mechanical engineering MCQs – Page 65

Practise multiple-choice questions from mechanical engineering for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

3201. To reduce the possibility of knock in the C.I. engines, the first elements of fuel and air should have_______________?
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A. reactive mixture

B. high temperature

C. high density

D. short delay

E. all of the above
3202. A fuel will detonate less if it has___________________?
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A. proper self ignition temperature

B. lower self ignition temperature

C. none of the above

D. higher self ignition temperature

E. self ingition temperature has nothing to do with detonation

3203. A 5 BHP engine running at full load would consume diesel of the order of_________________?
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A. 0.3 kg/hr

B. 1 kg/hr

C. 3 kg/hr

D. 5 kg/hr

E. 10 kg/hr

3204. Flash point of fuel oil is __________________?
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A. temperature at which it catches fire without external aid

B. temperature at which it solidifies or congeals

C. minimum temperature to which1 oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in contact with a flame

D. indicated by 90% distillation temperature, i.e. when 90% of sample oil has distilled off

E. none of the above

3205. Scavenging air in diesel engine means___________________?
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A. burnt air containing products of combustion

B. air used for forcing burnt gases out of engines cylinder during the exhaust period

C. forced air for cooling cylinder

D. air fuel mixture

E. air used for combustion sent under pres-sure

3206. Kerosene is distilled at________________?
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A. 350 450C

B. 30 65C

C. 220 350C

D. 450-550C

E. 65 220C

3207. Fuel consumption with increase in back pressure will________________?
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A. depend on other factors

B. increase

C. decrease

D. remain unaffected

E. none of the above

3208. Excess quantities of sulphur in diesel fuel are Objectionable because it may cause the following______________?
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A. ch of the following is false statement?

3209. The function of a distributor in an automobile is to__________________?
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A. regulate power

B. distribute charge, equally to all the cylinders

C. feed lub oil to all moving parts

D. inject fuel at appropriate time

E. time the spark
3210. In open combustion chamber in diesel engines____________________?
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A. fuel is injected into an auxiliary chamber that is separated from the cylinder by an orifice or throat

B. the shape and layout of the piston crown, the inlet port, and the valve produce the turbulent effect on fuel mixture

C. fuel is injected at atmospheric pressure

D. there are no valves.

E. only a part of air charge is contained in an auxiliary chamber in which the fuel starts to burn with insufficient air which due to explosion tendency mixes thoroughly into main cylinder charge

3211. It the temperature of intake air in IC engines is lowered, then its efficiency will_______________________?
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A. decrease upto certain limit and then in-crease

B. decrease

C. increase upto certain limit and then decrease

D. increase

E. remain same

3212. According to Recardos theory, detonation occurs due to______________________?
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A. none of the above

B. instantaneous auto-ignition of last part of charge to be burnt

C. improper mixing of air and fuel

D. self ignition temperature has nothing to do with detonation

E. improper combustion

3213. The essential equipment for producing high vlotage for sparking in petrol engines with battery is_______________?
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A. ignition coil, contact breaker and con-denser

B. ignition coil

C. ignition coil and distributor

D. ignition coil and contact breaker

E. ignition coil and condenser

3214. Fuel consumption of diesef engines is not guaranteed at one quarter load because at such low loads________________?
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A. the engine is rarely operated

B. the friction is unpredictable

C. none of the above

D. the small difference in cooling water temperature or in internal friction has a disproportionate effect

E. the friction is high

3215. The compression ratio of motor cars is___________________?
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A. 13

B. 16

C. 5

D. 10

E. 7
3216. An engine indicator is used to determine the following___________________?
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A. volume of cylinder

B. speed

C. BHP

D. temperature

E. m.e.p. and I.H.P.
3217. A heat engine utilises the_________________?
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A. mean heat value of oil

B. calorific value of oil

C. low heat value of

D. high heat value of oil

E. all of the above

3218. Ethyl fluid is used_______________________?
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A. as a defrosting agent

B. as a superior type of fluid compared to others

C. to increase the cetane rating of the fuel

D. to increase the octane rating of the fuel

E. to improve lubricating quality of fuel

3219. The fuel air ratio in a petrol engine fitted with suction carburettor, operating with dirty air filter as compared to clean filter will be________________?
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A. remain unaffected

B. higher

C. none of the above

D. lower

E. unpredictable

3220. Petrol is distilled at a temperature in range of__________________?
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A. 450-550C

B. 220-350C

C. 350-450C

D. 65 220C

E. 30 65C

3221. Installation of supercharger on a four-cycle diesel engine can result in the following percentage increase in power_____________?
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A. upto 75%

B. upto 25%

C. upto 35%

D. upto 50%

E. upto 100%.
3222. As a result of detonation in an I.C. engine, following parameter attains very high value _____________________?
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A. peak temperature

B. rate of rise of pressure

C. rate of rise of temperature

D. peak pressure

E. rate of rise of horse-power

3223. The air-fuel ratio of the petrol engine is controlled by__________________?
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A. injector

B. governor

C. fuel pump

D. carburettor

E. scavenging

3224. For low speed operation or for idling in petrol engines, the engine requirements are for_______________?
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A. lean mixture

B. rich mixture

C. theoretically correct mixture

D. lean/rich mixture depending upon capacity of engine

E. any type of mixture

3225. The top piston ring nearer to the piston crown is known as_____________________?
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A. leading ring

B. oil ring

C. compression ring

D. scrapper ring

E. groove ring

3226. In a typical medium speed 4-stroke cycle diesel engine the inlet valve_____________________?
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A. may open or close anywhere

