ignoring tyre choice; confusing 4WD traction under power with braking capability. Final Answer: ensures effective transmission of engine torque to all four wheels, even on slippery road surfaces

Question 4

Automotive hydraulics — primary function of brake fluid in service brakes In a conventional hydraulic brake system with a master cylinder and wheel cylinders/calipers, what is the chief role of the brake fluid during braking?

Accepted Answer

Introduction / Context: Hydraulic brakes rely on the incompressibility of a fluid to transmit pedal force to friction elements. Selecting the correct function clarifies why brake fluids have stringent boiling-point and compressibility specifications. Given Data / Assumptions: Hydraulic brake system with master cylinder and calipers/wheel cylinders. DOT-rated brake fluid free of air and moisture at serviceable condition. Normal operating temperatures and pressures are considered. Concept / Approach: The primary role of brake fluid is to transmit force and motion from the pedal via the master cylinder to the wheel brakes. Because it is effectively incompressible under normal conditions, small pedal movements create proportional pressure rises, clamping the pads or expanding the shoes. Step-by-Step Solution: Pedal force acts on the master cylinder piston area to create hydraulic pressure.Pressure propagates through brake lines nearly undiminished to the calipers/cylinders.Caliper pistons convert hydraulic pressure back into mechanical clamping force at the disc/drum.Thus, the fluid’s key function is power (force) transmission. Verification / Alternative check: Pascal’s law explains uniform pressure in a confined fluid; pressure gauges placed near master and caliper show near-equal readings when the system is bled correctly. Why Other Options Are Wrong: Lubrication: a minor secondary effect inside components; not the principal purpose. Cooling: brake fluid is not a heat sink; rotors and airflow do most cooling. None of these or rust prevention only: contrary to hydraulic design intent. Common Pitfalls: Allowing moisture contamination that lowers boiling point and increases compressibility; confusing hydraulic transmission with mechanical advantage at pedal and caliper. Final Answer: power transmission

Question 5

Engine fundamentals — firing order of a horizontally opposed (boxer) four-cylinder engine Select the commonly used firing order for an opposed four-cylinder internal combustion engine used in automotive applications.

Accepted Answer

Introduction / Context: Firing order is the sequence in which cylinders deliver power strokes. It affects engine balance, vibration, crankshaft design, and exhaust pulsing. Boxer four engines (horizontally opposed) typically use a firing order optimized for smoothness and even exhaust intervals. Given Data / Assumptions: Four-cylinder boxer layout with 180° opposed banks. Crankpins arranged to achieve even firing intervals over 720° of crank rotation. Automotive spark-ignition application. Concept / Approach: For a four-cylinder engine, power strokes occur every 180° of crank rotation. In the boxer layout, the firing order 1-4-3-2 yields good balance and exhaust separation. While inline-4 engines often use 1-3-4-2, boxer-4s commonly adopt 1-4-3-2 in many classic designs. Step-by-Step Solution: Note that 720°/4 = 180° between firings.Select a sequence that alternates banks to minimize rocking couples.The order 1-4-3-2 provides satisfactory smoothness and timing for exhaust manifolding. Verification / Alternative check: Service manuals for well-known boxer engines list 1-4-3-2 as the firing order, confirming the common choice. Why Other Options Are Wrong: 1-2-3-4 and 4-3-2-1: lead to uneven balance and undesirable pulsation. 1-3-4-2: more typical of inline-4 engines. 1-3-2-4: not standard for most boxer-4 automotive applications. Common Pitfalls: Confusing cylinder numbering conventions between manufacturers; assuming inline and boxer engines share the same firing order. Final Answer: 1-4-3-2

Question 6

Exhaust constituents of a petrol (gasoline) engine Under normal operation, which set correctly represents key constituents present in the exhaust gas of a spark-ignition petrol engine?

