250+ TOP MCQs on Combustion in S.I. Engine and Answers

IC Engines Multiple Choice Questions on “Combustion In S.I. Engine”.

1. Swirl is the rotational flow of charge within the cylinder about the axis.
a) True
b) False
Answer: a
Clarification: None.

2. The _____________ is defined by the parallel portion of the piston and cylinder head which almost touch each other as the piston approaches T.D.C.
a) turbulence
b) swirl
c) quench area
d) none of the mentioned
Answer: c
Clarification: The quench area is defined by the parallel portion of the piston and cylinder head which almost touch each other as the piston approaches T.D.C. while turbulence consists of randomly dispersed vortices of different sizes which become superimposed into the air and petrol mixture flow stream.

3. ____________ consists of randomly dispersed vortices of different sizes which become superimposed into the air and petrol mixture flow stream.
a) Turbulence
b) Swirl
c) Quench area
d) None of the mentioned
Answer: a
Clarification: Only turbulence consists of randomly dispersed vortices of different sizes which become superimposed into the air and petrol mixture flow stream while quench area is defined by the parallel portion of the piston and cylinder head which almost touch each other as the piston approaches T.D.C.

4. The amount of vortex activity,and the disintegration of others, _____________ the turbulent flow with rising engine speed.
a) increases
b) decreases
c) remains same
d) none of the mentioned
Answer: a
Clarification: None.

5. The degree of turbulence increases _____________ with the piston speed.
a) indirectly
b) directly
c) linearly
d) none of the mentioned
Answer: b
Clarification: The degree of turbulence is directly proportional to piston speed, hence it increases directly with the piston speed.

6. Turbulence decreases the heat flow to the cylinder wall and in the limit excessive turbulence may extinguish the flame.
a) True
b) False
Answer: b
Clarification: In fact, turbulence increase the heat flow to the cylinder wall and in the limit excessive turbulence may extinguish the flame.

7. The flame propagation velocities range from _____________
a) 10 to 15 m/s
b) 15 to 70 m/s
c) 20 to 80 m/s
d) 30 to 90 m/s
Answer: a
Clarification: None.

8. When ignition occurs the nucleus of the flame spreads with the whirling or rotating vortices in the form of ragged burning crust from the initial spark plug ignition site.
a) True
b) False
Answer: a
Clarification: None.

9. Swirl ratio is defined as the ratio of air rotational speed to crankshaft rotational speed.
a) True
b) False
Answer: a
Clarification: None.

10. Abnormal combustion knock produced by surface ignition in SI engines is not harmful as normal combustion knock.
a) True
b) False
Answer: b
Clarification: In fact, abnormal combustion knock produced by surface ignition in SI engines is more harmful than normal combustion knock.