B. opens at top dead center and closes at bottom dead center

C. opens at 20 before top dead center and closes at 35 after the bottom dead center

D. opens at 10 after top dead center and closes 20 before the bottom dead center

E. remains open for 200.

3227. Air fuel ratio for idling speed of a petrol engine is approximately_________________?
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A. 10:1

B. 15:01

C. 5:01

D. 1:01

E. 20:01

3228. Compression loss in I.C engines occurs due to_________________?
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A. increase in clearance volume caused b bearing-bushing wear

B. clogged air-inlet slots

C. leaking piston rings

D. all of the above

E. use of thick head gasket

3229. Which of the following is false statement. Some of the methods used to reduce diesel smoke are as follows ________________?
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A. using additives in the fuel

B. engine derating i.e. reducing the maxi-mum flow of fuel

C. adherence to proper fuel specification

D. avoidance of overloading

E. increasing the compression ratio
3230. The air standard efficiency of an Otto cycle compared to diesel cycle for the given compression ratio is__________________?
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A. unpredictable

B. less

C. more or less depending on power rating

D. more

E. same

3231. Combustion in compression ignition engines is____________________?
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A. homogeneous

B. heterogeneous

C. both A. and B.

D. laminar

E. turbulent

3232. For maximum power generation, the air fuel ratio for a petrol engine for vehicles, is of the order of _________________?
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A. 18:01

B. 9:01

C. 20:01

D. 15:01

E. 12 : 1
3233. Ignition lag is__________________?
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A. time before actual fuel injection and the pump plunger starts to pump fuel

B. time corresponding to actual injection and top dead center

C. none of the above

D. the time taken by fuel after injection (before top dead center) to reach upto auto-ignition temperature

E. time corresopnding to actual ingition and top dead center

3234. Volatility of diesel fuel oil is_________________?
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A. minimum temperature to which oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in contact with a flame

B. temperature at which it flows easily

C. temperature at which it solidifies or congeals

D. it catches fire without external aid

E. indicated by 90% distillation temperature, i.e., when 90% of sample oil has distilled off
3235. Which of the following is the lightest and most volatile liquid fuel________________?
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A. gasoline

B. diesel

C. lub oil

D. kerosene

E. fuel oil

3236. In a typical medium speed 4 stroke cycle diesel engine_______________?
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A. exhaust valve opens at bottom dead center and closes at top dead center

B. exhaust valve opens at 35 before bot-tom dead center and closes at 20 after top dead center

C. exhaust valve opens just after bottom dead center and closes just before top dead center

D. may open and close anywhere

E. none of the above is true

3237. The fuel in diesel engine is normally injected at pressure of_________________?
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A. 20-25 kg/cm2

B. 150-250 kg/cm2

C. 90-130 kg/cm2

D. 60-80 kg/cm2

E. 5-10 kg/cm2

3238. The output of a diesel engine can be increased without increasing the engine revolution or size in following way_________________?
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A. increasing flywheel size

B. supercharging

C. scavenging

D. heating incoming air

E. feeding more fuel

3239. Polymerisation is a chemical process in which molecules of a compound become________________?
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A. smaller

B. gaseous

C. larger

D. liquid

E. slowed down

3240. Method of governing used in diesel engine is__________________?
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A. nit and miss governing

B. combined governing

C. quantity governing

D. quality governing

E. partial governing

3241. The thermal efficiecny of a diesel cycle having fixed compression ratio, with increase in cut-off ratio will___________________?
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A. may increase or decrease depending on other factors

B. be independent

C. none of the above

D. increase

E. decrease
3242. A diesel engine has_________________?
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A. 3 valves

B. 1 valve

C. 2 valves

D. no valve

E. 4 valves

3243. The magneto in an automobile is basically__________________?
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A. transformer

B. capacitor

C. a.c. generator

D. d.c. generator

E. magnetic circuit

3244. Which is more viscous lub oil_________________?
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A. SAE 80

B. SAE 4

C. SAE 50

D. SEA 30

E. SAE 70

3245. For the same power developed in I.C. engines, the cheaper system is_____________?
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A. supercharged

B. naturally aspirated

C. centrifugal pump

D. turbo charger

E. none of the above

3246. Pick up the wrong statement about supercharging __________________?
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A. supercharging is essential in aircraft engines

B. there can be limited supercharging in petrol engines because of detonation

C. supercharging reduces knocking in diesel engines

D. supercharging at high altitudes is essential

E. supercharging results in fuel economy
3247. In petrol engine, increase of cooling water temperature will_________________?
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A. unpredictable

B. increase or decrease knocking tendency depedning on strength and time of spark

C. not affect the knocking tendency

D. decrease the knocking tendecny

E. increase the knocking tendency
3248. If diesel is fed by mistake in the oil tank of a petrol engien, then engine will________________?
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A. knock

B. detonate

C. give lot of smoke

D. run for some time and then stop

E. not run
3249. The specific fuel consumption per BHP hour for diesel engine is approximately___________________?
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A. 0.25 kg

B. 0.2 kg

C. 0.15 kg

D. 0.3 kg

E. 0.35 kg

3250. The pressure and temperature at the end of compression stroke in a petrol engine are of the order of___________________?
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A. 6 12 kg/cm2 and 250 350C

B. 12 20 kg/cm2 and 350 450C

C. 20 30 kg/cm2 and 450 500C

D. 4 6 kg/cm2 and 200 250C

E. 30 40 kg/cm2 and 500 700C