Accepted Answer

Introduction / Context: Petrol engines combust hydrocarbon fuel with air. Real-world combustion is never perfectly complete, so the exhaust contains a mixture of desired and undesired species. Recognizing major components is fundamental to emissions control and after-treatment design. Given Data / Assumptions: Conventional petrol engine with three-way catalyst (may be warming up or at stoichiometric). Typical pump gasoline without high ethanol fraction. Normal load and temperature conditions. Concept / Approach: Combustion of hydrocarbons produces carbon dioxide and water. Due to mixture variations, there will also be carbon monoxide (from incomplete oxidation), unburned hydrocarbons (fuel vapours), nitrogen oxides, residual oxygen, and nitrogen. Therefore, petrol vapours, water vapour, and carbon monoxide are all present to some extent. Step-by-Step Solution: Hydrocarbons + O2 → CO2 + H2O ideally, but real engines yield CO and unburned HC.Cold starts and transients increase HC and CO until the catalyst lights off.Hence, petrol vapours, water vapour, and CO are all found in exhaust streams. Verification / Alternative check: Gas analyzers routinely measure CO, HC, CO2, O2, and NOx in inspection and diagnostic procedures, confirming the mixture of species. Why Other Options Are Wrong: Single-component answers are incomplete. Only nitrogen and oxygen: ignores products and intermediates of combustion. Common Pitfalls: Assuming a fully warmed catalyst eliminates all CO and HC; during warm-up and aggressive transients, these still appear. Final Answer: all of these

Question 7

Lead-acid battery service — composition of electrolyte when fully charged For a fully charged automotive lead-acid battery at room temperature, which statement best describes the approximate composition of the electrolyte by weight?

Accepted Answer

Introduction / Context: Electrolyte concentration determines battery open-circuit voltage, internal resistance, and freezing/boiling characteristics. Technicians often relate acid strength to specific gravity to assess state of charge. Given Data / Assumptions: Standard flooded lead-acid battery in automotive use. Room temperature and fully charged condition. No additives or gel/AGM variants considered. Concept / Approach: When fully charged, electrolyte specific gravity is typically around 1.26–1.28 at 25°C, which corresponds to roughly 36% sulphuric acid and 64% water by weight. As the battery discharges, sulphuric acid is consumed and water fraction increases, lowering specific gravity. Step-by-Step Solution: Relate state of charge to specific gravity (hydrometer reading).Use standard tables mapping 1.26–1.28 SG to approximately 36% H2SO4 by weight.Identify the option that matches this proportion. Verification / Alternative check: Service manuals and battery datasheets list the same nominal composition for a fully charged state. Why Other Options Are Wrong: Pure water or pure acid: neither exists in a working flooded cell. 90/10 or 50/50: do not match the specific gravity required for proper voltage and capacity. Common Pitfalls: Ignoring temperature corrections on hydrometers; confusing volume percent with weight percent. Final Answer: the electrolyte is a mixture of 64% distilled water and 36% sulphuric acid by weight

Question 8

Automatic transmissions — working medium in a torque converter In a hydrodynamic torque converter used with automatic transmissions, which medium actually transfers torque between pump and turbine elements?

Accepted Answer

Introduction / Context: A torque converter is a fluid coupling with torque multiplication capability. Understanding the working medium clarifies maintenance needs and the role of fluid properties such as viscosity and oxidation stability. Given Data / Assumptions: Pump (impeller), turbine, and stator are present. Converter is filled with the specified ATF to the correct level. Automatic transmission with appropriate cooling circuit. Concept / Approach: Torque transfer occurs by momentum exchange of the working fluid. The pump accelerates the ATF, which then impinges on the turbine blades, imparting torque. The stator redirects returning flow to enhance multiplication at high slip. Step-by-Step Solution: Engine spins the converter pump (impeller).Impeller imparts angular momentum to ATF.ATF flow strikes the turbine, producing torque on the transmission input shaft.Stator improves efficiency by redirecting flow during stall/acceleration. Verification / Alternative check: Loss of ATF or contamination leads to poor coupling, overheating, shudder, and converter clutch issues, proving the fluid’s central role. Why Other Options Are Wrong: Air: would cavitate and cannot transmit torque effectively in this design. Gears and steel belt: belong to mechanical transmissions (gearboxes, CVTs), not torque converters. Silicone grease: unsuitable and not used as a hydrodynamic working medium. Common Pitfalls: Using incorrect ATF type or running low on fluid; confusing fluid coupling with mechanical gear reduction. Final Answer: automatic transmission fluid (ATF)

Question 9

Engine boosting — definition of supercharging What is the engineering term for the process in which intake air is supplied to an engine cylinder at a pressure higher than the surrounding atmospheric pressure?

