Explore topic-wise MCQs in Mechanical Engineering Questions.

This section includes 202 Mcqs, each offering curated multiple-choice questions to sharpen your Mechanical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.

1.

Air injection in I.C. engines refers to injection of___________________?
A. air only
B. liquid fuel only
C. liquid fuel and air
D. supercharging
E. does not exist
Answer» D. supercharging
Discussion
2.

According to Recardo’s theory, detonation occurs due to______________________?
A. instantaneous auto-ignition of last part of charge to be burnt
B. improper mixing of air and fuel
C. improper combustion
D. self ignition temperature has nothing to do with detonation
E. none of the above
Answer» B. improper mixing of air and fuel
Discussion
3.

In the crankcase method of scavenging, the air pressure is produced by_________________?
A. supercharger
B. centrifugal pump
C. natural aspirator
D. movement of engine piston
E. reciprocating pump
Answer» E. reciprocating pump
Discussion
4.

Freezing temperature of petrol is usually__________________?
A. 0°C
B. – 10°C
C. 10°C
D. less than – 30°C
E. less than – 273°C
Answer» E. less than – 273°C
Discussion
5.

The ignition of charge by some hot surface in the engine cylinder before operation of spark plug is known as________________?
A. auto ignition
B. preignition
C. retarded ignition
D. accelerated ignition
E. detonation
Answer» C. retarded ignition
Discussion
6.

Compression ratio of LC. engines is ___________________?
A. the ratio of volumes of air in cylinder before compression stroke and after compression stroke
B. volume displaced by piston per stroke and clearance volume in cylinder
C. ratio of pressure after compression and before compression
D. swept volume/cylinder volume
E. cylinder volume/swept volume
Answer» B. volume displaced by piston per stroke and clearance volume in cylinder
Discussion
7.

The knocking in diesel engines for given fuel, will be__________________?
A. enhanced by increasing compression ratio
B. enhanced by decreasing compression ratio
C. unaflected by compression ratio
D. first enhanced by increasig compression ratio upto a limit beyond which it will be suppressed
E. dependent on other factors
Answer» C. unaflected by compression ratio
Discussion
8.

Fuel oil consumption guarantees for I .C. engine are usually based on__________________?
A. low heat value of oil
B. high heat value of oil
C. net calorific value of oil
D. calorific value of fuel
E. all of the above
Answer» C. net calorific value of oil
Discussion
9.

All heat engines utilize_____________________?
A. low heat value of oil
B. high heat value of oil
C. net claorific value of oil
D. calorific value of fuel
E. all of the above
Answer» B. high heat value of oil
Discussion
10.

The calorific value of gaseous fuels is expressed in terms of__________________?
A. kcal
B. kcal/kg
C. kcal/m2
D. kcal/m²
E. all of the above
Answer» E. all of the above
Discussion
11.

Supercharging is the process of_____________________?
A. supplying the intake of an engine with air at a density greater than the density of the surrounding atmosphere
B. providing forced cooling air
C. injecting excess fuel for raising more load
D. supplying compressed air to remove combustion products fully
E. raising exhaust pressure
Answer» B. providing forced cooling air
Discussion
12.

In a diesel engine, the fuel is ignited by___________________?
A. spark
B. injected fuel
C. heat resulting from compressing air that is supplied for combustion
D. ignition
E. combustion chamber
Answer» D. ignition
Discussion
13.

If the intake air temperature of I.C. engine increases, its efficiency will_________________?
A. increase
B. decrease
C. remain same
D. unpredictable
E. depend on other factors
Answer» C. remain same
Discussion
14.

The inlet value of a four stroke cycle I.C engine remains open for nearly___________________?
A. 180°
B. 125°
C. 235°
D. 200°
E. 275
Answer» D. 200°
Discussion
15.

Fuel consumption of diesef engines is not guaranteed at one quarter load because at such low loads________________?
A. the friction is high
B. the friction is unpredictable
C. the small difference in cooling water temperature or in internal friction has a disproportionate effect
D. the engine is rarely operated
E. none of the above
Answer» D. the engine is rarely operated
Discussion
16.

The rating of a diesel engine, with increase in airintlet temperature, will ___________________?
A. increase linearly
B. decrease linearly
C. increase parabolically
D. decrease parabolically
E. first decrease linearly and then increase parabolically
Answer» C. increase parabolically
Discussion
17.

A heat engine utilises the_________________?
A. calorific value of oil
B. low heat value of
C. high heat value of oil
D. mean heat value of oil
E. all of the above
Answer» D. mean heat value of oil
Discussion
18.

