[RustyLugNut]

. . . that needs to be addressed is the idea of increased temperature at lean mixtures.

The charts that have been produced and the discussion that has ensued has mixed up the concepts of flame temperature and mixture (working fluid) temperature.

At part throttle, the flame temperature may be high but the over all mixture temperature may be different dependent on mixture mass and combustion dynamics.

Also, with mixtures richer than lambda, power production is increased even though no more heat is produced as all oxygen is consumed. The power increase is partly a function of the greater specific mass of the working fluid.

At mixtures just lean of lambda, there is a secondary fuel source in the nitrogen if there is enough flame temperature to provide the energy to dissociate the nitrogen gas to gain the exothermic energy in its oxidation to NOx. This is that range around 16:1 AFR that pilots can lean their aero engines for max fuel economy. Beyond that AFR, the specific heat of energy starts dropping and so does the production of NOx.

As your mixtures becomes leaner, as a previous poster noted, unburned hydrocarbons (UBHCs) and carbon monoxide (CO) start increasing as flame irregularities increase. Using in cylinder pressure traces, combustion engineers use a 5% coefficient of variability (COV) as the break point at which flame fronts become unstable by definition ( 5% variation in pressure ).

The vaporization of gasoline is easily attained in modern engines by the time combustion takes place. We can all agree the 98% fuel combustion claimed by most manufacturers for modern engines is an undisputed fact by all but the most uninformed. However, as Stovie is finding out, the total vaporization of the constituents of gasoline is not a trivial undertaking. And, by the time you have used heated fuel, heated air and mechanical turbulence - you have added all the ingredients for a more reactive fuel mixture! Combustion of all the fuel is not the issue, but HOW you combust it is. Attempts to externally vaporize the gasoline fuel bring with it the attendant qualities that make for more rapid combustion at lambda mixtures and increased stability at extremely lean mixtures. Pgfpro and Iveyjh, have work that corroborates this. I think Stovie's work will too.

And I trust Stovie has more than enough clarity of thought to keep from blowing himself up while providing us with continued data of experience.