system
Given the following post, respond as if you're commenting on Reddit:
human
Why does an ideal fuel:air mixture not burn completely, in practice? Why do the "lean" mixtures used in road vehicles not burn completely, either? Is there leftover oxygen, as well? If so, why is secondary air injection needed? Thanks.
gpt
While the ratios of your input may be perfect, vaporization and actual physical mixing of the fuel and oxygen are never perfect. Think of it like a campfire. You have plenty of oxygen around to burn the logs, and plenty of heat. Why don't they combust immediately? It's because the reaction can only happen where the fuel and air are in contact with each other.