The specific fuel consumption per BH hour for a petrol engine is approximately__________________?
A. 0.15 kg
B. 0.2 kg
C. 0.25 kg
D. 0.3kg
E. 0.35 kg
Answer» D. 0.3kg
Discussion
19.

A diesel engine as compared to petrol engine (both running ar rated load) is ____________________?
A. more efficient
B. less efficient
C. equally efficient
D. unperdictable
E. other factors will decide it
Answer» B. less efficient
Discussion
20.

The term scavenging is generally associated with______________________?
A. 2-stroke cycle engines
B. 4-stroke cycle engines
C. aeroplane engines
D. diesel engines
E. high efficiency engines
Answer» F.
Discussion
21.

In precombustion chamber in diesel engine________________?
A. The shape and layout of the pistion crown, the inlet port, and the valve produce the turbulent effect of fuel mixture
B. Fuel is injected into an auxiliary chamber that is separated from the cylinder by an orifice or throat
C. 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
D. There are no valves
Answer» D. There are no valves
Discussion
22.

The cam shaft of a four stroke I.C. engine running at 1500 rmp will run at __________________?
A. 1500 rpm
B. 750 rpm
C. 3000 rpm
D. any value independent of engine speed
E. none of the above
Answer» C. 3000 rpm
Discussion
23.

Most high speed compression engines operate on ___________________?
A. Otto cycle
B. Diesel cycle
C. Dual cycle
D. Carnot cycle
E. Two stroke cycle
Answer» D. Carnot cycle
Discussion
24.

In a cycle, the spark lasts roughly for ____________________?
A. 1 sec
B. 0.1 sec
C. 0.01 sec
D. 0.001 sec
E. 0.0001 sec
Answer» E. 0.0001 sec
Discussion
25.

Which of the following is false statement. Some of the methods used to reduce diesel smoke are as follows ________________?
A. using additives in the fuel
B. engine derating i.e. reducing the maxi-mum flow of fuel
C. increasing the compression ratio
D. adherence to proper fuel specification
E. avoidance of overloading
Answer» D. adherence to proper fuel specification
Discussion
26.

In diesel engine the diesel fuel injected into cylinder would burn instantly at about compressed air temperature of____________________?
A. 250°C
B. 500°C
C. 1000°C
D. 150CPC
E. 2000°C
Answer» D. 150CPC
Discussion
27.

In case of gas turbines, the gaseous fuel consumption guarantees are based on________________?
A. high heat value
B. low heat value
C. net calorific value
D. middle heat value
E. calorific value
Answer» C. net calorific value
Discussion
28.

If one cylinder of a diesel engine receives more fuel than the others, then for that cylinder the________________?
A. exhaust will be smoky
B. piston rings would stick into piston grooves
C. exhaust temperature will be high
D. engine starts overheating
E. scavenging occurs
Answer» F.
Discussion
29.

It the temperature of intake air in IC engines is lowered, then its efficiency will_______________________?
A. increase
B. decrease
C. remain same
D. increase upto certain limit and then decrease
E. decrease upto certain limit and then in-crease
Answer» B. decrease
Discussion
30.

As a result of detonation in an I.C. engine, following parameter attains very high value _____________________?
A. peak pressure
B. rate of rise of pressure
C. rate of rise of temperature
D. peak temperature
E. rate of rise of horse-power
Answer» C. rate of rise of temperature
Discussion
31.

For the same compression ratio_____________________?
A. Otto cycle is more efficient than the Diesel
B. Diesel cycle is more efficient’than Otto
C. both Otto and Diesel cycles are, equally efficient
D. compression ratio has nothing to do with efficiency
E. which is more efficient would depend on engine capacity
Answer» B. Diesel cycle is more efficient’than Otto
Discussion
32.

Most high speed compression engines operate on __________________?
A. Diesel cycle
B. Otto cycle
C. Dual combustion cycle
D. Special type of air cycle
E. Carnot cycle
Answer» D. Special type of air cycle
Discussion
33.

Which of the following medium is compressed in a Diesel engine cylinder __________________?
A. air aione
B. air and fuel
C. air and lub oil
D. fuel alone
E. air, fuel and lub oil
Answer» B. air and fuel
Discussion
34.

The magneto in an automobile is basically__________________?
A. transformer
B. d.c. generator
C. capacitor
D. magnetic circuit
E. a.c. generator
Answer» C. capacitor
Discussion
35.

