Internal Combustion Engines MCQs 2026

Wankel rotary engine uses

1. Atrochoidal rotor in epitrochoidal housing✓
2. Breciprocating piston only✓
3. Csteam turbine blades✓
4. Dexternal boiler✓

Dual fuel engine runs on

1. Awater emulsion only✓
2. Bpure hydrogen without air✓
3. Csolid coal dust only✓
4. Dgaseous fuel with pilot diesel injection✓

Miller cycle uses

1. Alate exhaust only✓
2. Bdiesel injection in SI✓
3. Cno turbo✓
4. Dearly intake valve closing to reduce effective compression✓

Atkinson cycle achieves higher efficiency by

1. Ahigher friction losses✓
2. Bexpanding more than compressing (over-expansion)✓
3. Cconstant volume heat add only✓
4. Dno expansion stroke✓

Uniflow scavenging uses

1. Aonly side ports both ends✓
2. Bno exhaust path✓
3. Cspark at exhaust port✓
4. Dpiston-controlled ports and cylinder head exhaust valve✓

Loop scavenging in two-stroke uses

1. Aseparate blower only always✓
2. Bincoming charge to push exhaust through ports✓
3. Cfour valves per cylinder✓
4. Dturbo only✓

Scavenging in two-stroke engine means

1. Alubricating crankshaft only✓
2. Bcooling radiator✓
3. Cfiltering oil✓
4. Dreplacing exhaust gas with fresh charge✓

NOx formation increases with

1. Alow temperature only✓
2. Brich mixture only always✓
3. Chigh peak combustion temperature and oxygen availability✓
4. Dretarded spark only always✓

CO in exhaust indicates

1. Aperfect stoichiometric burn always✓
2. Bhigh NOx only✓
3. Clow oil consumption✓
4. Dincomplete combustion due to insufficient oxygen✓

HC emissions in exhaust are primarily

1. Anitrogen gas from air always counted as HC✓
2. Bcarbon dioxide only✓
3. Cwater vapor only✓
4. Dunburned or partially burned hydrocarbons✓

Lambda sensor measures

1. Afuel temperature only✓
2. Boxygen content in exhaust for air-fuel ratio control✓
3. Ccoolant level✓
4. Dcrank position only✓

Catalytic converter reduces

1. Aengine noise only✓
2. Bfuel octane requirement✓
3. CCO, HC and NOx in exhaust✓
4. Dintake air temperature✓

Exhaust gas recirculation (EGR) reduces

1. ACO always to zero✓
2. Bfuel consumption always increases HC only✓
3. CNOx by lowering peak combustion temperature✓
4. Dengine power always to zero✓

Piston rings primary functions include

1. Acooling radiator water✓
2. Bsealing combustion gas and controlling oil consumption✓
3. Cdriving camshaft✓
4. Dfiltering intake air✓

Oil pump in engine typically provides

1. Afuel injection pressure 200 bar always✓
2. Bcoolant circulation✓
3. Cpressurized oil to bearings and sliding parts✓
4. Dintake boost✓

SAE viscosity grade 20W-40 indicates

1. Asingle viscosity at 100 °C only✓
2. Bfuel octane rating✓
3. Cmultigrade oil meeting winter and high temperature specs✓
4. Dcoolant concentration✓

Engine lubrication oil reduces

1. Acombustion temperature directly✓
2. Bintake air density always✓
3. Cfriction, wear and carries heat from bearings✓
4. Dexhaust oxygen content✓

Radiator pressure cap raises boiling point by

1. Aincreasing system pressure✓
2. Bvacuum in cooling system✓
3. Cadding antifreeze only without pressure✓
4. Dreducing coolant flow✓

Thermosyphon cooling relies on

1. Anatural convection without water pump✓
2. Bforced pump circulation only✓
3. Crefrigerant evaporation in cylinder✓
4. Doil spray on pistons only✓

