Combustion And Combustion Chambers Of IC Engine - 2


20 Questions MCQ Test Topicwise Question Bank for GATE Mechanical Engineering | Combustion And Combustion Chambers Of IC Engine - 2


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QUESTION: 1

Which of the following combustion design features reduce (s) detonation in SI engines ?
1. Spark plug located near the exhaust valve.
2. L-head
3. Wedge shaped combustion chamber
4. Short flame travel distance

Select the correct answer :

Solution:
QUESTION: 2

Which of the following type of valve arrangement is actuated by two cams mounted on two camshafts driven by the crankshaft through timing gears ?

Solution:

F - head type have E valve in head and I valve in the cylinder block which are separately actuated by two cams mounted on two camshafts driven by the crankshaft through gears.

QUESTION: 3

The delay period in Cl engine depends upon
1. Temperature and pressure in the cylinder at the time of injection.
2. Strength of fuel mixture.
3. Relative velocity between the fuel injection and air turbulence pressure of residual gas.
4. Engine output.

Select the correct answer :

Solution:

Factors affecting the delay period:
(i) Compression ratio
(ii) Engine speed
(iii) Output
(iv) Atomization of fuel injection duration
(v) Injection timing
(vi) Quality of the fuel
(vii) Intake temperature
(viii) Intake pressure

QUESTION: 4

All of the following parameters reduce knocking tendency in a compression ignition engine, except

Solution:

The delay period increases with increase in injection advance which favour knocking tendency.

QUESTION: 5

Consider the following measures:
1. Increasing the compression ratio
2. Increasing the intake air temperature
3. Increasing the length to diameter ratio of the cylinder
4. Increasing the engine speed

The measures necessary to reduce the tendency to knock in Cl engines would include

Solution:

Characteristics tending to reduce detonation or knock

QUESTION: 6

Which of the following is not direct-injection type?

Solution:

QUESTION: 7

Which of the following type of combustion chamber has negligible squish ?

Solution:

In shallow depth chamber, the depth of the cavity provided in the piston is quite small. The squish is negligible due to very large cavity diameter. All these types are direct-injection chamber.

QUESTION: 8

Consider the following characteristics of indirect-injection combustion chambers:
1. Low injection pressure
2. No cold starting problem
3. Direction of spraying is not significant
4. High specific fuel consumption
Q. Which of these are valid?

Solution:

Advantages

  • Injection pressure required is low
  • Direction of spraying is not very important

Disadvantages

  • Poor cold starting performance requiring heater plugs
  • Sfc is high because there is a less of pressure due to air motion through the duct and heat less due to large heat transfer area.
QUESTION: 9

The phenomenon of pre-ignition

Solution:
QUESTION: 10

Consider the following statements regarding a Cl engine:
1. Cl engine known can be reduced by increasing compression ratio.
2. Thermal efficiency of Cl is lower relative to a SI engine.
3. Cl engine has a higher specific output relative to SI engine.
4. Cl engines use leaner mixture relative to SI engine.
Q. Which of the above statements are correct?

Solution:
QUESTION: 11

Self ignition temperature of diesel as compared to petrol is

Solution:

Self ignition temperature of diesel is around 450°C and for petrol is around 550°C.

QUESTION: 12

The silencer of an internal combustion engine

Solution:

The silencer of an internal combustion engine is a device to reduce the noise level of engine so that it does’t harm the people.

QUESTION: 13

In an I.C. engine, the process of removing the burnt gases from the combustion chamber of the engine cylinder is known as

Solution:

At the end of the expansion stroke, the combustion chamber of a two-stroke engine is left full of combustion product. This is because, unlike four-stroke engine there is no exhaust stroke available to clear the cylinder of burnt gases.
The process of clearing the cylinder, after the expansion stroke is called scavenging process.

QUESTION: 14

In the operation of four-stroke diesel engines, the term ‘squish’ refers to the

Solution:

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

QUESTION: 15

With dissociation peak temperature is obtained

Solution:

With no dissociation maximum temperature is attained with chemically correct fuel air mixture while with dissociation maximum temperature is obtained when mixture is about 10% rich.

QUESTION: 16

Fuel-air ratio affects maximum power output of the engine due to

Solution:
QUESTION: 17

Mean effective pressure at a given compression ratio is maximum when the air-fuel ratio is

Solution:
QUESTION: 18

Cycles with lean to very lean mixture tend towards

Solution:

As quantity of air increases, the cycle tends towards the air standard cycle since in air standard cycle working fluid is air only.

QUESTION: 19

When the mixture is lean

Solution:

Due to less amount of fuel and more amount of air thermal efficiency at leaner mixture will be high but due to less amount of fuel heat generated will be less and hence less power output.

QUESTION: 20

For a given compression ratio, as the mixture is made progressively rich from lean, the mean effective pressure

Solution: