Maximum temperature of fuel air cycle

[pnkj115]

When Stiochiometrically correct mixture(equivalence ratio=1) is burned in air fuel cycle some of the air is still left after point 3 in P-V diagram...Theoretically the whole fuel and air should combust till point 3..Then why is some air left out there.And thus the max temp is when mixture is 6% richer.Wh is this so??. Please help me

 

[Lok]

Theoretically the whole fuel and air should combust till point 3..

That is the theory. In practice the fuel air mixture does not burn completely and it would be quite a bother to make it combust to full completion in the whole RPM range. It is easier to make the mixture air rich for better performance, thus more fuel is burned and some air is still left.

The main problem is with the flame front that would prefer a spherical combustion cavity, yet that is not practical, and thus at the cylinder edges the flame does not perform too well.

There are linear spark plugs that start the flame front in a line and get a more or less cylindrical flame front, but they have issues too. The Flame front performs differently in the middle that next to the walls of the cavity, as you have surface effects, thermal cooling and reflection of thermal radiation and not to forget different air/fuel mixtures.

 

[Chronos]

If you can design a solution for thermodynamic inefficiencies in a combustion engine, you have a bright future in the engine business.