Engine cooling system primary purpose is to

1. Amaintain optimal metal temperatures and prevent overheating✓
2. Bincrease exhaust temperature✓
3. Celiminate friction entirely✓
4. Draise combustion temperature unlimited✓

Intercooler after compressor reduces

1. Afuel octane requirement to zero✓
2. Bexhaust temperature to ambient always✓
3. Cintake air temperature and increases density✓
4. Dengine displacement✓

Supercharger differs from turbocharger because it is

1. Amechanically driven from crankshaft✓
2. Bexhaust driven always✓
3. Celectric only always✓
4. Dnot a compressor✓

Turbocharger on IC engine increases power by

1. Amechanical supercharger belt only always✓
2. Bburning fuel in turbine✓
3. Cusing exhaust energy to compress intake air✓
4. Dreducing CR✓

Glow plugs in diesel aid

1. Acold starting by heating combustion chamber air✓
2. Bhigh speed turbo spool only✓
3. Cexhaust gas recirculation cooling✓
4. Dlubrication at operating temperature✓

Common rail diesel injection provides

1. Alow pressure gravity feed only✓
2. Bmechanical jerk pump only per cylinder✓
3. Ccarburetor venturi✓
4. Dhigh pressure fuel available continuously to injectors✓

Fuel injection in modern SI engines improves

1. Aalways eliminates air filter✓
2. Bfuel distribution, efficiency and emission control✓
3. Creduces CR requirement to 4✓
4. Dremoves need for spark✓

Carburetor function is to

1. Aatomize and mix fuel with air in correct proportion✓
2. Bcompress air only✓
3. Cignite mixture✓
4. Dcool exhaust gas✓

Specific fuel consumption (BSFC) is

1. Apower per fuel volume only✓
2. Bair flow per stroke✓
3. Ctorque per RPM only✓
4. Dfuel mass flow per unit brake power✓

Brake thermal efficiency is

1. Aindicated power / fuel energy✓
2. Bvolumetric efficiency squared✓
3. Cbrake power / energy in fuel supplied✓
4. DBMEP / IMEP only✓

Mechanical efficiency of engine is

1. Aindicated / brake✓
2. Bbrake power / indicated power✓
3. Cthermal / volumetric✓
4. Dfuel energy / heat loss✓

Indicated mean effective pressure (IMEP) is measured using

1. Aexhaust gas analyzer only✓
2. Bfuel flow meter alone✓
3. Cengine indicator or cylinder pressure diagram✓
4. Dspeedometer✓

Brake mean effective pressure (BMEP) is

1. Apeak firing pressure✓
2. Binlet manifold vacuum only✓
3. Coil gallery pressure✓
4. Daverage pressure producing brake power over displacement volume✓

Lean mixture improves

1. Aalways increases knock✓
2. Bfuel economy and reduces CO at cost of NOx control challenge✓
3. Celiminates need for ignition✓
4. Dincreases volumetric efficiency always✓

Rich mixture in SI engine generally produces

1. Amaximum fuel economy always✓
2. Bmore power but lower thermal efficiency and higher HC/CO✓
3. Czero CO emissions✓
4. Dlower exhaust temperature always✓

Air-fuel ratio for petrol stoichiometric is approximately

1. A22:1 by mass✓
2. B4:1 by mass✓
3. C14.7:1 by mass✓
4. D50:1 by mass✓

Combustion in CI engine is primarily

1. Ahomogeneous premixed only✓
2. Bspark initiated always✓
3. Cisothermal✓
4. Ddiffusion controlled after vaporization✓

Combustion in SI engine is ideally

1. Aflame propagation through premixed charge✓
2. Bdiffusion controlled spray burning only✓
3. Cconstant pressure always✓
4. Dexternal combustion✓

Ignition delay in CI engine is time between

1. Aspark and power stroke✓
2. Bstart of injection and start of combustion✓
3. Cintake and exhaust✓
4. DTDC and BDC only✓

