Automotive Engine Auxiliary Systems Questions and Answers – Conventional Ignition System – Spark Plug

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This set of Automotive Engine Auxiliary Systems Multiple Choice Questions & Answers (MCQs) focuses on “Conventional Ignition System – Spark Plug”.

1. Which of the following is the hottest part of the spark plug?
a) Terminal
b) Insulator tip
c) Shell
d) Gasket
View Answer

Answer: b
Explanation: The insulator nose length is the distance from the firing end of the insulator to the point where the insulator meets the metal shell. The insulator tip is the hottest part of the spark plug, which makes the tip temperature, the main factor in pre-ignition and fouling.
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2. Which of the following is not the main part of a spark plug?
a) The center electrode
b) The ground electrode
c) Distributor cap
d) The insulator
View Answer

Answer: d
Explanation: The spark plug has three main parts, the center electrode, the ground electrode, and the insulator separating them. Besides these, there are the body shell, the sealing ring, and the gasket washer. The distributor cap is not a main part of the spark plug.

3. What is the function of the sealing between the insulator and the body shell?
a) Prevents the hot gas from leaking
b) Prevents the pressure increase
c) Prevents the temperature increase
d) Prevents Current leakage
View Answer

Answer: a
Explanation: The body shell serves to house the electrodes and the insulator. A gas-tight seal is necessary to prevent the hot gas from leaking between the insulator and the body shell and between the insulator and the center electrode.
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4. What is the total resistance in ohms offered by primary winding in the ignition coil?
a) 5
b) 7
c) 3
d) 4
View Answer

Answer: c
Explanation: The battery winding consists of 200-300 turns of thick wire of total resistance about 3 ohms while the secondary is made up of a large number of turns about 15,000-20,000 of fine wire.

5. Which of the following is used as a material for the body shell of the spark plug?
a) Low carbon steel
b) Ceramic
c) Paper
d) Wood
View Answer

Answer: a
Explanation: The body shell is generally made of low carbon steel. The body is formed by impact extrusion. The threads are cold rolled to provide a low friction profile. Porcelain was used initially for insulation, but this has a disadvantage of brittleness and low resistance.
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6. Which of the following is.used as a material for the ground electrode of the spark plug?
a) Nickel
b) Cast iron
c) Brass
d) Bronze
View Answer

Answer: a
Explanation: The ground electrode is usually formed of nickel or sometimes an alloy of nickel and manganese. The addition of manganese is about 2.5-3.5 percent which improves the tensile strength and the resistance to the sulfur attack at high temperatures.

7. What is the correct range of gap size in the millimeter of a spark plug?
a) 0.35-0.45
b) 0.6-0.1
c) 1-2
d) 2-4
View Answer

Answer: b
Explanation: The correct spark plug gap size is specified by the manufacturers varies in general from 0.6 to 1millimeter. For the new spark plug, the gap is generally 0.6 millimeters, but with use it is increased, thus requiring higher voltage for the spark to jump across it.
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8. Which of the following material is used to fill the space between the plug electrodes in a surface discharge plug?
a) Semiconductor
b) Plastic
c) Rubber
d) Wood
View Answer

Answer: a
Explanation: Surface discharge plug is a special type of spark plug where the space between the plug electrodes is filled with some semiconductor material. Thus the spark has to jump across this material instead of air in the ordinary plugs.

9. How is the frequency of firing in a two-stroke concerning the value of four-stroke engines?
a) Same as the value of four-stroke
b) Twice the value of four-stroke
c) Has no relationship with four-stroke
d) Four times the value of four-stroke
View Answer

Answer: b
Explanation: The frequency of firing in the two-stroke engine is twice the value for four-stroke engines. Therefore expected spark plug life in a motorcycle with two-stroke engines is only half the life in case of cars that always have four-stroke.
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10. Which of the following does not affect overheating?
a) Weak mixture
b) Defective cooling system
c) Loose-fitting
d) Engine speed
View Answer

Answer: d
Explanation: Metallic particle on insulator tip, eroded electrode indicates that the plug as running overheated this may arise due to weak mixture, defective cooling system, loose-fitting causing the exhaust gases to leak.

11. Which among the following is not a requirement of a spark plug?
a) Very high resistance to current leakage
b) Contacts must close without bounce
c) Resistance to corrosion
d) Gas tightness
View Answer

Answer: b
Explanation: The essential requirements of a good spark plug is to provide very high resistance to current leakage,gas tightness, resistance to corrosion, electrode temperature should be maintained between certain limits.

12. Due to which of the following there are carbon deposits on the spark plug?
a) Overheating of plug
b) Burning of fuel on the plug
c) Erosion of electrodes
d) Engine speed
View Answer

Answer: b
Explanation: The carbon deposits due to the burning of petrol on the spark plug are recognized by their black color and dry, fluffy nature. The main cause for this is due to a defective fuel system delivering extra rich mixture.

13. Which of the following spark plug increases the resistance to increase the voltage required to jump across the spark plug gap?
a) Rheostat spark plug
b) Wire wound spark plug
c) MOSFET spark plug
d) Resistor spark plug
View Answer

Answer: d
Explanation: The center electrode contains a built-in resistance in series with the electrode. This resistance also increases the plug life by cutting down peak currents that would burn the electrodes. The resistance increases the voltage required to jump across the spark plug gap. Such plugs are called resistor spark plugs.

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To practice all areas of Automotive Engine Auxiliary Systems, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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