Accepted Answer

Introduction / Context: Modern engines frequently use devices to increase air mass flow so that more fuel can be burned efficiently, improving power density. The general umbrella term for raising the intake pressure above atmospheric is important terminology. Given Data / Assumptions: Intake pressure at the manifold exceeds ambient pressure. Pressure rise may be produced by a turbocharger or mechanically driven supercharger. Four-stroke spark-ignition or compression-ignition engine. Concept / Approach: Supercharging denotes any method that increases intake manifold absolute pressure above ambient. Turbocharging is a form of supercharging using exhaust-gas energy; mechanically driven compressors are another form. The result is increased air density, enabling more fuel while maintaining proper air–fuel ratio. Step-by-Step Solution: Compare manifold pressure to atmospheric pressure.If manifold pressure > ambient, the engine is being supercharged.This raises cylinder charge density and potential indicated mean effective pressure. Verification / Alternative check: Boost gauges show manifold pressure above 1 bar absolute (sea level) during boost events, confirming supercharging. Why Other Options Are Wrong: Auto-ignition and detonation: combustion phenomena, not air-supply methods. Scavenging: process of clearing exhaust and filling with fresh charge, typically in two-stroke or boosted engines. Aftertreatment: refers to catalytic converters and filters, not intake pressurization. Common Pitfalls: Confusing turbocharging as separate from supercharging; both raise intake pressure and fall under supercharging. Final Answer: supercharging

Question 10

Thermodynamic cycle of a petrol (gasoline) engine On which idealized thermodynamic cycle is a conventional spark-ignition petrol engine modeled for analysis and instruction?

Accepted Answer

Introduction / Context: Ideal cycles provide a simplified framework to analyze engine performance. Spark-ignition petrol engines are classically associated with the constant-volume heat-addition Otto cycle. Given Data / Assumptions: Four-stroke spark-ignition engine with near-stoichiometric fueling. Ideal analysis (no pumping, friction, heat losses). Constant-volume heat addition approximation during combustion. Concept / Approach: The Otto cycle consists of isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection. This approximates combustion that occurs quickly near top dead center in SI engines. Step-by-Step Solution: Match engine type (SI) to constant-volume heat addition model.Recognize that diesel engines align with the constant-pressure Diesel cycle.Select Otto cycle for petrol engine modeling. Verification / Alternative check: Textbooks and engine courses consistently pair petrol engines with the Otto cycle in idealized analyses. Why Other Options Are Wrong: Carnot: theoretical maximum efficiency, not a practical engine cycle. Diesel: constant-pressure addition fits CI engines. Rankine: steam power plants. Miller: a valve-timing-modified variant; not the baseline teaching cycle. Common Pitfalls: Assuming real combustion exactly matches constant volume; in practice, it is neither perfectly constant-volume nor instantaneous. Final Answer: Otto cycle

Question 11

Engine cooling — primary function of the radiator fan Within a liquid-cooled automotive engine, what is the main purpose of the radiator fan during low vehicle speed or high thermal load operation?

Accepted Answer

Introduction / Context: Radiator fans (engine-driven or electric) maintain airflow across the radiator core when ram-air from vehicle motion is insufficient. This prevents coolant temperatures from exceeding limits in traffic, at idle, or under high load at low speed. Given Data / Assumptions: Liquid-cooled engine with thermostat, radiator, and fan shroud. Fan control may be viscous clutch or ECU-controlled electric motor. Ambient and load conditions where natural airflow is inadequate. Concept / Approach: The radiator rejects heat from the coolant to ambient air. The fan’s purpose is to force or pull air through the radiator fins, sustaining the heat transfer rate independent of vehicle speed. Step-by-Step Solution: Coolant absorbs heat from the engine and flows to the radiator.Fan induces airflow through the core, increasing convective heat transfer.Temperature is controlled by thermostat and fan switching to maintain optimal engine temperature. Verification / Alternative check: Fan activation at idle coincides with rising coolant temperature; switching off the fan typically causes temperature to climb, confirming its role. Why Other Options Are Wrong: Driving the water pump by wind: water pumps are belt or gear/electric driven, not by fan wind. Blowing directly on the block: primary heat rejection occurs in the radiator, not by air on the block. Drawing heat out of the engine bay: incidental, not the primary design purpose. Dehumidifying intake air: unrelated to the cooling system fan. Common Pitfalls: Missing shrouds which greatly reduce fan effectiveness; incorrect fan rotation; failed relays/sensors preventing timely activation. Final Answer: it blows air through the radiator when necessary

Question 12

Intake systems — main purpose of an engine air cleaner (air filter) In a road vehicle, what is the principal function of the engine’s air cleaner assembly located upstream of the throttle/air-meter?

