⚙️ Mechanical Eng Solved MCQs with Answers

Practice 934 approved ⚙️ Mechanical Eng questions with verified answers from the 🛠️ Engineering Essentials subject for Pakistan exams.

934 solved MCQs

In a four stroke cycle, the minimum temperature inside the engine cylinder occurs at theAnswer: beginning of suction stroke In a centrifugal compressor, an increase in speed at a given pressure ratio causesAnswer: increase in flow and decrease in efficiency In hit and miss governing, the fuel supply is cut-off completely during one or more number of cycles.Answer: Yes A large clearance Volume in a reciprocating compressor results inAnswer: reduced volume flow rate The thermal efficiency of a standard Otto cycle for a compression ratio of 5.5 will beAnswer: 50% A closed cycle gas turbine gives __________ efficiency as compared to an open cycle gas turbine.Answer: higher The ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston is calledAnswer: volumetric efficiency Gas turbine as compared to steam turbineAnswer: all of these The exhaust valve in a four stroke cycle petrol engineAnswer: opens at 50° before bottom dead centre and closes at 15° after top dead centre Intercooling in gas turbinesAnswer: increases net output but decreases thermal efficiency Nuclear reactors are usedAnswer: all of these When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is __________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.Answer: equal to A moderator generally used in nuclear power plants isAnswer: graphite and concrete The predominent isotope of the naturally occuring element isAnswer: U₂₃₈ The brake power of a diesel engine, keeping other parameters constant, can be increased byAnswer: increasing the pressure of intake air In diesel engines, the fuel is injected in the form of very fine spray, into the engine cylinder, which gets ignited due to high temperature of the compressed air.Answer: Agree Pre-ignition is caused by the spontantaneous combustion of the mixture before the end of the compression stroke, and is due toAnswer: any one of these The expansion of fuel in a four stroke cycle diesel engineAnswer: starts at 15° after top dead centre and ends at 30° before bottom dead centre The object of supercharging the engine isAnswer: all ofthe above In open combustion chamber in diesel engines, the shape and layout of the piston crown, the inlet port and the valve produce the turbulent effect of fuel mixture.Answer: True In a four stroke cycle petrol engine, the charge is ignited atAnswer: 30° before top dead centre A moderator, in nuclear power plants, is a medium introduced into the fuel mass in order toAnswer: slow down the speed of fast moving neutrons Where reactor operation is designed with fast neutrons such as in reactors using highly enriched fuel, the moderator used isAnswer: no moderator is needed In a diesel engine, the duration between the time of injection and ignition, is known asAnswer: delay period The detonating tendency in petrol engines increases with increase of compression ratio.Answer: True Each fission of U₂₃₅ produces on the average __________ fast neutrons as a product of reaction.Answer: 2.46 Reactors for propulsion applications are designed forAnswer: enriched uranium The primary fuel used in nuclear power plants isAnswer: U₂₃₅ In petrol engine, using a fixed octane rating fuel and fixed compression ratio, supercharging will __________ the knocking tendency.Answer: increase Ordinary water is sometimes used as moderator when enriched uranium is used as a fuel in nuclear power plants.Answer: Yes