RFNA

RFNA is a rocket fuel (a storeable oxidiser): red fuming nitric acid. HNO₃ + 13% N₂O₄ and 3% H₂O. The colour of the resulting red fuming nitric acid is imparted by N₂O₄, which breaks down partially to form NO₂, the actual source of the color.

Usually used with an inhibitor (various, sometimes secret, substances - hydrogen flouride is one - it is then referred to as IRFNA) because HNO₃ attacks most container materials.

It can also be a monopropellant; with substances like ammonium nitrates dissolved in it, it can be used as the sole fuel in a rocket. It is not normally used this way however.

More at: http://www.astronautix.com/props/nitidjpx.htm