Accepted Answer

Introduction / Context: Combustion engines consume large volumes of air that may carry dust, sand, pollen, and other particulates. The air cleaner is a critical first line of defense preventing abrasive particles from damaging the cylinders, piston rings, and turbocharger compressors. Given Data / Assumptions: Pleated paper or synthetic media element in a sealed airbox. Properly maintained filter with correct fitment and sealing gaskets. Normal on-road or off-road dusty environments. Concept / Approach: Filtration removes contaminants above a target particle size while keeping pressure drop within allowable limits. Clean intake air reduces wear, maintains sensor accuracy (MAF/MAP), and protects turbocharger blades from erosion. Step-by-Step Solution: Unfiltered air contains abrasive particles that would score cylinder walls.The air cleaner media traps these particles while allowing sufficient airflow.Result: reduced engine wear and sustained performance over service intervals. Verification / Alternative check: Oil analysis shows lower silicon (dust) levels with proper filtration; visual inspection of throttle bodies and compressor wheels reveals less contamination when filters are sound. Why Other Options Are Wrong: Controlling air volume: primarily managed by throttle or ECU; filter only imposes a pressure drop. Noise reduction and rain ingress prevention: secondary benefits, not the main purpose. Increasing boost: the filter cannot raise boost; excessive restriction reduces it. Common Pitfalls: Running without a filter, using oiled filters that foul MAF sensors, or installing with leaks that bypass the media. Final Answer: prevents dust and other foreign matter from entering the engine

Question 13

Compression ignition (Diesel) engine — typical pressure at the end of compression For a standard automotive Diesel (compression-ignition) engine in healthy condition, the cylinder pressure at the end of the compression stroke is generally of the ord…

Accepted Answer

Introduction / Context: The question checks basic engine-thermodynamics awareness for compression-ignition (Diesel) engines. Knowing the typical end-of-compression pressure helps in diagnostics (compression testing) and in understanding why Diesel fuel auto-ignites without a spark plug. Given Data / Assumptions: Light-duty automotive Diesel engine (not a large stationary or marine unit). Normal compression ratio in the range of about 16:1 to 22:1. Healthy engine with standard cranking speed and minimal leakage. Concept / Approach: End-of-compression pressure depends on compression ratio, inlet conditions, heat losses, and polytropic exponent. Typical service values for road Diesels fall in the tens of bar, substantially higher than spark-ignition engines, enabling auto-ignition at the appropriate temperature. Step-by-Step Solution: Recognise that CI engines need high pressure and temperature at the end of compression for auto-ignition.Practical workshop data for automotive Diesels commonly show end-of-compression pressures around the mid-30s bar at running conditions.Select the closest realistic figure among the choices: 35 bar. Verification / Alternative check: Compression test specifications from OEM service manuals typically report acceptable ranges whose central tendency is near 30–40 bar for light-duty Diesels. This corroborates the 35 bar order-of-magnitude choice. Why Other Options Are Wrong: 15 bar: Too low for reliable CI operation in automotive engines. 25 bar: Possible in marginal cases but low as a general “order of magnitude.” 45 bar: Seen in some heavy-duty or high-CR cases; higher than the common automotive baseline. Common Pitfalls: Confusing peak firing pressure (hundreds of bar) with end-of-compression pressure before combustion; these are very different values. Final Answer: 35 bar

Question 14

Engine NVH control — primary purpose of a balancer shaft in automotive engines In modern engines, what is the main function of a balancer shaft with counterweights?

Accepted Answer

Introduction / Context: Engines generate unbalanced forces and moments that lead to vibration and noise. Balancer shafts are used in many inline-3 and inline-4 engines (and others) to improve refinement (NVH: noise, vibration, harshness). Given Data / Assumptions: Shaft has counterweights rotating at specific speeds and phases. Purpose is related to vibration mitigation, not valve timing. Applies to production automotive engines. Concept / Approach: Balancer shafts create controlled counter-inertial forces that oppose primary or secondary shaking forces produced by reciprocating masses and crankshaft rotation. Proper phasing reduces the amplitude of felt vibrations transmitted to the vehicle body. Step-by-Step Solution: Identify the problem: crankshaft and reciprocating mass imbalance.Balancer shaft(s) rotate(s) to generate opposing forces at the same frequency.Result: reduced vibrations perceived by occupants and reduced stress on mounts. Verification / Alternative check: Engine design texts specify single or twin balance shafts (e.g., Lanchester shafts) turning at crankshaft speed or twice speed to cancel primary/secondary forces. Why Other Options Are Wrong: Timing of piston groups or valve events is handled by crank/valvetrain, not balancer shafts. Increasing inertia is the opposite of the goal; added mass is used only to counter forces. Common Pitfalls: Confusing cam phasing (VVT) with balance shafts; they serve entirely different purposes. Final Answer: reduce vibrations caused by the crankshaft rotation