Cetane number indicates

1. Aknock resistance of petrol✓
2. Boctane blending value✓
3. Cignition quality of diesel fuel✓
4. Dsteam quality✓

Pre-ignition occurs when

1. Acharge ignites before spark due to hot spots✓
2. Bflame propagates normally after spark✓
3. Conly at very retarded timing✓
4. Dfuel is pure octane✓

Detonation differs from surface ignition in that detonation is

1. Arapid auto-ignition of end gas with pressure waves✓
2. Bglow ignition from hot deposits only✓
3. Cpre-ignition from spark plug fault always✓
4. Dnormal flame propagation✓

Low volumetric efficiency at high speed in SI engine is mainly due to

1. Aincreased CR always✓
2. Breduced time for intake and valve flow restrictions✓
3. Czero friction✓
4. Dperfect scavenging✓

Volumetric efficiency is defined as

1. Aactual mass inducted / mass at STP filling swept volume✓
2. Bbrake power / indicated power✓
3. Cfuel consumed / air mass✓
4. Dexhaust pressure / inlet pressure✓

Two-stroke engine produces power stroke

1. Aevery two revolutions✓
2. Bevery crankshaft revolution✓
3. Cevery four revolutions✓
4. Donly at idle✓

Four-stroke engine completes one power stroke in

1. Aone revolution✓
2. Btwo crankshaft revolutions✓
3. Cfour revolutions✓
4. Dhalf revolution✓

Compression ignition engine relies on

1. Aauto-ignition of fuel injected into hot compressed air✓
2. Bspark at TDC always✓
3. Ccarburetor mixture only✓
4. Dsteam injection✓

Otto cycle consists of

1. Atwo constant pressure and two isothermal✓
2. Bfour constant volume only✓
3. Ctwo isentropic and two constant volume processes✓
4. Done isentropic and three isobaric✓

Diesel cycle differs from Otto cycle by having

1. Aconstant volume heat rejection only✓
2. Bconstant pressure heat addition✓
3. Cisothermal compression✓
4. Dno expansion stroke✓

Compression ratio of SI engine is typically limited to about

1. A20 to 25✓
2. B4 to 6✓
3. C30 to 35✓
4. D10 to 12✓

Thermal efficiency of Otto cycle increases with

1. Adecreasing CR✓
2. Bcompression ratio✓
3. Cincreasing exhaust back pressure only✓
4. Dreducing specific heat ratio✓

Thermal efficiency of Diesel cycle for same compression ratio is

1. Aalways higher than Otto✓
2. Bequal to Carnot always✓
3. Cindependent of CR✓
4. Dlower than Otto cycle✓

Spark ignition engine uses

1. Acompression alone at CR 18✓
2. Bglow plug only always✓
3. Cspark plug to initiate flame✓
4. Dturbine blades✓

Engine firing order affects

1. Aoctane number of fuel✓
2. Bcoolant boiling point only✓
3. Ctire pressure✓
4. Dvibration, crankshaft loading and exhaust tuning✓

Flywheel on engine stores energy to

1. Aincrease exhaust temperature✓
2. Bcompress intake air✓
3. Csmooth speed fluctuations between power strokes✓
4. Dfilter fuel✓

TDC means

1. Atop dead center — piston at highest position✓
2. Bbottom of stroke✓
3. Cmid stroke only✓
4. Dcrank horizontal only✓

Valve overlap period allows

1. Acompression during both valves closed only✓
2. Bscavenging and intake charge preparation near exhaust TDC✓
3. Cfuel injection into exhaust✓
4. Dzero gas exchange✓

Compression stroke in four-stroke engine has

1. Aboth valves closed✓
2. Bintake valve open✓
3. Cexhaust valve open✓
4. Dboth valves open✓

Power stroke delivers work when

1. Apiston moves up compressing✓
2. Bonly exhaust valve opens✓
3. Cfuel is pumped to tank✓
4. Dexpanding gases push piston from TDC toward BDC✓