In a typical medium speed, 4-stroke cycle diesel engine ___________________?
A. fuelinjection starts at 10° before to dead center and ends at 20° after tor dead center
B. fuel injection starts at top dead center and ends at 20° after top dead center
C. fuel injection starts at just before top dead center and ends just after top deac center
D. may start and end anywhere
E. none of the above
Answer» B. fuel injection starts at top dead center and ends at 20° after top dead center
Discussion
36.

The fuel in diesel engine is normally injected at pressure of_________________?
A. 5-10 kg/cm2
B. 20-25 kg/cm2
C. 60-80 kg/cm2
D. 90-130 kg/cm2
E. 150-250 kg/cm2
Answer» E. 150-250 kg/cm2
Discussion
37.

The pressure and temperature at the end of compression stroke in a petrol engine are of the order of___________________?
A. 4 – 6 kg/cm2 and 200 – 250°C
B. 6 – 12 kg/cm2 and 250 – 350°C
C. 12 – 20 kg/cm2 and 350 – 450°C
D. 20 – 30 kg/cm2 and 450 – 500°C
E. 30 – 40 kg/cm2 and 500 – 700°C
Answer» C. 12 – 20 kg/cm2 and 350 – 450°C
Discussion
38.

The knock in diesel engine occurs due to____________________?
A. instantaneous and rapid burning of the first part of the charge
B. instantaneous atuo iginition of last part of charge
C. delayed burning of the first part of the charge
D. reduction of delay period
E. all ot the above
Answer» B. instantaneous atuo iginition of last part of charge
Discussion
39.

Diesel engine can work on very lean air fuel ratio of the order of 30 : 1. A petrol engine can also work on such a lean ratio provided__________________?
A. it is properly designed
B. best quality fuel is used
C. can not work as it is impossible
D. flywheel size is proper
E. engine cooling is stopped
Answer» D. flywheel size is proper
Discussion
40.

Crankcase explosion in I.C. engines usuall occurs as ___________________?
A. first a mild explosion followed by a bi explosion
B. first a big explosion followed by a mil explosion
C. both mild and big explosions occi simultaneously
D. never occurs
E. unpredictable
Answer» B. first a big explosion followed by a mil explosion
Discussion
41.

The maximum temperature in the I.C. engine cylinder is of the order of ________________?
A. 500- 1000°C
B. 1000- 1500°C
C. 1500-2000°C
D. 2000-2500°C
E. 2500-3000°C
Answer» E. 2500-3000°C
Discussion
42.

A diesel engine has_________________?
A. 1 valve
B. 2 valves
C. 3 valves
D. 4 valves
E. no valve
Answer» D. 4 valves
Discussion
43.

In a diesel engine, injection pressure developed by injector is of the order of______________?
A. 10 kg/cm2
B. 100 kg/cm2
C. 500 kg/cm2
D. 1400 kg/cm2
Answer» E.
Discussion
44.

The theoretically correct air fuel ratio for petrol engine is of the order of___________________?
A. 6 : 1
B. 9 : 1
C. 12 : 1
D. 15 : 1
E. 20 : 1
Answer» E. 20 : 1
Discussion
45.

The working cycle in case of four stroke engine is completed in following number of revolutions of crankshaft___________________?
A. 1/2
B. 1
C. 2
D. 4
E. 8
Answer» D. 4
Discussion
46.

Flash point of fuel oil is __________________?
A. minimum temperature to which1 oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in cont
B. temperature at which it solidifies or congeals
C. temperature at which it catches fire without external aid
D. indicated by 90% distillation temperature, i.e. when 90% of sample oil has distilled off
E. none of the above
Answer» B. temperature at which it solidifies or congeals
Discussion
47.

A 5 BHP engine running at full load would consume diesel of the order of_________________?
A. 0.3 kg/hr
B. 1 kg/hr
C. 3 kg/hr
D. 5 kg/hr
E. 10 kg/hr
Answer» C. 3 kg/hr
Discussion
48.

The operation of forcing additional air under pressure in the engine cylinder is known as________________?
A. scavenging
B. turbulence
C. supercharging
D. pre-ignition
E. dissociation and carburretion of fuel
Answer» D. pre-ignition
Discussion
49.

Scavenging air in diesel engine means___________________?
A. air used for combustion sent under pres-sure
B. forced air for cooling cylinder
C. burnt air containing products of combustion
D. air used for forcing burnt gases out of engine’s cylinder during the exhaust period
E. air fuel mixture
Answer» E. air fuel mixture
Discussion
50.

For the same power developed in I.C. engines, the cheaper system is_____________?
A. naturally aspirated
B. supercharged
C. centrifugal pump
D. turbo charger
E. none of the above
Answer» C. centrifugal pump
Discussion