Question 15

Ignition system fundamentals — role of the ignition coil in SI engines In a conventional spark-ignition system, the ignition coil primarily serves to:

Accepted Answer

Introduction / Context: Spark-ignition engines require a high-voltage pulse to jump the spark plug gap and ignite the air–fuel mixture. The ignition coil is the device that generates this high voltage from the vehicle’s low-voltage electrical system. Given Data / Assumptions: Nominal system voltage 12–14 V. Spark requirement tens of kilovolts depending on gap, pressure, and mixture. Coil is a transformer-like component with primary and secondary windings. Concept / Approach: The coil stores energy in its magnetic field when current flows in the primary winding. When the primary current is rapidly interrupted, the collapsing field induces a much higher voltage in the secondary winding due to its higher turns count, producing a high-voltage pulse to the plug. Step-by-Step Solution: Identify desired output: high voltage to fire the spark plug.A transformer operation is used: low-voltage primary, high-turn secondary.Therefore, the coil’s role is to step up voltage. Verification / Alternative check: Typical coils generate 15–40 kV depending on system design (distributor, coil-on-plug, CDI/inductive). Why Other Options Are Wrong: Step up/down current: not the primary specification; current is limited by circuitry. Step down voltage: opposite of requirement for spark discharge. Common Pitfalls: Confusing coil function with the ignition module/ECU that controls dwell and timing. Final Answer: step up voltage

Question 16

Engine cooling — purpose of a thermostat in the coolant circuit In an automotive liquid-cooling system, the thermostat's main function is to:

Accepted Answer

Introduction / Context: Thermostats improve engine efficiency, emissions, and durability by regulating coolant flow. They help achieve and maintain the optimal operating temperature. Given Data / Assumptions: Wax-pellet thermostat with a set opening temperature (e.g., 85–95°C). Pressurised cooling system with a separate radiator cap. Coolant temperature sensor and gauge are independent components. Concept / Approach: When cold, the thermostat stays closed, restricting flow to the radiator and recirculating coolant within the engine. This reduces warm-up time. As temperature rises to the set point, the thermostat opens progressively, allowing heat rejection through the radiator and stabilising temperature. Step-by-Step Solution: On cold start: thermostat closed → quick warm-up.At operating temp: thermostat modulates flow to maintain setpoint.Therefore, its primary purpose is to allow the engine to warm up quickly and then regulate temperature. Verification / Alternative check: Cooling systems without thermostats suffer from excessive warm-up time and unstable temperatures, harming fuel economy and wear. Why Other Options Are Wrong: Prevent boiling/pressurise system: handled mainly by radiator cap and system design. Indicate temperature: that is the sensor/gauge function. Common Pitfalls: Assuming thermostat controls pressure; it only controls flow using temperature-sensitive actuation. Final Answer: allow the engine to warm up quickly

Question 17

Vehicle resistance on grades — gradient (grade) resistance for a 980 kg car at 10° incline Compute the component of weight acting down the slope (gradient resistance) for a vehicle of mass 980 kg climbing a 10° incline. Use g = 9.81 m/s^2.

Accepted Answer

Introduction / Context: When a vehicle climbs an incline, a component of its weight acts along the slope and opposes motion. This is called gradient (or grade) resistance and is essential for tractive effort and power calculations. Given Data / Assumptions: Mass m = 980 kg. Incline angle θ = 10°. Acceleration due to gravity g = 9.81 m/s^2. Neglect rolling and aerodynamic resistances; compute only the gravitational component along the slope. Concept / Approach: The gravitational force is W = m * g. The component acting along the slope is W * sin(θ). This is the gradient resistance that the powertrain must overcome (in addition to other resistances) to maintain speed uphill. Step-by-Step Solution: W = m * g = 980 * 9.81 = 9603.8 Nsin(10°) ≈ 0.173648Gradient resistance = W * sin(θ)Gradient resistance = 9603.8 * 0.173648 ≈ 1669.4 N Verification / Alternative check: For small angles, sin(θ) ≈ θ in radians. 10° ≈ 0.1745 rad; 9603.8 * 0.1745 ≈ 1675 N, close to the precise 1669.4 N, confirming the calculation. Why Other Options Are Wrong: 1.6694 N and 16.694 N: orders of magnitude too small. 166.94 N: off by a factor of 10. Common Pitfalls: Using cos(θ) instead of sin(θ) or forgetting to convert degrees to radians when using approximations. Also, mixing mass (kg) with weight (N) is a frequent mistake. Final Answer: 1669.4 N

