mechanical engineering MCQs – Page 66

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 Review each marked answer and report any item that may be outdated or unclear.

3251. In a naturally aspirated diesel engine, the air is supplied by________________?
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A. a vacuum chamber

B. a supercharger

C. forced chamber

D. an injection tube

E. a centrifugal blower

3252. The spark plug gap is normally maintained at________________?
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A. 0.6 to 0.8 mm

B. 0.2 to 0.4 mm

C. 0.8 to 1 mm

D. 0.1 to 0.2 mm

E. 0.45 to 0.6 mm
3253. High carbon content in diesel oil used for diesel engine leads to_________________?
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A. production of highly corrosive gases corroding the cylinder walls and exhaust system

B. excessive engine wear

C. damaging of both the storage tank and the engine

D. deposition on engine parts

E. none of the above.

3254. Gaseous-fuel guarantees are based on___________________?
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A. high heat value of oil

B. low heat value of oil

C. calorific value of oil

D. mean heat value of oil

E. all of the above

3255. Injection lag is_________________?
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A. time corresponding to actual ignition and top dead center

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

C. time corresponding to actual injection and top dead center

D. time before actual fuel injection and the pump pluger starts to pump fuel

E. none of the above

3256. Which of the following statements is correct ?
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A. All the irreversible engines have same efficiency

B. All the reversible engines have same efficiency

C. Both Rankine and Caront cycles have same efficiency between same temperature limits

D. All reversible engines working between same temperature limits have same-efficiency

E. Between same temperature limits, both petrol and diesel engines have same efficiency

3257. The knocking in diesel engines for given fuel, will be__________________?
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A. enhanced by increasing compression ratio

B. dependent on other factors

C. first enhanced by increasig compression ratio upto a limit beyond which it will be suppressed

D. enhanced by decreasing compression ratio

E. unaflected by compression ratio

3258. Does the supply of scavenging air at a density greater than that of atmosphere mean engine is supercharged ?
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A. depends on other factors

B. no

C. to some extent

D. unpredictable

E. yes

3259. Ignition quality of diesel-fuel oil is expressed by an index called__________________?
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A. octane number

B. calorific value

C. carbon content

D. ignition temperature

E. cetane number
3260. If overhead clearance is less, then the following type of engine should be selected__________________?
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A. Radial

B. Vertical

C. V-type

D. Horizontal

E. In-line

3261. For the same size and weight, a two stroke engine as compared to four stroke engine will generate power_________________?
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A. about 1.7 times

B. about 0.5 times

C. about twice

D. nearly equal

E. about 5 times

3262. The cooling water requirement for diesel engine is of the order of________________?
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A. 10 to 20 liters per minute per h.p.

B. 5 to 10 liters per minute per h.p

C. 1 to 3 liters per minute per h.p.

D. 20-30 liters per minute per h.p

E. 0.2 to 1.0 liter per minute per h.p.

3263. The precess of breaking up or a lipuid into fine droplets by spraying is called___________________?
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A. ionisation

B. injection

C. atomisation

D. vaporisation

E. carburetion

3264. The pressure at the end of compression in the case of diesel engine is of the order of___________________?
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A. 27.5 kg/cmz

B. 20 kg/cmz

C. 12kg/cmz

D. 6 kg/cm

E. 35 kg/cm
3265. A 75 cc engine has following parameter as 75 cc ___________________?
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A. clearance volume

B. lub oil capacity

C. fuel tank capacity

D. cylinder volume

E. swept volume
3266. With increase in speed of vehicle, the back pressure will________________?
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A. depend on other factors

B. remain unalfected

C. none of the above

D. increase

E. decrease

3267. Self-ignition temperature of petrol is of the order of___________________?
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A. 450C

B. 370C

C. 240C

D. more than 500C.

E. 150C

3268. Leakage past the piston rings and valve seats in I.C. engines with increase in speed_______________?
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A. unpredictable

B. increases.

C. remains same

D. none of the above

E. decreases
3269. Theoretically, the following engine should have maximum efficiency________________?
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A. steam engine

B. 2-stroke S.I. engine

C. gas engine

D. 4-stroke C.I. engine

E. 4-stroke S.I. engine

3270. The specific fuel consumption of a petrol engine compared to diesel engine of same H.P. is_______________?
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A. more

B. less or more depending on operating conditions

C. less

D. unpredictable

E. same

3271. The cam shaft of a four stroke I.C. engine running at 1500 rmp will run at __________________?
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A. 1500 rpm

B. any value independent of engine speed

C. 750 rpm

D. none of the above

E. 3000 rpm

3272. In order to prevent knock in the S.I. engines, the charge away from the spark plug should have___________________?
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A. rich mixture

B. all of the above

C. low density

D. long ignition delay

E. low temperature

3273. Diesel engines have low specific fuel consumption compared to petrol engine. This statement is____________________?
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A. not true

B. true at full load

C. true at part load

D. true at both part and full load

E. there could not be any such criterion

3274. The accunmulation of carbon in a cylinder results in increase of________________?
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A. volumetric efficiency

B. effective compression ratio

C. valve travel time.

D. clearance volume

E. ignition time

3275. The rating of a diesel engine, with increase in airintlet temperature, will ___________________?
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A. decrease linearly

B. increase linearly

C. increase parabolically

D. first decrease linearly and then increase parabolically

E. decrease parabolically

3276. In diesel engine, the compression ratio in comparison to expansion ratio is_______________?
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A. more/less depending on engine capacity.

