Reheat / afterburners
 

A question that occurred to me the other day...

An afterburner, as I understand it, is a fairly low-tech device whereby raw fuel is injected into the hot exhaust gases of a jet engine. The raw fuel burns, creating greatly increased thrust, although at the expense of greatly increased fuel burn rate.

I would have assumed that, for any well-designed and correctly-tuned internal combustion engine, the exhaust gases shouldn't contain any oxygen - the oxygen should all have been used up by ensuring that the fuel/air mix was correct to start with. However, if that was the case, the afterburner fuel wouldn't have anything to react with.

What am I missing? Are the just engines leaned off when afterburner is selected, allowing some oxygen to make it through?

Cheers for any pointers...

There is a huge surplus of oxygen in a turbine engine exhaust.
After an excellent landing you can use the airplane again.

Gas turbine engines don't come close to using all the oxygen in the airflow; if they did the turbine temperatures would be ENORMOUS - both due to the huge amount of combustion going on and due to the lack of (unconsumed) air to use as cooling flow.

Tuning a combustion process so that there is excess air is normal - in large industrial boilers for instance, control of excess air is vital to the running of the boiler.

Car engines are no different. As mentioned before, stoichiometric (perfect fuel/air mix) mixtures burn at very high temps and the engine management system will only allow those kind of mixtures under light load - if the engine is under heavy load, detonation may occur.