Editing Rocket engine (section)

==Jet physics==
[[File:Armadillo Aerospace Pixel Hover.jpg|thumb|right|[[Quad (rocket)|Armadillo Aerospace's quad vehicle]] showing visible banding (shock diamonds) in the exhaust jet]]
Rocket jets vary depending on the rocket engine, design altitude, altitude, thrust and other factors.

Carbon-rich exhausts from kerosene-based fuels such as [[RP-1]] are often orange in colour due to the [[black-body radiation]] of the unburnt particles, in addition to the blue [[Swan band]]s. [[high test peroxide|Peroxide]] oxidiser-based rockets and hydrogen rocket jets contain largely [[steam]] and are nearly invisible to the naked eye but shine brightly in the [[ultraviolet]] and [[infrared]] ranges. Jets from [[solid-propellant rocket]]s can be highly visible, as the propellant frequently contains metals such as elemental aluminium which burns with an orange-white flame and adds energy to the combustion process. Rocket engines which burn liquid hydrogen and oxygen will exhibit a nearly transparent exhaust, due to it being mostly [[superheated steam]] (water vapour), plus some unburned hydrogen.

The nozzle is usually over-expanded at sea level, and the exhaust can exhibit visible [[shock diamonds]] through a [[schlieren#Schlieren flow visualization|schlieren effect]] caused by the [[incandescence]] of the exhaust gas.

The shape of the jet varies for a fixed-area nozzle as the expansion ratio varies with altitude: at high altitude all rockets are grossly under-expanded, and a quite small percentage of exhaust gases actually end up expanding forwards.