In SI engines, energy is delivered by the flame propagation, so the fuel farther away from spark plug will be ignited.
In CI engines, how is the fuel ignited after the first ignition site occurs? Is the flame propagation also play a significant effect? Or for other reasons?
And in HCCI engines, how the fuel is ignited? Is is because the fuel is heated and compressed by the first ignited sites? How about the role of flame propagation?
Thank you for your attention and help
in CI engine diffusion flames exists and combustion is controlled by the mixing rate of fuel with air. After chemical delay the rapid ignition of fuel which has mixed with air within flammability limit rapidly ignited at different location with in the combustion chamber.
Dear Yaopeng,
I agree with Mahir, indeed in CI engines you have a diffusion flame and do not speak of a flame front. The ignitions comes at a certain pressure inside the piston which leads to the ignition of different regions inside the chamber. An ideal HCCI engine is an extreme case of this, where you have a perfect fuel distribution inside the entire combustion chamber. Consequently, the fuel-air mixture ignites in the entire chamber in the same moment. (In practical applications this is difficult to achieve. Here the fuel injection is performed very early in order to allow for fuel mixing. The result is, that you have a high quanitiy of regions where ignition starts - this process is called PCCI in practice).
If you have other questions do not hesitate.
Best regards,
Marek
Hi Marek
So no flame exists in HCCI combustion in theory. In PCCI, some sites are firstly ignited, then the rest sites are ignited then. I want to know how the rest sites be ignited, are they are compressed and heated by the first ignited sites, or for other reasons?
Thank you
Yaopeng
Dear Yaopeng,
It depends what you call a "flame", but indeed in HCCI you cannot observe a real flame propagation such as in SI engines. For PCCI I would agree with your suggested description. Here wo links for a better undertanding, the first a video showing different iginitions and the second a description of different ways to operate an engine.
https://www.youtube.com/watch?v=oNCBbcINHuk
http://www.ni.com/white-paper/13516/en/
See you,
Marek
Dear Marek
I understand, and I really appreciate for your kind help.
Yaopeng
- Badges
- Science topic