# IC Engine: Objective Questions

## IC Engine Objective Questions

Here are a few important Automobile Engineering or IC Engine Objective Questions with Answers for IES, GATE, ISRO, and DRDO Exams. You must practice these IC Engine Objective Questions before appearing for the exams.

Read More- Fluid Mechanics: Objective Questions

1. The method of determination of indicated power of a multi-cylinder SI engine is by the use of-

A. Morse test

B. Heat Balance test

C. Motoring test

D. Prony brake test

Click for Answer/Explanation

Correct Answer is A

Morse test- Since frictional power can be easily calculated.

2. The presence of nitrogen in the process of combustion ensures that:

A. air is used for the combustion

B. incomplete combustion of fuels occur

C. complete combustion of a fuel occurs

D. dry products of combustion are analyzed

Click for Answer/Explanation

Correct Answer is A

Since it doesn’t take part in combustion, it indicates that air is used for combustion.

3. For the same maximum pressure and heat input, the most efficient cycle is-

A. Diesel Cycle

B. Otto Cycle

C. Brayton Cycle

D. Diesel Cycle

Click for Answer/Explanation

Correct Answer is A

4. In a variable-speed SI engine, the maximum torque occurs at the maximum-

A. Brake Power

B. Speed

C. Volumetric Efficiency

D. Indicated Power

Click for Answer/Explanation

The correct Answer is A

Brake Power = (2×π×N×T)/60

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5. The amount of CO2 produced by 1 kg of carbon on complete combustion is-

A. 3/11 kg

B. 3/8 kg

C. 8/3 kg

D. 11/3

Click for Answer/Explanation

The correct answer is D

$C\quad +\quad { O }_{ 2 }\quad \rightarrow \quad { CO }_{ 2 }$

Here 12 kg pf C reacts with 32 kg of ${ O }_{ 2 }$, and produces 44 kg ${ CO }_{ 2 }$

Hence, 1 kg of C ? 44/12 = 11/3

6. Methane burns with a stoichiometric quantity of air. The air-fuel ratio by weight is-

A. 14.7

B. 1/4

C. 4

D. 17.4

Click for Answer/Explanation

The correct answer is D

Read More- Heat and Mass Transfer: Objective Questions with Answers

7. The Cetane Number of automotive diesel fuel used in India is-

A. range of 30 – 40

B. range of 41 – 50

C. range of 51 – 60

D. range of 61 – 70

Click for Answer/Explanation

Correct Answer is B

8. Where does the mixing of fuel and air take place in the case of diesel engines?

A. Injector

B. Inlet manifold

C. Injection pump

D. Engine cylinder

Click for Answer/Explanation

Correct Answer is D

9. Piston compression rings are made up of which one of these-

A. Aluminum

B. Bronze

C. Cast Iron

D. Brass

Click for Answer/Explanation

Correct Answer is C

Gray Cast Iron has the property of self-lubrication & damping of small vibrations.

10. An I.C. engine has a bore and stroke each equal to 2 units. The total area to calculate heat loss from the engine can be taken as-

A. 4π

B. 8π

C. 12π

D. 2π

Click for Answer/Explanation

Correct Answer is A

Area = π×D×L

11. Air injection in I.C. Engine refers to the injection of –

A. Liquid Fuel only

B. Air only

C. Liquid fuel and Air

D. Supercharging Air

Click for Answer/Explanation

Correct Answer is B

12. Pistons of Diesel Engine are usually cooled by-

A. Water

B. Air

C. Fuel Oil

D. Lubricating Oil

Click for Answer/Explanation

Correct Answer is D

13. The volumetric efficiency of a well-designed SI Engine is in the range of (in %) –

A. 40-50

B. 55-65

C. 60-70

D. 70-90

Click for Answer/Explanation

The correct answer is D

SI Engine – 80-85

CI Engine – 85-90

14. Auto ignition time for petrol air-mixture is minimum when the ratio of the actual fuel-air ratio and the chemically correct fuel-air ratio is –

A. 0.8

B. 1

C. 1.2

D. 1.5

Click for Answer/Explanation

Correct Answer is C

When the mixture is nearly 10% richer than stoichiometric, the ignition lag is minimal.

