In some book both words are use with si and ci engine.
in some ci and sI engine both have knocking.
what is actually difference between these two word??
Detonation is the word generally used when there is more severe problem For example it leads to melting of piston rings or seizure of piston in the cylinder etc...Knocking is the word used for less severe problem.even when it happens not much damage occurs .Or in the words depending on the severity we can use these words but both are problems associated with abnormal combustion.
Hello,
What needs to be very well understood is that knock and detonation (or knock and super-knock) are not the same phenomena.
Konijeti described very well the influence of both phenomena over a piston engine. What you observe in the chamber when a detonation occurs (instead of an autoignition/knock) is pressure oscillation with higher amplitude which induces more damage to the engine and more particularly to the piston.
In a more fondamental way, knock is associated to end-gas autoignition, which is basically a spontaneous and exothermic chemical reaction that occurs for high temperature and high pressure conditions. Bradley et al. demonstrated via numerical studies that this reactive front followed the temperature gradient. Therefore, with low temperature gradient in the remaining fresh gas, autoignition propagates fast in the chamber and may generate pressure waves -> pressure osccillations from small to intermediate amplitude.
A detonation occurs when there is a coupling between the reactive zone (typically the autoignition) and a shockwave. In that case, the reactive front is supersonic and therefore induces much more damage to the engine.
In PPRIME Institute, Poitiers, we worked on the transition to detonation via the autoignition. I recommend you to read the article I wrote on that subject.
Best regards,
Hugo Quintens
- Badges
- Science topic
- Similar topics
- Books