Two photos taken a few seconds apart will show nearly identical images. Premixed means that the fuel and the oxidizer are mixed before the combustion zone occurs. A laminar diffusion flame is a candle. In such systems, the air and the fuel are premixed in some burner device. Since the flames are turbulent, two sequential photos would show a greatly different flame shape and location.
Most unwanted fires fall into the category of turbulent diffusion flames.
Since no burner or other mechanical device exists for mixing fuel and air, the flames are diffusion type. Adiabatic' means without losing heat. For methane burning in air, the adiabatic flame temperature is 1949 C, while for propane it is 1977 C, for example. The value for wood is nearly identical to that for propane. The adiabatic flame temperatures for most common organic substances burned in air are, in fact, nearly indistinguishable.