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15. The order of values of thermal efficiency of Otto, Diesel, and Dual Cycle is when they have equal compression ratio and heat rejection-

A. ηOtto > ηdiesel > ηdual

B. ηOtto > ηdual > ηdiesel

C. ηdual > ηOtto > ηdual

D. ηdiesel > ηOtto > ηdual

Click for Answer/Explanation

Correct Answer is B

16. The stoichiometric air-fuel ratio by volume for combustion of methane in air is-

A. 15:1

B. 17.16:1

C. 10.58:1

D. 9.52:1

Click for Answer/Explanation

The correct answer is B

{(64/16) × (100/23)} = 17.39 ~ 17.16

17. The tendency of knocking in the CI Engine is reduced by

A. By decreasing the injection pressure

B. decreasing the jacket water temperature

C. injection of fuel just before TDC

D. high self-ignition temperature of fuel

Click for Answer/Explanation

The correct answer is C

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18. If the performance of diesel engines of different sizes, cylinder dimensions, and power rating are to be compared, which of these parameters can be used to compare-

A. Air fuel ratio

B. Swept volume

C. Volumetric efficiency

D. Specific brake fuel consumption

Click for Answer/Explanation

The correct answer is C

19. In some carburetors, a meter rod and economizer device are used for

A. power enrichment

B. idling

C. cold starting

D. accelerator

Click for Answer/Explanation

The correct Answer is A

The economizer is basically a valve that remains closed at normal cruise operation and gets opened to supply a rich mixture at full-throttle operation. It regulates the additional fuel supply during full-throttle operation. So, it can be called a power enrichment system.

20. Which of the following cannot be caused by a hot spark plug?

1. Pre-ignition
2. Post-ignition
3. Detonation
4. Run-on-ignition

A. 1 only

B. 2 only

C. 1 and 4 only

D. 3 only

Click for Answer/Explanation

The correct answer is B

21. The discharge of hydrocarbons from petrol automobile exhaust is minimal when the vehicle is-

A. Cruising

B. Idling

C. Accelerating

D. Decelerating

Click for Answer/Explanation

Correct Answer is C

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22. What do you mean by a higher Octane Number of SI fuel?

A. higher heating value

B. lower volatility

C. longer ignition delay

D. higher flash point

Click for Answer/Explanation

The correct Answer is C

Longer ignition delay which prevents knocking.

23. A gas engine has a swept volume of 300 cc and a clearance volume of 25 cc. Its volumetric efficiency is 0.88 and its mechanical efficiency is 0.99. The volume of the mixture taken in per stroke-

A. 254 cc

B. 264 cc

C. 282 cc

D. 284 cc

Click for Answer/Explanation

Correct Answer is B

24. In the operation of 4-stroke diesel engines, the term ‘Squish‘ refers to

A. stripping of fuel from the core

B. injection of fuel in the pre-combustion chamber

C. discharge of gases from the pre-combustion chamber

D. entry of air into the combustion chamber

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Click for Answer/Explanation

The correct answer is D

It is the flow of air, radially inwards towards the combustion recess by squeezing it out from between the piston and cylinder head as they approach each other at the end of the stroke.

25. A 40 kW engine has a mechanical efficiency of 80%. If the frictional power is assumed to be constant with load, what is the approximate value of the mechanical efficiency at 50% of the rated load-

A. 40%

B. 51%

C. 66%

D. 77%

Click for Answer/Explanation

Correct Answer is C

Step -1

Find IP

ηmech = 0.8 = BP/IP

Step- 2

Get FP, using the formula

FP = IP – BP

Step-3

Find IP at 50% Load where BP = 20kW & FP = 10kW

Step- 4

Again

ηmech = (20/30) × 100 = 66.6%

26. The purpose of employing supercharging for an engine is-

A. to provide forced cooling

B. to inject excess fuel to cope with a higher load

C. to raise exhaust pressure

D. to supply an intake of air at a density greater than the density of the surrounding atmosphere

Click for Answer/Explanation

The correct answer is D

With Supercharging a greater mass flow rate is provided, hence more oxygen to support combustion. This allows more fuel to be burned and more work per cycle.

27. Which one of these fuels can be obtained by fermentation of vegetable matter-

A. Alcohol

B. Gasoline

C. Diesel

D. Benzene

Click for Answer/Explanation

The correct Answer is A

28. Which of the following cannot be controlled by a three-way catalytic converter?

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A. CO Emission

B. HC Emission

C. SPM Emission

D. NOx

Click for Answer/Explanation

The correct answer is C

Three-way catalytic converter-

• Palladium → CO
• Rhodium → NOx
• Platinum → HC

Cannot control the emission of particulate matters

29.