Knocking can cause overheating of the spark-plug points, erosion of the combustion chamber surface, and rough, inefficient operation.
What are effects of knocking?
Knocking combustion causes major engine damage, and also reduces the efficiency. … The variation of pressure signal is gradually increased and smoothly reduced to minimum during normal combustion. The rapid rise of pressure signal has occurred during knocking combustion.
What are the effects of knocking Mcq?
What are the effects of knocking? vi) preignition. 8. Increase of pressure increases the self ignition temperature and the induction period.
How is the knocking tendency increased?
Solution(By Examveda Team)
In SI engine, knocking tendency increases with increase in compression ratio. … In CI engine, knocking tendency decreases with increase in compression ratio. If compression ratio is low in CI engine, there will not be enough temperature generation for ignition of the fuel air mixture.
What is knocking tendency?
When the spark is advanced, burning gas is compressed by the rising piston and therefore temperature and pressure are increased, thus, the tendency to knock increases. … In SI engine, knocking occurs before TDC and because of early combustion of charge/more than one flame propagation.
What do you mean by knocking in SI engines differentiate between knocking phenomenon in SI and CI engines?
In S.I. engines detonation is caused by the auto-ignition of end gas towards the end of combustion whereas knocking in CI engines is due to auto-ignition of the first charge at the start of combustion.
Which of the following reduces knocking in SI engine?
In spark ignition (SI) engines, the possibility of knocking can be reduced by decreasing compression ratio as a reduction in compression ratio will result in the generation of lower peak temperature. In SI engine, knocking occurs before TDC and because of early combustion of charge/more than one flame propagation.
What is the effect of delay period on knock in CI engine?
The pressure reached during the second stage of combustion is dependent on the duration of the delay period. More delay leads to more increase in pressure and leads to knocking. Hence, shorter ignition delays are preferred.
Which of the following action increases the knocking tendency in SI engine?
Low inlet pressure and temperature reduce knocking tendency in SI engines but increase the knocking tendency in CI engines.
What is the main objective of supercharging of the engine?
The objective of supercharging is to increase the charge density of the working medium (air or air-fuel mixture), by any means and with the help of a suitable system, before it enters the work cylinder, i.e., to precompress the charge.
What are the factors affecting combustion in CI engine?
The most important factors are explained below.
- Molecular structure of fuel.
- Temperature of self ignition.
- Affect of high temperature and pressure after compression.
- Temperature of combustion wall chamber.
- Rate of burning.
- Spark timing.
- Spark intensity and duration.
- Air-fuel ratio.
How can we reduce knocking?
Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine’s ignition timing schedule, and careful design of the engine’s combustion chambers and …
What is knock control?
A knock control system which detects a knock occurring in an engine, a knock detector for detecting the occurrence of the knock in accordance with a knock sensor signal produced by the sensor, a first adjuster for adjusting knock control factors so as to suppress the knock on the basis of a detected signal from the …
What is the difference between knocking and detonation?
Knocking vs Detonation
Knocking is the making sharp sounds due to uneven combustion of fuel in the cylinder of a vehicle engine. Detonation is the process of pre-ignition or auto-ignition of a fuel in an engine’s combustion chamber.