Quote:
Originally Posted by Daox
In that graph, NOx starts coming down, but HC (hydrocarbons, or gasoline) start going up because of misfiring.
I'm not exactly sure where that graph comes from. I believe its from a Toyota paper. Its obviously from some engine, and an engine designed for lean burn obviously isn't going to misfire at 18:1. So, you may be right, but we can't really know for sure because we don't have details on it.
|
NOx is reduced after 18:1 AFR and beyond, but HC starts climbing. In vehicles designed for lean burn ( Honda lean burn engines as an example ), the HC line can be held flat up until 22:1 or so. Liberal use of EGR and combustion chamber turbulence allow Honda engines to minimize partial combustion and misfires. At some point however, the HC starts climbing again as partial/mis fires become dominant. Honda engines can be run lean up to just under 26:1 AFR but the unburned hydrocarbons is unacceptable as pollutants and as wasted fuel. 28:1 AFR is the "magic" number as NOx is almost non existent at that fuel mix but producing useable torque is the issue.