[hoseja]

How do you burn it without releasing a lot of nitrogen oxides? I realize the main reaction id 4 NH3 + 3 O2 -> 2 N2 + 6 H2O but there must be a lot of trace sideproducts, no?

edit: By using excess ammonia, you reduce nitrogen oxides with a mechanism similar to AdBlue in diesel engines.

[adrian_b]

Using excess ammonia might have the risk of releasing unburnt ammonia in the atmosphere.

Fuel cells using ammonia seem much safer, but they are farther from being a commercially available solution.

[ncmncm]

The exhaust doesn't have ammonia. The nitrogen really likes to link up, giving up protons to do it. You would be left traces of unburnt hydrogen.

[ncmncm]

Note that hydrogen is itself a greenhouse gas, so you would want to tune the mixture carefully to leave minimal unburnt hydrogen. Hydrogen acts to promote a greenhouse effect by several mechanisms: 6x directly, but also by prolonging methane lifetime, and by promoting lower-atmosphere ozone, making its greenhouse impact up to 200x CO2.

Water vapor is itself another greenhouse gas, so it could be important for big users of hydrogen and ammonia fuels to make an effort to condense out exhaust vapor, e.g. by using it to warm incoming fuel, or air after the initial compression stage. Probably natural-gas burners should be doing it already, as burning methane produces copious water vapor.

Condensing exhaust water vapor from these systems could increase efficiency by creating a vacuum at the exhaust.