Internal Combustion Engines MCQs 2026

Scavenging in two-stroke engine means

1. A lubricating crankshaft only ✓
2. B cooling radiator ✓
3. C filtering oil ✓
4. D replacing exhaust gas with fresh charge ✓

NOx formation increases with

1. A low temperature only ✓
2. B rich mixture only always ✓
3. C high peak combustion temperature and oxygen availability ✓
4. D retarded spark only always ✓

CO in exhaust indicates

1. A perfect stoichiometric burn always ✓
2. B high NOx only ✓
3. C low oil consumption ✓
4. D incomplete combustion due to insufficient oxygen ✓

HC emissions in exhaust are primarily

1. A nitrogen gas from air always counted as HC ✓
2. B carbon dioxide only ✓
3. C water vapor only ✓
4. D unburned or partially burned hydrocarbons ✓

Lambda sensor measures

1. A fuel temperature only ✓
2. B oxygen content in exhaust for air-fuel ratio control ✓
3. C coolant level ✓
4. D crank position only ✓

Catalytic converter reduces

1. A engine noise only ✓
2. B fuel octane requirement ✓
3. C CO, HC and NOx in exhaust ✓
4. D intake air temperature ✓

Exhaust gas recirculation (EGR) reduces

1. A CO always to zero ✓
2. B fuel consumption always increases HC only ✓
3. C NOx by lowering peak combustion temperature ✓
4. D engine power always to zero ✓

Piston rings primary functions include

1. A cooling radiator water ✓
2. B sealing combustion gas and controlling oil consumption ✓
3. C driving camshaft ✓
4. D filtering intake air ✓

Oil pump in engine typically provides

1. A fuel injection pressure 200 bar always ✓
2. B coolant circulation ✓
3. C pressurized oil to bearings and sliding parts ✓
4. D intake boost ✓

Otto cycle consists of

1. A two constant pressure and two isothermal ✓
2. B four constant volume only ✓
3. C two isentropic and two constant volume processes ✓
4. D one isentropic and three isobaric ✓

Diesel cycle differs from Otto cycle by having

1. A constant volume heat rejection only ✓
2. B constant pressure heat addition ✓
3. C isothermal compression ✓
4. D no expansion stroke ✓

SAE viscosity grade 20W-40 indicates

1. A single viscosity at 100 °C only ✓
2. B fuel octane rating ✓
3. C multigrade oil meeting winter and high temperature specs ✓
4. D coolant concentration ✓

Engine lubrication oil reduces

1. A combustion temperature directly ✓
2. B intake air density always ✓
3. C friction, wear and carries heat from bearings ✓
4. D exhaust oxygen content ✓

Radiator pressure cap raises boiling point by

1. A increasing system pressure ✓
2. B vacuum in cooling system ✓
3. C adding antifreeze only without pressure ✓
4. D reducing coolant flow ✓

Compression ratio of SI engine is typically limited to about

1. A 20 to 25 ✓
2. B 4 to 6 ✓
3. C 30 to 35 ✓
4. D 10 to 12 ✓

Thermal efficiency of Otto cycle increases with

1. A decreasing CR ✓
2. B compression ratio ✓
3. C increasing exhaust back pressure only ✓
4. D reducing specific heat ratio ✓

Thermal efficiency of Diesel cycle for same compression ratio is

1. A always higher than Otto ✓
2. B equal to Carnot always ✓
3. C independent of CR ✓
4. D lower than Otto cycle ✓

Spark ignition engine uses

1. A compression alone at CR 18 ✓
2. B glow plug only always ✓
3. C spark plug to initiate flame ✓
4. D turbine blades ✓

Glow plugs in diesel aid

1. A cold starting by heating combustion chamber air ✓
2. B high speed turbo spool only ✓
3. C exhaust gas recirculation cooling ✓
4. D lubrication at operating temperature ✓

Turbocharger on IC engine increases power by

1. A mechanical supercharger belt only always ✓
2. B burning fuel in turbine ✓
3. C using exhaust energy to compress intake air ✓
4. D reducing CR ✓

Supercharger differs from turbocharger because it is

1. A mechanically driven from crankshaft ✓
2. B exhaust driven always ✓
3. C electric only always ✓
4. D not a compressor ✓

Intercooler after compressor reduces

1. A fuel octane requirement to zero ✓
2. B exhaust temperature to ambient always ✓
3. C intake air temperature and increases density ✓
4. D engine displacement ✓

Thermosyphon cooling relies on

1. A natural convection without water pump ✓
2. B forced pump circulation only ✓
3. C refrigerant evaporation in cylinder ✓
4. D oil spray on pistons only ✓

Engine cooling system primary purpose is to

1. A maintain optimal metal temperatures and prevent overheating ✓
2. B increase exhaust temperature ✓
3. C eliminate friction entirely ✓
4. D raise combustion temperature unlimited ✓

White smoke from diesel at cold start is mainly

1. A pure NOx gas ✓
2. B unburned fuel droplets and water vapor ✓
3. C lubricating oil always ✓
4. D carbon particles only always ✓

