Meaning of Flammability Limits and reaction in Air of Ammonia I have read on Wikipedia that the flammable limits of gaseous ammonia are between 15&ndash;25% and I have also read that the autoignition temperature is $651\rm~^\circ C$.  And that the combustion of ammonia in air is $$\ce{4NH3 + 3O2 -&gt; 2N2 + 6H2O}$$  My understanding of this is that with a 20% air to $\ce{NH3}$ that I could hold a flame.  Outside of that range, I cannot hold a flame.

My question is if I am at 30% air and above $651\rm~^\circ C$ will Ammonia still combust/react with Air or will it stay $\ce{NH3}$?

My follow up question would be that when if I sprayed ammonia into a heated chamber (above $650\rm~^\circ C$) would flames/the exothermic reaction only happen when the ammonia vapor and the air reach that 15&ndash;25% range as the vapor propagates into the air and not react outside that range?
Chemical reaction would proceed in an air/ammonia mix, even outside the concentration range at which the reaction is self-sustaining, particularly if there were a catalyst to help. It is just that at the specified concentration range, when it reaches $651^{\circ}\mathrm{C}$ at one point in the mixture, the reaction proceeds fast enough to heat the rest of the mixture to that ignition temperature.

This is similar to an Otto cycle spark-ignition engine: with the correct mixture, the flame front propagates from the spark plug throughout the cylinder.

In the Ostwald process, a $1:10$ ration of $\ce{NH3}$ and air can sustain the reaction at the surface of a catalyst.

In a similar fashion, hot copper can catalyze the oxidation of acetone, methanol or ethanol, providing a surface where the reactants can combine fast enough to keep the surface hot.