B. more

C. less

D. same

E. variable

3277. For low load operation, more suitable (economical) engine is_______________?
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A. S.I. engine

B. C.I. engine

C. both are equally good

D. multicylinder engine

E. two stroke engine

3278. The ratio of indicated thermal efficiency to the corresponding air standard cycle efficiency is called__________________?
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A. cycle efficiency

B. efficiency ratio

C. relative efficiency

D. overall efficiency

E. net efficiency

3279. Most high speed compression engines operate on ___________________?
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A. Two stroke cycle

B. Dual cycle

C. Otto cycle

D. Diesel cycle

E. Carnot cycle

3280. Most high speed compression engines operate on __________________?
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A. Diesel cycle

B. Carnot cycle

C. Otto cycle

D. Dual combustion cycle

E. Special type of air cycle

3281. The air requirement of a petrol engine during starting compared to theoretical airequired for complete combustion is___________________?
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A. loss

B. more

C. may be more or less depending on engine capacity

D. unpredictable

E. same

3282. If the compression ratio of an engine working on Otto cycle is increased from 5 to 7, the %age increase in efficiency will be________________?
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A. 14%

B. 27%.

C. 4%

D. 8%

E. 2%

3283. The m.e.p. of a petrol engine first increases as the fuel air ratio is increased and then decreases on further increase in fuel air ratio. The M.E.P is maximum in the zone of________________?
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A. rich mixture

B. unpredictable

C. none of the above

D. lean mixture

E. chemically correct mixture

3284. The pistons are usually given a coating such as tin plating in order to________________?
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A. increase lubrication effect

B. reduce possibility of scoring

C. conduct heat efficiently

D. reduce friction

E. reduce weight

3285. Which of the following is not an interns combustion engine___________________?
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A. 2-stroke petrol engine

B. 4-stroke petrol engine

C. gas turbine

D. diesel engine

E. steam turbine
3286. When crude oil is heated, then which of the following hydrocarbon is given off first______________?
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A. gasoline

B. diesel

C. natural gas

D. paraffin

E. kerosene

3287. With increase in engine speed, the ignition of spark in petrol engine has to be __________________?
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A. Increased

B. Decreased

C. Unaltered

D. Advanced
3288. If petrol is used in a diesel engine, then______________?
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A. low power will be produced

B. efficiency will be low

C. black smoke will be produced

D. lot of fuel will remain unburnt

E. higher knocking will occur
3289. In precombustion chamber in diesel engine________________?
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A. 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

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

C. There are no valves

D. Fuel is injected into an auxiliary chamber that is separated from the cylinder by an orifice or throat

3290. The thermal efficiency of a semi-diesel cycle having fixed compression ratio and fixed quantity of heat, with increase in pressure ratio will_______________?
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A. increase

B. remain unaffected

C. decrease

D. first increase and then decrease

E. increase/decrease depending upon engine capacity

3291. The following type of carburettor is preferred_______________?
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A. none of the above

B. eccentric type

C. horizontal type

D. concentric type

E. vertical type

3292. The theoretically correct mixture of air and petrol is approximately ________________?
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A. 0.500694444

B. 0.625694444

C. 0.834027778

D. 0.334027778

3293. Pick up false statement?
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A. For petrol and large gas engines, quantity governingds preferred

B. In quantity governing, air fuel ratio is almost constant and quantity of charge is changed depending on load

C. In hit and miss governing, fuel supply is completely cut off during one or more number of cycles

D. In quality governing, quantity of fuel is varied to suit the load and total charge of air is varied

E. For close regulation of speed, combination of both quality and quantity governing is used

3294. Diesel Cycle is also known as : __________?
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A. Constant Pressure Cycle

B. All of above

C. Constant Volume cycle

D. Constant temperature cycle

3295. In a diesel engine, injection pressure developed by injector is of the order of______________?
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A. 1400 kg/cm2

B. 100 kg/cm2

C. 10 kg/cm2

D. 500 kg/cm2

3296. In the case of compression ignition engine, the %age of CO in exhaust gases is________________?
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A. Zero

B. Depends on load

C. 5-10%

D. Considerable percent

3297. The patrol is distilled at a temperature from :
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A. 6 to 20

B. 15 to 120

C. 220 to 345

D. 65 to 220
3298. The natural solid fuels are : ________?
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A. All of above

B. Peat

C. Wood

D. Lignite

3299. Carburretion is done to________________?
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A. break up and mix the petrol with air

B. govern the engine

C. scavenge the cylinder

D. feed petrol into cylinder

E. heat up the charge to cylinder

3300. Which of the following solid fuel has high caloric value : ___________?
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A. Peat

B. Bituminous coal

C. Wood

D. Anthracite coal