Dual fuel engine runs on

1. A water emulsion only ✓
2. B pure hydrogen without air ✓
3. C solid coal dust only ✓
4. D gaseous fuel with pilot diesel injection ✓

Miller cycle uses

1. A late exhaust only ✓
2. B diesel injection in SI ✓
3. C no turbo ✓
4. D early intake valve closing to reduce effective compression ✓

Atkinson cycle achieves higher efficiency by

1. A higher friction losses ✓
2. B expanding more than compressing (over-expansion) ✓
3. C constant volume heat add only ✓
4. D no expansion stroke ✓

Wankel rotary engine uses

1. A trochoidal rotor in epitrochoidal housing ✓
2. B reciprocating piston only ✓
3. C steam turbine blades ✓
4. D external boiler ✓

Uniflow scavenging uses

1. A only side ports both ends ✓
2. B no exhaust path ✓
3. C spark at exhaust port ✓
4. D piston-controlled ports and cylinder head exhaust valve ✓

Loop scavenging in two-stroke uses

1. A separate blower only always ✓
2. B incoming charge to push exhaust through ports ✓
3. C four valves per cylinder ✓
4. D turbo only ✓

Compression ignition engine relies on

1. A auto-ignition of fuel injected into hot compressed air ✓
2. B spark at TDC always ✓
3. C carburetor mixture only ✓
4. D steam injection ✓

Four-stroke engine completes one power stroke in

1. A one revolution ✓
2. B two crankshaft revolutions ✓
3. C four revolutions ✓
4. D half revolution ✓

Two-stroke engine produces power stroke

1. A every two revolutions ✓
2. B every crankshaft revolution ✓
3. C every four revolutions ✓
4. D only at idle ✓

Volumetric efficiency is defined as

1. A actual mass inducted / mass at STP filling swept volume ✓
2. B brake power / indicated power ✓
3. C fuel consumed / air mass ✓
4. D exhaust pressure / inlet pressure ✓

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

1. A increased CR always ✓
2. B reduced time for intake and valve flow restrictions ✓
3. C zero friction ✓
4. D perfect scavenging ✓

Detonation differs from surface ignition in that detonation is

1. A rapid auto-ignition of end gas with pressure waves ✓
2. B glow ignition from hot deposits only ✓
3. C pre-ignition from spark plug fault always ✓
4. D normal flame propagation ✓

Pre-ignition occurs when

1. A charge ignites before spark due to hot spots ✓
2. B flame propagates normally after spark ✓
3. C only at very retarded timing ✓
4. D fuel is pure octane ✓

Cetane number indicates

1. A knock resistance of petrol ✓
2. B octane blending value ✓
3. C ignition quality of diesel fuel ✓
4. D steam quality ✓

Ignition delay in CI engine is time between

1. A spark and power stroke ✓
2. B start of injection and start of combustion ✓
3. C intake and exhaust ✓
4. D TDC and BDC only ✓

Combustion in SI engine is ideally

1. A flame propagation through premixed charge ✓
2. B diffusion controlled spray burning only ✓
3. C constant pressure always ✓
4. D external combustion ✓

Combustion in CI engine is primarily

1. A homogeneous premixed only ✓
2. B spark initiated always ✓
3. C isothermal ✓
4. D diffusion controlled after vaporization ✓

Air-fuel ratio for petrol stoichiometric is approximately

1. A 22:1 by mass ✓
2. B 4:1 by mass ✓
3. C 14.7:1 by mass ✓
4. D 50:1 by mass ✓

Rich mixture in SI engine generally produces

1. A maximum fuel economy always ✓
2. B more power but lower thermal efficiency and higher HC/CO ✓
3. C zero CO emissions ✓
4. D lower exhaust temperature always ✓

Lean mixture improves

1. A always increases knock ✓
2. B fuel economy and reduces CO at cost of NOx control challenge ✓
3. C eliminates need for ignition ✓
4. D increases volumetric efficiency always ✓

Brake mean effective pressure (BMEP) is

1. A peak firing pressure ✓
2. B inlet manifold vacuum only ✓
3. C oil gallery pressure ✓
4. D average pressure producing brake power over displacement volume ✓

Indicated mean effective pressure (IMEP) is measured using

1. A exhaust gas analyzer only ✓
2. B fuel flow meter alone ✓
3. C engine indicator or cylinder pressure diagram ✓
4. D speedometer ✓

Mechanical efficiency of engine is

1. A indicated / brake ✓
2. B brake power / indicated power ✓
3. C thermal / volumetric ✓
4. D fuel energy / heat loss ✓

Brake thermal efficiency is

1. A indicated power / fuel energy ✓
2. B volumetric efficiency squared ✓
3. C brake power / energy in fuel supplied ✓
4. D BMEP / IMEP only ✓

Specific fuel consumption (BSFC) is

1. A power per fuel volume only ✓
2. B air flow per stroke ✓
3. C torque per RPM only ✓
4. D fuel mass flow per unit brake power ✓

Carburetor function is to

1. A atomize and mix fuel with air in correct proportion ✓
2. B compress air only ✓
3. C ignite mixture ✓
4. D cool exhaust gas ✓