Brake power is measured at

1. Ainside cylinder PV diagram only✓
2. Bfuel tank level✓
3. Cengine output shaft using dynamometer✓
4. Dradiator inlet✓

Morris test or rope brake dynamometer measures

1. Aindicated pressure only✓
2. Bexhaust composition only✓
3. Ccoolant flow only✓
4. Dbrake torque and hence power✓

Heat balance on IC engine shows largest loss typically as

1. Auseful brake work majority always✓
2. Bradiation only✓
3. Czero loss at full load✓
4. Dexhaust and coolant heat rejection✓

Delay period in diesel combustion should be kept short to avoid

1. Alow efficiency always✓
2. Bcomplete combustion failure always✓
3. Czero power always✓
4. Drapid pressure rise and rough running✓

Fumigation in CI engine means

1. Aintroducing gaseous fuel with intake air✓
2. Binjecting water in cylinder only✓
3. Cusing only electric spark✓
4. Deliminating air intake✓

Engine bore is

1. Astroke length✓
2. Bcylinder internal diameter✓
3. Ccrank radius only✓
4. Dconnecting rod length only✓

Engine stroke is

1. Abore diameter✓
2. Bvalve lift only✓
3. Cdistance piston travels between TDC and BDC✓
4. Dcrank web width✓

Swept volume per cylinder is

1. Abore × stroke only without π✓
2. Bstroke² × bore✓
3. Cπ/4 × bore² × stroke✓
4. Dπ × bore only✓

Clearance volume is volume at

1. ABDC only✓
2. BTDC with piston at top including combustion chamber✓
3. Cmid stroke only✓
4. Dcrankcase only✓

Compression ratio r is

1. AVs / Vc only without adding Vc✓
2. BVc / Vs✓
3. C(Vs + Vc) / Vc✓
4. Dbore/stroke ratio✓

Engine displacement is

1. Aclearance volume only✓
2. Bintake manifold volume✓
3. Cfuel tank capacity✓
4. Dtotal swept volume of all cylinders✓

Indicated power from PV diagram is

1. Abrake torque only✓
2. Bfuel heating value only✓
3. Ccoolant heat rejection✓
4. Dwork per cycle × cycles per second✓

Friction power equals

1. Aindicated power minus brake power✓
2. Bbrake plus indicated✓
3. Cfuel energy input✓
4. Dexhaust enthalpy✓

Willans line in steam engine analogy for IC testing relates

1. Aoctane to cetane✓
2. Bfuel consumption to brake power linearly at constant speed✓
3. Cbore to stroke only✓
4. Dcoolant to oil viscosity✓

Misfiring limit in SI engine occurs when mixture is

1. Atoo lean or too rich to propagate flame reliably✓
2. Balways stoichiometric✓
3. Calways at best economy point✓
4. Dat maximum CR only✓

Ignition timing advance increases

1. Aexhaust temperature decrease always unlimited✓
2. Bpeak pressure before TDC improving efficiency up to knock limit✓
3. Calways reduces power✓
4. Ddelays combustion always✓

Retarded spark timing generally

1. Areduces knock but lowers efficiency and raises exhaust temperature✓
2. Beliminates all emissions✓
3. Cincreases peak pressure always✓
4. Dincreases volumetric efficiency always✓

Engine octane requirement increases with

1. Adecreasing CR✓
2. Bcold dense air only always✓
3. Ccompression ratio and inlet temperature✓
4. Dretarded timing only always✓

Automotive diesel injection pressure in common rail may exceed

1. A1500 bar✓
2. B5 bar✓
3. C50 bar✓
4. Datmospheric only✓

White smoke from diesel at cold start is mainly

1. Apure NOx gas✓
2. Bunburned fuel droplets and water vapor✓
3. Clubricating oil always✓
4. Dcarbon particles only always✓