Why do diesel internal combustion engines require no spark plug to ignite the fuel unlike petrol engines?

To know the reason, we should first understand the processes in both engines.
In petrol engine, air-fuel mixture is administrated into the cylinder. The compression ratio of petrol engines is lower than diesel engines, i.e, 6–10. So when the charge is compressed inside the cylinder , the temperature of the charge will be less than the auto ignition point of the petrol and hence will not ignite. So a spark is produced by the spark plug to ignite the charge.

In diesel engines, the compression ratio is much higher,i.e 16–20. 

In this engine, only air is administrated into the cylinder. When the air is compressed in the compression stroke, the temperature of the air will be very high. Now when the fuel is injected by the fuel injector under high pressure, the fuel mixes with air in the cylinder and since the temperature of air is sufficiently high, the fuel will ignite without any external aid.


1-The ascending order of evolution of materials used for making the cutting tools is
(A) bronze – stone – steel – iron
(B) iron – steel – bronze – stone
(C) stone – bronze – iron – steel
(D) bronze – stone – steel – iron
(Ans: C)

2-The materials are added to cutting tools to increase their properties. Match the following
  1. Tungsten      a. Hardness
  2. Carbon         b. Hot hardness
  3. Vanadium     c. Wear resistance
The correct order is
(A) 1-b, 2-a, 3-c
(B) 1-c, 2-a, 3-b
(C) 1-b, 2-c, 3-a
(D) 1-a, 2-b, 3-c
(Ans: A)

3-Which of the following is second hardest substance known?
(A) Ceramics
(B) Cermets
(C) Cubic Boron Nitride (CBN)
(D) Diamond
(Ans: C)

4-Which of the following tools are generally manufactured by Powder metallurgy?
(A) Low carbon steel
(B) Abrasives
(C) High carbon steel
(D) Cemented carbides
(Ans: D)

5-Which of the following is hardest known material?
(A) Cemented carbide
(B) Ceramics
(C) Cubic boron nitride (CBN)
(D) Diamond
(Ans: D)

6-Corrundum is a/an
(A) Diamond
(B) Abrasive
(C) Ceramic
(D) None of the above
(Ans: B)

7-The cutting tool wears due to
(A) Edge wear
(B) Crater wear
(C) Flank wear
(D) All of the above
(Ans: D)

8-The built up edge in cutting tools can be eliminated by
(A) Fast cutting speed
(B) Higher rake angles
(C) High pressure cutting fluid
(D) All of the above
(Ans: D)

9-The cutting speed of High speed steels is ___ times faster than Carbon steel
(A) 2
(B) 4
(C) 6
(D) 8
(Ans: B)

10-Which of the following cutting tool has highest hot hardness?
(A) Ceramics
(B) Cast alloys
(C) High speed steels
(D) Carbon tool steel
(Ans: A)

11-Which of the following cutting conditions greatly affects the tool wear?
(A) Cutting speed
(B) Feed
(C) Depth of cut
(D) None of the above
(Ans: A)

12-Which of the following is not a constituent of High speed steel?
(A) V
(B) Cr
(C) W
(D) Ni
(Ans: D)

13-In a single point turning operation with a cemented carbide and steel combination having a Taylor exponent of 0.25, if the cutting speed is halved, then the tool life will become
(A) Half
(B) Two times
(C) Eight times
(D) Sixteen times
(Ans: D)

14-A drill bit of 20mm diameter rotating at 500 rpm with a feed rate of 0.2 mm/revolution is used to drill a through hole in Mild Steel plate of 20mm thickness. The depth of cut in this drilling operation is
(A) 100 mm
(B) 20 mm
(C) 10 mm
(D) 0.2 mm
(Ans: C)

15-The tool life increases with the
(A) Increase in side cutting edge angle
(B) Decrease in side rake angle
(C) Decrease in nose radius
(D) Decrease in back rake angle
(Ans: A)
 16-Which one of the following grinding wheels (with grade, grit and bond) is suitable for cutter grinding?
(A) K 60 vitrified
(B) K 320 vitrified
(C) T 60 resinoid
(D) T 320 resinoid
(Ans: A)


1-Probability of the event that might occur X Severity of the event if it occurs =
(A) Accident
(B) Hazard
(C) Risk
(D) None of the above
(Ans: C)

2-Industrial safety management if that branch of management which is concerned with ______ hazards from the industries.
(A) Reducing
(B) Controlling
(C) Eliminating
(D) All of the above
(Ans: D)

3-The following is indirect cost of accident
(A) Money paid for treatment of worker
(B) Compensation paid to worker
(C) Cost of lost time of injured worker
(D) All of the above
(Ans: C)

4-The following is(are) physical hazard agent(s)
(A) Falls
(B) Electricity
(C) Inhalation
(D) All of the above
(Ans: D)

5-Check list for Job Safety Analysis (JSA) consists of
(A) Work area, material, machine, tools
(B) Men, machine, material, tools
(C) Men, machine, work area, tools
(D) Men, work area. Material, tools
(Ans: A)

6-A safety programme consists of
(A) Three E’s
(B) Four E’s
(C) Five E’s
(D) Six E’s
(Ans: B)

7-For household wiring and small units, the following should be used for safety measure
(Ans: A)

8-Which of the following colour is used for radiation hazard?
(A) Red
(B) Orange
(C) Green
(D) Purple
(Ans: D)

9-Decibel (db) is a unit used to measure
(A) Light
(B) Sound
(C) Frequency
(D) None of the above
(Ans: B)

10-The following is (are) are generally provided with limit switch to prevent motion beyond preset limit
(A) Hoists
(B) Conveyors
(C) Machine tables
(D) All of the above
(Ans: D)

11-The following is (are) used as safety device(s) in machines
(A) Fail safe
(B) Safety interlocks
(C) Limit switches
(D) All of the above
(Ans: D)

12-Class-A fire consists of fire due to
(A) Wood
(B) Oil
(C) Transformer
(D) Chemical
(Ans: A)

13-Water is used to extinguish
(A) Class-A fires
(B) Class-B fires
(C) Class-C fires
(D) All of the above
(Ans: A)

14-The following class of fire occur in electrical equipment
(A) Class-A fires
(B) Class-B fires
(C) Class-C fires
(D) All of the above
(Ans: C)

15-The following extinguisher is suitable for cotton or other textile fire
(A) Water
(B) Soda acid
(C) Foam
(D) Dry chemicals
(Ans: D)
16-_____ is best suited to extinguishing oil or flammable liquid fire.
(A) Soda acid
(B) Vaporizing liquid
(C) Foam
(D) Dry chemical
(Ans: C)