Fuel injection in modern SI engines improves

1. A always eliminates air filter ✓
2. B fuel distribution, efficiency and emission control ✓
3. C reduces CR requirement to 4 ✓
4. D removes need for spark ✓

Common rail diesel injection provides

1. A low pressure gravity feed only ✓
2. B mechanical jerk pump only per cylinder ✓
3. C carburetor venturi ✓
4. D high pressure fuel available continuously to injectors ✓

Engine firing order affects

1. A octane number of fuel ✓
2. B coolant boiling point only ✓
3. C tire pressure ✓
4. D vibration, crankshaft loading and exhaust tuning ✓

Flywheel on engine stores energy to

1. A increase exhaust temperature ✓
2. B compress intake air ✓
3. C smooth speed fluctuations between power strokes ✓
4. D filter fuel ✓

TDC means

1. A top dead center — piston at highest position ✓
2. B bottom of stroke ✓
3. C mid stroke only ✓
4. D crank horizontal only ✓

Valve overlap period allows

1. A compression during both valves closed only ✓
2. B scavenging and intake charge preparation near exhaust TDC ✓
3. C fuel injection into exhaust ✓
4. D zero gas exchange ✓

Compression stroke in four-stroke engine has

1. A both valves closed ✓
2. B intake valve open ✓
3. C exhaust valve open ✓
4. D both valves open ✓

Power stroke delivers work when

1. A piston moves up compressing ✓
2. B only exhaust valve opens ✓
3. C fuel is pumped to tank ✓
4. D expanding gases push piston from TDC toward BDC ✓

Brake power is measured at

1. A inside cylinder PV diagram only ✓
2. B fuel tank level ✓
3. C engine output shaft using dynamometer ✓
4. D radiator inlet ✓

Morris test or rope brake dynamometer measures

1. A indicated pressure only ✓
2. B exhaust composition only ✓
3. C coolant flow only ✓
4. D brake torque and hence power ✓

Heat balance on IC engine shows largest loss typically as

1. A useful brake work majority always ✓
2. B radiation only ✓
3. C zero loss at full load ✓
4. D exhaust and coolant heat rejection ✓

Delay period in diesel combustion should be kept short to avoid

1. A low efficiency always ✓
2. B complete combustion failure always ✓
3. C zero power always ✓
4. D rapid pressure rise and rough running ✓

Fumigation in CI engine means

1. A introducing gaseous fuel with intake air ✓
2. B injecting water in cylinder only ✓
3. C using only electric spark ✓
4. D eliminating air intake ✓

Engine bore is

1. A stroke length ✓
2. B cylinder internal diameter ✓
3. C crank radius only ✓
4. D connecting rod length only ✓

Engine stroke is

1. A bore diameter ✓
2. B valve lift only ✓
3. C distance piston travels between TDC and BDC ✓
4. D crank web width ✓

Swept volume per cylinder is

1. A bore × stroke only without π ✓
2. B stroke² × bore ✓
3. C π/4 × bore² × stroke ✓
4. D π × bore only ✓

Clearance volume is volume at

1. A BDC only ✓
2. B TDC with piston at top including combustion chamber ✓
3. C mid stroke only ✓
4. D crankcase only ✓

Compression ratio r is

1. A Vs / Vc only without adding Vc ✓
2. B Vc / Vs ✓
3. C (Vs + Vc) / Vc ✓
4. D bore/stroke ratio ✓

Engine displacement is

1. A clearance volume only ✓
2. B intake manifold volume ✓
3. C fuel tank capacity ✓
4. D total swept volume of all cylinders ✓

Indicated power from PV diagram is

1. A brake torque only ✓
2. B fuel heating value only ✓
3. C coolant heat rejection ✓
4. D work per cycle × cycles per second ✓

Friction power equals

1. A indicated power minus brake power ✓
2. B brake plus indicated ✓
3. C fuel energy input ✓
4. D exhaust enthalpy ✓

Willans line in steam engine analogy for IC testing relates

1. A octane to cetane ✓
2. B fuel consumption to brake power linearly at constant speed ✓
3. C bore to stroke only ✓
4. D coolant to oil viscosity ✓

Misfiring limit in SI engine occurs when mixture is

1. A too lean or too rich to propagate flame reliably ✓
2. B always stoichiometric ✓
3. C always at best economy point ✓
4. D at maximum CR only ✓

Ignition timing advance increases

1. A exhaust temperature decrease always unlimited ✓
2. B peak pressure before TDC improving efficiency up to knock limit ✓
3. C always reduces power ✓
4. D delays combustion always ✓

Retarded spark timing generally

1. A reduces knock but lowers efficiency and raises exhaust temperature ✓
2. B eliminates all emissions ✓
3. C increases peak pressure always ✓
4. D increases volumetric efficiency always ✓

Engine octane requirement increases with

1. A decreasing CR ✓
2. B cold dense air only always ✓
3. C compression ratio and inlet temperature ✓
4. D retarded timing only always ✓

Automotive diesel injection pressure in common rail may exceed

1. A 1500 bar ✓
2. B 5 bar ✓
3. C 50 bar ✓
4. D atmospheric only ✓