Which of the following statements is wrong?a)In compression ignition engines, detonation occurs near the beginning of combustionb)Since the fuel in compression ignition engines is injected at the end of the compression stroke; therefore the second there will be no pre-ignitionc)To eliminate knock-in compression ignition engines, we want to achieve auto-ignition not early and desire a long delay periodd)In compression ignition engines, because of a heterogeneous mixture, the rate of pressure rise is comparatively lowerCorrect answer is option 'C'. Can you explain this answer?

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Which of the following statements is wrong?

a)
In compression ignition engines, detonation occurs near the beginning of combustion
b)
Since the fuel in compression ignition engines is injected at the end of the compression stroke; therefore the second there will be no pre-ignition
c)
To eliminate knock-in compression ignition engines, we want to achieve auto-ignition not early and desire a long delay period
d)
In compression ignition engines, because of a heterogeneous mixture, the rate of pressure rise is comparatively lower

Correct answer is option 'C'. Can you explain this answer?

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Which of the following statements is wrong?a)In compression ignition ...

Knocking in a CI engine occurs because of an ignition lag in the combustion of fuel between the time of injection and the time of actual burning.

As the ignition lag increases, the amount of fuel accumulated in the combustion chamber increases. When combustion actually takes place, an abnormal amount of energy is suddenly released, causing an excessive rate of pressure rise, which results in a knock.

The CI engine knock can be controlled by reducing the delay period. The delay is reduced by the following :

a. High charge temperature

b. High fuel temperature

c. Good turbulence

d. Injection of fuel just before TDC

To decrease the tendency of knock, it is necessary to start the actual burning as early as possible after the injection begins. In other words, it is necessary to decrease the ignition delay and thus decrease the amount of fuel present when the actual burning of the first few droplets starts.

The following are the differences in the knocking phenomenon of the S.I. and C.I. engines:

In the S.I engine, the detonation occurs near the end of combustion, whereas in the C.I engine detonation occurs near the beginning of combustion
The detonation in the S.I engine is of a homogeneous charge causing a very high rate of pressure rise and very high maximum pressure.
In the C.I. engine, the fuel and air are imperfectly mixed, and hence the rate of pressure rise is normally lower than that in the detonating part of the charge in the S.I engine.
In the C.I. engine, the fuel is injected into the cylinder only at the end of the compression stroke; there is no question of pre-ignition as in S.I. engine.
In the S.I. engine, it is relatively easy to distinguish between knocking and non-knocking operations as the human ear easily finds the distinction.

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Which of the following statements is wrong?a)In compression ignition engines, detonation occurs near the beginning of combustionb)Since the fuel in compression ignition engines is injected at the end of the compression stroke; therefore the second there will be no pre-ignitionc)To eliminate knock-in compression ignition engines, we want to achieve auto-ignition not early and desire a long delay periodd)In compression ignition engines, because of a heterogeneous mixture, the rate of pressure rise is comparatively lowerCorrect answer is option 'C'. Can you explain this answer?

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