Question 18

Cylinder liners in aluminium engine blocks — common material choice In modern aluminium cylinder blocks, which material is typically used for the cylinder liners to provide wear resistance and durability?

Accepted Answer

Introduction / Context: Aluminium blocks are valued for low mass and thermal conductivity, but aluminium alone lacks the wear resistance required for piston–ring contact surfaces. Liners or surface treatments are used to ensure longevity. Given Data / Assumptions: Conventional aluminium blocks with replaceable liners. Focus on typical material selection, not specialised coatings like Nikasil or plasma spraying. Concept / Approach: Cast iron liners offer excellent scuff resistance, good compatibility with common ring materials, and adequate thermal stability. They are widely used as dry or wet liners in aluminium blocks for passenger vehicles. Step-by-Step Solution: Identify performance needs: wear resistance, machinability, cost.Cast iron meets these needs better than aluminium, brass, or bulk ceramics for mainstream engines.Therefore, select cast iron. Verification / Alternative check: Manufacturer literature and engine rebuild practices commonly reference grey or alloyed cast iron liners in aluminium blocks. Why Other Options Are Wrong: Aluminium: insufficient wear resistance at the bore without coatings. Ceramic: excellent hardness but impractical and costly as full liners. Brass: poor wear properties for cylinder bores. Common Pitfalls: Assuming the block bore material equals the liner; many modern designs use inserted liners or advanced coatings instead. Final Answer: cast iron

Question 19

Automotive starting system — core components included Which combination correctly lists the primary components of a typical automotive starting system?

Accepted Answer

Introduction / Context: The starting system is responsible for cranking the engine to a speed at which it can run on its own. Understanding its elements aids troubleshooting. Given Data / Assumptions: Conventional 12 V system. Focus on starting (cranking) hardware, not ignition spark distribution. Starter solenoid is part of the starter assembly. Concept / Approach: The ignition switch commands current from the battery to the starter (via relays/solenoid). The starter motor engages the flywheel ring gear to crank the engine. A distributor is part of older ignition systems and is not a starting system component. Step-by-Step Solution: Identify core needs: energy source (battery), actuator (starter), user command (ignition switch).Distributor handles spark distribution, not cranking.Hence the correct set is battery + starter + ignition switch. Verification / Alternative check: Wiring diagrams show the start circuit from the ignition switch to the starter relay/solenoid and starter motor powered by the battery. Why Other Options Are Wrong: Options including distributor confuse ignition with starting. Common Pitfalls: Assuming “ignition switch” relates only to spark. It also contains the start position that energises the starter circuit. Final Answer: a battery, a starter, and an ignition switch

Question 20

Lighting and signalling — typical flash rate for turn indicators For an automotive side-turn indicator, what is the usual flashing frequency (flashes per minute)?

Accepted Answer

Introduction / Context: Turn indicators must flash within a regulatory frequency band to ensure recognisable signalling to other road users. The typical design target is near 90 flashes per minute. Given Data / Assumptions: Passenger vehicle turn indicators. Standard automotive flasher modules or BCM-controlled flashing. Ambient conditions nominal. Concept / Approach: Most standards specify a range (for example, roughly 60 to 120 flashes per minute). Manufacturers commonly calibrate around the middle of the band, near 90 fpm, for visibility and compliance. Step-by-Step Solution: Recognise typical regulation band.Select the central common value: approximately 90 fpm. Verification / Alternative check: Automotive service literature and indicator relay specifications often list nominal 90 ± 30 fpm. Why Other Options Are Wrong: 9: far too slow. 900 or 9000: orders of magnitude too fast. Common Pitfalls: Confusing flashes per minute with hertz. 90 fpm corresponds to 1.5 Hz. Final Answer: 90

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