When I think of ammonia, cleaning products and fertilizer spring to mind. It seems it can also be used as a “green” fuel for our cars; with vehicles requiring very few modifications to use it.
   
I thought this must have been a fairly recent development, but according to Wikipedia, ammonia was used to fuel buses in Belgium during World War II and also in the X-15 rocket airplane. 
   
While ammonia doesn’t have the energy density of other fuels (around half that of gasoline), it’s still fairly potent stuff. The X-15 still holds the official world record for the fastest speed ever attained by a manned rocket-powered aircraft; a record set way back in 1961. 

4,092 mph (6,585 km/h) is certainly fast; but the fuel tanks on the X-15 were massive and the craft burned 15,000 pounds (6804 kg) of fuel in 80 seconds. Thankfully our cars don’t need to zip along at 4,092 mph – nor fly.
 
Ammonia does occur in nature – for example, it can be one of the gases produced during composting; but its prevalence is nowhere near the levels required even for our current use – so it can’t be “harvested” as such.
 
Over 131 million tonnes of ammonia was made during 2010, with over 80% of it used for fertilizer. The way it’s made is by converting fossil fuels such natural gas into hydrogen; then combining with nitrogen extracted from the air to produce ammonia. This is called the Haber-Bosch process. It’s energy intensive and given ammonia produced in this way is so widely used in agriculture; we’re basically eating fossil fuels.
 
However, ammonia can be made from water, air and cleaner energy sources – and this is where solar power or wind energy could play a role. 
 
When burned, the emissions from ammonia (when properly combusted) are said to be just water and nitrogen gas – there is no carbon. But I’ve read this nitrogen gas is actually a “small amount” nitrous oxide. If it was just nitrogen, then all that is happening is what was taken from the air is being returned to it. If it’s nitrous oxide (which seems to make more sense given the combustion); that is a very potent greenhouse gas, with a global warming potential (GWP) of  296  times that of carbon.
 
Ammonia vapor is flammable, assuming a range of 16% to 25% by volume in air and a strong ignition source. Some modern test vehicles have been successfully running on a mixture of  80% ammonia and 20% gasoline.
 
There’s been a lot of research and advancements in using hydrogen as a fuel, so what advantages does ammonia have over it? 

According to Green NH3, ammonia costs less; is easier to produce, handle and distribute and is safer. If all this is true, why hydrogen is stealing the limelight is curious; but I guess the devil is in the detail – ammonia is rather dangerous stuff if an accident does occur and the nitrous oxide is also a concern.
 
The other potential application for ammonia is in fuel cells, as it holds 18% hydrogen by mass – and this would get around the nitrous oxide issue.
 
While I still think electric cars recharged by renewable sources such as wind and solar power are the way we need to go, the potential of ammonia as a “green” fuel is fascinating given it can be used in the cars we drive today.
 
If you’d like to learn more, here are a couple of links:
 
NH3 Fuel Association
Iowa Energy Center