Deck 8: Combustion and Engine Performance in IC Engines

Question 1

with increase in compression ratio flame speed

A)increases
B)decreases
C)remains the same
D)none of the above

Answer 1

increases

Question 2

With increase in speed the crank angle required for fame propagation

A)increases
B)decreases
C)not affected
D)none of the above

Answer 2

not affected

Question 3

Increasing the compression ratio in SI engines the knocking tendency

A)decreases
B)increases
C)not affected
D)none of the above

Answer 3

increases

Question 4

Decreasing the cooling water temperature in SI engines the knocking tendency

A)increases
B)decreases
C)not affected
D)none of the above

Question 5

Detonation in SI engines occur due to

A)pre ignition of the charge before the spark
B)sudden ignition of the charge before the spark
C)autoignition of the charge after the spark in struck
D)none of the above

Question 6

Desirable characteristics of the combustion chamber for SI engines to avoid knock is

A)small bore
B)short ratio of fame path to bore
C)absence of hot surfaces in the last region of the charge
D)all of the above

Question 7

In CI engines with increase in compression ratio the delay period

A)increases
B)decreases
C)first increases and then decreases
D)not affected

Question 8

Knocking takes place in CI engines

A)at the start of combustion
B)at the end of combustion
C)during combustion
D)none of the above

Question 9

In CI engines knocking tendency increases with

A)increase in compression ratio
B)increasing inlet temperature of air
C)decrease in compression ratio
D)increasing coolant water temperature

Question 10

In CI engines by increasing inlet air pressure the knocking tendency

A)increases
B)decreases
C)not affected
D)first decreases and then increases

Question 11

Open combustion chambers in CI engines require

A)high injection pressures
B)accurate metering of fuel by the injection system
C)both (a) and (b)
D)none of the above

Question 12

The advantages of the indirect injection combustion chambers are

A)low injection pressure
B)direction of spray is not critical
C)both (a) and (b)
D)good cold starting performance

Question 13

In CI engines the delay period is affected by

A)compression ratio
B)engine speed
C)output
D)all of the above

Question 14

Crankcase explosion in I.C. engines usually 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

Question 15

Compression loss in I.C engines occurs duto

A)leaking piston rings
B)use of thick head gasket
C)clogged air-inlet slots
D)all of the above.

Question 16

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

Question 17

The precess of breaking up or a liquid into fine droplets by spraying is called

A)vaporisation
B)carburetion
C)ionisation
D)atomisation.

Question 18

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

Question 19

Which of the following statements is correct?

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

Question 20

The accumulation of carbon in a cylinder results in increase of

A)clearance volume
B)volumetric efficiency
C)ignition time
D)effective compression ratio

Question 21

In diesel engine the diesel fuel injected intc cylinder would burn instantly at about compressed air temperature of

A)250°C
B)500°C
C)1000°C
D)150CPC

Question 22

In a cycle, the spark lasts roughly for

A)1 sec
B)0.1 sec
C)0.01 sec
D)0.001 sec

Question 23

Excess quantities of sulphur in diesel fuel are Objectionable because it may cause the following

A)piston ring and cylinder wear
B)formation of hard coating on piston skirts
C)oil sludge in the engine crank case
D)detonation

Question 24

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

Question 25

A high flame speed is obtained in diesel engine when air fuel ratio is

A)uniform throughout the mixture
B)chemically correct mixture
C)about 3-5% rich mixture
D)about 10% rich mixture